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[3T3-L1 adipocytes reduces Kir6.2 channel expression in MIN6 insulin-secreting cells in vitro]
Yu-Feng Zhao1, Yun-Long Zhu, Chen Chen
1Department of Physiology, Fourth Military Medical University, Xi'an 710032, China.
Abstract:
Dysfunction of the pancreatic beta-cell is an important defect in the pathophysiological changes of type 2 diabetes, and type 2 diabetes is evidently associated with obesity. But the role of the adipocyte in the dysfunction of the pancreatic beta-cell remains unknown. In the present study, we examined the direct effects of 3T3-L1 adipocytes on the expression of ATP-sensitive potassium channels (K(ATP) channels) in MIN6 insulin-secreting cells. MIN6 cells were divided into two groups as control group, where MIN6 cells were cultured in normal culture medium, and coculture group, where MIN6 cells were cocultured with differentiated 3T3-L1 adipocytes for 1 week. Semi-quantitative RT-PCR was employed to measure the expression of K(ATP) channel subunit Kir6.2 in MIN6 cells. Fura-2 was used to reflect changes in intracellular calcium concentration ([Ca(2+)](i)) in MIN6 cells. The secretary function of MIN6 cells from both groups was estimated by radioimmunoassay method. The results showed that the Kir6.2 cDNA levels corrected by GAPDH cDNA levels after densitometric analysis were 0.989+/-0.035 in control group and 0.726+/-0.087 in coculture group. The expression of Kir6.2 was significantly decreased in MIN6 cells in the coculture group as compared with that in control. MIN6 cells cocultured with 3T3-L1 adipocytes lost the ability to increase [Ca(2+)](i) when stimulated by tolbutamide (0.1 mmol/L), a highly selective KATP channel closer. In contrast, MIN6 cells in control group had typical responses to tolbutamide with a significant increase in [Ca(2+)](i). The magnitudes to basal levels of [Ca(2+)](i) after tolbutamide stimulation were 1.520+/-0.203 in control and 1.114+/-0.097 in coculture group (P<0.05, n=6). MIN6 cells in control showed a significant increase in insulin secretion from 0.38+/-0.099 mU/min to 2.87+/-0.248 mU/min after being stimulated by tolbutamide, whereas MIN6 cells in coculture group did not increase insulin secretion when stimulated by tolbutamide (0.21+/-0.055 mU/min to 0.22+/-0.082 mU/min). It is demonstrated that 3T3-L1 adipocytes decrease the expression of K(ATP) channels in MIN6 cells through secreting certain factors, which impair the secretary function of MIN6 cells. The present results indicate that adipocytes are directly involved in pancreatic beta-cell dysfunction, which may facilitate the development of type 2 diabetes.
Insights
Adipocytes directly impair pancreatic beta-cell function by reducing ATP-sensitive potassium (KATP) channel expression. This dysfunction in KATP channels affects insulin secretion, potentially contributing to type 2 diabetes development.
Area of Science:
- Endocrinology and Metabolism
- Cell Biology
- Molecular Medicine
Context:
- Pancreatic beta-cell dysfunction is a key feature of type 2 diabetes, often linked with obesity.
- The specific role of adipocytes in beta-cell dysfunction remains largely unexplored.
- Understanding adipocyte-beta-cell interactions is crucial for elucidating type 2 diabetes pathogenesis.
Purpose:
- To investigate the direct impact of 3T3-L1 adipocytes on ATP-sensitive potassium (KATP) channel expression in MIN6 insulin-secreting cells.
- To determine how adipocyte co-culture affects MIN6 cell responses to KATP channel modulation and insulin secretion.
Summary:
- Co-culturing MIN6 cells with 3T3-L1 adipocytes significantly decreased the expression of the KATP channel subunit Kir6.2.
- Adipocyte co-culture impaired MIN6 cells' ability to increase intracellular calcium concentration ([Ca2+]i) upon stimulation with tolbutamide, a KATP channel closer.
- Insulin secretion in response to tolbutamide was significantly reduced in MIN6 cells co-cultured with adipocytes compared to controls.
Impact:
- Adipocytes secrete factors that downregulate KATP channel expression in pancreatic beta-cells, thereby impairing their secretory function.
- This study provides direct evidence for adipocyte involvement in pancreatic beta-cell dysfunction.
- These findings suggest a novel mechanism linking obesity-associated adipocyte dysfunction to the development of type 2 diabetes.
