Peroxisome abundance and lipid-toxicity of pancreatic B-cells in response to saturated fats

Abstract

Lipotoxicity results from the accumulation of fats within non‐adipose tissue, and is one of the causes of insulin resistance and β‐cell dysfunction in type 2 diabetes. Recently candidate gene studies have identified a gene variant at the PEX11α gene locus which is associated with reduced β‐cell function. PEX11α and PEX11β encode proteins involved in the division and proliferation of peroxisomes, which are responsible for the initial oxidation of very long chain and long chain fatty acids prior to complete oxidation in the mitochondria. The aim of this thesis was to explore the impact of altered PEX11α and PEX11β expression on peroxisome abundance and insulin secretion in cultured pancreatic β‐cells. siRNAs specific for PEX11α and PEX11β were used to knock down expression in MIN6 cells. Transfection resulted in 70% knockdown of PEX11α at all time points examined. There was no significant difference in the levels of insulin secreted at 25mM glucose between the PEX11α knockdown and the scrambled control cells. At 25mM glucose, 250μM palmitate decreased insulin secretion by 50% compared with the BSA control in the scrambled control cells. This was unchanged by PEX11α knockdown. Transfection with siRNA specific for PEX11β resulted in >80% reduction in expression at all time points examined. At 96hrs a 35% reduction in PMP‐70 protein levels, a marker of peroxisome abundance, was also seen. Incubation with palmitate in the PEX11β knockdowns resulted in a significant increase in insulin secretion at 25mM glucose compared with the scrambled palmitate control. Palmitate incubation decreased insulin secretion at 25mM glucose in untransfected control cells. However, PEX11α knockdown did not alter insulin secretion in the presence or absence of palmitate. PEX11β knockdown resulted in a decrease in PMP‐ 70 protein. Unexpectedly, PEX11β knockdown led to the partial recovery of the inhibitory effect of palmitate on insulin secretion.