Progressive histopathological changes and β-cell loss in the pancreas of a new spontaneous rat model of type 2 diabetes

Pigment Epithelium-Derived Factor: Inhibition of Phosphorylation of Insulin Receptor (IR)/IR Substrate (IRS), Osteogeneration from Adipocytes, and Increased Levels Due to Doxorubicin Exposure

OBJECTIVES

Pigment epithelium-derived factor (PEDF) has been recently linked to insulin resistance and is capable of differentiating myocytes to bone. We examined in more detail the intricate signalling of the insulin pathway influenced by PEDF in skeletal myocytes. We tested whether this serpin is also capable of generating de novo bone from adipocytes in vitro and in vivo, and how the anticancer drug doxorubicin links with PEDF and cellular metabolism.

METHODS AND KEY FINDINGS

We demonstrate that PEDF can inhibit phosphorylation of insulin receptor (IR) and insulin receptor substrate (IRS) in skeletal myocytes. PEDF constitutively activates p42/44 MAPK/Erk, but paradoxically does not affect mitogenic signalling. PEDF did not perturb either mitochondrial activity or proliferation in cells representing mesenchymal stem cells, cardiomyocytes, and skeletal myocytes and adipocytes. PEDF induced transdifferentiation of adipocytes to osteoblasts, promoting bone formation in cultured adipocytes in vitro and gelfoam fatpad implants in vivo. Bone formation in white adipose tissue (WAT) was better than in brown adipose tissue (BAT). The frontline anticancer drug doxorubicin increased levels of PEDF in a human breast cancer cell line, mirroring the in vivo finding where cardiac muscle tissue was stained increasingly for PEDF as the dose of doxorubicin increased in mice. PEDF also increased levels of reactive oxygen species (ROS) and glutathione (GSH) in the breast cancer cell line.

CONCLUSIONS

PEDF may be used to regenerate bone from adipose tissue in cases of trauma such as fractures or bone cancers. The increased presence of PEDF in doxorubicin-treated tumour cells need further exploration, and could be useful therapeutically in future. The safety of PEDF administration in vivo was further demonstrated in this study.

Extracellular volume fraction of the pancreas predicts glucose intolerance in patients undergoing major pancreatic surgeries

PURPOSE

Pancreatic T1 value and extracellular volume fraction (ECV) are potential imaging biomarkers for pancreatic exocrine and endocrine function. This study aims to evaluate the ability of native T1 value and ECV of the pancreas in predicting postoperative new-onset diabetes (NODM) and worsened glucose tolerance in patients undergoing major pancreatic surgeries.

METHODS

This retrospective study involved 73 patients who underwent 3 T pancreatic MRI with pre- and postcontrast T1 mapping before major pancreatic surgeries. Patients were divided into non-diabetic, pre-diabetic and diabetic groups based on their glycated hemoglobin (HbA1c) value. Preoperative native T1 value and ECV of the pancreas were compared among the three groups. The correlation of pancreatic T1 value and ECV with HbA1c was assessed by linear regression analysis, and the ability of pancreatic T1 value and ECV for predicting postoperative NODM and worsened glucose tolerance was assessed using Cox Proportional hazards regression analysis.

RESULTS

Native pancreatic T1 value and ECV were both significantly higher in diabetic patients compared to pre-diabetic/non-diabetic patients, and ECV was also significantly higher in pre-diabetic patients compared to non-diabetic patients (all p < 0.05). Both native pancreatic T1 value and ECV showed positive correlation with preoperative HbA1c value (r = 0.50 and 0.55, respectively, both p < 0.001). ECV > 30.7% was the only independent predictor for NODM (HR = 5.687, 95% CI: 1.557, 13.468, p = 0.012) and worsened glucose tolerance (HR = 6.783, 95% CI:, 1.753, 15.842, p = 0.010) after surgery.

CONCLUSIONS

Pancreatic ECV predicts the risk of postoperative NODM and worsened glucose tolerance in patients undergoing major pancreatic surgeries.

1,25D/VDR inhibits pancreatic β cell ferroptosis by downregulating FOXO1 expression in diabetes mellitus

BACKGROUND

Type 2 diabetes mellitus (T2DM) is a global health problem that seriously threatens human health. Vitamin D (VD) has antidiabetic effects. However, the protective mechanism of 1,25-dihydroxyvitamin D3 (1,25D) on T2DM is still unclear.

METHODS

A rat model of T2DM was constructed using a high-fat diet combined with intraperitoneal injection of streptozotocin (STZ). Glucose tolerance was assessed by an oral glucose tolerance test (OGTT). Insulin secretion in blood and cell supernatant was determined by ELISA. Cell viability was analysed by CCK-8 assay. The level of ROS was detected by the DCFH-DA fluorescent probe method. The iron level in pancreatic tissues and cells was detected by an iron assay kit. Immunofluorescence staining was used to detect the expression of the pancreatic β cell marker CD49a. Furthermore, the protein expression levels of ferroptosis pathway-related proteins and vitamin D receptor (VDR) were detected by western blot. Downstream VDR targets were screened by proteomic sequencing.

