Glycerol-Stimulated Proinsulin Biosynthesis in Isolated Pancreatic Rat Islets via Adenoviral-Induced Expression of Glycerol Kinase Is Mediated via Mitochondrial Metabolism
- Pacific Northwest Research Institute and Department of Pharmacology, University of Washington, Seattle, WA 98112.
Abstract
In this study, we examined whether adenoviral-mediated glycerol kinase (AdV-CMV-GlyK) expression in isolated rat pancreatic islets could introduce glycerol-induced proinsulin biosynthesis. In AdV-CMV-GlyK–infected islets, specific glycerol-induced proinsulin biosynthesis translation and insulin secretion were observed in parallel from the same islets. The threshold concentration of glycerol required to stimulate proinsulin biosynthesis was lower (0.25–0.5 mmol/l) than that for insulin secretion (1.0–1.5 mmol/l), reminiscent of threshold differences for glucose-stimulated proinsulin biosynthesis versus insulin secretion. The dose-dependent glycerol-induced proinsulin biosynthesis correlated with the rate of glycerol oxidation in AdV-CMV-GlyK–infected islets, indicating that glycerol metabolism was required for the response. However, glycerol did not significantly increase lactate output from AdV-CMV-GlyK–infected islets, but the dihydroxyacetone phosphate (DHAP) to α-glycerophosphate (α-GP) ratio significantly increased in AdV-CMV-GlyK–infected islets incubated at 2 mmol/l glycerol compared with that at a basal level of 2.8 mmol/l glucose (P ≤ 0.05). The DHAP:α-GP ratio was unaffected in AdV-CMV-GlyK–infected islets incubated at 2 mmol/l glycerol in the added presence of α-cyanohydroxycinnaminic acid (α-CHC), an inhibitor of the plasma membrane and mitochondrial lactate/pyruvate transporter. However, α-CHC inhibited glycerol-induced proinsulin biosynthesis and insulin secretion in AdV-CMV-GlyK–infected islets (>75%; P = 0.05), similarly to glucose-induced proinsulin biosynthesis and insulin secretion in AdV-CMV-GlyK–infected and control islets. These data indicated that in AdV-CMV-GlyK–infected islets, the importance of mitochondrial metabolism of glycerol was required to generate stimulus–response coupling signals to induce proinsulin biosynthesis and insulin secretion.
Footnotes
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Address correspondence and reprint requests to Christopher J. Rhodes, PhD, Pacific Northwest Research Institute, 720 Broadway, Seattle, WA 98112.
Received for publication 24 January 2001 and accepted in revised form 9 May 2001.
AdV-CMV-GlyK, adenoviral-mediated glycerol kinase; AdV-CMV-βGal, adenoviral-mediated β-galactosidase; α-CHC, α-cyano-4-hydroxycyanocinnamate; α-GP, α-glycerophosphate (glycerol 3-phosphate); BSA, bovine serum albumin; DHAP, dihydroxyacetone phosphate.
