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Overweight-induced Hypogonadism as major factor for the generation and/or perpetuation of Metabolic Co-morbidities of Obesity: Contribution of Epigenetic Regulatory Mechanisms

Periodic Reporting for period 1 - ReprObesity (Overweight-induced Hypogonadism as major factor for the generation and/or perpetuation of Metabolic Co-morbidities of Obesity: Contribution of Epigenetic Regulatory Mechanisms)

Période du rapport: 2016-10-01 au 2018-09-30

Obesity has become one of the major health issues in the EU and worldwide. This complex medical condition is frequently linked to serious metabolic complications and deregulation of hormonal axes. Interestingly, different studies have suggested a potential link between obesity and hypogonadism, a reproductive disorder that might also promote metabolic alterations, thus setting a vicious circle in the generation and perpetuation of obesity co-morbidities. While the targets and molecular mechanisms underlying this phenomenon are still unknown, emerging evidence suggests the potential role of (i) the hypothalamic Kiss1/NKB neurons, which are deregulated in experimental models of metabolic stress linked to reproductive dysfunction, and (ii) epigenetic regulatory mechanisms, which have been shown to modulate the hypothalamic expression of Kiss1 under physiological conditions. In the above context, this project aimed to elucidate the pathophysiological relevance of epigenetic regulatory mechanisms in obesity-induced hypogonadism and its impact on the control of hypothalamic Kiss1/NKB neurons and the generation and maintenance of the metabolic complications of overweight. To this end, we have characterized the time-course of alterations of key hormonal and epigenetic factors in preclinical models of obesity and we have evaluated the contribution of epigenetic modifications in deregulation of hypothalamic Kiss1/NKB neurons in conditions of overweight. This project has allowed identifying specific molecular targets and epigenetic mechanisms responsible for the metabolic perturbations linked to obesity-induced hypogonadism, which will aid to define better tools for the treatment of these complications.
"Firstly, we generated different experimental models of obesity-induced hypogonadism in male and female rats, including (i) rats bred in small litters (SL) and subjected to high fat diet (HFD) after weaning (SL/HFD), (ii) rats subjected to gonadectomy (GNX), (iii) rats subjected to a combination of the above manipulations (SL/HFD/GNX), and (iv) rats subjected to a protocol of neonatal androgenization with testosterone propionate (TP) or a combination of such protocol with nutritional manipulation (SL/HFD/TP), in the specific case of females. After the generation of those pre-clinical models, we evaluated the instauration and progression of obesity-induced hypogonadism as well as its metabolic co-morbidities in those animal models. Our results suggest that early overweight induced by nutritional manipulations not only evoke alterations in the activity of gonadotropic axis at early ages but also impaired metabolic and reproductive function later in life. Yet, the latter seems to be more pronounced in SL/HFD male rats.
Secondly, we measured (i) the circulating levels of the adipose hormone leptin and the pancreatic hormone insulin, as endocrine targets, and (ii) the hypothalamic content of the histone deacetylase Sirtuin 1 (SIRT1) and a specific microRNA (miRNA), as epigenetic markers, in SL/HFD animal models. Interestingly, our hormonal analyses suggest that early alterations in leptin and insulin serum levels might serve as potential endocrine markers for obesity-induced hypogonadism and/or altered reproductive function in male and female rats, respectively. Furthermore, our expression studies of the above epigenetic regulatory elements revealed that alterations in the hypothalamic expression of SIRT1 might contribute to the altered reproductive function observed in SL/HFD female rats, while changes in the hypothalamic expression of a specific miRNA may underlie the phenotype of obesity-induced hypogonadism observed in SL/HFD male rats.
Thirdly, we evaluated the specific impact of the above alterations on the hypothalamic KNDy neurons, epitomized by Kiss1, and its contribution to the phenotype of impaired reproductive function and obesity-induced hypogonadism in SL/HFD female and male rats, respectively. Our data show that SIRT1 alters the activity of KNDy neurons by an epigenetic regulatory mechanism that affects Kiss1 expression in SL/HFD female rats with altered reproductive function. Moreover, we found that a specific miRNA regulates Kiss1 expression in SL/HFD male rats with obesity-induced hypogonadism and that the central manipulation of this miRNA ameliorates such phenotype and its metabolic co-morbidities.
Finally, it is worth to mention that exploitation and dissemination of the results have taken place as planned in the original proposal. All results derived from this project were shared with the scientific community through (i) multidisciplinary seminars and weekly meetings organized by the host group (Tena-Sempere's lab); (ii) International scientific conferences (e.g. Endocrine Society Annual Meeting and International Congress of Neuroendocrinology); and (iii) scientific publications in reputed peer-review journals. Indeed, part of the results of this project has been published in the journal Nature Communications. In addition, the fellow have actively participated in different outreach activities, including 1 seminar with school students (IMIBIC, Cordoba, 2016), (ii) 1 seminar with members of ""Asociación Cultural Capella Cordubensis"" (IMIBIC, Cordoba, 2017), and (iii) 3 exhibitions: 2 European Researcher's Night (Cordoba, 2017 and 2018) and “Paseo por la Ciencia” (Cordoba, 2017).
The research work developed by the fellow during the implementation of this project has allowed (i) to gain new insights into the neurohormonal and epigenetic mechanisms for the reproductive and metabolic perturbations associated to obesity and (ii) to identify novel epigenetic targets for the early detection and eventual treatment of conditions prone to development of reproductive and metabolic complications. In particular, the results derived from this project have allowed unveiling the key role of the hypothalamic Kiss1 neurons and its (de)regulation by epigenetic mechanisms, involving SIRT-1/histone modifications and miRNAs, in the development of obesity-induced hypogonadism. These findings provide key knowledge for the design of improved strategies to palliate the increasing incidence of reproductive disorders putatively associated with metabolic causes not only in EU but also in non-European countries.
Overview of the project