Mitochondrial-encoded gene regulation in rat pancreatic islets

Mitochondrial adenosine triphosphate (ATP) generation plays a major role in insulin secretion in pancreatic islet beta cells. The relationship between age and nutritional status of the islet and mitochondrial gene messenger R NA (mRNA) expression was investigated. Three animal groups were studied: in fant (12-day-old) rats fed either mother's milk or a high carbohydrate (HC) diet; young (2 to 4-month-old) rats; and old (12 to 14-month-old) rats. Th e expression of mitochondrial cytochrome oxidase (CYO) (subunits I, II, and III). beta -nicotinamide adenine dinucleotide, reduced form dehydrogenase subunit 4 (NADH-DH4). and ATP synthase (subunit 6) (ATP-SYN6) mRNAs was cha racterized by semiquantitative reverse-transcriptase polymerase chain react ion (RT-PCR). The mitochondrial gene mRNAs ware identified in each of the g roups of rat islets and in RINm5F cells. CYO-II mRNA expression in young an d old rat pancreatic islets was 12.7- and 8.2-fold higher, respectively, co mpared with the level in infant rat islets, The expression of NADH-DH4 and ATP-SYN6 mRNAs was 47% and 40% lower, respectively, in young rat islets com pared with the level in infant rat islets. CYO-I, CYO-III, and cytoplasmic glyceraldehyde-3-phosphate dehydrogenase (GPDH) mRNA expression did not dif fer between experimental groups. Artificial rearing of infant rat pups on a HC diet for 8 days lead to a 3.3-fold increase in islet CYO-II mRNA expres sion compared with mother-fed pups. However, glucose (11 mmol/L) stimulatio n of cultured isolated islets from young and old rats for 4 days failed to affect the expression level of mitochondrial gene mRNAs. Thus, aging affect ed the differential expression of CYO-II. NADH-DH4. and ATP-SYN6 mRNAs in r at islets. CYO-II mRNA expression was modulated only in infant rat islets a fter in vivo administration of carbohydrate. Copyright (C) 2001 by W.B. Sau nders Company.