Altered insulin receptor messenger ribonucleic acid splicing in liver is associated with deterioration of glucose tolerance in the spontaneously obese and diabetic rhesus monkey: Analysis of controversy between monkey and human studies

There are two insulin receptor (TR) isoforms (designated type A and type B), derived from alternative splicing of exon 11 of the IR gene. Recently, we reported (Huang Z., Bodkin N.L., Ortmeyer H.K., Hansen B.C., Shuldiner A. R., 1994, J Clin Invest, 94:1289-1296) that an increase in the exon 11- (i.e. lacking exon 11) (type A) IR messenger RNA (mRNA) variant in muscle is associated with hyperinsulinemia, an early risk factor for noninsulin-dependent diabetes mellitus (NIDDM), in the spontaneously obese, diabetic rhesus monkey. To explore further the role of IR mRNA splicing in insulin resistance of NIDDM, we studied liver, another target organ that is resistant to insulin action in NIDDM. The relative amounts of the two IR mRNA-splicing variants in liver were quantitated by RT-PCR in normal, prediabetic, and diabetic (NIDDM) monkeys. The percentage of the exon 11- mRNA variant in liver (n = 24) was significantly correlated with fasting plasma glucose (r = 0.55, P < 0.01) and intravenous glucose disappearance rate(r = -0.45, P < 0.05). The exon 11- mRNA variant was increased significantly from 29.8 +/- 1.6% in monkeys with normal fasting glucose to 39.2 +/- 2.9% in monkeys with elevated fasting glucose (P < 0.01). These studies provide the first direct evidence in vivo that the relative expression of the two IR mRNA-splicing variants is altered in liver and suggest that increased expression of the exon 11- IR isoform may contribute to hepatic insulin resistance and NIDDM or may compensate for some yet unidentified defect.