- Email: [email protected]
Editorial: Mechanistic underpinnings of stem cell therapy for neurological disorders
Brain Research 1729 (2020) 146643
Contents lists available at ScienceDirect
Brain Research journal homepage: www.elsevier.com/locate/brainres
Editorial
Editorial: Mechanistic underpinnings of stem cell therapy for neurological disorders
T
ABSTRACT
This special issue entitled “Mechanistic underpinnings of stem cell therapy for neurological disorders” brings together academicians, clinicians and industry partners with vested interest in the safe and effective translation of stem cell-based therapeutics from the laboratory to the clinic. Despite the scientific advances and limited clinical trials of stem cell therapy for neurological disorders, the mechanisms of action remain not fully understood. Here, we provide critical analyses of the therapeutic pathways postulated to mediate stem cell therapy. The views expressed here are based on scientific evidence, but also well-rationalized speculative hypotheses are encouraged in order to guide the field in exploiting the likely responsive pathways, as well as in exploring novel candidate targets which may open venues in optimizing the therapeutic effects of stem cell therapy. In the end, our goal is to coalesce the concerted efforts from stem cell researchers in probing the mechanistic triggers of cell-based treatments towards ensuring the safety and efficacy profiles of stem cell therapy.
This special issue coalesces numerous milestone studies examining the mechanistic underpinnings of cell-based therapy in several central nervous system disorders. Presented below are brief summaries of these studies, with special attention paid to the novel innovations and mechanistic analyses of each contribution. Cell based treatments have shown efficacy in numerous models of ischemic stroke; however, the mechanisms responsible for these improvements are poorly understood. In the study (Orczykowski et al., 2019) by Dr. May Orczykowski and colleagues, they administered intravenous infusions of human umbilical tissue-derived cells (hUTC) to non-human primates that had been subjected to controlled cortical ischemia in the hand area of the primary motor cortex. hUTC transplants afforded not only functional motor improvements of the affected hand, but also corresponded with decreases in oxidative damage and perilesional iron levels as well as increases in activated microglia density. These novel observations suggest a possible mechanism for the improvements furnished by cell-based treatments for stroke. Little conclusive information exists about the development of the rare cerebrovascular disorder Moyamoya disease (MMD), although some studies have implicated circular RNAs (circRNAs) and neutrophils as possible mediators. Here, Dr. Yumin Luo’s group probed the role of circRNA expression in the neutrophil transcriptome via microarray and quantitative reverse-transcription PCR of neutrophil samples from asymptomatic MMD patients and healthy controls (Ma et al., 2019). This revealed differences in 123 circRNAs largely related to metabolism, angiogenesis, and immune response. These pilot results break ground on a new area of investigation for MMD and other brain disorders, indicate a possible mechanism underlying its development and progression, and posit potential targets for stem cell therapy for MMD. Recognizing the preponderance of evidence substantiating the reparative and protective effects of stem cell transplants for Parkinson’s disease (PD), focus has shifted to optimizing the efficacy of cell transplants by addressing the practical and translational concerns indicated by prior studies. Primary among these is the tendency for rejection of grafted cells by the host system in the absence of systemically delivered https://doi.org/10.1016/j.brainres.2019.146643
Available online 31 December 2019 0006-8993/ © 2019 Published by Elsevier B.V.
cyclosporine-A (CsA), an immunosuppressant. In this article (Yu et al., 2019), Dr. Yun Wang and coworkers promulgate a novel administration method of CsA, in the form of locally transplanted, long-term release NanoCsA, in order to circumvent the side-effects presented by systemic delivery. Grafts of induced pluripotent stem cells (iPSCs) and these nanoparticles impart improved locomotor activity over stand-alone iPSC transplants or iPSC transplants combined with systemic CsA in a long-term, 6-hydroxydopamine rodent model of PD. Crucially, this investigation also sheds light on potential mechanisms, including tyrosine hydroxylase and human marker Stem121 immunoreactivity, underpinning the benefits procured by NanoCsA. Cardiopulmonary resuscitation (CPR) is the primary treatment method for cardiac arrest (CA); thus, attention has been directed at optimizing its survival outcomes. Following auspicious in vitro results, Dr. Xiali Jing’s research team investigates the effect and potential immunomodulatory mechanisms of mesenchymal stem cells derived from iPSCs (iPSC-MSCs) infusions in a rodent model of CA (Yu et al., 2019). The authors demonstrated that rats treated with iPSC-MSC infusions exhibited greater survival at 24 h post-CA as well as downregulated classically activated (deleterious) macrophages (M1) and upregulated