In search of the missing link in the regulation of appetite and body weight

Nutrition 25 (2009) 252–254 www.nutritionjrnl.com

Award for General Nutrition

In search of the missing link in the regulation of appetite and body weight Sergueï O. Fetissov, M.D., Ph.D.* Digestive System and Nutrition Laboratory (ADEN EA3234), Institute of Biomedical Research, Rouen University, IFR23, Rouen, France Manuscript received and accepted October 2, 2008.

How humans and animals regulate appetite and body weight has been explored in numerous studies dealing with genetic, biochemical, environmental, and psychological factors, yet the diseases that primarily affect these physiologic functions remain largely unsolved issues of modern medicine. The origin of diseases such as anorexia and bulimia nervosa or binge-eating obesity is often referred to as multifactorial, implying that a combination of the factors cited above should fall into a certain pattern that would trigger disease development. Although this might be true, it does not exclude that there exist biological changes in the organism that may be common and critical for the development of each specific form of eating or metabolic disease. Recent research by me and my colleagues has revealed a new and unexpected biological mechanism that appears as a fundamental part of the homeostatic control of motivated behavior including food intake. In fact, based on clinical and experimental data, we proposed that the regulation of appetite and body weight is under constant control by the immune system by secretion of autoantibodies (autoAbs) directed against neuropeptide or peptide hormones involved in the regulation of energy homeostasis [1,2]. Furthermore, we showed the first evidence that production of such autoAbs can be influenced by luminal antigens, indicating that these autoAbs may serve as a link between nutrients or gut microflora and brain control of appetite and emotion [3]. I am very grateful that the 12th John M. Kinney Award for General Nutrition was given to recognize the potential importance of this discovery recently reported in Nutrition [3]. The path that led me to identify this new biological mechanism was long and I believe could only become possible due to complementary skills acquired in different laboratories in four countries during my research career. * Corresponding author. Tel.: ⫹33-0-2-3514-8455; fax: ⫹33-0-23514-8226. E-mail address: [email protected] (S. O. Fetissov). 0899-9007/09/$ – see front matter © 2009 Published by Elsevier Inc. doi:10.1016/j.nut.2008.10.002

Having graduated as a medical doctor from the Medical Military Academy in St. Petersburg, Russia, and accomplishing a general surgery internship, I was hesitating if I should start full-time scientific research but meeting with my future Ph.D. supervisor Prof. Michael Ugrumov at the Koltzov Institute of Developmental Biology of the Russian Academy of Science in Moscow helped me to make the choice of selecting science. However, my doctoral research project was closely related to my intention of remaining connected to neurosurgery because it dealt with the transplantation of embryonic dopaminergic neurons for eventual application in Parkinson’s disease or for hyperprolactinemia. In particular, I worked with embryonic arcuate nucleus grafts years before this small hypothalamic structure was recognized as a key brain area responsible for appetite and body weight control and before the emergence of stem cell therapy. From this perspective, it was very useful to become familiar with the arcuate neurons from anatomic and biochemical aspects. However, the critical event that turned my subsequent research career toward the study of brain control of appetite and body weight happened in 1994 in France. During my Ph.D. training, in collaboration with the Institute of Neuroscience directed by Prof. André Calas at Pierre and Marie Curie University in Paris, I met with Prof. Stelianos Nicolaïdis. He was at the time head of the laboratory at the College de France in Paris, applying several behavioral, metabolic, and neurochemical approaches to study the brain control of appetite and body weight and formulating an ischymetric hypothesis of food intake control. Being a former neurosurgeon, he appreciated my surgical skills and invited me to participate in a postdoctoral training to study the effects of transplantation of embryonic arcuate neurons in obese Zucker rats. During 2 y of work in his laboratory, we found that the arcuate neurons grafted from the lean Zucker rats in the hypothalamus of obese rats resulted in a significant reduction of body weight gain and an improvement of insulin resistance. We also found that the obese

