Novel role for matricellular proteins in the regulation of islet ß cell survival: the effect of SPARC on survival, proliferation, and signaling.

Understanding the mechanisms regulating islet growth and survival is critical for developing novel approaches to increasing or sustaining ß cell mass in both type 1 and type 2 diabetes patients. Secreted protein acidic and rich in cysteine (SPARC) is a matricellular protein that is important for the regulation of cell growth and adhesion. Increased SPARC can be detected in the serum of type 2 diabetes patients. The aim of this study was to investigate the role of SPARC in the regulation of ß cell growth and survival. We show using immunohistochemistry that SPARC is expressed by stromal cells within islets and can be detected in primary mouse islets by Western blot. SPARC is secreted at high levels by pancreatic stellate cells and is regulated by metabolic parameters in these cells, but SPARC expression was not detectable in ß cells. In islets, SPARC expression is highest in young mice, and is also elevated in the islets of non-obese diabetic (NOD) mice compared with controls. Purified SPARC inhibits growth factor-induced signaling in both INS-1 ß cells and primary mouse islets, and inhibits IGF-1-induced proliferation of INS-1 ß cells. Similarly, exogenous SPARC prevents IGF-1-induced survival of primary mouse islet cells. This study identifies the stromal-derived matricellular protein SPARC as a novel regulator of islet survival and ß cell growth.

Genetic risk for the polycystic ovary syndrome, bone mineral density and fractures in women and men: A UK Biobank Mendelian randomisation study.

INTRODUCTION: There is conflicting data on the effect of polycystic ovary syndrome (PCOS) on bone mineral density (BMD) and fracture risk. Recent genetic data suggest that men may also carry genetic risk factors for PCOS; the associations of these factors with parameters of bone health remains unknown. We aimed to investigate if the genetic risk of PCOS is associated with BMD and fracture risk in women and men in the UK Biobank dataset. METHODS: We used Mendelian randomisation (MR) analysis to test the association of genetic risk of excess testosterone in PCOS with BMD and fractures in the UK biobank study. The MR analysis was performed using linear regression analysis with the weighted genetic risk score (wGRS) as an independent variable adjusting for age, BMI and population eigenvectors. The horizontal pleiotropy in the MR analysis was tested using MR-Egger regression analysis. RESULTS: The study consisted of 221,086 Caucasian women (mean age ± SD: 56.7 ± 7.9 years, mean body mass index [BMI] ± SD: 27.0 ± 5.1 kg/m2, mean BMD ± SD: 0.50 ± 0.11 g/cm2) and 187,816 Caucasian men (mean age ± SD: 57.1 ± 8.1 years, mean BMI ± SD: 27.7 ± 4.1 kg/m2 and mean BMD ± SD: 0.56 ± 0.12 g/cm2). Women and men self-reported 24,797 (11%) and 17,076 (10%) fractures over the last 5 years, respectively. The MR analysis showed that one SD increase in the wGRS for clinical or biochemical hyperandrogenism in PCOS was associated with significantly higher heel BMD (Beta = 0.0007 [±0.0002], P-value = 0.001) and a significantly reduced risk of fractures (OR = 0.97, P-value = 0.003) in women. A similar wGRS in men was not associated with BMD or risk of fractures. CONCLUSION: In this study, we showed that the excess genetic risk for hyperandrogenism in women with PCOS is associated with a higher BMD and reduced risk of fractures.

Modulation of Rab7a-mediated growth factor receptor trafficking inhibits islet beta cell apoptosis and autophagy under conditions of metabolic stress.

Regenerative medicine approaches to enhancing beta cell growth and survival represent potential treatments for diabetes. It is known that growth factors such as insulin, IGF-1 and HGF support beta cell growth and survival, but in people with type 2 diabetes the destructive effects of metabolic stress predominate and beta cell death or dysfunction occurs. In this study we explore the novel hypothesis that regulation of growth factor receptor trafficking can be used to promote islet beta cell survival. Growth factor signalling is dependent on the presence of cell surface receptors. Endosomal trafficking and subsequent recycling or degradation of these receptors is controlled by the Rab GTPase family of proteins. We show that Rab7a siRNA inhibition enhances IGF-1 and HGF signalling in beta cells and increases expression of the growth factor receptors IGF-1R and c-Met. Furthermore, Rab7a inhibition promotes beta cell growth and islet survival, and protects against activation of apoptosis and autophagy pathways under conditions of metabolic stress. This study therefore demonstrates that Rab7a-mediated trafficking of growth factor receptors controls beta cell survival. Pharmaceutical Rab7a inhibition may provide a means to promote beta cell survival in the context of metabolic stress and prevent the onset of type 2 diabetes.

Effects of novel antidiabetes agents on apoptotic processes in diabetes and malignancy: Implications for lowering tissue damage.

Apoptosis is a complicated process that involves activation of a series of intracellular signaling. Tissue injuries from diabetes mellitus mostly occur as a consequence of higher rate of apoptosis process due to activation of a series of molecular mechanisms. Several classes of anti-hyperglycaemic agents have been developed which could potentially modulate the apoptotic process resulting in fewer tissue damages. Novel types of anti-hyperglycaemic medications such as sodium glucose cotransporters-2 inhibitors, glucagon like peptide-1 receptor agonists and dipeptidyl peptidase 4 inhibitors have shown to provide potent anti-hyperglycaemic effects, but their influences on diabetes-induced apoptotic injuries is largely unknown. Therefore, in the current study, we reviewed the published data about the possible effects of these anti-hyperglycaemic agents on apoptosis in diabetic milieu as well as in cancer cells.