Abstract
Tuberous Sclerosis Complex (TSC) is caused by mutations in TSC1 or TSC2, which encode negative regulators of the mTOR signaling pathway. The renal abnormalities associated with TSC include angiomyolipoma, cysts, and renal cell carcinoma. Here we report that specific ablation of Tsc1 using the mesenchymal stem cell-osteoblast lineage markers induced cystogenesis in mice. Using Rosa-tdTomato mice, we found that Prx1- or Dermo1-labeled cells were present in the nephron including glomerulus but they were not stained by markers for podocytes, mesangial cells, endothelial cells, or proximal or loop of Henle tubular cells, while Osx is known to label tubular cells. Tsc1 deficiency in Prx1 lineage cells caused development of mild cysts that were positive only for Tamm-Horsfall protein (THP), a loop of Henle marker, while Tsc1 deficiency in Osx lineage cells caused development of cysts that were positive for Villin, a proximal tubular cell marker. On the other hand, Tsc1 deficiency in the Dermo1 lineage did not produce detectable phenotypical changes in the kidney. Cyst formation in Prx1-Cre; Tsc1f/f and Osx-Cre; Tsc1f/f mice were associated with increase in both proliferative and apoptotic cells in the affected tissue and were largely suppressed by rapamycin. These results suggest that Prx1 and Osx lineages cells may contribute to renal cystogenesis in TSC patients.
Highlights
Tuberous sclerosis complex (TSC) is an autosomal dominant genetic disease caused by mutations in TSC1 or TSC2
The mTOR pathway consists of mTOR complex 1 and mTOR complex 2. mTORC1 is composed of mTOR and regulatory associated protein of mTOR (Raptor), while mTORC2 is composed of mTOR and rapamycin independent companion of mTOR (Rictor)
Quantitative analysis of TUNEL-stained sections revealed a higher percentage of TUNEL-positive cells, after normalized to DAPI-stained nuclei, in Prx1-Cre; Tsc1f/f kidney than controls (Fig. 3D,E). These results suggest that enhanced cell proliferation underlies cystogenesis in Prx1-Cre; Tsc1f/f mice, while increased apoptosis may be a secondary effect of increased cell proliferation
Summary
Lineage tracing identified Prx1-expressing cells in mouse kidney. MSCs harbor the potentials to differentiate into many cell types, especially osteoblasts, chondrocytes, and adipocytes. The result revealed an increase in the number of proliferative cells in the kidney of Prx1-Cre; Tsc1f/f mice compared to controls (Fig. 3C). Quantitative analysis of TUNEL-stained sections revealed a higher percentage of TUNEL-positive cells, after normalized to DAPI-stained nuclei, in Prx1-Cre; Tsc1f/f kidney than controls (Fig. 3D,E). Tissue area were significantly reduced in rapamycin-treated Osx-Cre; Tsc1f/f mice (Fig. 4E) These results suggested that the renal abnormalities observed in Osx-Cre; Tsc1f/f mice were caused by activated mTORC1. DAPI-stained nuclei, were observed in the kidney of the Osx-Cre; Tsc1f/f mice compared to control mice (Fig. 5B– E) These results suggested that elevated cell proliferation was involved in the development of cysts in Osx-Cre; Tsc1f/f mice, similar to what was observed in Prx1-Cre; Tsc1f/f mice (Fig. 3B–E). Results suggested significant functional differences between Tsc[1] and Tsc[2] in renal cell proliferation and apoptosis when their expression was under the control of Dermo[1] promoter
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