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Zucker rats display neurochemical modifications in the hypothalamus typical for dehydration. The molecular mechanisms underlying the beneficial effects of such grafts later became clear after discoveries by other scientists of leptin as a hormone signaling the amount of adipose tissue, of leptin receptors expressed by arcuate neurons, and of the mutation of these receptors responsible for obesity in Zucker rats. Next, being eager to learn more about the brain mechanisms of appetite control, I was very lucky that Prof. Michael Meguid, the director of the Neuroscience Program, Surgical Metabolism and Nutrition Laboratory at Upstate Medical University in Syracuse, New York, was interested in taking me on as a postdoctoral fellow. In fact, he was looking to replace his colleague who just returned to medical practice and who was supposed to perform grafts of embryonic dopaminergic and serotonergic neurons into the hypothalamus of rats to study the effect of dopamine and serotonin on food intake and body weight. Following Prof. Meguid’s hypothesis of the role of these monoamines in the regulation of meal size and meal frequency, we performed many interesting experiments in rat models of obesity or cancer anorexia using a combination of neurotransplantation, microdialysis, and molecular biology, resulting in significant clarification of this mechanism [4]. Then, by 2000, neuropeptides emerged as important modulators of food intake and I was interested to see if monoamines were interacting with neuropeptides in the regulation of appetite and body weight. I wrote to Prof. Tomas Hökfelt, one of the founders of the neuropeptide concept, to ask if he would be interested to study the role of monoamine–neuropeptide interactions in body weight control in his laboratory at the Karolinska Institutet in Stockholm, Sweden. After half a year of correspondence I could join his laboratory, where I spent 4 very fruitful years. Soon after coming to Stockholm, I realized that working with Prof. Hökfelt meant being involved in a dozen projects in addition to my initial research program. In fact, we explored the role of several neuropeptides in various animal models ranging from alteration of body weight to epilepsy and extensive studies on neuroanatomic characterization of several neuropeptidergic systems. It was in his laboratory that I made a key finding that shaped my further research interest. We showed that autoAbs directed against ␣-melanocyte–stimulating hormone (␣-MSH), one of the key neuropeptides in appetite control, exist in humans and that patients with anorexia nervosa and bulimia display increased binding of these autoAbs to brain sections [5]. This idea, to apply sera from patients with eating disorders to rat brain sections, came to me after initial observations by Prof. Hökfelt that sera from subjects with autoimmune polyendocrine syndrome very nicely stain certain monoaminergic neurons in the rat brain [6]. As we later discussed with Prof. Hökfelt, these discoveries could become possible at least in part due to the recent availability of a very sensitive tyramide amplification immunohistochemical technique. Thus, based on the identification of ␣-MSH autoAbs in

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subjects with anorexia and bulimia, we proposed a new hypothesis on the origin of eating disorders postulating that ␣-MSH autoAbs may alter melanocortin signaling leading to a disturbed appetite in anorexia and bulimia. However, it was counterintuitive to propose that autoAbs against a satiety messenger such as ␣-MSH could be involved in restrictive anorexia. Moreover, the confusing fact that some control subjects also displayed ␣-MSH autoAbs was probably one reason that our finding did not attract significant attention by the research community. However, I was persuaded that we needed to pursue this line of research and in a follow-up study we showed that the levels of autoAbs directed against ␣-MSH, but not against some other neuropeptides including corticotropin, oxytocin, or vasopressin, significantly correlated with core psychopathologic symptoms in patients with eating disorders [7]. Importantly, these correlations were opposite in patients with restrictive anorexia versus bulimia, suggesting that, indeed, autoAbs could be involved in both forms of eating disorders. How it might be possible was not clear at the time and our finding remained relatively unnoticed except from some media coverage such as an article in The Economist [8]. I should also acknowledge Prof. Jaanus Harro and his colleagues from the University of Tartu in Estonia, without whom this work would not be possible, because they provided sera from patients with eating disorders and their careful psychological evaluation. To bring further insight to the matter and to test our hypothesis on the origin of eating disorders, the next step was the creation of an adequate animal model. Such an opportunity came from Prof. Pierre Déchelotte by his invitation to join his laboratory at the Rouen University in France as an associate professor. His laboratory was ideally suited to study feeding behavior in animals in conjunction with the common research facilities of the Biomedical Research Institute in Rouen, allowing state-of-the-art studies in immunology and neuroscience. Therefore, after moving back to France in 2004, I started to set up animal models of eating disorders based on active and passive transfers of ␣-MSH autoAbs, similar to established experimental protocols for models of some autoimmune diseases. However, what we found after 2 y of work came as a surprise. First, we realized that even without immunization, rats naturally display ␣-MSH autoAbs. This finding suggested that ␣-MSH autoAbs may play a hitherto unknown physiologic role and that rats could be used as an easily available model for the exploration of these autoAbs. Second, we found that ␣-MSH autoAbs may play a dual role with regard to ␣-MSH signaling by being acting as agonists or antagonists depending on their affinity values. In a most recent paper, we reported these data revealing the physiologic role of ␣-MSH autoAbs in the regulation of feeding and anxiety as an intrinsic biological mechanism of stress adaptation [9]. These results might finally help to explain how autoAbs directed against the same neuropeptide can be involved in restrictive anorexia and bulimia, as was suggested by our previous studies. We are currently verify-

