The barrier, airway particle clearance, placental and detoxification functions of autism susceptibility genes

Accepted Manuscript The barrier, airway particle clearance, placental and detoxification functions of autism susceptibility genes C.J. Carter PII:

S0197-0186(16)30148-6

DOI:

10.1016/j.neuint.2016.06.003

Reference:

NCI 3881

To appear in:

Neurochemistry International

Received Date: 12 April 2016 Revised Date:

11 May 2016

Accepted Date: 7 June 2016

Please cite this article as: Carter, C.J., The barrier, airway particle clearance, placental and detoxification functions of autism susceptibility genes, Neurochemistry International (2016), doi: 10.1016/ j.neuint.2016.06.003. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

1

ACCEPTED MANUSCRIPT

The barrier, airway particle clearance, placental and detoxification functions of Autism susceptibility genes. C.J.Carter, PolygenicPathways, Flat 2, 40 Baldslow Road, Hastings, East Sussex, TN34 2EY, UK

Running title : Barrier, clearance and detoxifying autism genes.

RI PT

[email protected] Tel: 0044 (0)1424 422362 : Mobile 0044(0)7854659602

SC

Key words: autism; blood/brain barrier; intestine; skin, airways; placenta, cilia Abstract

M AN U

Even taking problems of diagnosis into account, a five-fold increase in the incidence of autism in recent decades, in the absence of any known changes in the human gene pool suggests a strong environmental influence. Numerous pollutants have been implicated in epidemiological studies, including pesticides, heavy metals, industrial solvents, air pollutants, particulate matter, bisphenol A,

TE D

phthalates and flame retardants. Many genes have been implicated in autism, some of which are directly related to detoxification processes. Many are also expressed prenatally in the frontal cortex when the effects of such toxins on neurodevelopment are most relevant. To gain access to the

EP

foetal brain, toxins must pass placental and blood/brain barriers and access to maternal or children’s blood necessitates passage across skin, airway and intestinal barriers. Literature survey of a subset

AC C

of 206 genes, defined as prime autism susceptibility candidates from an Autworks/Genotator analysis, revealed that most could be related to barrier function at blood/brain, skin, intestinal, placental or other interfaces. These genes were highly enriched in proteome datasets from blood/brain and placental trophoblast barriers and many localised to skin, intestinal, lung, umbilical and placental compartments. Many were also components of the exosomal/transcytosis pathway that is involved in the transfer of compounds across cells themselves, rather than between them. Several are involved in the control of respiratory cilia that sweep mucus and noxious particles from the airways. A key role of autism susceptibility genes may thus relate to their ability to modulate the

2

ACCEPTED MANUSCRIPT access of numerous toxins to children, and adults and, during gestation, to the developing foetal

AC C

EP

TE D

M AN U

SC

RI PT

brain.

3

ACCEPTED MANUSCRIPT Introduction. The incidence of autism spectrum disorders in the UK increased 5 fold in the 1990’s, reaching a plateau in the 2000’s up to 2010 (Taylor et al., 2013). In the USA, this increase has persisted with an incidence rising 2.2 fold from 2000 to 2010 (Wingate et al., 2014). These figures may in part be

RI PT

confounded by over- or misdiagnosis (Blumberg et al., 2015;Polyak et al., 2015) but the underlying increase, in the absence of any known changes in the human gene pool, suggest a strong environmental influence. Recent reviews have highlighted the dangers of environmental

SC

neurodevelopmental toxicants (pesticides, phthalates, polychlorinated biphenyl , solvents, toxic waste sites, air pollutants and heavy metals) in relation to autism and related disorders (Grandjean

M AN U

and Landrigan, 2014;Rossignol et al., 2014). Many such compounds are endocrine disruptors capable of modifying foetal and childhood neurodevelopmental pathways (de Cock et al., 2012;Gore et al., 2014;Kajta and Wojtowicz, 2010;Kalkbrenner et al., 2014). Endocrine disruptors have been associated with autism, IQ loss and associated intellectual disability, attention-deficit hyperactivity

TE D

disorder, childhood obesity, adult obesity and diabetes, cryptorchidism, and male infertility. It has been estimated that the burden of health and economic costs attributable to endocrine disruptor

2016).

EP

exposure in the European Union amounts to 163 billion euros (Trasande et al., 2015;Trasande et al.,

AC C

Many genes have been implicated in autism and in a twin study susceptibility to autism spectrum disorders was suggested to have moderate genetic heritability and a substantial shared twin environmental component (Hallmayer et al., 2011). Autism is a neurodevelopmental disorder and the symptoms and pathology clearly neurally related. Autism related genes are preferentially expressed prenatally in the frontal cortex suggesting that an inherent genetic susceptibility may be confined to this period (Birnbaum et al., 2014)The high component of chemical pollutant risk is also concentrated in the prenatal period (Matelski and Van de, 2016).

4

ACCEPTED MANUSCRIPT Many studies, not unnaturally, have focussed on the neurobiological roles of autism susceptibility genes (Berbel et al., 2014;Chiocchetti et al., 2014;Kazdoba et al., 2016;Kleijer et al., 2014). Pathway analyses of autism genes have identified disruption of many functions including protein synthesis,

transcriptional/epigenetic regulation, neurodevelopment and synaptic and immune signalling (Estes

RI PT

and McAllister, 2015;Sahin and Sur, 2015;Voineagu and Eapen, 2013) . Certain autism susceptibility genes including paraoxonase (PON1), glutathione transferases (GSTM1 and GSTP1), δ-aminolevulinic acid dehydratase (ALAD) , the iron transporter SLC11A3 and the metal regulatory transcription

SC

factor 1 modify (MTF1) can be directly related to detoxification pathways (Rossignol et al., 2014). To gain access to the developing brain, chemicals have to traverse several barrier systems including

M AN U

the placental and blood brain barriers, while the passage of such compounds on the maternal side or in childhood depends on other barriers including skin, airway and intestinal interfaces. Intestinal barrier function is compromised in autistic subjects and their first degree relatives (de Magistris et al., 2010) . Compromised placental function has also been associated with autism as evidenced by a

TE D

high incidence of pre-eclampsia and of trophoblast inclusions in the mothers of autistic children (Anderson et al., 2007;Walker et al., 2013;Walker et al., 2015). Modified transport of amino acids (alanine, tyrosine) has also been observed in skin fibroblasts from autistic patients (Fernell et al.,

EP

2007). Comorbidity between autism and atopic dermatitis has also been observed, with the latter characterised by epidermal permeability defects (Billeci et al., 2015). Psoriasis is also common in

AC C

autistic subjects (Wu et al., 2015;Zerbo et al., 2015) and this condition also affects skin permeability (Stawczyk-Macieja et al., 2015). The importance of barrier function in relation to multiple environmental pollutants and autism, particularly during critical developmental periods when barrier components are still being formed has also been noted by others (Julio-Pieper et al., 2014;Liu et al., 2005;Ratajczak, 2011;Viggiano et al., 2015;Wong et al., 2015).

5

ACCEPTED MANUSCRIPT This article focuses on the barrier function of a subset of 206 autism susceptibility genes defined as prime autism susceptibility candidates based on an Autworks study of the Genotator association database (Nelson et al., 2012). The results suggest that a common feature of these candidates relates to diverse barriers in the human body.

RI PT

Methods

Genes associated with autism are catalogued at the Autworks database using a ranking system

SC

derived from analysis of the Genotator association database (Nelson et al., 2012;Wall et al., 2010)

http://tools.autworks.hms.harvard.edu/gene_sets/580/genes . This provided a list of 206 autism

M AN U

susceptibility genes regarded as prime susceptibility candidates. The genes and their definitions are listed in supplementary data. HUGO Gene Nomenclature Committee gene symbols are used, and those belonging to this list are highlighted in bold throughout the text.

The tissue and cellular distribution of the 206 Autism genes were analysed using the functional

TE D

enrichment analysis tool (FUNRICH). (Pathan et al., 2015) http://funrich.org/index.html . This tool derives proteomic and genomic distribution data from >1.5 million annotations. It provides the total number of genes in datasets from each region sampled and returns the significance of any

AC C

test.

EP

enrichment for members of the uploaded 206 autism genes, using the hypergeometric probability

Autism gene enrichment was also analysed in two published blood brain barrier proteome datasets of mouse cerebral arteries (6620 proteins) (Badhwar et al., 2014) and mouse brain microvessel membranes and basal lamina components (4054 proteins) (Chun et al., 2011), as well as in a proteome dataset of the placental syncytial trophoblast (Vandre et al., 2012). Ciliary proteomic datasets from the choroid plexus (Narita et al., 2012) and the membrane proteome of respiratory cilia were also analysed (Kuhlmann et al., 2014).

6

ACCEPTED MANUSCRIPT The presence of the autism genes in exosomes (a means of transit across rather than between cells (Haqqani et al., 2013;Mathivanan et al., 2010;Sun et al., 2013)) was assessed using ExoCarta (

http://www.exocarta.org ) a manually curated database of exosomal proteins, RNA and lipids (Simpson et al., 2012)

RI PT

For a genome of 26846 coding genes and 206 autism genes, one would expect 206/26846 (0.77%) to exist in any other dataset. This figure was used to define expected values and the significance of enrichment values (observed/expected) in other datasets was calculated using the hypergeometric

SC

probability test. Values were considered significant at P < 0.05. As most of the data relate to

anatomical location rather than comparison of activity, the presence of multiple autism genes in any

M AN U

location dataset itself suggests a functional relevance ,irrespective of statistical significance, but the precise roles cannot be inferred from anatomical data. Literature survey was therefore used to highlight the roles of certain of the autism genes specifically in relation to barrier function.

