In vitro skeletal muscle models for type 2 diabetes

Effect of viral hepatitis on type 2 diabetes: A Mendelian randomization study

BACKGROUND

The effects of viral hepatitis (VH) on type 2 diabetes (T2D) remain controversial.

AIM

To analyze the causal correlation between different types of VH and T2D using Mendelian randomization (MR).

METHODS

Single nucleotide polymorphisms of VH, chronic hepatitis B (CHB), chronic hepatitis C (CHC) and T2D were obtained from the BioBank Japan Project, European Bioinformatics Institute, and FinnGen. Inverse variance weighted, MR-Egger, and weighted median were used to test exposure-outcome associations. The MR-Egger intercept analysis and Cochran's Q test were used to assess horizontal pleiotropy and heterogeneity, respectively. Leave-one-out sensitivity analysis was used to evaluate the robustness of the MR analysis results.

RESULTS

The MR analysis showed no significant causal relationship between VH and T2D in Europeans [odds ratio (OR) = 1.028; 95% confidence interval (CI): 0.995-1.062, P = 0.101]. There was a negative causal association between CHB and T2D among East Asians (OR = 0.949; 95%CI: 0.931-0.968, P < 0.001), while there was no significant causal association between CHC and T2D among East Asians (OR = 1.018; 95%CI: 0.959-1.081, P = 0.551). Intercept analysis and Cochran's Q test showed no horizontal pleiotropy or heterogeneity (P > 0.05). Sensitivity analysis showed that the results were robust.

CONCLUSION

Among East Asians, CHB is associated with a reduced T2D risk, but this association is limited by HBV load and cirrhosis. Although VH among Europeans and CHC among East Asians are not associated with the risk of T2D, focusing on blood glucose in patients with CHC is still relevant for the early detection of T2D induced by CHC-mediated pathways of hepatic steatosis, liver fibrosis, and cirrhosis.

Diabetes diminishes muscle precursor cell-mediated microvascular angiogenesis

The skeletal muscles of Type II diabetic (T2D) patients can be characterized by a reduced vessel density, corresponding to deficiencies in microvascular angiogenesis. Interestingly, T2D also inhibits the function of many myogenic cells resident within skeletal muscle, including satellite cells, which are well-known for the role they play in maintaining homeostasis. The current study was undertaken to gain a better understanding of the mechanisms whereby satellite cell progeny, muscle precursor cells (MPCs), influence microvascular angiogenesis. Network growth and the expression of genes associated with angiogenesis were reduced when microvessels were treated with conditioned media generated by proliferating MPCs isolated from diabetic, as compared to control rat skeletal muscle, a phenomenon that was also observed when myoblasts from control or diabetic human skeletal muscle were used. When only exosomes derived from diabetic or control MPCs were used to treat microvessels, no differences in microvascular growth were observed. An evaluation of the angiogenesis factors in control and diabetic MPCs revealed differences in Leptin, vascular endothelial growth factor (VEGF), IL1-β, interleukin 10, and IP-10, and an evaluation of the MPC secretome revealed differences in interleukin 6, MCP-1, VEGF, and interleukin 4 exist. Angiogenesis was also reduced in tissue-engineered skeletal muscles (TE-SkM) containing microvessels when they were generated from MPCs isolated from diabetic as compared to control skeletal muscle. Lastly, the secretome of injured control, but not diabetic, TE-SkM was able to increase VEGF and increase microvascular angiogenesis. This comprehensive analysis of the interaction between MPCs and microvessels in the context of diabetes points to an area for alleviating the deleterious effects of diabetes on skeletal muscle.

In Vitro Insulin Resistance Model: A Recent Update

Insulin resistance, which affects insulin-sensitive tissues, including adipose tissues, skeletal muscle, and the liver, is the central pathophysiological mechanism underlying type 2 diabetes progression. Decreased glucose uptake in insulin-sensitive tissues disrupts insulin signaling pathways, particularly the PI3K/Akt pathway. An in vitro model is appropriate for studying the cellular and molecular mechanisms underlying insulin resistance because it is easy to maintain and the results can be easily reproduced. The application of cell-based models for exploring the pathogenesis of diabetes and insulin resistance as well as for developing drugs for these conditions is well known. However, a comprehensive review of in vitro insulin resistance models is lacking. Therefore, this review was conducted to provide a comprehensive overview and summary of the latest in vitro insulin resistance models, particularly 3T3-L1 (preadipocyte), C2C12 (skeletal muscle), and HepG2 (liver) cell lines induced with palmitic acid, high glucose, or chronic exposure to insulin.