alternatively activated (beneficial) macrophages (M2) as compared to the saline-infused rats. These results constitute an important step forward in CA treatment optimization as well as a key mechanistic analysis of the benefits provided by cell-based therapy. Aspirin is often prescribed as an anticoagulant following stroke. Cognizant of the growing amount of research into cell-based therapy for this disorder, possible interactions and confounds introduced by the combination of aspirin with cell transplants and host immune cells warrants investigation. Dr. Nikunj Satani and collaborators performed in vitro assessments of the effect of aspirin on marrow stromal cells, monocytes (Mo), and a combination of the two from both stroke patients and healthy controls reveals differences in their secretome profiles (Satani et al., 2019). These findings advance an important mediator that requires greater attention and study as a possible confound as well as novel evidence of the effect of aspirin on stroke and cell
Brain Research 1729 (2020) 146643
Editorial
transplants. While research into cell-based, technical, and pharmacological treatments for PD is ongoing, there remains no established treatment that comprehensively mitigates its chronic neurodegenerative pathology. However, accumulating evidence positions physical exercise as such a potential therapy. Here, Dr. Yung- Hsiao Chiang and collaborators support this hypothesis by evaluating the effect of voluntary exercise on PD motor symptoms and brain biochemistry using the transgenic MitoPark murine model of PD (Lai et al., 2019). In addition to significant locomotor improvements, exercising mice also displayed recuperated nigrostriatal dopamine markers, as measured by high performance liquid chromatography (HPLC) and positron emission tomography (PET), as well as increased oxygen consumption, implicating that aerobic mitochondrial oxidative metabolism was favored over glycolysis. These data bolster the promise of physical exercise as a treatment for PD and provide critical evidence for metabolically driven mechanisms of action, further supporting this assertion. Mesenchymal stem cells (MSCs) have shown to have therapeutic potential in spinal cord injury, but whether regulating the autophagy in MSCs affects their potency has not been reported. Dr. Jianhong Zhu and colleagues found that autophagic MSCs in vivo had increased levels of LC3-positive autophagosomes in the cytoplasm and neurotrophic factors, including vascular endothelial growth factor and brain derived neurotrophic factor (Ma et al., 2019). Furthermore, more Hoechst labelled autophagic MSCs migrated to the lesion site compared to normal MSCs. Altogether, these results suggest that regulation of autophagy in MSCs prior to transplantation in vivo may serve as a potential therapeutic intervention for spinal cord injury. Stem and progenitor cells have shown to be promising interventional strategies for brain regeneration in neurodegenerative diseases such as Parkinson’s disease, however, growing evidence suggests that the regenerative properties of the cells can be attributed to paracrine factor secretion. Dr. Hans Widmer and coworkers demonstrated that midbrain progenitor cultured cells treated with Endothelial Progenitor Cell-conditioned medium (EPC-CM), after exposure of MPP+, significantly increased the densities of TH-ir neurons, beta-III-tubulin positive neurons, and Iba-1-ir microglial cells (Di Santo et al., 2019). Interestingly, the increased survival of dopaminergic neurons was not initiated by cell proliferation as revealed by the Edu incorporation assay. These findings indicate that EPC-CM may serve to enhance VM neuron survival by the secretion of paracrine factors from stem and progenitor cells. Although PD is largely an idiopathic disease, approximately 5% of cases can be linked to hereditary mutations in the G2019S LRRK2 genes, which is highly prevalent in Ashkenazi Jewish populations. Dr. Marcel Daadi’s group performed single cell RNA-seq transcriptomic that uncovered three subpopulations within neural stem cells: a committed neuronal population, intermediate stage population, and undifferentiated stage population (Kim and Daadi, 2019). Furthermore, genes that were significantly affected were engaged in mitochondrial function, DNA repair, protein degradation, oxidative stress, lysosome biogenesis, ubiquitination, endosome function, autophagy and mitochondrial quality control. Taken together, mutations in G2019S LRRK2 genes may affect several cell types in a non-cell autonomous mechanism of PD pathology and may serve as a therapeutic target for cell-based therapies. Angiotensin-II (Ang-II) plays a role in neurogenesis, angiogenesis, and CNS remodeling and should be taken into context when applying restorative therapies for CNS injuries. Dr. Eng Lo and collaborators analyzed IHC and pulse-chase experiments in vitro to discover that paraand trans-cellular pathways were involved. Additionally, Candesartan blocked Ang-II permeability while PD123319 did not, suggesting Ang-II may act via type 1 receptor (Guo et al., 2019). Lastly, endothelial permeability induced by Ang-II was ameliorated by PPARalpha agonists. In all, this report indicates that Ang-II may alter para- and transcellular permeability in the cerebral endothelium, while PPARalpha-