TE D

Results

The tissue distribution of the autism genes.

Except where mentioned for specific targeted proteomics datasets, all expression data are from the

EP

Funrich tool. Tissues expressing > 100 autism genes are depicted in Fig 1. Apart from brain tissues,

AC C

most genes were expressed in plasma (a source of exosomes) (Baranyai et al., 2015), Human umbilical vein endothelial cells (HUVEC) as well as in the placenta, testis and ovary, liver, lung, intestine, skin, muscle and the thyroid, prostate, pancreas and adrenal glands. These genes are not restricted to brain tissue and their preferential distribution in umbilical, placental, lung, colon, duodenum, small intestine and skin areas is relevant to the barrier theme. Figure 1 The number of autism genes (where N >100 of the 206 input) expressed in different tissues. Data are ranked by the number of genes per tissue (HUVEC = human umbilical vein epithelial cells).

7

ACCEPTED MANUSCRIPT

Brain distribution and enrichment of the autism genes The autism genes are primarily localised in the cerebral cortex, hippocampus and cerebellum .Many

RI PT

are also found in the lateral ventricle, a site of the choroid plexus which eliminates xenobiotics and endogenous waste from the cerebrospinal fluid to prevent accumulation in the brain (Kusuhara and Sugiyama, 2004), and highly enriched in the two blood-brain barrier proteome datasets (BBBa

SC

(mouse cerebral arteries) (Badhwar et al., 2014) and BBBb (mouse brain microvessel membranes and basal lamina)(Chun et al., 2011). The autism genes were also enriched in a proteomics dataset of

M AN U

the swine choroid plexus epithelial ciliome (Narita et al., 2012) Figure 2

The number of autism genes (of 206) expressed in brain tissues (Funrich data) and in blood brain barrier proteome datasets (BBBa (mouse cerebral arteries) and BBBb (mouse brain microvessel

TE D

membranes and basal lamina) and from the swine choroid plexus ciliome (Narita et al., 2012) . The enrichment values (observed/expected) are shown after each tissue name on the X axis. The associated P values, derived from the hypergeometric test, are shown on the right Y axis, which is set

AC C

EP

at a maximum of 0.05.

Distribution and enrichment of the autism genes in detoxification (liver/kidney) and intestinal locations. Many of the 206 autism genes were expressed and significantly enriched in the liver and kidney and in all intestinal regions. This would concur with reports of gastrointestinal pathology in autistic

8

ACCEPTED MANUSCRIPT children extending from the oesophagus to the colon, as well as with reports of impaired liver and

kidney function (Cubala-Kucharska, 2010;Horvath and Perman, 2002;White, 2003). It is also relevant to the barrier theme of this review.

RI PT

Figure 3 The number of autism genes (of 206) expressed liver, kidney and intestinal regions (Funrich data) The enrichment values (observed/expected) are shown after each tissue name on the X axis. The

SC

associated P values, derived from the hypergeometric test, are shown on the right Y axis, which is

M AN U

set at a maximum of 0.05.

TE D

The airway and skin distribution of the autism genes

The autism genes are also expressed and enriched in lung and airway datasets and in the skin and in a proteomics dataset of 4403 proteins restricted to the respiratory cilia (Kuhlmann et al., 2014). The

AC C

Figure 4

EP

function of the respiratory and other cilia is discussed below.

The number of autism genes (of 206) expressed in respiratory and skin regions (Funrich data) and in a proteomics dataset of the respiratory cilia. The enrichment values (observed/expected) are shown after each tissue name on the X axis. The associated P values, derived from the hypergeometric test, are shown on the right Y axis, which is set at a maximum of 0.05.

9

ACCEPTED MANUSCRIPT Distribution and enrichment of the autism genes in reproductive tissues.

Many of the autism genes are expressed in reproductive tissues, particularly in human umbilical vein endothelial cells (HUVECs), the placenta, testis and ovary. While not enriched in the placenta, the 126/206 autism genes expressed in this tissue evidently have a placental function that might be

RI PT

compromised by the polymorphisms therein. Both the ovaries and placenta are a source of maternal oestrogen for the foetus. The autism genes were significantly enriched in many other male and

female reproductive tissues, particularly in the endometrium and uterine cervix and also in a smaller

SC

proteomics dataset of the placental syncitiotrophoblast (Vandre et al., 2012) .

M AN U

The cervix is lined with mucus-secreting epithelial cells expressing many barrier proteins including junctional complexes, microvilli and cilia, innate immune receptors, antimicrobial peptides, and mucins. The cervix forms an important barrier between the microbe-rich vaginal cavity and the relatively sterile endometrium (Iyer et al., 2009;Radtke et al., 2012). The endometrium also plays a role in immune defence (King et al., 2003). These barriers are primarily designed against infectious

TE D

agents but many industrial pollutants also have toxic effects on the reproductive tissues in which these autism genes are concentrated (Miller et al., 2004) . Several studies have linked maternal

and Van de, 2016).

AC C

Figure 5

EP

infection during pregnancy with the subsequent development of autism in the offspring (Matelski

The number of autism genes (of 206) expressed in reproductive tissues (Funrich data). The enrichment values (observed/expected) are shown after each tissue name on the X axis. The associated P values, derived from the hypergeometric test, are shown on the right Y axis, which is set at a maximum of 0.05.

10

ACCEPTED MANUSCRIPT

Glandular expression and enrichment of the autism genes Relatively large numbers of the autism genes are expressed and enriched in the thyroid and

RI PT

parathyroid. Maternal thyroid hormones (thyroxine, triiodothyronine and calcitonin) play an important role in prenatal neurodevelopment (Andersen et al., 2015) and a family history of

hypothyroidism has been associated with the development of childhood autism (Wu et al., 2015).

SC

The autism genes are also expressed and enriched in the pancreas and this is relevant to associations between maternal diabetes and autism (Ornoy et al., 2015). The autism genes are also expressed

M AN U

and enriched in the adrenals which secrete many steroid hormones (e.g. aldosterone, cortisol, and androgens )with multiple functions and an important role in neurodevelopment (Gore et al., 2014). Figure 6

The number of autism genes (of 206) expressed in glandular tissues (Funrich data). The enrichment

TE D

values (observed/expected) are shown after each tissue name on the X axis. The associated P values, derived from the hypergeometric test, are shown on the right Y axis, which is set at a maximum of

AC C

EP

0.05.

Expression and enrichment of the autism genes in other organs. Many of these genes are expressed and enriched in plasma (a source of exosomes) (Baranyai et al., 2015)) and in the Exocarta exosome dataset (Simpson et al., 2012). Fewer were expressed but enriched in macrophages, monocytes and blood vessels. Many were also expressed and enriched in immune tissues (spleen, bone marrow, tonsils and lymph nodes), in cardiac and other muscles, the

11

ACCEPTED MANUSCRIPT

bladder and in foetal and embryonic tissue. Some are expressed and enriched in optic, and in bone, cartilage and fat derived cells. Figure 7

RI PT

The number of autism genes (of 206) expressed in other diverse cells and tissues (Funrich data). The enrichment values (observed/expected) are shown after each tissue name on the X axis. The

associated P values, derived from the hypergeometric test, are shown on the right Y axis, which is set

M AN U

SC

at a maximum of 0.05.

A summary of the tissue distribution data.

These autism genes, while expressed in brain areas relevant to neuropathology, are also mostly

TE D

expressed and/or enriched in many areas relevant to barrier function (intestine, airways, blood vessels, skin, placenta and cervix) and specifically in blood/brain barrier, trophoblast and respiratory cilia proteomic datasets. Their distribution is relevant to the many pollutants implicated in autism

EP

(Grandjean and Landrigan, 2014;Rossignol et al., 2014), which have to cross such barriers, and to the “leaky gut” scenario in autism (de Magistris et al., 2010;Liu et al., 2005;White, 2003). The importance

AC C

of the blood brain barrier in autism has been stressed by others (Demeestere et al., 2015;Wong et al., 2015), although its integrity, or that of the skin or airway barriers, do not appear to have been assessed in human studies. Many autism genes are also expressed and enriched in organs of detoxification (liver and kidney) and in endocrine organs releasing steroid hormones relevant to neurodevelopment and to studies relating environmental endocrine disruptors to autism (de Cock et al., 2012;Kajta and Wojtowicz, 2010;Kajta and Wojtowicz, 2013;Kalkbrenner et al., 2014). The susceptibility genes thus lie at an interface between cause and effect. Their polymorphisms have

12

ACCEPTED MANUSCRIPT downstream consequences affecting human neurophysiology, but the genes are also situated in regions allowing them to regulate access of the upstream environmental influences. Specific barrier functions of autism genes.

RI PT

Several of the Autworks genes, highlighted in bold below, play important roles in barrier function. For example adhesion molecules (HEPACAM MAG MOG NRCAM PECAM1 PXN) , cadherins and protocadherins (CDH8 CDH9 CDH10 PCDH10, PCDH11Y, PCDH19) , junction molecules (GAP43 GJA1)

SC

and catenins (armadillo repeat gene ARVCF) play important roles in blood-brain and intestinal

barrier function(Sanders, 2005;Vorbrodt and Dobrogowska, 2003) and in the placental trophoblast

M AN U

(Aplin et al., 2009).Integrins (ITGA4 ITGB3) also play an important role in barrier function(Del Zoppo et al., 2006;Larjava et al., 2011;Milner and Campbell, 2002;Wu, 2005).

