ACTA ENDOCRINOLOGICA (BUC)

Vertebrate nonapeptide neurohormones constitute an evolutionarily conserved family, involved in vital functions, such as hydro-osmotic balance regulation, reproduction and social behaviour. Two human members of this family are known, vasopressin (AVP) and oxytocin (OXT), with their highly homologous genes closely located on Chr 20p13. Presence of vasotocin (AVT) in man has been suggested, but remains controversial, and genetic evidence is lacking. AVT activity could be explained by the presence of a third distinct gene for AVT or an RNA-processing mechanism involving products of AVP and/or OXT genes. To test the first hypothesis, we developed bioinformatics and experimental approaches using genomic DNA and fetal tissues mRNAs. Family-specific primers for AVT and neurophysin were designed based on CODEHOP strategy and used in our experiments. Results of bioinformatics and genomic DNA experiments (family-specific and Alu step-out PCR) suggest there is no evidence for an AVT gene in the genome. RNA-based techniques 3?-RACE and Family-Specific Domain Restriction Fragment RTPCR provided evidence for new transcript species that could code for AVT. Further experiments will be needed to characterize them. We discuss potential mechanisms of AVT mRNA generation based on AVP and OXT mRNAs, by alternative splicing, heterologous transsplicing or RNA-editing. While all methods we developed proved feasible, current results suggest there is no AVT gene in the genome, but specific mRNAs could be present in fetal tissues. Their full characterization may potentially allow identification of vasotocin mRNA and shed light on a subject of fundamental scientific interest.

Branched chained amino acids (BCAA) are essential components of the human diet and important nutrient signals, which regain particular interest in recent years with the avenue of metabolomics studies suggesting their potential role as biomarkers. There is now compelling evidence for predictive role of BCAA in progression of diabetes, but causality relationship is still debated concerning insulin resistance and genetic versus nongenetic pathogenesis. Mendelian randomization studies in large cohorts of diabetes indicated pathogenic role of PPM1K (protein phosphatase Mg2+/Mn2+ dependent 1K) on Chr 4q22.1 gene, encoding for a phosphatase that activate BCKDH (branched chain keto acid dehydrogenase) complex. Recent studies indicated that insulin rapidly and dose-dependently regulates gene expression of the same complex, but the relationship with systemic insulin resistance and glucose levels is complex. Rare genetic syndromes due to Mendelian mutations in key genes in BCAA catabolism may be good models to understand potential role of gene of BCAA catabolism. However, in studying complex disorders geneticists are faced to complete new aspects of metabolic regulation complicating understanding genetics of obesity, diabetes or metabolic syndrome. A review of genetic syndromes of BCAA metabolism suggests that insulin resistance is not present, except rare cases of methylmalonic aciduria due to MUT (methylmalonyl-coA mutase) gene on Chr 6p12.3. Another aspect that complicates understanding is the new role of central nervous system (CNS) in insulin resistance. For long time the hypothalamic hunger/satiety neuronal system was considered a key site of nutrient regulation. Genes may also affect the brain rewarding system (BRS) that would regulate food intake by modulating the motivation to obtain food and considering hedonic properties. Nutrigenomic and nutrigenetic investigations taking into account concurrently BCAA intake, metabolic regulation and gene variation have large perspectives to merge genetic and nutritional understanding in complex disorders.

Human populations are faced to the COVID-19 pandemic due to the emerging SARS-CoV-2 coronavirus originating from Wuhan (China) and with dramatic Public Health consequences. Despite periods of panic, the scientific community demonstrated an incredible innovation potential and energy ending up in one year with new vaccines to be used in population. Researchers are interrogating on how individual genetic differences contribute to the diversity of clinical manifestations or ethnic and geographic disparities of COVID-19. While efforts were spent to understand mechanistically the infectious potential of the virus, recent progresses in molecular genetics and bioinformatics allowed the characterization of viral sequence and construction of phylogeographical maps of viral dispersion worldwide. These data will help understanding epidemiological disparities among continents and ethnic populations. Much effort was also spent in analyzing host genetics by studying individual genes involved in innate and immune responses or explaining pathogenesis of comorbidities that complicate the fate of elderly patients. Several international consortia launched already Genome wide Association Studies (GWAS) and whole genome sequencing strategies to identify genetic markers with immediate application in patients at risk of respiratory failure. These new genetic data are important not only for understanding susceptibility factors for COVID-19 but they also contain an important message of hope for mankind warranting our survival and health.

Osteoporosis (OP) is a disease predisposing postmenopausal women to fractures, and often accompanied by insulin resistance (IR) and metabolic syndrome (MetS). Previous studies provided contradictory results concerning prevalence of MetS in postmenopausal OP. To better understand the pathogenesis of IR, we reviewed cellular and molecular aspects and systematically reviewed studies providing homeostasis model assessment (HOMA) index. Bone is an active endocrine organ maintaining its integrity by orchestrated balance between bone formation and resorption. Both osteoblasts and osteoclasts contain receptors for insulin and insulin-like growth factor-1 (IGF-1) operating in skeletal development and in the adult life. Defects in this system generate systemic IR and bone-specific IR, which in turn regulates glucose homeostasis and energy metabolism through osteocalcin. Examination of genetic syndromes of extreme IR revealed intriguing features namely high bone mineral density (BMD) or accelerated growth. Studies of moderate forms of IR in postmenopausal women reveal positive correlations between HOMA index and BMD while correlations with osteocalcin were rather negative. The relation with obesity remains complex involving regulatory factors such as leptin and adiponectin to which the contribution of potential genetic factors and in particular, the correlation with the degree of obesity or body composition should be added.

Genome Wide Association Studies (GWAS) are excellent opportunities to define culprit genes in complex disorders such as the polycystic ovary syndrome (PCOS). PCOS is a prevalent disorder characterized by anovulation, hyperandrogenism and polycystic ovaries, which benefitted from several GWASs in Asians and Europeans revealing more than 20 potential culprit genes near associated single nucleotide variations (SNV). Translation of these findings into the clinical practice raises difficulties since positive hits are surrogate SNVs linked with causative mutations by linkage disequilibrium (LD). Studies in Mediterranean populations (e.g. Southern Europe and North Africa) raise supplementary problems because of a different LD-pattern, which may disrupt the link with causative mutations. Our experience in MEDIGENE program between Tunisia and France enforces the necessity of genetic anthropology studies before translating GWAS data. Tunisians are a heterogeneous population with ancestral Berbers, European, Arab and Sub-Saharan African components while South Europeans display a high level of genetic diversity, partially explained by gene flow from North Africa. Human diversity studies require sampling from Middle East and North Africa (MENA) region that will help to understand genetic factors in complex diseases.