related networks may serve as a therapeutic option for restorative cellbased therapies. Stem cell-based therapies are an appealing treatment option due to their ability to aid neurogenesis and replace damaged neurons. Dr. Walter Low’s research team described that neural stem cells (NSCs) have demonstrated efficacy in pre-clinical and clinical trials with the mechanism of action being attributed to their ability to form new neurons and promote neuroregeneration (Chrostek et al., 2019). Bone marrow stem cells (BMSCs) and MSCs have shown to increase neurogenesis in pre-clinical models via intracerebral transplantation but lack clinical evidence. Lastly, intravenous and intra-arterial delivery of BMSCs and MSCs have shown to weaken the secondary inflammatory response that follows stroke, thus potentially improving recovery. Selective endovascular cooling (SEC) to ameliorate the splenic inflammatory response following stroke has yet to be investigated. Our group showed here that in an in vivo model, animals that received SEC displayed increased expression in brain-derived neurotrophic factor (BDNF) and IL-10, indicating a change in the peripheral inflammatory response (Corey et al., 2019). Additionally, in vitro analysis revealed that “cold” rat splenocytes protected primary rat neurons by upregulating BDNF and IL-10. This data indicates that SEC may be neuroprotective by upregulating BDNF and IL-10 in the periphery and further support the pathological link between the brain and spleen. Several pre-clinical studies reveal that oligodendrocyte precursor cells (OPCs) may be an effective treatment for demyelinating diseases. However, a protocol must be developed to shorten the significant amount of time it currently takes to prepare them. Dr. Ken Arai and collaborators advanced the concept that DNA methylation’s role in oligodendrocyte differentiation is still largely unknown, but preliminary studies indicate methylation may be a useful tool in both shortening preparation time and increasing treatment efficacy (Egawa et al., 2019). Dr. Yuchuan Ding and colleagues showed in this study that hypothermia combined with mesenchymal stem cells (MSCs) provides superior neuroprotection to stroke victims than either modality used alone (Wei et al., 2019). The probable mechanism for this was the transfer of mitochondria from MSCs to neurons via Miro1, a key mitochondrial transfer-associated protein which is upregulated by hypothermia. Additionally, this combination therapy yielded an increase in Bcl-2 (anti-apoptotic) and VEGF (vascular endothelial growth factor) while decreasing IL-1B (inflammatory factor) and BAX (pro-apoptotic). Treatment with MSCs has been shown to reduce neuroinflammation in neurodegenerative diseases. Dr. Yi Liu and coworkers demonstrated in this paper how tumor necrosis factor-α-induced gene/protein 6 (TSG6) secreted from MSCs plays an essential role in reducing lipopolysaccharide (LPS)-induced neuroinflammation both in vitro and in vivo (Liu et al., 2019). Previous studies have shown MSC treatment switch microglia from the proinflammatory M1 phenotype to the anti-inflammatory M2 phenotype. This study shows that siTSG-6 inhibits obtaining the M2 phenotype, thus indicating TSG-6 secretion from MSCs is essential for M2 polarization. Amyotrophic lateral sclerosis (ALS) is a neurovascular disease. Evidence reveals ALS causes the impairment of the blood spinal cord barrier (BSCB) via endothelial cell degeneration. Human bone marrow endothelial progenitor cells (hBMEPCs) transplant appears to be a viable treatment. Dr. Svitlana Garbuzova-Davis’s research team described the therapeutic mechanism of hBMEPCs by using different time points in vitro, as well as assessing their viability for repairing the central nervous system endothelium in ALS (Garbuzova-Davis et al., 2019). The study supports that hBMEPCS contribute to vascular homeostasis by increasing endothelial cell to cell “tightness” lost during ALS, and repair damaged endothelium with secretion of angiogenic factors. Aging reduces the efficacy of using autologous bone marrow mesenchymal stem cells (BMSCs) to treat stroke. Dr. Xunming Ji's group presented that in vitro preparation of aged BMSCs with hypoxia conditioning significantly improves their therapeutic effect in stroke 2
Brain Research 1729 (2020) 146643
Editorial
victims (Zhang et al., 2019). Hypoxia conditioning promoted an increase in VEGF, which has been demonstrated to provide neuroprotection in previous studies. Postmortem assays are currently the only way to definitively diagnose someone with Alzheimer’s disease (AD). Therefore, innovation of quick and easy ways to obtain early biomarkers is imperative to provide early intervention and treatment. Dr. Marcella Reale and collaborators advanced the concept that saliva contains stem cells and may offer a non-invasive cost-effective screening to facilitate this goal (Reale et al., 2019). Furthermore, salivary glands are shown to contain stem cells that age prematurely, and may allow detection of β-amyloid plaque accumulation of both hyperphosphorylated and acetylated tau. Standardized collection and processing protocols should be established to effectively assess its validity.