Presynaptic neurexins (NRXN1 NRXN2) and their postsynaptic neuroligin partners (NLGN1 NLGN3 NLGN4X NLGN4Y) bridge the synapse and promote adhesion between axons and dendrites (Dean

TE D

and Dresbach, 2006). Neurexins and neuroligins are also involved in intestinal function and decreased expressions of Ghrelin, Neurexin, and Neuroligin proteins can induce the loss or dysfunction of ganglion cells in the distal intestinal canal (Shangjie et al., 2015). Neuropilins and

EP

semaphorins (NRP2 SEMA5A) also play a role in epithelial and endothelial junction and barrier formation (Treps et al., 2013). Synapsin (SYN1) is a synaptic protein also found in bovine brain

AC C

capillaries of the blood brain barrier (Pardridge et al., 1985). The transcription factor FOXP1, the ribosomal protein RPL10 and the ubiquitin ligase UBE3A are all highly expressed in the human choroid plexus epithelium that forms the outer blood-brain barrier (Janssen et al., 2013) . Aquaporin (AQP4), calcium (CACNA1C CACNA1G CACNA1H) and sodium (SCN2A SCN3A ) channels as well as receptor operated channels (gamma aminobutyric acid: GABRA1 GABRA5 glutamate GRIA2 GRIK2 GRIN2A and serotonin HTR3C) and the cystic fibrosis transmembrane regulator (CFTR) , transporters (SLC1A1 (glutamate) SLC19A1 (folate) SLC25A12 (mitochondrial glutamate/aspartate

13

ACCEPTED MANUSCRIPT

exchange) SLC6A3 (dopamine) SLC6A4 (serotonin) SLC6A8 (creatine) ) and pumps (ATP1A1 ATP10A) regulate chemical/ion entry at the cell membrane itself. Other genes related to adhesion or junctions include CD38 (ADP ribosyl cyclase)(Funaro and Malavasi, 1999) DOCK4 (dedicator of cytokinesis) (Gadea and Blangy, 2014) and the focal adhesion kinase (PTK2) (Hanks et al., 2003). In

RI PT

cancer cells, the dead box helicase DDX53 increases the phosphorylation of PTK2 (Shim et al., 2006) Cadherins and integrins are each associated with their particular “adhesomes”, networks of scaffold molecules and signalling molecules (Winograd-Katz et al., 2014;Zaidel-Bar et al., 2007;Zaidel-Bar,

SC

2013). The cadherin adhesome contains 174 genes (Zaidel-Bar, 2013) , 8 of which belong to the autism gene set (ARVCF CDH8 CDH9 CDH10 MET PTEN TUBA1B SRC) (Observed/expected = 5.99: p=

M AN U

0.000054). Focal adhesion network components of the integrin adhesome (Zaidel-Bar et al., 2007) are listed at http://www.adhesome.org/components/index.htm . Of the 157 components (to which were added the integrins, ITGA4 and ITGB3) 7 belong to the autism gene set (ITGA4 ITGB3 MAPK1 PTEN PTK2 PXN SRC) (Observed/expected = 5.81: p= 0.00019)

TE D

These genes affect many aspects of brain function and neurodevelopment but their barrier role is also pertinent to the multiple toxins that have been implicated in autism, placing the genes at an

EP

interface between environment and effect. Genes involved in placental function

AC C

Folate is essential for embryonic development and the folate transporter (SLC19A1) (Patterson et al., 2008) as well as dihydrofolate reductase (DHFR) and 5,10-methylenetetrahydrofolate reductase (MTHFR) (Jarabak and Bachur, 1971) (Cherukad et al., 2012) are expressed in the placenta. ASMT is Involved in placental melatonin synthesis (Iwasaki et al., 2005) and melatonin regulates trophoblast differentiation (Soliman et al., 2015). Secretin (SCT) is also localised in this organ (Knox et al., 2011). BNDF (brain-derived neurotrophic factor) and its receptor NTRK2 are expressed in the human placenta and regulate trophoblast growth (Dhobale et al., 2012). HGF (hepatocyte growth factor)

14

ACCEPTED MANUSCRIPT and its receptor MET also influence the cytotrophoblast throughout the process of placental formation and growth (Clark et al., 1996). The expression of adenosine deaminase (ADA) at the

maternal-foetal interface is essential for early post-implantation development in mice (Blackburn et al., 1997), and the adenosine receptor, ADORA2A, is also placentally localised (Versen-Hoynck et al.,

RI PT

2009). Neurotransmitter receptors that are placentally localised include the dopamine receptor DRD4 (Matsumoto et al., 1995) the serotonin receptor , HTR2A (Paquette et al., 2013) and the beta2 adrenergic receptor, ADRB2, which regulates the contractility of human term placental vessels

SC

(Resch et al., 2003). ADBR2 stimulation increases progesterone release in cells from human term placental cells (Caritis et al., 1983). The serotonin transporter (SLC6A4) (Ramamoorthy et al., 1992)

M AN U

and enzymes related to monoamine metabolism including COMT (catechol-O-methyltransferase) (Lundstrom et al., 1991) and monoamine oxidase (MAOA) (Zhang et al., 2010) are also placentally localised.

The androgen receptor (AR) is localised in cells involved in formation of the placental barrier and in

TE D

the umbilical cord (Wieciech et al., 2013). Extraembryonic tissues and in particular trophoblasts constitute an interface at risk from maternal complement during pregnancy. Membrane cofactor protein regulates complement C4 activity (C4B) on the maternal-facing surfaces of extraembryonic

EP

tissues during human development (Vanderpuye et al., 1994).Macrophage inhibitory factor (MIF) inhibition interferes with trophoblast cell migration in the placenta (Jovanovic et al., 2015). Other

AC C

placentally expressed genes include calbindin (CALB1) which is expressed in human placental trophoblasts (Belkacemi et al., 2003) and MAPK8IP2 which protects against oxidative stress in the placenta and is down-regulated by placental implantation factor secreted by viable embryos (Barnea et al., 2012). NFKB1 is activated in preeclampsia, and by oxidative stress in a trophoblast-like cell line (Vaughan and Walsh, 2012). Acetylcholinesterase (ACHE) is localised in many regions including the placenta , where it plays a significant role in pesticide effects on foetal development (Souza et al., 2005). A splice variant of the Rett syndrome protein MECP2 regulates placental development (Itoh et al., 2012) and the translation initiation factor eIF4E prevents final extravillous

15

ACCEPTED MANUSCRIPT trophoblast cell differentiation and supports placental cell proliferation and survival (Kawamura et al., 2011;Kitroser et al., 2012)The kinesin KIF17 is highly expressed in the developing vascular endothelium in early pregnancy (Sati et al., 2009) and the synaptic scaffold protein SHANK2 is also localised in the placenta and one of a group of imprinted genes where expression patterns

RI PT

distinguish between new-born neurobehavioral profiles (Green et al., 2015) Respiratory Cilia

SC

DYX1C1 (dyslexia susceptibility 1 candidate 1) is involved in the regulation of respiratory cilia that sweep mucus, debris and noxious particles away from airways. Deleting exons 2-4 of Dyx1c1 in mice

M AN U

produces a phenotype resembling primary ciliary dyskinesia, a disorder characterized by chronic airway disease, laterality defects and male infertility (Tarkar et al., 2013). Other autism related genes also regulate these cilia. Adenomatosis polyposis coli (APC) controls genetic programmes related to respiratory cilia differentiation (Li et al., 2013). Arginine vasopressin (AVP) increases cilia beat frequency in airway epithelia via a calcium-dependent mechanism (Cholewa and Paolone, 2012) and

TE D

substance P (TAC1) also stimulates respiratory cilia beat frequency (Takizawa, 1990). ATP, UTP, or adenosine (ADA, adenosine deaminase ADSL adenylosuccinate lyase) also increase the beat

EP

frequency of airway respiratory cilia (Gonzalez et al., 2013) and the cystic fibrosis transmembrane regulator (CFTR) increases ciliary beat frequency via binding to and augmentation of the effects of

AC C

the adenosine receptor ADORA2B (Watson et al., 2011) . Adrenaline increases cilia beat frequency via the beta-2 adrenoceptor ADRB2 (Shiima-Kinoshita et al., 2004) . Beat frequency between cilia is coordinated by gap junctions and connexin 43 (GJA1) has been suggested to play a role in such coordination, as it is highly expressed in nasal epithelial cells (Yeh et al., 2003). TAS2 bitter taste receptors (TAS2R1) are also expressed in these cilia (Green, 2012). In the upper airways TAS2 receptors are expressed in nasal solitary chemosensory cells and their activation results in the secretion of antimicrobial peptides, suggesting an important role in immune defence (Lee et al., 2014). NOS1 is also localised to the respiratory cilia axoneme (a central microtubule rich structure)

16

ACCEPTED MANUSCRIPT (Jackson et al., 2015) . IL6 promotes regeneration of airway ciliated cells from basal stem cells (Tadokoro et al., 2014). The Kinesin, KIF17, transports cargos to the distal tips of flagella or cilia

(Wong-Riley and Besharse, 2012). Hepatocyte growth factor (HGF : receptor = MET) is an important fibroblast-derived factor that contributes to the development of bronchial epithelial cells and

RI PT

ciliogenesis (Myerburg et al., 2007) . Interleukin 6 (IL6) promotes regeneration of airway ciliated cells from basal stem cells (Tadokoro et al., 2014;Watson et al., 2011). Tumor necrosis factor (TNF)

regulates ciliary beat frequency in human sinus epithelial cells possibly via nitric oxide (Chen et al.,

SC

2000) and human respiratory cilia express the neuronal nitric oxide synthase , NOS1(Jackson et al., 2015). The beat frequency of these cilia is inhibited by cigarette smoke (Wang et al., 2012) or other

M AN U

airborne pollutants including sulphur dioxide(Riechelmann et al., 1994) or diesel exhaust particles (Bayram et al., 1998).

