Activation of extracellular signal-regulated protein kinases 1 and 2 (ERK1/2) by free fatty acid receptor 1 (FFAR1/GPR40) protects from palmitate-induced beta cell death, but plays no role in insulin secretion.

AIMS: GPR40/FFAR1 mediates palmitate-induced stimulation of insulin secretion but its involvement in lipotoxicity is controversial. Our previous observations suggest that FFAR1/GPR40 agonists protect against lipotoxicity although the underlying mechanism remains elusive. The present study examines the role of ERK1/2 and GPR40/FFAR1 in palmitate-induced stimulation of insulin secretion and beta cell death. METHODS: Insulin secretion of INS-1E cells was measured by radioimmunoassay. Protein phosphorylation was examined on Western blots. Apoptosis was assessed by TUNEL staining. RESULTS: Palmitate and the GPR40/FFAR1 agonist TUG-469 increased phosphorylation of ERK1/2 at low (2.8 mmol/L) and high (12 mmol/L) glucose but stimulated insulin secretion only at high glucose. The MEK1 inhibitor PD98059 significantly reduced phosphorylation of ERK1/2 but did not reverse the stimulation of secretion induced by glucose, palmitate or TUG-469. PD98059 rather augmented glucose-induced secretion. Prolonged exposure to palmitate stimulated apoptosis, an effect counteracted by TUG-469. PD98059 accentuated palmitate-induced apoptosis and reversed TUG-469-mediated inhibition of cell death. CONCLUSIONS: Activation of ERK1/2 by palmitate and GPR40/FFAR1 agonist correlates neither with stimulation of insulin secretion nor with induction of apoptosis. The results suggest a significant anti-apoptotic role of ERK1/2 under conditions of lipotoxicity.

Detection of free fatty acid receptor 1 expression: the critical role of negative and positive controls.

AIMS/HYPOTHESIS: Adequate evaluation of protein expression is a crucial prerequisite for functional studies. Commonly used strategies comprise detection of proteins by specific antibodies using western blotting and immunohistochemical staining, or detection of mRNA by in situ hybridisation and RT-PCR. We evaluated the tools for the detection of free fatty acid receptor 1 (FFAR1) expression. METHODS: Commercially available antibody preparations were used to detect endogenous expression of the FFAR1 receptor and this was compared with cell preparations deficient or overexpressing the mouse or human receptor. Concentrations of mRNA were evaluated by RT-PCR. RESULTS: All insulin-secreting cells, INS-1E, Min6 and mouse islets showed specific expression of Ffar1 at the mRNA level. However, none of the commercially available antibodies specifically detected rat, mouse or human FFAR1. CONCLUSIONS/INTERPRETATION: Proper positive and negative controls are an important prerequisite for the evaluation of FFAR1 expression.