Garbuzova-Davis, S., Ehrhart, J., Mustafa, H., Llauget, A., Boccio, K.J., Sanberg, P.R., Appel, S.H., Borlongan, C.V., 2019. Phenotypic characteristics of human bone marrow-derived endothelial progenitor cells in vitro support cell effectiveness for repair of the blood-spinal cord barrier in ALS. Brain Res. 1724, 146428. Guo, S., Som, A.T., Arai, K., Lo, E.H., 2019. Effects of angiotensin-II on brain endothelial cell permeability via PPARalpha regulation of para- and trans-cellular pathways. Brain Res. 1722, 146353. Kim, J., Daadi, M.M., 2019. Non-cell autonomous mechanism of Parkinson's disease pathology caused by G2019S LRRK2 mutation in Ashkenazi Jewish patient: Single cell analysis. Brain Res. 1722, 146342. Lai, J.H., Chen, K.Y., Wu, J.C., Olson, L., Brené, S., Huang, C.Z., Chen, Y.H., Kang, S.J., Ma, K.H., Hoffer, B.J., Hsieh, T.H., Chiang, Y.H., 2019. Voluntary exercise delays progressive deterioration of markers of metabolism and behavior in a mouse model of Parkinson's disease. Brain Res. 1720, 146301. Liu, Y., Zeng, R., Wang, Y., Huang, W., Hu, B., Zhu, G., Zhang, R., Li, F., Han, J., Li, Y., 2019. Mesenchymal stem cells enhance microglia M2 polarization and attenuate neuroinflammation through TSG-6. Brain Res. 1724, 146422. Ma, F., Li, R., Tang, H., Zhu, T., Xu, F., Zhu, J., 2019. Regulation of autophagy in mesenchymal stem cells modulates therapeutic effects on spinal cord injury. Brain Res. 1721, 146321. Ma, Q., Li, L., Yu, B., Jiao, L., Han, Z., Zhao, H., Li, G., Ma, Y., Luo, Y., 2019. Circular RNA profiling of neutrophil transcriptome provides insights into asymptomatic Moyamoya disease. Brain Res. 1719, 104–112. Orczykowski, M.E., Calderazzo, S.M., Shobin, E., Pessina, M.A., Oblak, A.L., Finklestein, S.P., Kramer, B.C., Mortazavi, F., Rosene, D.L., Moore, T.L., 2019. Cell based therapy reduces secondary damage and increases extent of microglial activation following cortical injury. Brain Res. 1717, 147–159. Reale, M., Gonzales-Portillo, I., Borlongan, C.V., 2019. Saliva, an easily accessible fluid as diagnostic tool and potent stem cell source for Alzheimer's Disease: Present and future applications. Brain Res. 25, 146535. https://doi.org/10.1016/j.brainres.2019. 146535. Satani, N., Giridhar, K., Cai, C., Wewior, N., Norris, D.D., Olson, S.D., Aronowski, J., Savitz, S.I., 2019. Aspirin in stroke patients modifies the immunomodulatory interactions of marrow stromal cells and monocytes. Brain Res. 1720, 146298. https://doi. org/10.1016/j.brainres.2019.06.017. Wei, W., Wu, D., Duan, Y., Elkin, K.B., Chandra, A., Guan, L., Peng, C., He, X., Wu, C., Ji, X., Ding, Y., 2019. Neuroprotection by mesenchymal stem cell (MSC) administration is enhanced by local cooling infusion (LCI) in ischemia. Brain Res. 1724, 146406. Yu, Y., Wang, D., Li, H., Fan, J., Liu, Y., Zhao, X., Wu, J., Jing, X., 2019. Mesenchymal stem cells derived from induced pluripotent stem cells play a key role in immunomodulation during cardiopulmonary resuscitation. Brain Res. 1720, 146293. Yu, S.J., Wang, Y.C., Chang, C.Y., Hsieh, W., Chen, S., Yang, C.S., Lin, S.Z., Wang, Y., 2019. NanoCsA improves the survival of human iPSC transplant in hemiparkinsonian rats. Brain Res. 1719, 124–132. Zhang, Y., Ma, L., Su, Y., Su, L., Lan, X., Wu, D., Han, S., Li, J., Kvederis, L., Corey, S., Borlongan, C.V., Ji, X., 2019. Hypoxia conditioning enhances neuroprotective effects of aged human bone marrow mesenchymal stem cell-derived conditioned medium against cerebral ischemia in vitro. Brain Res. 1725, 146432.
1. Conclusion Detailing mechanisms of stem cell therapy by optimizing in vitro preparation techniques of stem cells, discovering biomarkers, and utilization of combination therapies are all essential to achieve our collective goal of increasingly improving treatment efficacy. DNA methylation manipulation, hypoxia conditioning, and choosing to potentially pair these adjunctive treatments with a cell line such as human bone marrow endothelial progenitor cells, while implementing these therapies in combination with other neuroprotective and neuroregenerative approaches, such as hypothermia, presents exciting opportunities to seek better treatment efficacy of stem cells. Advancements in diagnostics such as saliva, as well as finding strategies designed to increase therapeutic proteins including tumor necrosis factor-α-induced gene/ protein 6 (TSG-6), also present worthy challenges. References Chrostek, M.R., Fellows, E.G., Crane, A.T., Grande, A.W., Low, W.C., 2019. Efficacy of stem cell-based therapies for stroke. Brain Res. 1722, 146362. https://doi.org/10. 1016/j.brainres.2019.146362. Corey, S., Abraham, D.I., Kaneko, Y., Lee, J.Y., Borlongan, C.V., 2019. Selective endovascular cooling for stroke entails brain-derived neurotrophic factor and splenic IL10 modulation. Brain Res. 1722, 146380. Di Santo, S., Seiler, S., Ducray, A.D., Widmer, H.R., 2019. Conditioned medium from Endothelial Progenitor Cells promotes number of dopaminergic neurons and exerts neuroprotection in cultured ventral mesencephalic neuronal progenitor cells. Brain Res. 1720, 146330. Egawa, N., Chung, K.K., Takahashi, R., Lo, E.H., Inoue, H., Arai, K., 2019. Brief review: Can modulating DNA methylation state help the clinical application of oligodendrocyte precursor cells as a source of stem cell therapy? Brain Res. 1723, 146386.
Brooke Bonsack, Chase Kingsbury, John Brown, Cesar V. Borlongan Center of Excellence for Aging and Brain Repair, Department of Neurosurgery and Brain Repair, University of South Florida College of Medicine, Tampa, FL 33612, USA E-mail address: [email protected] (C.V. Borlongan).
⁎
⁎ Corresponding author at: Department of Neurosurgery and Brain Repair, University of South Florida Morsani College of Medicine, 12901 Bruce B Downs Blvd, Tampa, FL 33612, USA.