Respiratory cilia are motile and such cilia are also found on spermatozoa and in cerebrospinal fluid barriers, including the choroid plexus, but related to non-motile primary cilia .Both types of cilia

TE D

respond to environmental, mechanical and chemical stimuli and signal to the cell body (Kleene and Van Houten, 2014). Both types of cilia are structurally similar with a microtubule backbone (the axoneme) with nine outer microtubule doublets, and only in the case of motile cilia a central

EP

microtubule doublet, the whole surrounded by a plasma membrane (Pedersen and Rosenbaum, 2008). Cilia are expressed in all cells and it has been noted that several psychiatric risk genes

AC C

converge on processes related to cilia. Those within this autism gene set include dopamine receptors (DRD1, DRD4) disrupted in schizophrenia 1 (DISC1), the forkhead transcription factor, FOXP1 and neurexin, NRXN1 (Marley and von Zastrow, 2010;Marley and von Zastrow, 2012). The proteomic composition of motile (9+2 microtubules) and non-motile cilia (9+0 microtubules) from previously published data has been reviewed by Narita et al (Narita et al., 2012). Motile cilia contained 172 proteins, of which 6 are autism genes (ARVCF, ATP1A1, MAPK3, RPL10, SRC, TUBA1B) (Observed/expected = 4.54 P= 0.0018) and non-motile cilia 435 proteins of which 8 belong

17

ACCEPTED MANUSCRIPT to the autism gene set (ARVCF ATP1A1 COMT GFAP MAPK3 SRC SYN1 TUBA1B) (Observed/expected = 2.39 P= 0.0129). They also identified 1001 proteins of the ciliome from

juvenile swine choroid plexus epithelial cells, 18 of which belong to the autism gene set (ABAT ADSL ARVCF ATP1A1 COMT CTSD EGF GAP43 GFAP MAOA MAPK3 NOS1 RPL10 SRC SYN1 SYNGAP1

RI PT

TUBA1B TXNRD2)(Observed/expected = 2.34 P= 0.00047). The exosomal pathway.

SC

Another route across barriers is the exosome pathway, in which receptors and their bound ligands on the luminal side of the barrier are imported via endocytosis, and the resulting microvesicles

M AN U

transported via endocytic pathways and exported by transcytosis/exocytosis to the other side of the barrier. This is an important means of communicating information across cellular barriers, using the cell itself rather than the gaps between them. Exosomal vesicles are found in all bodily fluids (Mathivanan et al., 2010).

TE D

ExoCarta ( http://www.exocarta.org ) is a manually curated database of exosomal proteins, RNA and lipids (Simpson et al., 2012), and interrogation of this database showed that 58/206 (28.2%) of the proteins encoded by the Autism gene set are present in a dataset of 5320 proteins found in

EP

human exosomes .(Observed/expected = 1.42: P= 0.00097).

AC C

Genes involved in detoxification.

These include glutathione peroxidase (GPX1) and transferase (GSTM1) and thioredoxin reductase (TXNRD2) (Narita et al., 2012)These are generally involved in protection against oxidative stress , produced for example by heavy metals (Flora et al., 2013). Paraoxonase 1(PON1) is involved in the detoxification of organophosphate pesticides (Richter et al., 2010). Caveats and future directions

18

ACCEPTED MANUSCRIPT This review shows that many of the autism genes are localised in barrier sites but is primarily

concerned with anatomy rather than function, although the primary role of the adhesion, cadherins, integrin and junction molecules does relate to barriers, and other genes do relate to barrier or cilia control (see above). Most animal studies in relation to these genes have focussed on brain function

RI PT

and there is essentially no data in relation to the effects of the gene polymorphisms on barrier function in animal models. While intestinal permeability does appear to be modified in autistic patients, effects on skin, blood/brain or placental barriers or on airway clearance seem to be

SC

uncharted. Some of these problems could be addressed in animal studies with the same procedures used to unravel brain function (e.g. transgenics, knockouts and pharmacology). In the human

M AN U

condition, skin permeability tests are feasible and it may be possible to examine transport and permeability in at-term delivered placentas. Nasal mucociliary clearance can be measured in the clinic, and nasal respiratory cilia from healthy volunteers have been studied in vitro and their study is also possible in vivo using optical techniques (Lindberg and Runer, 1994;Selwyn et al., 1996) .

TE D

Blood brain barrier measurements in the clinic are rather more invasive although feasible. In relation to pharmacology, adenosine (adenosine deaminase ADA, receptor ADORA2A) (Bynoe et al., 2015) and vasopressin(AVP AVPR1A)(Nagao, 1998) are known to regulate blood-brain barrier

EP

permeability which is also increased by Corticotropin-releasing hormone(CRH) (Theoharides and Konstantinidou, 2007). The serotonin precursor 5-hydroxytryptophan (TPH1 TPH2) reinforces the

AC C

intestinal barrier in healthy controls , but not in patients with irritable bowel syndrome(Keszthelyi et al., 2014) . The serotonin receptor (HTR1B) is also involved in the control of vascular permeability in the brain (Riad et al., 1998), while substance P (TAC1) regulates vascular permeability in the intestine, skin and brain (Annunziata et al., 2002;Holzer, 1998;Lordal et al., 1996) . Somatostatin is also involved in the control of vascular permeability via SSTR5 and tight junction control (Lei et al., 2014). Leptin (LEP) increases colonic epithelial permeability in lean rats, also via tight junction control (Le Drean et al., 2014). Melatonin (synthesised by ASMT; receptors = MTNR1A MTNR1B)

19

ACCEPTED MANUSCRIPT

improves duodenal barrier function in ethanol treated rats (Sommansson et al., 2013). Adrenaline increases intestinal permeability in rats via the beta-2 receptor (ADRB2)(Lange and Delbro, 1995) and dopamine inhibits vasopressin (AVP)-dependent sodium transport and water permeability in rat kidney cortical collecting ducts via the DRD4 receptor(Sun and Schafer, 1996).While glutamate and

RI PT

GABA (gaba transaminase and glutamate decarboxylase: ABAT GAD1 ) are primarily brain

neurotransmitters, GABA is able to accelerate skin barrier repair in an in vitro model using cultured keratinocytes while glutamate has the opposite effect. The calcium ionophore ionomycin (CACNA1C

SC

CACNA1G CACNA1H) delayed barrier recovery and a chloride ionophore accelerated repair after barrier disruption (Denda et al., 2003). This effect is related to NMDA (GRIN2A) rather than AMPA

M AN U

receptors and to GABA-A ionotropic (GABRA1 GABRA5 GABRB3 GABRG2 GABRG3) rather that GABAB receptors , although the subunit identities were not analysed (Denda et al., 2002;Fuziwara et al., 2003). In rats, prenatal treatment with valproic acid, which has been linked to autism in Man, produces autistic-like behaviour and pathology and increases blood brain barrier permeability,

TE D

effects reversed by the NMDA receptor antagonist memantine (Kumar and Sharma, 2016) suggesting a link between autism genesis and blood/brain barrier function. Thus, while there is virtually no functional data on barrier function outside the intestine, in relation to autism or to the individual

EP

genetic polymorphisms, there is clear evidence that the genes are localised in barrier sites and that these barriers are controlled by the transmitters and signalling networks relevant to the autism

AC C

genes. Conclusion

This literature and distribution survey shows that, in addition to effects these genetic variants may have on autism neurophysiology and neuropathology, they possess barrier properties are highly relevant to the multiple environmental agents that have been implicated in autism in epidemiological studies. Key autism genes identified from the Autworks meta-analysis are involved in blood/brain and placental barriers that regulate the delivery of toxins to the foetal brain, as well

20

ACCEPTED MANUSCRIPT as in skin and intestinal barrier function that regulates access of the toxins to maternal and childhood blood. They are also concentrated in exosomal/transcytosis pathways and control the

respiratory cilia that sweep mucus and entrapped particles upwards and outwards from the airways, a role that is relevant to particulate matter and air-borne pollutants. While many are expressed in

RI PT

brain areas, they are also concentrated in umbilical and placental tissue, as well as in airway, skin, and intestinal tissue, all of which are important barrier sites. These are regulated by autism-related transmitters and signalling networks. Polymorphisms in these genes are thus in a position to modify

SC

the access of many of the toxins that have been suggested as potential causes of the autism

epidemic. This places the susceptibility genes at the interface between cause and effect and further

M AN U

suggests that removal of the toxins and more rigorous environmental and toxicological control might be the most appropriate means of stemming and reversing the autism epidemic.

AC C

EP

TE D

The author reports no conflict of interest and no funding source.

