Under control of the Ren-1c promoter, locally produced transforming growth factor-beta1 induces accumulation of glomerular extracellular matrix in transgenic mice.

Abstract

Our purpose was to elucidate the hypothesis that paracrine-produced transforming growth factor (TGF)-beta1 regulates the accumulation of extracellular matrix (ECM) in renal glomeruli, a hallmark of diabetic nephropathy. To produce TGF-beta1 from the juxtaglomerular apparatus in mouse kidneys, we cloned a mouse Ren-1c promoter fragment (-4.100 to +6 base pairs) upstream of porcine TGF-beta1 (pTGF-beta1) cDNA, mutated to ensure secretion of biologically active TGF-beta beta1. The resulting transgenic mice had significantly more TGF-beta1 in their kidneys than was in those of nontransgenic controls, as confirmed by immunohistochemistry, and the production of TGF-beta1 was enhanced in vivo by captopril-induced stimulation of the Ren-1c promoter. Overproduction of pTGF-beta1 close to the glomerulus resulted in a local accumulation of ECM, composed partly of collagen type IV and laminin, and thickening of the basement membrane, characteristic features of diabetic nephropathy. Interstitial accumulation of ECM and signs of tubular atrophy were present only in older mice (>5 months of age). Results from in situ hybridization and immunohistochemistry suggest that pTGF-beta1 stimulated the production of endogenous TGF-beta1 along collecting ducts and connecting tubules. The increased amount of biologically active TGF-beta1, transgenic as well as endogenous, was corroborated by heightened proteoglycan synthesis from incubated kidney slices. This transgenic model demonstrates that sustained local expression of TGF-beta1 leads to glomerulopathy. We conclude that autocrine- or paracrine-produced TGF-beta1 may play a role in the development of glomerular diseases, such as diabetic nephropathy.

TGF-β1–Induced Glomerular Disorder Is Associated with Impaired Concentrating Ability Mimicking Primary Glomerular Disease with Renal Failure in Man

“…It is a common belief that if the amount of glomerular TGF-␤1 in a situation with reversible glomerular damage increases above a threshold level, or if the TGF-␤1 expression is prolonged, a progression to irreversible glomerulopathy may be provoked (Border and Noble, 1997;Border and Ruoslahti, 1992). This hypothesis is supported by the observation of a TGF-␤1-dose-effect on the progression of kidney fibrosis in antithymocyte-induced glomerulonephritis (Yamamoto et al, 1994) and a gene-dosis effect in transgenic mice expressing TGF-␤1 in the kidney under control of the Ren-1 c promoter (Wogensen et al, 1999).…”

“…glomerular ultramorphology was so anomalous that accurate quantitations of the PBM surface, basement membrane thickness (BMT), V v (mes/glom), and V v (matrix/glom) were difficult. Interestingly, at this age the glomeruli of the transgenic mice occupy 2.6 Ϯ 0.2% of the kidney volume (n ϭ 7) compared with 1.4 Ϯ 0.1% in the nontransgenic animals (n ϭ 7) (p Ͻ 0.01), despite a decreased kidney weight/BW ratio (Wogensen et al, 1999). The data suggests that the transgenic mice develop larger glomeruli than their negative littermates at the expense of renal tubules and interstitial tissue.…”

“…The hypotonic polyuria was not reversed by desmopressin (ddAVP) (0.4 g/kg BW, given after water deprivation for 12 hours) (Ma et al, 1998) because the urine osmolarity of the transgenic mice increased only from 854 Ϯ 33.5 mOsm to 967 Ϯ 59.5 mOsm (⌬ ϭ 113 Ϯ 93 mOsm, n ϭ 2), whereas the increase was from 3291 Ϯ 642 mOsm to 3826 Ϯ 173 mOsm (⌬ ϭ 535 Ϯ 124 mOsm, n ϭ 3) in the nontransgenic mice. We have previously shown that the inner part of the medulla in older transgenic mice is rich in collagen Type I deposits, whereas this collagen type is very rare in nontransgenic mice (Wogensen et al, 1999). We now report that, simultaneously with the progression of polyuria at 6 and 8 weeks of age, 3 of 6 and 9 of 10 transgenic mice, respectively, developed collagen Type I deposits in the inner medulla in contrast to 0 of 6 and 1 of 9 nontransgenic mice, respectively, (p Ͼ 0.05 and p ϭ 0.02) (Fisher's test) (data not shown).…”

“…Thus, to study a single factor in detail, the transgenic approach is especially useful. Therefore, the aim of the present project was to explore the functional consequences of localized overproduction of TGF-␤1 in relation to the glomerular ultrastructure and the composition of the ECM in the inner medulla using our transgenic mouse with overexpression of TGF-␤1 in the juxtaglomerular apparatus (JGA) (Wogensen et al, 1999).…”

Putative pathophysiological role of growth factors and cytokines in experimental diabetic kidney disease

“…In addition, a sustained increase in glomerular TGF-b1 mRNA expressions in long-term STZ-diabetic rats with a diabetes duration for up to 24 weeks has been described [85]. Further, in a non-diabetic transgenic mouse model overexpressing glomerular TGF-b1, accumulation of extracellular matrix components (i. e. laminin and collagen IV) was observed [100]. Previous studies [85, 97±99], have focussed on changes in only one TGF-b isoforms (i. e. TGF-b1) and, in most studies, only the mRNA expressions were examined.…”