3
Contents lists available at ScienceDirect
Brain Research journal homepage: www.elsevier.com/locate/brainres
Editorial
Editorial: Mechanistic underpinnings of stem cell therapy for neurological disorders
T
ABSTRACT
This special issue entitled “Mechanistic underpinnings of stem cell therapy for neurological disorders” brings together academicians, clinicians and industry partners with vested interest in the safe and effective translation of stem cell-based therapeutics from the laboratory to the clinic. Despite the scientific advances and limited clinical trials of stem cell therapy for neurological disorders, the mechanisms of action remain not fully understood. Here, we provide critical analyses of the therapeutic pathways postulated to mediate stem cell therapy. The views expressed here are based on scientific evidence, but also well-rationalized speculative hypotheses are encouraged in order to guide the field in exploiting the likely responsive pathways, as well as in exploring novel candidate targets which may open venues in optimizing the therapeutic effects of stem cell therapy. In the end, our goal is to coalesce the concerted efforts from stem cell researchers in probing the mechanistic triggers of cell-based treatments towards ensuring the safety and efficacy profiles of stem cell therapy.
This special issue coalesces numerous milestone studies examining the mechanistic underpinnings of cell-based therapy in several central nervous system disorders. Presented below are brief summaries of these studies, with special attention paid to the novel innovations and mechanistic analyses of each contribution. Cell based treatments have shown efficacy in numerous models of ischemic stroke; however, the mechanisms responsible for these improvements are poorly understood. In the study (Orczykowski et al., 2019) by Dr. May Orczykowski and colleagues, they administered intravenous infusions of human umbilical tissue-derived cells (hUTC) to non-human primates that had been subjected to controlled cortical ischemia in the hand area of the primary motor cortex. hUTC transplants afforded not only functional motor improvements of the affected hand, but also corresponded with decreases in oxidative damage and perilesional iron levels as well as increases in activated microglia density. These novel observations suggest a possible mechanism for the improvements furnished by cell-based treatments for stroke. Little conclusive information exists about the development of the rare cerebrovascular disorder Moyamoya disease (MMD), although some studies have implicated circular RNAs (circRNAs) and neutrophils as possible mediators. Here, Dr. Yumin Luo’s group probed the role of circRNA expression in the neutrophil transcriptome via microarray and quantitative reverse-transcription PCR of neutrophil samples from asymptomatic MMD patients and healthy controls (Ma et al., 2019). This revealed differences in 123 circRNAs largely related to metabolism, angiogenesis, and immune response. These pilot results break ground on a new area of investigation for MMD and other brain disorders, indicate a possible mechanism underlying its development and progression, and posit potential targets for stem cell therapy for MMD. Recognizing the preponderance of evidence substantiating the reparative and protective effects of stem cell transplants for Parkinson’s disease (PD), focus has shifted to optimizing the efficacy of cell transplants by addressing the practical and translational concerns indicated by prior studies. Primary among these is the tendency for rejection of grafted cells by the host system in the absence of systemically delivered https://doi.org/10.1016/j.brainres.2019.146643
Available online 31 December 2019 0006-8993/ © 2019 Published by Elsevier B.V.
cyclosporine-A (CsA), an immunosuppressant. In this article (Yu et al., 2019), Dr. Yun Wang and coworkers promulgate a novel administration method of CsA, in the form of locally transplanted, long-term release NanoCsA, in order to circumvent the side-effects presented by systemic delivery. Grafts of induced pluripotent stem cells (iPSCs) and these nanoparticles impart improved locomotor activity over stand-alone iPSC transplants or iPSC transplants combined with systemic CsA in a long-term, 6-hydroxydopamine rodent model of PD. Crucially, this investigation also sheds light on potential mechanisms, including tyrosine hydroxylase and human marker Stem121 immunoreactivity, underpinning the benefits procured by NanoCsA. Cardiopulmonary resuscitation (CPR) is the primary treatment method for cardiac arrest (CA); thus, attention has been directed at optimizing its survival outcomes. Following auspicious in vitro results, Dr. Xiali Jing’s research team investigates the effect and potential immunomodulatory mechanisms of mesenchymal stem cells derived from iPSCs (iPSC-MSCs) infusions in a rodent model of CA (Yu et al., 2019). The authors demonstrated that rats treated with iPSC-MSC infusions exhibited greater survival at 24 h post-CA as well as downregulated classically activated (deleterious) macrophages (M1) and upregulated alternatively activated (beneficial) macrophages (M2) as compared to the saline-infused rats. These results constitute an important step forward in CA treatment optimization as well as a key mechanistic analysis of the benefits provided by cell-based therapy. Aspirin is often prescribed as an anticoagulant following stroke. Cognizant of the growing amount of research into cell-based therapy for this disorder, possible interactions and confounds introduced by the combination of aspirin with cell transplants and host immune cells warrants investigation. Dr. Nikunj Satani and collaborators performed in vitro assessments of the effect of aspirin on marrow stromal cells, monocytes (Mo), and a combination of the two from both stroke patients and healthy controls reveals differences in their secretome profiles (Satani et al., 2019). These findings advance an important mediator that requires greater attention and study as a possible confound as well as novel evidence of the effect of aspirin on stroke and cell
