Blocking rpS6 Phosphorylation Exacerbates Tsc1 Deletion–Induced Kidney Growth

Abstract

The molecular mechanisms underlying renal growth and renal growth-induced nephron damage remain poorly understood. Here, we report that in murine models, deletion of the tuberous sclerosis complex protein 1 (Tsc1) in renal proximal tubules induced strikingly enlarged kidneys, with minimal cystogenesis and occasional microscopic tumorigenesis. Signaling studies revealed hyperphosphorylation of eukaryotic translation initiation factor 4E-binding protein 1 (4E-BP1) and increased phosphorylation of ribosomal protein S6 (rpS6) in activated renal tubules. Notably, knockin of a nonphosphorylatable rpS6 in these Tsc1-mutant mice exacerbated cystogenesis and caused drastic nephron damage and renal fibrosis, leading to kidney failure and a premature death rate of 67% by 9 weeks of age. In contrast, Tsc1 single-mutant mice were all alive and had far fewer renal cysts at this age. Mechanistic studies revealed persistent activation of mammalian target of rapamycin complex 1 (mTORC1) signaling causing hyperphosphorylation and consequent accumulation of 4E-BP1, along with greater cell proliferation, in the renal tubules of Tsc1 and rpS6 double-mutant mice. Furthermore, pharmacologic treatment of Tsc1 single-mutant mice with rapamycin reduced hyperphosphorylation and accumulation of 4E-BP1 but also inhibited phosphorylation of rpS6. Rapamycin also exacerbated cystic and fibrotic lesions and impaired kidney function in these mice, consequently leading to a premature death rate of 40% within 2 weeks of treatment, despite destroying tumors and decreasing kidney size. These findings indicate that Tsc1 prevents aberrant renal growth and tumorigenesis by inhibiting mTORC1 signaling, whereas phosphorylated rpS6 suppresses cystogenesis and fibrosis in Tsc1-deleted kidneys.

IL-17C has a pathogenic role in kidney ischemia/reperfusion injury

“…11,13,[18][19][20][21] To investigate whether IL-17C activated Th17 in AKI, we assessed Th17 cell quantity in the kidney using co-staining for CD4 and IL-17A as described previously. 22,23 The results showed that renal Th17 cell quantity was increased, whereas the numbers were decreased significantly by an IL-17C-neutralizing antibody or IL-17RE knockout in mice with IRI ( Figure 6a and b). IL-17A, mainly produced by Th17, was increased in the kidney of AKI mice, and it was decreased remarkably by an IL-17Cneutralizing antibody or IL-17RE knockout (Figure 6c).…”

“…27,45 Co-staining of CD4 and IL-17A was used to identify Th17 cells in the kidney, as described previously. 22,23 Regulatory T cells were identified using FOXP3 staining. 48 The number of CD4 þ /IL-17A þ cells or FOXP3 þ cells was quantified by analysis of 20 randomly chosen fields.…”

Metformin effectively treats Tsc1 deletion-caused kidney pathology by upregulating AMPK phosphorylation

“…Currently, mTORC1 is considered a pharmacological target for the treatment of TSC 7,10 . Unfortunately, mTORC1 inhibitors currently used in the clinic seemed to only have a limited cytostatic effect, as the TSC tumors grew again after mTORC1 inhibitors were discontinued, and long-term mTORC1 inhibition could cause detrimental side effects [11][12][13][14][15] . It is noteworthy that deletion of human TSC2 and PKD1 genes results in severe infantile polycystic kidney disease (PKD)-a contiguous gene syndrome 12 .…”

“…Neither sirolimus (rapamycin) nor everolimus (sirolimus analog) is effective in treating PKD, and these drugs have been reported to cause albuminuria (caused by sirolimus) and leukopenia (caused by everolimus) [16][17][18] . Moreover, our previous study demonstrated that either pharmacologic inhibition of mTORC1 or genetic deletion of rpS6 phosphorylation exacerbated structural and functional damage of the kidneys in Tsc1 gene-deleted mice 11 , suggesting that alternative strategies are needed for effective treatment of TSC-associated kidney disease.…”

“…For instance, modulating AMPK has been demonstrated to be an effective maneuver for treating primary breast cancer, ovarian cancer, and inflammatory bowel disease [22][23][24][25] . TSC-associated kidney pathology includes tubulointerstitial fibrosis 11 and decreased apoptosis 26 . Interestingly, pharmacological activation of AMPK has been demonstrated to be an effective strategy for the treatment of mouse Pkd1 deletion-induced PKD 21 .…”