RESULTS

The DM group had increased glucose levels and decreased insulin secretion, while 1,25D treatment decreased glucose levels and increased insulin secretion. 1,25D also suppressed DM-induced ferroptosis in pancreatic tissues in vivo. In addition, 1,25D significantly enhanced the viability of pancreatic β cells and reduced the levels of ROS and iron. 1,25D significantly upregulated the expression of VDR and the ferroptosis-related pathway protein GPX4 and downregulated the expression of ACSL4. Furthermore, knockdown of VDR reversed the effects of 1,25D on cell viability, ROS and iron levels, and ferroptosis-related protein expression in pancreatic β cells. Proteomic sequencing revealed that FOXO1 was the downstream target gene of VDR. Knockdown of FOXO1 reduced pancreatic β cell death, decreased ROS, iron and ACSL4 levels, and increased GPX4 levels.

CONCLUSION

1,25D/VDR inhibited pancreatic β cell ferroptosis in T2DM by downregulating the expression of FOXO1. This study provides a new theoretical basis for basic research on T2DM and is expected to establish a new idea for the treatment of T2DM.

Long chain polyunsaturated fatty acids (LCPUFAs) and nordihydroguaiaretic acid (NDGA) modulate metabolic and inflammatory markers in a spontaneous type 2 diabetes mellitus model (Stillman Salgado rats)

BACKGROUND

Diabetes mellitus (DM) is a complex disease with alterations in metabolic and inflammatory markers. Stillman Salgado rats (eSS) spontaneously develop type 2 DM by middle age showing progressive impairment of glucose tolerance with hyperglycemia, hypertriglyceridemia and hyperinsulinemia. We analyzed the effects of supplementation of ω-3 and ω-6 polyunsaturated fatty acids (PUFAs) with or without nordihydroguaiaretic acid (NDGA) added, an antioxidant and lipoxygenase inhibitor, on metabolic and inflammatory parameters in eSS rats to evaluate whether they can delay development and/or prevent progression of DM.

METHODS

After weaning, eSS rats received, intraperitoneally, once a month ω-3 (EPA 35% and DHA 40%-6.25 mg/Kg) or ω-6 (90% arachidonic acid- 6. 25 mg/Kg) for twelve months. Two additional groups of rats received 1.9 mg/kg NDGA added to ω-3 and ω-6 fatty acids. Blood samples were collected at day 40, and at the end of the 6th month and 12th month of age to determine plasma triglycerides (TGs), total plasma fatty acids (FA), A1C hemoglobin (HbA1C), C-reactive protein (CRP), gamma glutamyl transpeptidase (GGT), lipo and hydro peroxides, nitrites and IL-6 (in plasma and liver, kidney, and pancreas) and underwent oral glucose tolerance test (OGTT) as well. Wistar and eSS rats that received saline solution were used as controls.

RESULTS

Plasma lipids profile, TG, fasting and post-prandial blood glucose levels, and glycosylated HbA1C showed significant improvements in ω-3 and ω-3 + NDGA treated animals compared to eSS control group. ω-3 and ω-3 + NDGA groups showed an inverse correlation with fasting blood glucose and showed lower plasma levels of GGT, TG, and CRP. eSS rats treated with ω-3 LCPUFAs showed reduced level of inflammatory and oxidative indices in plasma and liver, kidney and pancreas tissues in comparison with eSS control (non-treated) and ω-6 treated groups.

CONCLUSIONS

eSS rats are a useful model to study type 2 DM pathophysiology and related inflammatory indices. ω-3 + NDGA supplementation, at the doses tested, ameliorated inflammatory, metabolic and oxidative stress markers studied.

Ageing is associated with molecular signatures of inflammation and type 2 diabetes in rat pancreatic islets

AIMS/HYPOTHESIS

Ageing is a major risk factor for development of metabolic diseases such as type 2 diabetes. Identification of the mechanisms underlying this association could help to elucidate the relationship between age-associated progressive loss of metabolic health and development of type 2 diabetes. We aimed to determine molecular signatures during ageing in the endocrine pancreas.

METHODS

Global gene transcription was measured in pancreatic islets isolated from young and old rats by Ilumina BeadChip arrays. Promoter DNA methylation was measured by Sequenom MassArray in 46 genes that showed differential expression with age, and correlations with expression were established. Alterations in morphological and cellular processes with age were determined by immunohistochemical methods.

RESULTS

Age-related changes in gene expression were found at 623 loci (>1.5-fold, false discovery rate [FDR] <5%), with a significant (FDR < 0.05) enrichment in genes previously implicated in islet-cell function (Enpp1, Abcc8), type 2 diabetes (Tspan8, Kcnq1), inflammatory processes (Cxcl9, Il33) and extracellular matrix organisation (Col3a1, Dpt). Age-associated transcriptional differences negatively correlated with promoter DNA methylation at several loci related to inflammation, glucose homeostasis, cell proliferation and cell-matrix interactions (Il33, Cxcl9, Gpr119, Fbp2, Col3a1, Dpt, Spp1).

CONCLUSIONS/INTERPRETATION

Our findings suggest that a significant proportion of pancreatic islets develop a low-grade 'chronic' inflammatory status with ageing and this may trigger altered functional plasticity. Furthermore, we identified changes in expression of genes previously linked to type 2 diabetes and associated changes in DNA methylation that could explain their age-associated dysregulation. These findings provide new insights into key (epi)genetic signatures of the ageing process in islets.