Reference List

Andersen,S.L., Olsen,J., Laurberg,P., 2015. Foetal programming by maternal thyroid disease. Clin Endocrinol (Oxf) 83, 751-758. Anderson,G.M., Jacobs-Stannard,A., Chawarska,K., Volkmar,F.R., Kliman,H.J., 2007. Placental trophoblast inclusions in autism spectrum disorder. Biol Psychiatry 61, 487-491. Annunziata,P., Cioni,C., Santonini,R., Paccagnini,E., 2002. Substance P antagonist blocks leakage and reduces activation of cytokine-stimulated rat brain endothelium. J Neuroimmunol 131, 41-49. Aplin,J.D., Jones,C.J., Harris,L.K., 2009. Adhesion molecules in human trophoblast - a review. I. Villous trophoblast. Placenta 30, 293-298. Badhwar,A., Stanimirovic,D.B., Hamel,E., Haqqani,A.S., 2014. The proteome of mouse cerebral arteries. J Cereb Blood Flow Metab 34, 1033-1046.

21

ACCEPTED MANUSCRIPT

Baranyai,T., Herczeg,K., Onodi,Z., Voszka,I., Modos,K., Marton,N., Nagy,G., Mager,I., Wood,M.J., El Andaloussi,S., Palinkas,Z., Kumar,V., Nagy,P., Kittel,A., Buzas,E.I., Ferdinandy,P., Giricz,Z., 2015. Isolation of Exosomes from Blood Plasma: Qualitative and Quantitative Comparison of Ultracentrifugation and Size Exclusion Chromatography Methods. PLoS One 10, e0145686. Barnea,E.R., Kirk,D., Paidas,M.J., 2012. Preimplantation factor (PIF) promoting role in embryo implantation: increases endometrial integrin-alpha2beta3, amphiregulin and epiregulin while reducing betacellulin expression via MAPK in decidua. Reprod Biol Endocrinol 10, 50.

RI PT

Bayram,H., Devalia,J.L., Khair,O.A., Abdelaziz,M.M., Sapsford,R.J., Sagai,M., Davies,R.J., 1998. Comparison of ciliary activity and inflammatory mediator release from bronchial epithelial cells of nonatopic nonasthmatic subjects and atopic asthmatic patients and the effect of diesel exhaust particles in vitro. J Allergy Clin Immunol 102, 771-782. Belkacemi,L., Gariepy,G., Mounier,C., Simoneau,L., Lafond,J., 2003. Expression of calbindin-D28k (CaBP28k) in trophoblasts from human term placenta. Biol Reprod 68, 1943-1950.

SC

Berbel,P., Navarro,D., Roman,G.C., 2014. An evo-devo approach to thyroid hormones in cerebral and cerebellar cortical development: etiological implications for autism. Front Endocrinol (Lausanne) 5, 146.

M AN U

Billeci,L., Tonacci,A., Tartarisco,G., Ruta,L., Pioggia,G., Gangemi,S., 2015. Association Between Atopic Dermatitis and Autism Spectrum Disorders: A Systematic Review. Am J Clin Dermatol 16, 371-388. Birnbaum,R., Jaffe,A.E., Hyde,T.M., Kleinman,J.E., Weinberger,D.R., 2014. Prenatal Expression Patterns of Genes Associated With Neuropsychiatric Disorders. Am J Psychiatry. Blackburn,M.R., Knudsen,T.B., Kellems,R.E., 1997. Genetically engineered mice demonstrate that adenosine deaminase is essential for early postimplantation development. Development 124, 3089-3097.

TE D

Blumberg,S.J., Zablotsky,B., Avila,R.M., Colpe,L.J., Pringle,B.A., Kogan,M.D., 2015. Diagnosis lost: Differences between children who had and who currently have an autism spectrum disorder diagnosis. Autism. Bynoe,M.S., Viret,C., Yan,A., Kim,D.G., 2015. Adenosine receptor signaling: a key to opening the blood-brain door. Fluids Barriers CNS 12, 20. Caritis,S.N., Hirsch,R.P., Zeleznik,A.J., 1983. Adrenergic stimulation of placental progesterone production. J Clin Endocrinol Metab 56, 969-972.

EP

Chen,J.H., Takeno,S., Osada,R., Ueda,T., Yajin,K., 2000. Modulation of ciliary activity by tumor necrosis factor-alpha in cultured sinus epithelial cells. Possible roles of nitric oxide. Hiroshima J Med Sci 49, 49-55.

AC C

Cherukad,J., Wainwright,V., Watson,E.D., 2012. Spatial and temporal expression of folate-related transporters and metabolic enzymes during mouse placental development. Placenta 33, 440-448. Chiocchetti,A.G., Bour,H.S., Freitag,C.M., 2014. Glutamatergic candidate genes in autism spectrum disorder: an overview. J Neural Transm (Vienna ) 121, 1081-1106. Cholewa,J.M., Paolone,V.J., 2012. Influence of exercise on airway epithelia in cystic fibrosis: a review. Med Sci Sports Exerc 44, 1219-1226. Chun,H.B., Scott,M., Niessen,S., Hoover,H., Baird,A., Yates,J., III, Torbett,B.E., Eliceiri,B.P., 2011. The proteome of mouse brain microvessel membranes and basal lamina. J Cereb Blood Flow Metab 31, 2267-2281. Clark,D.E., Smith,S.K., Sharkey,A.M., Sowter,H.M., Charnock-Jones,D.S., 1996. Hepatocyte growth factor/scatter factor and its receptor c-met: localisation and expression in the human placenta throughout pregnancy. J Endocrinol 151, 459-467. Cubala-Kucharska,M., 2010. The review of most frequently occurring medical disorders related to aetiology of autism and the methods of treatment. Acta Neurobiol Exp (Wars ) 70, 141-146.

22

ACCEPTED MANUSCRIPT de Cock,M., Maas,Y.G., van de,B.M., 2012. Does perinatal exposure to endocrine disruptors induce autism spectrum and attention deficit hyperactivity disorders? Review. Acta Paediatr 101, 811-818.

de Magistris,L., Familiari,V., Pascotto,A., Sapone,A., Frolli,A., Iardino,P., Carteni,M., De Rosa,M., Francavilla,R., Riegler,G., Militerni,R., Bravaccio,C., 2010. Alterations of the intestinal barrier in patients with autism spectrum disorders and in their first-degree relatives. J Pediatr Gastroenterol Nutr 51, 418-424. Dean,C., Dresbach,T., 2006. Neuroligins and neurexins: linking cell adhesion, synapse formation and cognitive function. Trends Neurosci 29, 21-29.

RI PT

Del Zoppo,G.J., Milner,R., Mabuchi,T., Hung,S., Wang,X., Koziol,J.A., 2006. Vascular matrix adhesion and the blood-brain barrier. Biochem Soc Trans 34, 1261-1266. Demeestere,D., Libert,C., Vandenbroucke,R.E., 2015. Therapeutic implications of the choroid plexuscerebrospinal fluid interface in neuropsychiatric disorders. Brain Behav Immun 50, 1-13.

SC

Denda,M., Fuziwara,S., Inoue,K., 2003. Influx of calcium and chloride ions into epidermal keratinocytes regulates exocytosis of epidermal lamellar bodies and skin permeability barrier homeostasis. J Invest Dermatol 121, 362-367.

M AN U

Denda,M., Inoue,K., Inomata,S., Denda,S., 2002. gamma-Aminobutyric acid (A) receptor agonists accelerate cutaneous barrier recovery and prevent epidermal hyperplasia induced by barrier disruption. J Invest Dermatol 119, 1041-1047. Dhobale,M., Mehendale,S., Pisal,H., D'Souza,V., Joshi,S., 2012. Association of brain-derived neurotrophic factor and tyrosine kinase B receptor in pregnancy. Neuroscience 216, 31-37. Estes,M.L., McAllister,A.K., 2015. Immune mediators in the brain and peripheral tissues in autism spectrum disorder. Nat Rev Neurosci 16, 469-486.

TE D

Fernell,E., Karagiannakis,A., Edman,G., Bjerkenstedt,L., Wiesel,F.A., Venizelos,N., 2007. Aberrant amino acid transport in fibroblasts from children with autism. Neurosci Lett 418, 82-86. Flora,S.J., Shrivastava,R., Mittal,M., 2013. Chemistry and pharmacological properties of some natural and synthetic antioxidants for heavy metal toxicity. Curr Med Chem 20, 4540-4574.

EP

Funaro,A., Malavasi,F., 1999. Human CD38, a surface receptor, an enzyme, an adhesion molecule and not a simple marker. J Biol Regul Homeost Agents 13, 54-61. Fuziwara,S., Inoue,K., Denda,M., 2003. NMDA-type glutamate receptor is associated with cutaneous barrier homeostasis. J Invest Dermatol 120, 1023-1029.

AC C

Gadea,G., Blangy,A., 2014. Dock-family exchange factors in cell migration and disease. Eur J Cell Biol 93, 466-477. Gonzalez,C., Espinosa,M., Sanchez,M.T., Droguett,K., Rios,M., Fonseca,X., Villalon,M., 2013. Epithelial cell culture from human adenoids: a functional study model for ciliated and secretory cells. Biomed Res Int 2013, 478713. Gore,A.C., Martien,K.M., Gagnidze,K., Pfaff,D., 2014. Implications of prenatal steroid perturbations for neurodevelopment, behavior, and autism. Endocr Rev 35, 961-991. Grandjean,P., Landrigan,P.J., 2014. Neurobehavioural effects of developmental toxicity. Lancet Neurol 13, 330338. Green,B.B., Kappil,M., Lambertini,L., Armstrong,D.A., Guerin,D.J., Sharp,A.J., Lester,B.M., Chen,J., Marsit,C.J., 2015. Expression of imprinted genes in placenta is associated with infant neurobehavioral development. Epigenetics 10, 834-841.

