Physiology and pathology of growth - studies in GH transgenic mice

Growth hormone (GH)-transgenic insulin-like growth factor 1 (IGF1)-deficient mice allow dissociation of excess GH and IGF1 effects on glomerular and tubular growth

Growth hormone (GH)‐transgenic mice with permanently elevated systemic levels of GH and insulin‐like growth factor 1 (IGF1) reproducibly develop renal and glomerular hypertrophy and subsequent progressive glomerulosclerosis, finally leading to terminal renal failure. To dissociate IGF1‐dependent and ‐independent effects of GH excess on renal growth and lesion development in vivo, the kidneys of 75 days old IGF1‐deficient (I^−/−) and of IGF1‐deficient GH‐transgenic mice (I^−/−/G), as well as of GH‐transgenic (G) and nontransgenic wild‐type control mice (I^+/+) were examined by quantitative stereological and functional analyses. Both G and I^−/−/G mice developed glomerular hypertrophy, hyperplasia of glomerular mesangial and endothelial cells, podocyte hypertrophy and foot process effacement, albuminuria, and glomerulosclerosis. However, I^−/−/G mice exhibited less severe glomerular alterations, as compared to G mice. Compared to I^+/+ mice, G mice exhibited renal hypertrophy with a significant increase in the number without a change in the size of proximal tubular epithelial (PTE) cells. In contrast, I^−/−/G mice did not display significant PTE cell hyperplasia, as compared to I^−/− mice. These findings indicate that GH excess stimulates glomerular growth and induces lesions progressing to glomerulosclerosis in the absence of IGF1. In contrast, IGF1 represents an important mediator of GH‐dependent proximal tubular growth in GH‐transgenic mice.

Systemic overexpression of growth hormone (GH) in transgenic FVB/N inbred mice: an optimized model for holistic studies of molecular mechanisms underlying GH-induced kidney pathology

Transgenic mice overexpressing growth hormone (GH) display a plethora of phenotypic alterations and provide unique models for studying and influencing consequences of chronic GH excess. Since the first report on GH transgenic mice was published in 1982, many different mouse models overexpressing GH from various species at different levels and with different tissue specificities were established, most of them on random-bred or hybrid genetic background. We have generated a new transgenic mouse model on FVB/N inbred background, expressing bovine (b) GH under the control of the chicken beta-actin promoter (cbetaa). cbetaa-bGH transgenic mice exhibit ubiquitous expression of bGH mRNA and protein and circulating bGH levels in the range of several microg/ml, resulting in markedly stimulated growth and the characteristic spectrum of pathological lesions which were described in previous GH overexpressing mouse models. Importantly, a consistent sequence of renal alterations is observed, mimicking progressive kidney disease in human patients. The novel, genetically standardized GH transgenic mouse model is ideal for holistic transcriptome and proteome studies aiming at the identification of the molecular mechanisms underlying GH-induced pathological alterations especially in the kidney. Moreover, genetically defined cbetaa-bGH mice facilitate random mutagenesis screens for modifier genes which influence the effects of chronic GH excess and associated pathological lesions.

Postnatally elevated levels of insulin-like growth factor (IGF)-II fail to rescue the dwarfism of IGF-I-deficient mice except kidney weight

This study tested whether elevated levels of IGF-II in the postnatal period can rescue the dwarfism in IGF-I-deficient mice. Heterozygous Igf1 mutant mice [I(+/-) II(wt)] were crossed with heterozygous Igf1 mutant, phosphoenolpyruvate carboxykinase promoter IGF-II transgenic mice [I(+/-) II(tg)], and [I(+/+) II(wt)], [I(+/+) II(tg)], [I(-/-) II(wt)], and [I(-/-) II(tg)] offspring were investigated. IGF-II levels were 11- and 6-fold higher in male and female [I(-/-) II(tg)] vs. [I(-/-) II(wt)] animals. Western ligand blot analysis revealed markedly reduced activities of 30- and 32-kDa IGF binding proteins (IGFBPs) (most likely IGFBP-1 and IGFBP-2) and the 39- to 43-kDa IGFBP-3 double band in serum from IGF-I-deficient mice. These binding proteins were partially restored by overexpression of IGF-II. Analysis of weight data from the early postnatal period until d 60 showed that, in the absence of IGF-I, elevated levels of IGF-II have no effect on body weight gain. A detailed analysis of body proportions, bone parameters, and organ weights of 60-d-old mice also failed to show effects of IGF-II with one important exception: in Igf1 mutant and also Igf1 intact male mice, IGF-II overexpression significantly increased absolute (+32.4 and +28.6%; P < 0.01) and relative kidney weights (+29.0 and +22.4%; P < 0.001). These changes in kidney weight were associated with reduced phosphorylation of p38 MAPK. In summary, our genetic model shows that substantial amounts of IGF-II in the circulation do not rescue the postnatal growth deficit of IGF-I-deficient mice but increase absolute and relative kidney weights of normal and IGF-I-deficient male mice, suggesting a gender-specific role of IGF-II for kidney growth.

Correlated responses to selection for large body size in oMt1a-oGH transgenic mice: organ traits

The objective of the present study was to compare correlated responses in liver, spleen, kidney, heart and testis absolute weights and as a percentage of 8-week body weight following selection for large 8-week body weight in twice-replicated nontransgenic and transgene-carrier lines of mice from two genetic backgrounds. The transgene was an ovine metallothionein 1a-ovine growth hormone (oMt1a-oGH) construct, which was activated by adding 25 mM ZnSO4 to the drinking water. Lines NM and NC were nontransgenic lines derived from a high-growth and randomly selected background, respectively. Lines TM and TC were transgene-carrier lines formed from the respective genetic backgrounds. Line CC was a nontransgenic control from the randomly selected background. At weaning, male mice from each line were assigned to either zinc supplemented or control drinking water. Toe-clips were assayed by PCR for the presence or absence of the transgene. Correlated responses of absolute weights of all organs in nontransgenic lines indicated moderately high genetic correlations of organ weights with body weight, but on a percentage of body weight basis, the correlated responses were much lower. The correlated responses in visceral organ weights were lower in the presence of the inactivated oMt1a-oGH transgene than in its absence. The presence of the activated oMt1a-oGH combined with the effects of selection for growth increase had a greater impact on increasing the size of the splanchnic organs than did selection for large body weight in the absence of the transgene.