Augmented and Accelerated Nephrogenesis in TGF-β2 Heterozygous Mutant Mice

Abstract

Several members of the transforming growth factor-␤ (TGF-␤) superfamily play key roles in kidney development, either directly or indirectly regulating nephron number. Although low nephron number is a risk factor for cardiovascular and renal disease, the implications of increased nephron number has not been examined due to the absence of appropriate animal models. Here, using unbiased stereology we demonstrated that kidneys from TGF-␤2 heterozygous (TGF-␤2 ϩ/Ϫ ) mice have approximately 60% more nephrons than wild-type mice at postnatal day 30. To determine whether augmented nephron number involved accelerated ureteric branching morphogenesis, embryonic day 11.5 metanephroi were analyzed via confocal microscopy. A 40% increase in total ureteric branch length was observed in TGF-␤2 ϩ/Ϫ kidneys, together with an extra generation of branching. In embryonic day 12.5 metanephroi cultured for 48 h the numbers of both ureteric tree tips and glomeruli were significantly greater in TGF-␤2 ϩ/Ϫ kidneys. These findings suggest that augmented nephron number in TGF-␤2 ϩ/Ϫ kidneys results from accelerated ureteric branching morphogenesis and nephron formation. Manipulation of TGF-␤2 signaling in vivo may provide avenues for protection or rescue of nephron endowment in fetuses at risk. T he development of the permanent mammalian kidney (metanephros) is a complex process requiring exquisite temporospatial regulation of multiple cellular events. Much has been learned in the past decade about these molecular regulatory processes (1-4), and the findings from recent microarray studies of gene expression during kidney development, including several studies from our own laboratory, provide much new information about the potential roles of specific genes and gene pathways (5-8).Several members of the transforming growth factor-␤ (TGF-␤) superfamily of signaling molecules have been shown to play key roles in kidney development. These include TGF-␤1 (9), Activin A (10 -12), bone morphogenetic protein 4 (13-15), bone morphogenetic protein 7 (16), and glial cell line-derived neurotrophic factor (GDNF) [reviewed in Shakya et al. (17,18) and 20)]. However, little is known about the role of TGF-␤2 in kidney development. TGF-␤2 protein is expressed earlier in metanephric development than TGF-␤1 and TGF-␤3 (21). TGF-␤2 gene expression has been detected in the kidney at embryonic day (E) 11.5 (22) and the protein localized in and around the ureteric epithelium and nephron structures from E12.5 (21,23). TGF-␤2 homozygous null mutant mice (TGF-␤2 Ϫ/Ϫ ) die within 24 h of birth due to defective lung development (24). The kidneys of these mice display progressive deterioration of the ureteric tubules and an enlarged renal pelvis after E15. No histologic renal phenotype has been reported in TGF-␤2 heterozygous null mutant mice (TGF-␤2 ϩ/Ϫ ). TGF-␤2 has been identified as a candidate molecule that is released from ureteric bud cells aiding in the survival and differentiation of metanephric mesenchyme (MM) (23). In combination with leukemia in...

β-Catenin Causes Renal Dysplasia via Upregulation of Tgfβ2 and Dkk1

“…41 Furthermore, Tgf␤2 heterozygous mice are characterized by increased ureteric branch length and nephron number, consistent with a physiologic inhibitory effect of Tgf␤2 in vivo. 31 Combined, these results support a role for TGF␤2 inhibiting ureteric branching in ␤-cat…”

“…Interestingly, those genes in the WNT pathway encoded WNT inhibitors including Dickkopf 1 (Dkk1), WNT inhibitory factor 1 (Wif1), and secreted frizzledrelated protein (sFrp) ( Table 5). Because previous studies demonstrated that Dkk1 and Tgf␤2 inhibit ureteric branching and nephrogenesis, respectively, 31,32 we proceeded with further analysis of these effectors. Upregulation of Tgf␤2 and Dkk1 was verified using quantitative real-time PCR on mRNA isolated from ␤-cat GOF-UB and WT kidneys (P ϭ 0.038) ( Figure 4J).…”

Absence of Canonical Smad Signaling in Ureteral and Bladder Mesenchyme Causes Ureteropelvic Junction Obstruction

“…7,10,19,22,23 Previous studies have shown that inactivation of Bmp4 disrupts the structural and functional organization of the kidney and lower urinary tract. 16 To specifically investigate the role of canonical Smaddependent TGF-b superfamily signaling in the development of the lower urinary tract, we have used the Tbx18-Cre transgene to mediate the inactivation of Smad4, the common Smad indispensible for the transcriptional responses of TGF-b superfamily signaling, in the ureteral mesenchyme.…”

Colony-Stimulating Factor-1 Promotes Kidney Growth and Repair via Alteration of Macrophage Responses

“…Total volume was calculated with the Cavalieri Principle. 35,36 Glomerular volume was estimated with the physical dissector/fractionator principle as previously described 37,38 where sections were projected on an unbiased 2 ϫ 2-cm grid at a final magnification of ϫ298.…”