Gain of Function of Malate Dehydrogenase 2 and Familial Hyperglycemia.

CONTEXT: Genes causing familial forms of diabetes mellitus are only partially known. OBJECTIVE: We set out to identify the genetic cause of hyperglycemia in multigenerational families with an apparent autosomal dominant form of adult-onset diabetes not due to mutations in known monogenic diabetes genes. METHODS: Existing whole-exome sequencing (WES) data were used to identify exonic variants segregating with diabetes in 60 families from the United States and Italy. Functional studies were carried out in vitro (transduced MIN6-K8 cells) and in vivo (Caenorhabditis elegans) to assess the diabetogenic potential of 2 variants in the malate dehydrogenase 2 (MDH2) gene linked with hyperglycemia in 2 of the families. RESULTS: A very rare mutation (p.Arg52Cys) in MDH2 strongly segregated with hyperglycemia in 1 family from the United States. An infrequent MDH2 missense variant (p.Val160Met) also showed disease cosegregation in a family from Italy, although with reduced penetrance. In silico, both Arg52Cys and Val160Met were shown to affect MDH2 protein structure and function. In transfected HepG2 cells, both variants significantly increased MDH2 enzymatic activity, thereby decreasing the NAD+/NADH ratio-a change known to affect insulin signaling and secretion. Stable expression of human wild-type MDH2 in MIN6-K8 cell lines enhanced glucose- and GLP-1-stimulated insulin secretion. This effect was blunted by the Cys52 or Met160 substitutions. Nematodes carrying equivalent changes at the orthologous positions of the mdh-2 gene showed impaired glucose-stimulated insulin secretion. CONCLUSION: Our findings suggest a central role of MDH2 in human glucose homeostasis and indicate that gain of function variants in this gene may be involved in the etiology of familial forms of diabetes.

A functional variant of the dimethylarginine dimethylaminohydrolase-2 gene is associated with myocardial infarction in type 2 diabetic patients.

BACKGROUND: Myocardial infarction is the main mortality cause in patients with type 2 diabetes (T2DM). Endothelial dysfunction due to reduced bioavailability of nitric oxide (NO) is an early step of atherogenesis. Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of NO synthesis, and it is metabolized by the enzymes dimethylarginine dimethylaminohydrolase (DDAH) 1 and 2. The functional variant rs9267551 C, in the promoter region of DDAH2, has been linked to increased DDAH2 expression, and lower ADMA plasma levels, and was associated with lower risk of coronary artery disease in large-scale genome-wide association studies (GWAS) performed in the general population. However, it is unknown whether this association holds true in T2DM patients. To address this issue, we investigated whether rs9267551 is associated with risk of myocardial infarction in two cohorts of T2DM patients. METHODS: SNP rs9267551 was genotyped in 1839 White T2DM patients from the Catanzaro Study (CZ, n = 1060) and the Gargano Heart Study-cross sectional design (GHS, n = 779). Cases were patients with a previous myocardial infarction, controls were asymptomatic patients with neither previous myocardial ischemia nor signs of it at resting and during a maximal symptom limited stress electrocardiogram. RESULTS: Carriers of allele rs9267551 C showed a dose dependent reduction in the risk of myocardial infarction [(CZ = OR 0.380, 95% CI 0.175-0.823, p = 0.014), (GHS = 0.497, 0.267-0.923, p = 0.027), (Pooled = 0.458, 0.283-0.739, p = 0.001)] which remained significant after adjusting for sex, age, BMI, smoking, HbA1c, total cholesterol HDL, and triglyceride levels [(CZ = 0.307, 0.106-0.885, p = 0.029), (GHS = 0.512, 0.270-0.970, p = 0.040), (Pooled = 0.458, 0.266-0.787, p = 0.005)]. CONCLUSIONS: We found that rs9267551 polymorphism is significantly associated with myocardial infarction in T2DM patients of European ancestry from two independent cohorts. It is possible that in subjects carrying the protective C allele less ADMA accumulates in endothelial cells causing vascular protection as a consequence of higher nitric oxide availability.

Effect of mitotane on mouse ovarian follicle development and fertility.

Mitotane (MTT) is an adrenolytic drug used in advanced and adjuvant treatment of adrenocortical carcinoma, in Cushing's disease and in ectopic syndrome. However, knowledge about its effects on the ovary is still scarce. The purpose of this study is to investigate the effect of MTT on the ovary using in vivo and in vitro models. The study was performed in CD1 mice and in the COV-434 human ovarian granulosa cell line. We examined ovarian morphology, follicle development, steroidogenesis and procreative function in mice and the effect of MTT on cell growth in vitro Our results revealed that treatment of CD1 mice with MTT induces a decrease in early antral follicles with a subsequent increase in the secondary follicles, measured by the increased levels of anti-Mullerian Hormone (P < 0.05) and decreased levels of FSH receptor (P < 0.05). Moreover, we observed a significant decrease in Cyp11a1 (P < 0.01) and Cyp17a1 (P < 0.001) mRNA level in MTT-treated animals. Ovulation, induced by PMSG/hCG stimulation, was also significantly impaired, with a reduction in the number of ovulated oocytes (P < 0.01) and fewer corpora lutea in treated animals. Likewise, the mating experiment demonstrated a delay in the time of conception as well as fewer pups per litter in MTT-treated mice (P < 0.05). Experiments performed on the COV-434 cell line showed a significant inhibition of growth followed by apoptosis (P < 0.01). In conclusion, our study highlights the key points of ovarian folliculogenesis affected by MTT and demonstrates impairment of the ovulation process with a negative impact on conception, which is nevertheless preserved.