Brain Research 1729 (2020) 146643
Editorial
transplants. While research into cell-based, technical, and pharmacological treatments for PD is ongoing, there remains no established treatment that comprehensively mitigates its chronic neurodegenerative pathology. However, accumulating evidence positions physical exercise as such a potential therapy. Here, Dr. Yung- Hsiao Chiang and collaborators support this hypothesis by evaluating the effect of voluntary exercise on PD motor symptoms and brain biochemistry using the transgenic MitoPark murine model of PD (Lai et al., 2019). In addition to significant locomotor improvements, exercising mice also displayed recuperated nigrostriatal dopamine markers, as measured by high performance liquid chromatography (HPLC) and positron emission tomography (PET), as well as increased oxygen consumption, implicating that aerobic mitochondrial oxidative metabolism was favored over glycolysis. These data bolster the promise of physical exercise as a treatment for PD and provide critical evidence for metabolically driven mechanisms of action, further supporting this assertion. Mesenchymal stem cells (MSCs) have shown to have therapeutic potential in spinal cord injury, but whether regulating the autophagy in MSCs affects their potency has not been reported. Dr. Jianhong Zhu and colleagues found that autophagic MSCs in vivo had increased levels of LC3-positive autophagosomes in the cytoplasm and neurotrophic factors, including vascular endothelial growth factor and brain derived neurotrophic factor (Ma et al., 2019). Furthermore, more Hoechst labelled autophagic MSCs migrated to the lesion site compared to normal MSCs. Altogether, these results suggest that regulation of autophagy in MSCs prior to transplantation in vivo may serve as a potential therapeutic intervention for spinal cord injury. Stem and progenitor cells have shown to be promising interventional strategies for brain regeneration in neurodegenerative diseases such as Parkinson’s disease, however, growing evidence suggests that the regenerative properties of the cells can be attributed to paracrine factor secretion. Dr. Hans Widmer and coworkers demonstrated that midbrain progenitor cultured cells treated with Endothelial Progenitor Cell-conditioned medium (EPC-CM), after exposure of MPP+, significantly increased the densities of TH-ir neurons, beta-III-tubulin positive neurons, and Iba-1-ir microglial cells (Di Santo et al., 2019). Interestingly, the increased survival of dopaminergic neurons was not initiated by cell proliferation as revealed by the Edu incorporation assay. These findings indicate that EPC-CM may serve to enhance VM neuron survival by the secretion of paracrine factors from stem and progenitor cells. Although PD is largely an idiopathic disease, approximately 5% of cases can be linked to hereditary mutations in the G2019S LRRK2 genes, which is highly prevalent in Ashkenazi Jewish populations. Dr. Marcel Daadi’s group performed single cell RNA-seq transcriptomic that uncovered three subpopulations within neural stem cells: a committed neuronal population, intermediate stage population, and undifferentiated stage population (Kim and Daadi, 2019). Furthermore, genes that were significantly affected were engaged in mitochondrial function, DNA repair, protein degradation, oxidative stress, lysosome biogenesis, ubiquitination, endosome function, autophagy and mitochondrial quality control. Taken together, mutations in G2019S LRRK2 genes may affect several cell types in a non-cell autonomous mechanism of PD pathology and may serve as a therapeutic target for cell-based therapies. Angiotensin-II (Ang-II) plays a role in neurogenesis, angiogenesis, and CNS remodeling and should be taken into context when applying restorative therapies for CNS injuries. Dr. Eng Lo and collaborators analyzed IHC and pulse-chase experiments in vitro to discover that paraand trans-cellular pathways were involved. Additionally, Candesartan blocked Ang-II permeability while PD123319 did not, suggesting Ang-II may act via type 1 receptor (Guo et al., 2019). Lastly, endothelial permeability induced by Ang-II was ameliorated by PPARalpha agonists. In all, this report indicates that Ang-II may alter para- and transcellular permeability in the cerebral endothelium, while PPARalpha-
