A novel spontaneous mutation of Irs1 in mice results in hyperinsulinemia, reduced growth, low bone mass and impaired adipogenesis

Abstract

A spontaneous mouse mutant, designated 'small' (sml), was recognized by reduced body size suggesting a defect in the IGF1/GH axis. The mutation was mapped to the chromosome 1 region containing Irs1, a viable candidate gene whose sequence revealed a single nucleotide deletion resulting in a premature stop codon. Despite normal mRNA levels in mutant and control littermate livers, western blot analysis revealed no detectable protein in mutant liver lysates. When compared with the control littermates, Irs1 sml /Irs1 sml (Irs1 sml/sml ) mice were small, lean, hearing impaired; had 20% less serum IGF1; were hyperinsulinemic; and were mildly insulin resistant. Irs1 sml/sml mice had low bone mineral density, reduced trabecular and cortical thicknesses, and low bone formation rates, while osteoblast and osteoclast numbers were increased in the females but not different in the males compared with the Irs1 C/C controls. In vitro, Irs1 sml/sml bone marrow stromal cell cultures showed decreased alkaline phosphatase-positive colony forming units (pre-osteoblasts; CFU-APC) and normal numbers of tartrate-resistant acid phosphatase-positive osteoclasts. Irs1 sml/sml stromal cells treated with IGF1 exhibited a 50% decrease in AKT phosphorylation, indicative of defective downstream signaling. Similarities between engineered knockouts and the spontaneous mutation of Irs1 sml were identified as well as significant differences with respect to heterozygosity and gender. In sum, we have identified a spontaneous mutation in the Irs1 gene associated with a major skeletal phenotype. Changes in the heterozygous Irs1 C/sml mice raise the possibility that similar mutations in humans are associated with short stature or osteoporosis.

Spontaneous Irs1 passenger mutation linked to a gene-targeted SerpinB2 allele

“…A spontaneous Irs1 mutation in an inbred C3.SW-H2b/SnJ mouse strain was also recently reported (30). Mice homozygous deficient for this mutation exhibit hyperinsulinemia, are small in stature, and exhibit bone abnormalities, with no reported effect on longevity (30).…”

“…Mice homozygous deficient for this mutation exhibit hyperinsulinemia, are small in stature, and exhibit bone abnormalities, with no reported effect on longevity (30). The normal lifespan observed in these mice may be a result of residual hypomorphic IRS1 function from the more distal truncation at amino acid 211, or of the difference in strain background (C3H/HeSnJ, except for a Swiss donor congenic fragment on chromosome 17).…”

Igfbp2 Deletion in Ovariectomized Mice Enhances Energy Expenditure but Accelerates Bone Loss

“…For analysis of blood glucose, mice were fasted overnight and then glucose levels were measured using the OneTouch Ultra Glucometer (LifeScan, Inc., Milpitas, California, USA) as described previously (28). For the insulin tolerance test, mice were fed ad libitum and injected IP with insulin at a dose of 1 U/kg.…”

Leaf Extract from Lithocarpus polystachyus Rehd. Promote Glycogen Synthesis in T2DM Mice

“…Meanwhile, insulin is recognized by IR, which upon activation provides docking sites for IRS proteins. mRNA relative expression is known to decrease after exogenous addition of glucose for T2DM [42, 46]. Under this condition, genes related to glycogen synthesis and genes inhibiting hepatic gluconeogenesis have also been reported [5]; for example, overexpression of phosphoenolpyruvate carboxykinase (PEPCK) and G-6-P.…”

“…Quantitative real-time PCR was performed in a Bio-Rad CFX96 ™ Real-Time System (C1000 Touch Thermal Cycler). The mRNA levels of all genes were normalized using GADPH as internal control [41–42]. …”