23

ACCEPTED MANUSCRIPT Green,B.G., 2012. Chemesthesis and the chemical senses as components of a "chemofensor complex". Chem Senses 37, 201-206. Hallmayer,J., Cleveland,S., Torres,A., Phillips,J., Cohen,B., Torigoe,T., Miller,J., Fedele,A., Collins,J., Smith,K., Lotspeich,L., Croen,L.A., Ozonoff,S., Lajonchere,C., Grether,J.K., Risch,N., 2011. Genetic heritability and shared environmental factors among twin pairs with autism. Arch Gen Psychiatry 68, 10951102.

RI PT

Hanks,S.K., Ryzhova,L., Shin,N.Y., Brabek,J., 2003. Focal adhesion kinase signaling activities and their implications in the control of cell survival and motility. Front Biosci 8, d982-d996. Haqqani,A.S., Delaney,C.E., Tremblay,T.L., Sodja,C., Sandhu,J.K., Stanimirovic,D.B., 2013. Method for isolation and molecular characterization of extracellular microvesicles released from brain endothelial cells. Fluids Barriers CNS 10, 4. Holzer,P., 1998. Neurogenic vasodilatation and plasma leakage in the skin. Gen Pharmacol 30, 5-11.

SC

Horvath,K., Perman,J.A., 2002. Autism and gastrointestinal symptoms. Curr Gastroenterol Rep 4, 251-258.

M AN U

Itoh,M., Tahimic,C.G., Ide,S., Otsuki,A., Sasaoka,T., Noguchi,S., Oshimura,M., Goto,Y., Kurimasa,A., 2012. Methyl CpG-binding protein isoform MeCP2_e2 is dispensable for Rett syndrome phenotypes but essential for embryo viability and placenta development. J Biol Chem 287, 13859-13867. Iwasaki,S., Nakazawa,K., Sakai,J., Kometani,K., Iwashita,M., Yoshimura,Y., Maruyama,T., 2005. Melatonin as a local regulator of human placental function. J Pineal Res 39, 261-265. Iyer,S., Gaikwad,R.M., Subba-Rao,V., Woodworth,C.D., Sokolov,I., 2009. Atomic force microscopy detects differences in the surface brush of normal and cancerous cells. Nat Nanotechnol 4, 389-393.

TE D

Jackson,C.L., Lucas,J.S., Walker,W.T., Owen,H., Premadeva,I., Lackie,P.M., 2015. Neuronal NOS localises to human airway cilia. Nitric Oxide 44, 3-7. Janssen,S.F., van der Spek,S.J., Ten Brink,J.B., Essing,A.H., Gorgels,T.G., van der Spek,P.J., Jansonius,N.M., Bergen,A.A., 2013. Gene expression and functional annotation of the human and mouse choroid plexus epithelium. PLoS One 8, e83345.

EP

Jarabak,J., Bachur,N.R., 1971. A soluble dihydrofolate reductase from human placenta: purification and properties. Arch Biochem Biophys 142, 417-425. Jovanovic,K.M., Stefanoska,I., Abu,R.T., Al Abed,Y., Stosic-Grujicic,S., Vicovac,L., 2015. Pharmacological inhibition of MIF interferes with trophoblast cell migration and invasiveness. Placenta 36, 150-159.

AC C

Julio-Pieper,M., Bravo,J.A., Aliaga,E., Gotteland,M., 2014. Review article: intestinal barrier dysfunction and central nervous system disorders--a controversial association. Aliment Pharmacol Ther 40, 1187-1201. Kajta,M., Wojtowicz,A., 2010. Neurodevelopmental disorders in response to hormonally active environmental pollutants. Przegl Lek 67, 1194-1199. Kajta,M., Wojtowicz,A.K., 2013. Impact of endocrine-disrupting chemicals on neural development and the onset of neurological disorders. Pharmacol Rep 65, 1632-1639. Kalkbrenner,A.E., Schmidt,R.J., Penlesky,A.C., 2014. Environmental Chemical Exposures and Autism Spectrum Disorders: A Review of the Epidemiological Evidence. Curr Probl Pediatr Adolesc Health Care. Kawamura,K., Kawamura,N., Kumazawa,Y., Kumagai,J., Fujimoto,T., Tanaka,T., 2011. Brain-derived neurotrophic factor/tyrosine kinase B signaling regulates human trophoblast growth in an in vivo animal model of ectopic pregnancy. Endocrinology 152, 1090-1100.

24

ACCEPTED MANUSCRIPT Kazdoba,T.M., Leach,P.T., Crawley,J.N., 2016. Behavioral phenotypes of genetic mouse models of autism. Genes Brain Behav 15, 7-26.

Keszthelyi,D., Troost,F.J., Jonkers,D.M., van Eijk,H.M., Lindsey,P.J., Dekker,J., Buurman,W.A., Masclee,A.A., 2014. Serotonergic reinforcement of intestinal barrier function is impaired in irritable bowel syndrome. Aliment Pharmacol Ther 40, 392-402. King,A.E., Critchley,H.O., Kelly,R.W., 2003. Innate immune defences in the human endometrium. Reprod Biol Endocrinol 1, 116.

RI PT

Kitroser,E., Pomeranz,M., Epstein,S.G., Fishman,A., Drucker,L., Sadeh-Mestechkin,D., Lishner,M., Tartakover-Matalon,S., 2012. The involvement of eukaryotic translation initiation factor 4E in extravillous trophoblast cell function. Placenta 33, 717-724. Kleene,S.J., Van Houten,J.L., 2014. Electrical Signaling in Motile and Primary Cilia. Bioscience 64, 1092-1102.

SC

Kleijer,K.T., Schmeisser,M.J., Krueger,D.D., Boeckers,T.M., Scheiffele,P., Bourgeron,T., Brose,N., Burbach,J.P., 2014. Neurobiology of autism gene products: towards pathogenesis and drug targets. Psychopharmacology (Berl) 231, 1037-1062.

M AN U

Knox,K., Leuenberger,D., Penn,A.A., Baker,J.C., 2011. Global hormone profiling of murine placenta reveals Secretin expression. Placenta 32, 811-816. Kuhlmann,K., Tschapek,A., Wiese,H., Eisenacher,M., Meyer,H.E., Hatt,H.H., Oeljeklaus,S., Warscheid,B., 2014. The membrane proteome of sensory cilia to the depth of olfactory receptors. Mol Cell Proteomics 13, 1828-1843. Kumar,H., Sharma,B., 2016. Memantine ameliorates autistic behavior, biochemistry & blood brain barrier impairments in rats. Brain Res Bull 124, 27-39.

TE D

Kusuhara,H., Sugiyama,Y., 2004. Efflux transport systems for organic anions and cations at the blood-CSF barrier. Adv Drug Deliv Rev 56, 1741-1763. Lange,S., Delbro,D.S., 1995. Adrenoceptor-mediated modulation of Evans blue dye permeation of rat small intestine. Dig Dis Sci 40, 2623-2629.

EP

Larjava,H., Koivisto,L., Hakkinen,L., Heino,J., 2011. Epithelial integrins with special reference to oral epithelia. J Dent Res 90, 1367-1376.

AC C

Le Drean,G., Haure-Mirande,V., Ferrier,L., Bonnet,C., Hulin,P., de Coppet,P., Segain,J.P., 2014. Visceral adipose tissue and leptin increase colonic epithelial tight junction permeability via a RhoA-ROCK-dependent pathway. FASEB J 28, 1059-1070. Lee,R.J., Kofonow,J.M., Rosen,P.L., Siebert,A.P., Chen,B., Doghramji,L., Xiong,G., Adappa,N.D., Palmer,J.N., Kennedy,D.W., Kreindler,J.L., Margolskee,R.F., Cohen,N.A., 2014. Bitter and sweet taste receptors regulate human upper respiratory innate immunity. J Clin Invest 124, 1393-1405. Lei,S., Cheng,T., Guo,Y., Li,C., Zhang,W., Zhi,F., 2014. Somatostatin ameliorates lipopolysaccharide-induced tight junction damage via the ERK-MAPK pathway in Caco2 cells. Eur J Cell Biol 93, 299-307. Li,A., Chan,B., Felix,J.C., Xing,Y., Li,M., Brody,S.L., Borok,Z., Li,C., Minoo,P., 2013. Tissue-dependent consequences of Apc inactivation on proliferation and differentiation of ciliated cell progenitors via Wnt and notch signaling. PLoS One 8, e62215. Lindberg,S., Runer,T., 1994. Method for in vivo measurement of mucociliary activity in the human nose. Ann Otol Rhinol Laryngol 103, 558-566. Liu,Z., Li,N., Neu,J., 2005. Tight junctions, leaky intestines, and pediatric diseases. Acta Paediatr 94, 386-393.

25

ACCEPTED MANUSCRIPT

Lordal,M., Hallgren,A., Nylander,O., Hellstrom,P.M., 1996. Tachykinins increase vascular permeability in the gastrointestinal tract of the rat. Acta Physiol Scand 156, 489-494. Lundstrom,K., Salminen,M., Jalanko,A., Savolainen,R., Ulmanen,I., 1991. Cloning and characterization of human placental catechol-O-methyltransferase cDNA. DNA Cell Biol 10, 181-189. Marley,A., von Zastrow,M., 2010. DISC1 regulates primary cilia that display specific dopamine receptors. PLoS One 5, e10902.

