The Combined Influence of Magnesium and Insulin on Central Metabolic Functions and Expression of Genes Involved in Magnesium Homeostasis of Cultured Bovine Adipocytes

At the onset of lactation, dairy cows suffer from insulin resistance, insulin deficiency or both, similar to human diabetes, resulting in lipolysis, ketosis and fatty liver. This work explored the combined effects of different levels of magnesium (0.1, 0.3, 1 and 3 mM) and insulin (25, 250 and 25,000 pM) on metabolic pathways and the expression of magnesium-responsive genes in a bovine adipocyte model. Magnesium starvation (0.1 mM) and low insulin (25 pM) independently decreased or tended to decrease the accumulation of non-polar lipids and uptake of the glucose analog 6-(N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino)-6-deoxyglucose (6-NBDG). Activity of glycerol 3-phosphate dehydrogenase (GPDH) was highest at 25 pM insulin and 3 mM magnesium. Expression of SLC41A1 and SLC41A3 was reduced at 0.1 mM magnesium either across insulin concentrations (SLC41A1) or at 250 pM insulin (SLC41A3). MAGT1 expression was reduced at 3 mM magnesium. NIPA1 expression was reduced at 3 mM and 0.1 mM magnesium at 25 and 250 pM insulin, respectively. Expression of SLC41A2, CNNM2, TRPM6 and TRPM7 was not affected. We conclude that magnesium promotes lipogenesis in adipocytes and inversely regulates the transcription of genes that increase vs. decrease cytosolic magnesium concentration. The induction of GAPDH activity by surplus magnesium at low insulin concentration can counteract excessive lipomobilization.

The Human Islet: Mini-organ with Mega-impact

This review focuses on the human pancreatic islet – including its structure, cell composition, development, function, and dysfunction. After providing a historical timeline of key discoveries about human islets over the past century, we describe new research approaches and technologies that are being used to study human islets and how these are providing insight into human islet physiology and pathophysiology. We also describe changes or adaptations in human islets in response to physiologic challenges such as pregnancy, aging, and insulin resistance and discuss islet changes in human diabetes of many forms. We outline current and future interventions being developed to protect, restore, or replace human islets. The review also highlights unresolved questions about human islets and proposes areas where additional research on human islets is needed.

A mutant α1antitrypsin in complex with heat shock proteins as the primary antigen in type 1 diabetes in silico investigation

Based on previous results demonstrating that complexes of a mutant α1-antitrypsin with the heat shock proteins (HSP)70 and glucose-regulated protein94 (Grp94) circulate in the blood of patients with type 1 diabetes, we raised the hypothesis that these complexes could represent the primary antigen capable of triggering the autoimmune reactions leading to overt diabetes. As a first approach to this issue, we searched whether A1AT and HSPs had a sequence similarity to major islet antigen proteins so as to identify among the similar sequences those with potential relevance for the pathogenesis of diabetes. A thorough in silico analysis was performed to establish the score of similarity of the human proteins: A1AT, pro-insulin (INS), GAD65, IAPP, IA-2, ICA69, Grp94, HSP70 and HSP60. The sequences of A1AT and HSPs with the highest score of similarity to the islet peptides reported in the literature as the main autoantigens in human diabetes were recorded. At variance with other HSPs, also including HSP90 and Grp78, Grp94 contained the highest number and the longest sequences with structural similarity to A1AT and to well-known immunogenic peptides/epitopes of INS, GAD65, and IA-2. The similarity of A1AT with Grp94 and that of Grp94 with INS also suggested a functional relationship among the proteins. Specific sequences were identified in A1AT, Grp94 and HSP70, with the highest score of cross-similarity to a pattern of eight different islet protein epitopes. The similarity also involved recently discovered autoantigens in type 1 diabetes such as a hybrid peptides of insulin and the defective ribosomal insulin gene product. The significant similarity displayed by specific sequences of Grp94 and A1AT to the islet peptides considered main antigens in human diabetes, is a strong indication for testing these sequences as new peptides of immunogenic relevance in diabetes.