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ing whether pathologic changes of affinity of ␣-MSH autoAbs can be responsible for the development of eating disorders in humans. An important question is what can trigger such changes in autoAb affinity? One possibility is the stimulation of the immune system by homologous antigens according to the concept of molecular mimicry [10]. Indeed, the initial idea to investigate the presence of molecular mimicry between ␣-MSH and microbial proteins came soon after our first report of ␣-MSH autoAbs, when I received an invitation to contribute a chapter for a book Neuropsychiatric Disorders and Infection edited by Dr. Hossein Fatemi. In analogy with the link between certain neuropsychiatric disorders and infection, I decided to search the public National Center for Biotechnology Information database of bacteria and viruses and I realized that a sequence homology of five consecutive amino acids of ␣-MSH was present in Escherichia coli and in some other micro-organisms [11]. At that stage, however, I was not aware that ␣-MSH autoAbs may represent a normal physiologic phenomenon. In fact, scarce data regarding the presence of autoAbs directed against neuropeptides existed in the literature, for instance, autoAbs against ␤-endorphin or somatostatin in some subjects with depression [12,13]. However, later when working in the nutrition laboratory in Rouen, I was studying the presence of autoAbs directed against other neuropeptides in healthy humans and in rats, and to my surprise all these test results returned positive. In an attempt to link the presence of such autoAbs with the concept of molecular mimicry, we studied healthy subjects for the presence of autoAbs directed against 14 key appetite-regulating neuropeptides or peptide hormones followed by in silico verification of all these peptides for sequence homology with proteins derived from bacteria, viruses, fungi, or archea. The results of this study provided the evidence that, indeed, autoAbs against neuropeptides represent a general physiologic phenomenon and that the concept of molecular mimicry can be applied to all these neuropeptides. Importantly, we found that the molecular mimicry involved not only pathogenic micro-organisms but also a number of species constituting commensal gut microflora, suggesting that luminal-derived proteins may represent the main source of antigenic stimulation for the production of autoAbs cross-reacting with neuropeptides. In fact, the detection of the immunoglobulin A class of such autoAbs supports this conclusion. However, these autoAbs were also detected in germ-free rats, although they displayed different levels versus specific pathogen-free rats, suggesting that gut microflora is not compulsory for autoAb generation but may selectively modulate their production [3]. This study opens a new view on the role of nutrition and

the gut including its pre- and probiotic contents as selective biochemical modulators of motivated behavior and emotion by secretion of autoAbs directed against neuropeptides involved in the regulation of these physiologic functions in the central and peripheral nervous systems. It is my firm conviction that further research of the origin and role of neuropeptide autoAbs in normal and pathologic conditions will help to develop specific and efficient diagnostic and therapeutic tools for several metabolic and neuropsychiatric diseases. References [1] Fetissov SO, Déchelotte P. The putative role of neuropeptide autoantibodies in anorexia nervosa. Curr Opin Clin Nutr Metab Care 2008;11:428 –34. [2] Fetissov SO, Hamze Sinno M, Coquerel Q, Do Rego JC, Coëffier M, Gilbert D, et al. Emerging role of autoantibodies against appetiteregulating neuropeptides in eating disorders. Nutrition 2008;24: 854 –9. [3] Fetissov SO, Hamze Sinno M, Coëffier M, Bole-Feysot C, Ducrotté P, Hökfelt T, et al. Autoantibodies against appetite-regulating peptide hormones and neuropeptides: putative modulation by gut microflora. Nutrition 2008;24:348 –59. [4] Meguid MM, Fetissov SO, Varma M, Sato T, Zhang L, Laviano A, et al. Hypothalamic dopamine and serotonin in the regulation of food intake. Nutrition 2000;16:843–57. [5] Fetissov SO, Hallman J, Oreland L, af Klinteberg B, Grenbäck E, Hulting AL, et al. Autoantibodies against a-MSH, ACTH, and LHRH in anorexia and bulimia nervosa patients. Proc Natl Acad Sci U S A 2002;99:17155– 60. [6] Fetissov SO, Bensing S, Mulder J, Le Maitre E, Hulting A-L, Harkany T, et al. Autoantibodies in autoimmune polyglandular syndrome type I patients react with major brain neurotransmitter systems. J Comp Neurol 2008(in press). [7] Fetissov SO, Harro J, Jaanisk M, Järv A, Podar I, Allik J, et al. Autoantibodies against neuropeptides are associated with psychological traits in eating disorders. Proc Natl Acad Sci U S A 2005;102: 14865–70. [8] Molecular self-loathing. Economist 2005;377:75– 6. [9] Hamze Sinno M, Do Rego JC, Coëffier M, Bole-Feysot C, Ducrotte P, Gilbert D, et al. Regulation of feeding and anxiety by ␣-MSH reactive autoantibodies. Psychoneuroendocrinology 2008(in press). Available online at doi:10.1016/j.psyneuen.2008.08.021. [10] Oldstone MB. Molecular mimicry, microbial infection, and autoimmune disease: evolution of the concept. Curr Top Microbiol Immunol 2005;296:1–17. [11] Fetissov SO. Autoimmune component in anorexia and bulimia nervosa. In: Fatemi SH, editor. Neuropsychiatric disorders and infection. London: Taylor & Francis; 2004. p. 253– 62. [12] Roy BF, Rose JW, McFarland HF, McFarlin DE, Murphy DL. Anti– beta-endorphin immunoglobulin G in humans. Proc Natl Acad Sci U S A 1986;83:8739 – 43. [13] Roy BF, Rose JW, Sunderland T, Morihisa JM, Murphy DL. Antisomatostatin IgG in major depressive disorder. A preliminary study with implications for an autoimmune mechanism of depression. Arch Gen Psychiatry 1988;45:924 – 8.