RI PT

Marley,A., von Zastrow,M., 2012. A simple cell-based assay reveals that diverse neuropsychiatric risk genes converge on primary cilia. PLoS One 7, e46647. Matelski,L., Van de,W.J., 2016. Risk factors in autism: Thinking outside the brain. J Autoimmun 67, 1-7. Mathivanan,S., Ji,H., Simpson,R.J., 2010. Exosomes: extracellular organelles important in intercellular communication. J Proteomics 73, 1907-1920.

SC

Matsumoto,M., Hidaka,K., Tada,S., Tasaki,Y., Yamaguchi,T., 1995. Full-length cDNA cloning and distribution of human dopamine D4 receptor. Brain Res Mol Brain Res 29, 157-162.

M AN U

Miller,K.P., Borgeest,C., Greenfeld,C., Tomic,D., Flaws,J.A., 2004. In utero effects of chemicals on reproductive tissues in females. Toxicol Appl Pharmacol 198, 111-131. Milner,R., Campbell,I.L., 2002. The integrin family of cell adhesion molecules has multiple functions within the CNS. J Neurosci Res 69, 286-291. Myerburg,M.M., Latoche,J.D., McKenna,E.E., Stabile,L.P., Siegfried,J.S., Feghali-Bostwick,C.A., Pilewski,J.M., 2007. Hepatocyte growth factor and other fibroblast secretions modulate the phenotype of human bronchial epithelial cells. Am J Physiol Lung Cell Mol Physiol 292, L1352-L1360.

TE D

Nagao,S., 1998. Vasopressin and blood-brain barrier. No To Shinkei 50, 809-815. Narita,K., Kozuka-Hata,H., Nonami,Y., Ao-Kondo,H., Suzuki,T., Nakamura,H., Yamakawa,K., Oyama,M., Inoue,T., Takeda,S., 2012. Proteomic analysis of multiple primary cilia reveals a novel mode of ciliary development in mammals. Biol Open 1, 815-825.

EP

Nelson,T.H., Jung,J.Y., Deluca,T.F., Hinebaugh,B.K., St Gabriel,K.C., Wall,D.P., 2012. Autworks: a crossdisease network biology application for Autism and related disorders. BMC Med Genomics 5, 56.

AC C

Ornoy,A., Reece,E.A., Pavlinkova,G., Kappen,C., Miller,R.K., 2015. Effect of maternal diabetes on the embryo, fetus, and children: congenital anomalies, genetic and epigenetic changes and developmental outcomes. Birth Defects Res C Embryo Today 105, 53-72. Paquette,A.G., Lesseur,C., Armstrong,D.A., Koestler,D.C., Appleton,A.A., Lester,B.M., Marsit,C.J., 2013. Placental HTR2A methylation is associated with infant neurobehavioral outcomes. Epigenetics 8, 796-801. Pardridge,W.M., Yang,J., Eisenberg,J., 1985. Blood-brain barrier protein phosphorylation and dephosphorylation. J Neurochem 45, 1141-1147. Pathan,M., Keerthikumar,S., Ang,C.S., Gangoda,L., Quek,C.Y., Williamson,N.A., Mouradov,D., Sieber,O.M., Simpson,R.J., Salim,A., Bacic,A., Hill,A.F., Stroud,D.A., Ryan,M.T., Agbinya,J.I., Mariadason,J.M., Burgess,A.W., Mathivanan,S., 2015. FunRich: An open access standalone functional enrichment and interaction network analysis tool. Proteomics 15, 2597-2601. Patterson,D., Graham,C., Cherian,C., Matherly,L.H., 2008. A humanized mouse model for the reduced folate carrier. Mol Genet Metab 93, 95-103. Pedersen,L.B., Rosenbaum,J.L., 2008. Intraflagellar transport (IFT) role in ciliary assembly, resorption and signalling. Curr Top Dev Biol 85, 23-61.

26

ACCEPTED MANUSCRIPT

Polyak,A., Kubina,R.M., Girirajan,S., 2015. Comorbidity of intellectual disability confounds ascertainment of autism: implications for genetic diagnosis. Am J Med Genet B Neuropsychiatr Genet 168, 600-608. Radtke,A.L., Quayle,A.J., Herbst-Kralovetz,M.M., 2012. Microbial products alter the expression of membraneassociated mucin and antimicrobial peptides in a three-dimensional human endocervical epithelial cell model. Biol Reprod 87, 132.

RI PT

Ramamoorthy,S., Cool,D.R., Leibach,F.H., Mahesh,V.B., Ganapathy,V., 1992. Reconstitution of the human placental 5-hydroxytryptamine transporter in a catalytically active form after detergent solubilization. Biochem J 286 ( Pt 1), 89-95. Ratajczak,H.V., 2011. Theoretical aspects of autism: causes--a review. J Immunotoxicol 8, 68-79.

Resch,B.E., Ducza,E., Gaspar,R., Falkay,G., 2003. Role of adrenergic receptor subtypes in the control of human placental blood vessels. Mol Reprod Dev 66, 166-171.

SC

Riad,M., Tong,X.K., el Mestikawy,S., Hamon,M., Hamel,E., Descarries,L., 1998. Endothelial expression of the 5-hydroxytryptamine1B antimigraine drug receptor in rat and human brain microvessels. Neuroscience 86, 1031-1035.

M AN U

Richter,R.J., Jarvik,G.P., Furlong,C.E., 2010. Paraoxonase 1 status as a risk factor for disease or exposure. Adv Exp Med Biol 660, 29-35. Riechelmann,H., Kienast,K., Schellenberg,J., Mann,W.J., 1994. An in vitro model to study effects of airborne pollutants on human ciliary activity. Rhinology 32, 105-108. Rossignol,D.A., Genuis,S.J., Frye,R.E., 2014. Environmental toxicants and autism spectrum disorders: a systematic review. Transl Psychiatry 4, e360.

TE D

Sahin,M., Sur,M., 2015. Genes, circuits, and precision therapies for autism and related neurodevelopmental disorders. Science. Sanders,D.S., 2005. Mucosal integrity and barrier function in the pathogenesis of early lesions in Crohn's disease. J Clin Pathol 58, 568-572. Sati,L., Seval-Celik,Y., Unek,G., Korgun,E.T., Demir,R., 2009. The presence of kinesin superfamily motor proteins KIFC1 and KIF17 in normal and pathological human placenta. Placenta 30, 848-854.

EP

Selwyn,D.A., Gyi,A., Raphael,J.H., Key,A., Langton,J.A., 1996. A perfusion system for in vitro measurement of human cilia beat frequency. Br J Anaesth 76, 111-115.

AC C

Shangjie,X., Xiaochun,Z., Wenyi,Y., Wuping,G., Ying,Z., Qiuming,H., Huimin,X., 2015. TGF-beta1, Ghrelin, Neurexin, and Neuroligin are predictive biomarkers for postoperative prognosis of laparoscopic surgery in children with Hirschsprung disease. Cell Biochem Biophys 71, 1249-1254. Shiima-Kinoshita,C., Min,K.Y., Hanafusa,T., Mori,H., Nakahari,T., 2004. Beta 2-adrenergic regulation of ciliary beat frequency in rat bronchiolar epithelium: potentiation by isosmotic cell shrinkage. J Physiol 554, 403416. Shim,H., Lee,H., Jeoung,D., 2006. Cancer/testis antigen cancer-associated gene (CAGE) promotes motility of cancer cells through activation of focal adhesion kinase (FAK). Biotechnol Lett 28, 2057-2063. Simpson,R.J., Kalra,H., Mathivanan,S., 2012. ExoCarta as a resource for exosomal research. J Extracell Vesicles 1. Soliman,A., Lacasse,A.A., Lanoix,D., Sagrillo-Fagundes,L., Boulard,V., Vaillancourt,C., 2015. Placental melatonin system is present throughout pregnancy and regulates villous trophoblast differentiation. J Pineal Res.

27

ACCEPTED MANUSCRIPT

Sommansson,A., Saudi,W.S., Nylander,O., Sjoblom,M., 2013. Melatonin inhibits alcohol-induced increases in duodenal mucosal permeability in rats in vivo. Am J Physiol Gastrointest Liver Physiol 305, G95-G105. Souza,M.S., Magnarelli,G.G., Rovedatti,M.G., Cruz,S.S., De D'Angelo,A.M., 2005. Prenatal exposure to pesticides: analysis of human placental acetylcholinesterase, glutathione S-transferase and catalase as biomarkers of effect. Biomarkers 10, 376-389. Stawczyk-Macieja,M., Szczerkowska-Dobosz,A., Rebala,K., Purzycka-Bohdan,D., 2015. Genetic background of skin barrier dysfunction in the pathogenesis of psoriasis vulgaris. Postepy Dermatol Alergol 32, 123-126.

RI PT

Sun,D., Schafer,J.A., 1996. Dopamine inhibits AVP-dependent Na+ transport and water permeability in rat CCD via a D4-like receptor. Am J Physiol 271, F391-F400. Sun,D., Zhuang,X., Zhang,S., Deng,Z.B., Grizzle,W., Miller,D., Zhang,H.G., 2013. Exosomes are endogenous nanoparticles that can deliver biological information between cells. Adv Drug Deliv Rev 65, 342-347.

SC

Tadokoro,T., Wang,Y., Barak,L.S., Bai,Y., Randell,S.H., Hogan,B.L., 2014. IL-6/STAT3 promotes regeneration of airway ciliated cells from basal stem cells. Proc Natl Acad Sci U S A 111, E3641-E3649.