An autophagy enhancer ameliorates diabetes of human IAPP-transgenic mice through clearance of amyloidogenic oligomer

We have reported that autophagy is crucial for clearance of amyloidogenic human IAPP (hIAPP) oligomer, suggesting that an autophagy enhancer could be a therapeutic modality against human diabetes with amyloid accumulation. Here, we show that a recently identified autophagy enhancer (MSL-7) reduces hIAPP oligomer accumulation in human induced pluripotent stem cell-derived β-cells (hiPSC-β-cells) and diminishes oligomer-mediated apoptosis of β-cells. Protective effects of MSL-7 against hIAPP oligomer accumulation and hIAPP oligomer-mediated β-cell death are significantly reduced in cells with knockout of MiTF/TFE family members such as Tfeb or Tfe3. MSL-7 improves glucose tolerance and β-cell function of hIAPP+ mice on high-fat diet, accompanied by reduced hIAPP oligomer/amyloid accumulation and β-cell apoptosis. Protective effects of MSL-7 against hIAPP oligomer-mediated β-cell death and the development of diabetes are also significantly reduced by β-cell-specific knockout of Tfeb. These results suggest that an autophagy enhancer could have therapeutic potential against human diabetes characterized by islet amyloid accumulation.

P0681TIMP-1 DEFICIENCY DAMPENS RENAL GALECTIN-3 RESPONSE IN DIABETES

Background and Aims Overexpression of tissue inhibitors of metalloproteases (TIMPs) are a hallmark of renal fibrosis, and elevated TIMP-1 has been reported in experimental and human diabetes. Also, renal galectin-3 (Lgals3) overproduction might link macrophages to fibrosis progression. However, the possible association of renal Lgals3 with TIMP-1 in diabetes is still unclear. Thus, we investigated nephropathy and renal Lgals3 in type-1 diabetic wild type and TIMP-1 knockout (KO) mice. Method Type-1 diabetes was induced in 6 week-old male TIMP-1 KO (DM KO, n=7) and wild type (DM, n=6) mice with daily intraperitoneal streptozotocin (50 mg/kg/day) injections for 5 consecutive days. Non-diabetic controls (CTL, n=5) were injected with vehicle. Fasting blood glucose was monitored, and after 8 weeks kidneys were analyzed for histology and mRNA expression. Results Both diabetic groups developed similar hyperglycemia (CTL: 6±2, DM: 29±5, DM KO: 33±7 mmol/l, p<0.01). However, serum creatinine was elevated only in wild type diabetic mice (CTL: 9±2, DM: 47±28, DM KO: 11±2 ug/dl, p<0.001). Histology revealed significant tubular damage in DM mice (score: CTL: 0.4±0.1, DM: 2.3±0.2, DM KO: 1.6±0.2, p<0.05), accompanied by 10-fold lipocalin-2 (CTL: 1.0±0.3, DM: 10.9±6.2, DM KO: 3.3±1.7, p<0.05) and 2-fold collagen-1 overexpression (CTL: 1.0±0.2, DM: 1.9±0.7, DM KO: 1.2±0.4, p<0.05), practically absent in diabetic KO kidneys. Similarly, TIMP-1 deficiency was associated with twofold decrease in renal Lgal3 (CTL: 1.0±0.6, DM: 2.0±1.1, DM KO: 0.8±0.3, p<0.05) and tenfold decrease in CCL2 expression levels (CTL: 1.0±0.3, DM: 20.2±4.2, DM KO: 2.3±1.5, p<0.01) as compared to DM. Conclusion In our model of type-1 diabetes, TIMP-1 deficiency attenuated the development of renal fibrotic and inflammatory response by reducing galectin-3 and CCL2 (MCP-1), preserved tubular integrity and renal function. This might implicate TIMP-1 to be a possible therapeutic target in the future.