related networks may serve as a therapeutic option for restorative cellbased therapies. Stem cell-based therapies are an appealing treatment option due to their ability to aid neurogenesis and replace damaged neurons. Dr. Walter Low’s research team described that neural stem cells (NSCs) have demonstrated efficacy in pre-clinical and clinical trials with the mechanism of action being attributed to their ability to form new neurons and promote neuroregeneration (Chrostek et al., 2019). Bone marrow stem cells (BMSCs) and MSCs have shown to increase neurogenesis in pre-clinical models via intracerebral transplantation but lack clinical evidence. Lastly, intravenous and intra-arterial delivery of BMSCs and MSCs have shown to weaken the secondary inflammatory response that follows stroke, thus potentially improving recovery. Selective endovascular cooling (SEC) to ameliorate the splenic inflammatory response following stroke has yet to be investigated. Our group showed here that in an in vivo model, animals that received SEC displayed increased expression in brain-derived neurotrophic factor (BDNF) and IL-10, indicating a change in the peripheral inflammatory response (Corey et al., 2019). Additionally, in vitro analysis revealed that “cold” rat splenocytes protected primary rat neurons by upregulating BDNF and IL-10. This data indicates that SEC may be neuroprotective by upregulating BDNF and IL-10 in the periphery and further support the pathological link between the brain and spleen. Several pre-clinical studies reveal that oligodendrocyte precursor cells (OPCs) may be an effective treatment for demyelinating diseases. However, a protocol must be developed to shorten the significant amount of time it currently takes to prepare them. Dr. Ken Arai and collaborators advanced the concept that DNA methylation’s role in oligodendrocyte differentiation is still largely unknown, but preliminary studies indicate methylation may be a useful tool in both shortening preparation time and increasing treatment efficacy (Egawa et al., 2019). Dr. Yuchuan Ding and colleagues showed in this study that hypothermia combined with mesenchymal stem cells (MSCs) provides superior neuroprotection to stroke victims than either modality used alone (Wei et al., 2019). The probable mechanism for this was the transfer of mitochondria from MSCs to neurons via Miro1, a key mitochondrial transfer-associated protein which is upregulated by hypothermia. Additionally, this combination therapy yielded an increase in Bcl-2 (anti-apoptotic) and VEGF (vascular endothelial growth factor) while decreasing IL-1B (inflammatory factor) and BAX (pro-apoptotic). Treatment with MSCs has been shown to reduce neuroinflammation in neurodegenerative diseases. Dr. Yi Liu and coworkers demonstrated in this paper how tumor necrosis factor-α-induced gene/protein 6 (TSG6) secreted from MSCs plays an essential role in reducing lipopolysaccharide (LPS)-induced neuroinflammation both in vitro and in vivo (Liu et al., 2019). Previous studies have shown MSC treatment switch microglia from the proinflammatory M1 phenotype to the anti-inflammatory M2 phenotype. This study shows that siTSG-6 inhibits obtaining the M2 phenotype, thus indicating TSG-6 secretion from MSCs is essential for M2 polarization. Amyotrophic lateral sclerosis (ALS) is a neurovascular disease. Evidence reveals ALS causes the impairment of the blood spinal cord barrier (BSCB) via endothelial cell degeneration. Human bone marrow endothelial progenitor cells (hBMEPCs) transplant appears to be a viable treatment. Dr. Svitlana Garbuzova-Davis’s research team described the therapeutic mechanism of hBMEPCs by using different time points in vitro, as well as assessing their viability for repairing the central nervous system endothelium in ALS (Garbuzova-Davis et al., 2019). The study supports that hBMEPCS contribute to vascular homeostasis by increasing endothelial cell to cell “tightness” lost during ALS, and repair damaged endothelium with secretion of angiogenic factors. Aging reduces the efficacy of using autologous bone marrow mesenchymal stem cells (BMSCs) to treat stroke. Dr. Xunming Ji's group presented that in vitro preparation of aged BMSCs with hypoxia conditioning significantly improves their therapeutic effect in stroke 2
Brain Research 1729 (2020) 146643
Editorial
victims (Zhang et al., 2019). Hypoxia conditioning promoted an increase in VEGF, which has been demonstrated to provide neuroprotection in previous studies. Postmortem assays are currently the only way to definitively diagnose someone with Alzheimer’s disease (AD). Therefore, innovation of quick and easy ways to obtain early biomarkers is imperative to provide early intervention and treatment. Dr. Marcella Reale and collaborators advanced the concept that saliva contains stem cells and may offer a non-invasive cost-effective screening to facilitate this goal (Reale et al., 2019). Furthermore, salivary glands are shown to contain stem cells that age prematurely, and may allow detection of β-amyloid plaque accumulation of both hyperphosphorylated and acetylated tau. Standardized collection and processing protocols should be established to effectively assess its validity.