M AN U

Takizawa,T., 1990. [Structure and function of airway epithelial cells]. Nihon Kyobu Shikkan Gakkai Zasshi 28, 1547-1556. Tarkar,A., Loges,N.T., Slagle,C.E., Francis,R., Dougherty,G.W., Tamayo,J.V., Shook,B., Cantino,M., Schwartz,D., Jahnke,C., Olbrich,H., Werner,C., Raidt,J., Pennekamp,P., Abouhamed,M., Hjeij,R., Kohler,G., Griese,M., Li,Y., Lemke,K., Klena,N., Liu,X., Gabriel,G., Tobita,K., Jaspers,M., Morgan,L.C., Shapiro,A.J., Letteboer,S.J., Mans,D.A., Carson,J.L., Leigh,M.W., Wolf,W.E., Chen,S., Lucas,J.S., Onoufriadis,A., Plagnol,V., Schmidts,M., Boldt,K., Roepman,R., Zariwala,M.A., Lo,C.W., Mitchison,H.M., Knowles,M.R., Burdine,R.D., Loturco,J.J., Omran,H., 2013. DYX1C1 is required for axonemal dynein assembly and ciliary motility. Nat Genet 45, 995-1003.

TE D

Taylor,B., Jick,H., Maclaughlin,D., 2013. Prevalence and incidence rates of autism in the UK: time trend from 2004-2010 in children aged 8 years. BMJ Open 3, e003219. Theoharides,T.C., Konstantinidou,A.D., 2007. Corticotropin-releasing hormone and the blood-brain-barrier. Front Biosci 12, 1615-1628.

EP

Trasande,L., Zoeller,R.T., Hass,U., Kortenkamp,A., Grandjean,P., Myers,J.P., DiGangi,J., Bellanger,M., Hauser,R., Legler,J., Skakkebaek,N.E., Heindel,J.J., 2015. Estimating burden and disease costs of exposure to endocrine-disrupting chemicals in the European union. J Clin Endocrinol Metab 100, 1245-1255.

AC C

Trasande,L., Zoeller,R.T., Hass,U., Kortenkamp,A., Grandjean,P., Myers,J.P., DiGangi,J., Hunt,P.M., Rudel,R., Sathyanarayana,S., Bellanger,M., Hauser,R., Legler,J., Skakkebaek,N.E., Heindel,J.J., 2016. Burden of disease and costs of exposure to endocrine disrupting chemicals in the European Union: an updated analysis. Andrology. Treps,L., Le Guelte,A., Gavard,J., 2013. Emerging roles of Semaphorins in the regulation of epithelial and endothelial junctions. Tissue Barriers 1, e23272. Vanderpuye,O.A., Beville,C.M., McIntyre,J.A., 1994. Characterization of cofactor activity for factor I: cleavage of complement C4 in human syncytiotrophoblast microvilli. Placenta 15, 157-170. Vandre,D.D., Ackerman,W.E., Tewari,A., Kniss,D.A., Robinson,J.M., 2012. A placental sub-proteome: the apical plasma membrane of the syncytiotrophoblast. Placenta 33, 207-213. Vaughan,J.E., Walsh,S.W., 2012. Activation of NF-kappaB in placentas of women with preeclampsia. Hypertens Pregnancy 31, 243-251.

28

ACCEPTED MANUSCRIPT Versen-Hoynck,F., Rajakumar,A., Bainbridge,S.A., Gallaher,M.J., Roberts,J.M., Powers,R.W., 2009. Human placental adenosine receptor expression is elevated in preeclampsia and hypoxia increases expression of the A2A receptor. Placenta 30, 434-442. Viggiano,D., Ianiro,G., Vanella,G., Bibbo,S., Bruno,G., Simeone,G., Mele,G., 2015. Gut barrier in health and disease: focus on childhood. Eur Rev Med Pharmacol Sci 19, 1077-1085.

Voineagu,I., Eapen,V., 2013. Converging Pathways in Autism Spectrum Disorders: Interplay between Synaptic Dysfunction and Immune Responses. Front Hum Neurosci 7, 738.

RI PT

Vorbrodt,A.W., Dobrogowska,D.H., 2003. Molecular anatomy of intercellular junctions in brain endothelial and epithelial barriers: electron microscopist's view. Brain Res Brain Res Rev 42, 221-242. Walker,C.K., Anderson,K.W., Milano,K.M., Ye,S., Tancredi,D.J., Pessah,I.N., Hertz-Picciotto,I., Kliman,H.J., 2013. Trophoblast inclusions are significantly increased in the placentas of children in families at risk for autism. Biol Psychiatry 74, 204-211.

SC

Walker,C.K., Krakowiak,P., Baker,A., Hansen,R.L., Ozonoff,S., Hertz-Picciotto,I., 2015. Preeclampsia, placental insufficiency, and autism spectrum disorder or developmental delay. JAMA Pediatr 169, 154-162.

M AN U

Wall,D.P., Pivovarov,R., Tong,M., Jung,J.Y., Fusaro,V.A., Deluca,T.F., Tonellato,P.J., 2010. Genotator: a disease-agnostic tool for genetic annotation of disease. BMC Med Genomics 3, 50. Wang,L.F., White,D.R., Andreoli,S.M., Mulligan,R.M., Discolo,C.M., Schlosser,R.J., 2012. Cigarette smoke inhibits dynamic ciliary beat frequency in pediatric adenoid explants. Otolaryngol Head Neck Surg 146, 659663. Watson,M.J., Worthington,E.N., Clunes,L.A., Rasmussen,J.E., Jones,L., Tarran,R., 2011. Defective adenosinestimulated cAMP production in cystic fibrosis airway epithelia: a novel role for CFTR in cell signaling. FASEB J 25, 2996-3003.

TE D

White,J.F., 2003. Intestinal pathophysiology in autism. Exp Biol Med (Maywood ) 228, 639-649. Wieciech,I., Durlej-Grzesiak,M., Slomczynska,M., 2013. Influence of the antiandrogen flutamide on the androgen receptor gene expression in the placenta and umbilical cord during pregnancy in the pig. Acta Histochem 115, 290-295.

EP

Wingate,M., Kirby,R.S., Pettygrove,S., Cunniff,C., Schulz,E., Ghosh,T., Robinson,C., 2014. Prevalence of autism spectrum disorder among children aged 8 years - autism and developmental disabilities monitoring network, 11 sites, United States, 2010. MMWR Surveill Summ 63, 1-21.

AC C

Winograd-Katz,S.E., Fassler,R., Geiger,B., Legate,K.R., 2014. The integrin adhesome: from genes and proteins to human disease. Nat Rev Mol Cell Biol 15, 273-288. Wong-Riley,M.T., Besharse,J.C., 2012. The kinesin superfamily protein KIF17: one protein with many functions. Biomol Concepts 3, 267-282. Wong,C.T., Wais,J., Crawford,D.A., 2015. Prenatal exposure to common environmental factors affects brain lipids and increases risk of developing autism spectrum disorders. Eur J Neurosci. Wu,M.H., 2005. Endothelial focal adhesions and barrier function. J Physiol 569, 359-366. Wu,S., Ding,Y., Wu,F., Li,R., Xie,G., Hou,J., Mao,P., 2015. Family history of autoimmune diseases is associated with an increased risk of autism in children: A systematic review and meta-analysis. Neurosci Biobehav Rev 55, 322-332. Yeh,T.H., Su,M.C., Hsu,C.J., Chen,Y.H., Lee,S.Y., 2003. Epithelial cells of nasal mucosa express functional gap junctions of connexin 43. Acta Otolaryngol 123, 314-320.

29

ACCEPTED MANUSCRIPT Zaidel-Bar,R., 2013. Cadherin adhesome at a glance. J Cell Sci 126, 373-378.

Zaidel-Bar,R., Itzkovitz,S., Ma'ayan,A., Iyengar,R., Geiger,B., 2007. Functional atlas of the integrin adhesome. Nat Cell Biol 9, 858-867. Zerbo,O., Leong,A., Barcellos,L., Bernal,P., Fireman,B., Croen,L.A., 2015. Immune mediated conditions in autism spectrum disorders. Brain Behav Immun 46, 232-236.

AC C

EP

TE D

M AN U

SC

RI PT

Zhang,H., Smith,G.N., Liu,X., Holden,J.J., 2010. Association of MAOA, 5-HTT, and NET promoter polymorphisms with gene expression and protein activity in human placentas. Physiol Genomics 42, 85-92.

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT Highlights

•

RI PT

SC

•

M AN U

•

TE D

•

EP

•

An increase in the incidence of autism in recent decades suggests a strong environmental influence and many industrial and agrochemical pollutants and endocrine disruptors have been implicated in the autism epidemic. To gain access to the developing brain in utero, such compounds have to pass placental barriers, and on the maternal side, or in childhood, access to the blood and brain is regulated by intestinal, skin and airway barrier systems and by the blood-brain barrier. An analysis of 206 autism genes showed that several, including adhesion and junction molecules, integrins and their signalling networks are directly concerned with barrier function. These and many others are localised and enriched in key barrier sites including the placental trophoblast, intestine, skin and blood-brain barriers. Several also control the respiratory cilia that sweep noxious particulate matter from the airways. While these genes are relevant to neurodevelopment they also have a key role in barrier function and these barriers are regulated by transmitters relevant to autism. A key barrier role for these genes is supported by reported defects in intestinal permeability in autism. This places the genes at an interface between upstream environmental cause(s) and downstream neurophysiological effect and further suggests that environmental control of the compounds that cross these barriers may be key to halting and reversing the autism epidemic.

AC C

•