Glucose Intolerance in Aging Male IGFBP-3 Transgenic Mice: Differential Effects of Human IGFBP-3 and Its Mutant IGFBP-3 Devoid of IGF Binding Ability

Abstract

We have reported a reduction of insulin secretion and glucose intolerance in young mice overexpressing human IGFBP-3 (phosphoglycerate kinase [PGK]BP3) or its mutant Gly56/Gly80/Gly81-IGFBP-3 (PGKmutBP3) under the PGK promoter. Here, we investigated changes in glucose and lipid homeostasis with age in PGKBP3 and PGKmutBP3 mice compared with wild-type mice. Body weight, glucose tolerance, insulin tolerance, visceral fat, interscapular brown adipose tissue (BAT), serum lipids, and pancreas histology were examined at age 3, 6, and 12 months. Murine IGFBP-3 was similar in all mouse genotypes and decreased with age in parallel with total IGF-1. Visceral fat and BAT masses increased in PGKmutBP3 mice, but not in PGKBP3 mice. Glucose tolerance was impaired in both PGKBP3 and PGKmutBP3 mice. However, PGKBP3 mice had increased expression of uncoupling protein-1 in BAT and reduced adiposity, and continued to have smaller pancreatic β-cell mass and reduced insulin secretion through age 12 months. In contrast, PGKmutBP3 mice developed insulin resistance with age in association with pancreatic β-cell hyperplasia, impaired expression of uncoupling protein-1 in BAT, and increased adiposity. In addition, both PGKBP3 and PGKmutBP3 mice had elevated glycerol in the circulation, but only PGKBP3 mice had elevated free fatty acids and only PGKmutBP3 mice had elevated triglycerides. Estimated free IGF-1 did not increase with age in transgenic mice, as it did in wild-type mice. Thus, overexpression of human IGFBP-3 or its mutant devoid of IGF binding ability leads to glucose intolerance with, however, different effects on insulin secretion, insulin sensitivity, and lipid homeostasis in aging mice.

In vitro differentiation of mouse brown preadipocytes is enhanced by IGFBP‐3 expression and reduced by IGFBP‐3 silencing

“…The effects of IGFBP-3 on brown adipocyte growth and differentiation have not been studied before. However, we have recently observed a similar reduction of brown adipose genes in aging PGKmutBP3 mice (14). Our study, in some respects, also agrees with the reports that IGFBP-3 stimulates growth of some cell types.…”

“…Our group has previously reported that the expression of endogenous mouse IGFBP-3 is not affected by hIGFBP-3 overexpression (15). Because of differences in IGF binding between hIGFBP-3 and its mutant, the quenching of IGF-I produced in brown preadipocytes was likely greater in PGKBP3 than in wild-type cells, and smallest in PGKmutBP3 cells (14,15). Therefore, free IGF-I level was likely greatest in PGKmutBP3 cells, smallest in PGKBP3 cells, and intermediate in wild-type cells.…”

“…It has been reported that circulating IGFBP-2 negatively predicts brown fat formation (12) and that brain IGFBP-6 reduces UCP1 expression in brown fat (13). More recently, we have shown that transgenic mice expressing human IGFBP-3 (hIGFBP-3) or its non-IGF-binding mutant Gly56/Gly80/Gly81-IGFBP-3 have increased UCP1 expression in brown adipose tissue (14). In this study, we demonstrate that IGFBP-3 is a factor regulating brown adipocyte growth and differentiation in vitro.…”

“…The cDNA was synthesized from 5 μg total RNA using Moloney murine leukemia virus reverse transcriptase and oligo(deoxythymidine) primers. CCAAT/enhancer‐binding protein ( C/EBP)‐α , peroxisome proliferator‐activated receptor ( PPAR)γ, PPAR γ coactivator (PGC)−1α , PR domain‐containing 16 ( PRDM16 ), UCP1 , IGF‐I , and IGFBP‐3 mRNAs, and 18S ribosomal RNA (house keeper) were determined using 40 amplification cycles (15 s at 95°C, 90 s at 60°C) and specific primers .…”

Germline Chd8 haploinsufficiency alters brain development in mouse

“…One sample each from WT and Chd8 +/del5 was removed from Q-fraction analysis due to difficulties in selecting the VZ. All immunolabeling was carried out on slide-mounted cryosections (18 μm) following standard protocols and using primary antibodies directed against Pax6 42 (PRB-278P-100; rabbit, 1:100, Covance, Princeton, NJ), Tbr2 (http://www.abcam.com/TBR2--Eomes-antibody-EPR19012-ab183991.pdf) (ab183991; rabbit, 1:400, Abcam, Cambridge, United Kingdom), or Ki67 43 (#12202; rabbit, 1:200, Cell Signaling, Danvers MA). Alexa Fluor secondary antibodies (488 and 594) were used at 1:200 concentrations (Thermo Fisher Scientific, Waltham, MA).…”