Garbuzova-Davis, S., Ehrhart, J., Mustafa, H., Llauget, A., Boccio, K.J., Sanberg, P.R., Appel, S.H., Borlongan, C.V., 2019. Phenotypic characteristics of human bone marrow-derived endothelial progenitor cells in vitro support cell effectiveness for repair of the blood-spinal cord barrier in ALS. Brain Res. 1724, 146428. Guo, S., Som, A.T., Arai, K., Lo, E.H., 2019. Effects of angiotensin-II on brain endothelial cell permeability via PPARalpha regulation of para- and trans-cellular pathways. Brain Res. 1722, 146353. Kim, J., Daadi, M.M., 2019. Non-cell autonomous mechanism of Parkinson's disease pathology caused by G2019S LRRK2 mutation in Ashkenazi Jewish patient: Single cell analysis. Brain Res. 1722, 146342. Lai, J.H., Chen, K.Y., Wu, J.C., Olson, L., Brené, S., Huang, C.Z., Chen, Y.H., Kang, S.J., Ma, K.H., Hoffer, B.J., Hsieh, T.H., Chiang, Y.H., 2019. Voluntary exercise delays progressive deterioration of markers of metabolism and behavior in a mouse model of Parkinson's disease. Brain Res. 1720, 146301. Liu, Y., Zeng, R., Wang, Y., Huang, W., Hu, B., Zhu, G., Zhang, R., Li, F., Han, J., Li, Y., 2019. Mesenchymal stem cells enhance microglia M2 polarization and attenuate neuroinflammation through TSG-6. Brain Res. 1724, 146422. Ma, F., Li, R., Tang, H., Zhu, T., Xu, F., Zhu, J., 2019. Regulation of autophagy in mesenchymal stem cells modulates therapeutic effects on spinal cord injury. Brain Res. 1721, 146321. Ma, Q., Li, L., Yu, B., Jiao, L., Han, Z., Zhao, H., Li, G., Ma, Y., Luo, Y., 2019. Circular RNA profiling of neutrophil transcriptome provides insights into asymptomatic Moyamoya disease. Brain Res. 1719, 104–112. Orczykowski, M.E., Calderazzo, S.M., Shobin, E., Pessina, M.A., Oblak, A.L., Finklestein, S.P., Kramer, B.C., Mortazavi, F., Rosene, D.L., Moore, T.L., 2019. Cell based therapy reduces secondary damage and increases extent of microglial activation following cortical injury. Brain Res. 1717, 147–159. Reale, M., Gonzales-Portillo, I., Borlongan, C.V., 2019. Saliva, an easily accessible fluid as diagnostic tool and potent stem cell source for Alzheimer's Disease: Present and future applications. Brain Res. 25, 146535. https://doi.org/10.1016/j.brainres.2019. 146535. Satani, N., Giridhar, K., Cai, C., Wewior, N., Norris, D.D., Olson, S.D., Aronowski, J., Savitz, S.I., 2019. Aspirin in stroke patients modifies the immunomodulatory interactions of marrow stromal cells and monocytes. Brain Res. 1720, 146298. https://doi. org/10.1016/j.brainres.2019.06.017. Wei, W., Wu, D., Duan, Y., Elkin, K.B., Chandra, A., Guan, L., Peng, C., He, X., Wu, C., Ji, X., Ding, Y., 2019. Neuroprotection by mesenchymal stem cell (MSC) administration is enhanced by local cooling infusion (LCI) in ischemia. Brain Res. 1724, 146406. Yu, Y., Wang, D., Li, H., Fan, J., Liu, Y., Zhao, X., Wu, J., Jing, X., 2019. Mesenchymal stem cells derived from induced pluripotent stem cells play a key role in immunomodulation during cardiopulmonary resuscitation. Brain Res. 1720, 146293. Yu, S.J., Wang, Y.C., Chang, C.Y., Hsieh, W., Chen, S., Yang, C.S., Lin, S.Z., Wang, Y., 2019. NanoCsA improves the survival of human iPSC transplant in hemiparkinsonian rats. Brain Res. 1719, 124–132. Zhang, Y., Ma, L., Su, Y., Su, L., Lan, X., Wu, D., Han, S., Li, J., Kvederis, L., Corey, S., Borlongan, C.V., Ji, X., 2019. Hypoxia conditioning enhances neuroprotective effects of aged human bone marrow mesenchymal stem cell-derived conditioned medium against cerebral ischemia in vitro. Brain Res. 1725, 146432.
1. Conclusion Detailing mechanisms of stem cell therapy by optimizing in vitro preparation techniques of stem cells, discovering biomarkers, and utilization of combination therapies are all essential to achieve our collective goal of increasingly improving treatment efficacy. DNA methylation manipulation, hypoxia conditioning, and choosing to potentially pair these adjunctive treatments with a cell line such as human bone marrow endothelial progenitor cells, while implementing these therapies in combination with other neuroprotective and neuroregenerative approaches, such as hypothermia, presents exciting opportunities to seek better treatment efficacy of stem cells. Advancements in diagnostics such as saliva, as well as finding strategies designed to increase therapeutic proteins including tumor necrosis factor-α-induced gene/ protein 6 (TSG-6), also present worthy challenges. References Chrostek, M.R., Fellows, E.G., Crane, A.T., Grande, A.W., Low, W.C., 2019. Efficacy of stem cell-based therapies for stroke. Brain Res. 1722, 146362. https://doi.org/10. 1016/j.brainres.2019.146362. Corey, S., Abraham, D.I., Kaneko, Y., Lee, J.Y., Borlongan, C.V., 2019. Selective endovascular cooling for stroke entails brain-derived neurotrophic factor and splenic IL10 modulation. Brain Res. 1722, 146380. Di Santo, S., Seiler, S., Ducray, A.D., Widmer, H.R., 2019. Conditioned medium from Endothelial Progenitor Cells promotes number of dopaminergic neurons and exerts neuroprotection in cultured ventral mesencephalic neuronal progenitor cells. Brain Res. 1720, 146330. Egawa, N., Chung, K.K., Takahashi, R., Lo, E.H., Inoue, H., Arai, K., 2019. Brief review: Can modulating DNA methylation state help the clinical application of oligodendrocyte precursor cells as a source of stem cell therapy? Brain Res. 1723, 146386.
Brooke Bonsack, Chase Kingsbury, John Brown, Cesar V. Borlongan Center of Excellence for Aging and Brain Repair, Department of Neurosurgery and Brain Repair, University of South Florida College of Medicine, Tampa, FL 33612, USA E-mail address: [email protected] (C.V. Borlongan).
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⁎ Corresponding author at: Department of Neurosurgery and Brain Repair, University of South Florida Morsani College of Medicine, 12901 Bruce B Downs Blvd, Tampa, FL 33612, USA.
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