Caloric restriction alleviates aging-related fibrosis of kidney through downregulation of miR-21 in extracellular vesicles.

Glomerulosclerosis and renal interstitial fibrosis occur with the aging kidney. In this study, we examined the expression of miR-21, peroxisome proliferator-activated receptor(PPARα), hypoxia-inducible factor(HIF-1α) in the kidney of 3-month-old rats fed ad libitum (YAL), 24-month-old rats fed ad libitum (OAL) and 24-month-old rats subjected to a 70% calorie-restricted diet for 8 months (OCR). We found long-term caloric restriction (CR) ameliorated aging and aging-related fibrosis. CR ameliorated the increment of miR-21 and HIF-1α, as well as the decrement of PPARα in old ad libitum group. Human proximal tubular cells (HPTCs) presented phenotypes of senescence and epithelial to mesenchymal transition (EMT) under high-glucose conditions, in which senescence occurred earlier than EMT. Senescent cells secreted extracellular vesicles (EVs) which contained miR-21 into the recipient cells. Inhibiting miR-21 of donor cells prevented the occurrence of EMT in recipient cells. In addition, miR-21 induced EMT through targeting PPARα protein and consequently enhancing HIF-1α expression, although other pathways cannot be ruled out. These findings demonstrated that miR-21-containing EVs derived from the senescent cells could facilitate EMT of HPTCs via PPARα-HIF-1α signaling pathway. Long-term caloric restriction and caloric restriction mimetics alleviated aging-related-fibrosis of kidney through downregulation of miR-21.

Alleviation of senescence and epithelial-mesenchymal transition in aging kidney by short-term caloric restriction and caloric restriction mimetics via modulation of AMPK/mTOR signaling.

Renal fibrosis contributes to declining renal function in the elderly. What is unclear however, is whether epithelial-mesenchymal transition (EMT) contributes to this age-related renal fibrosis. Here, we analyzed indicators of EMT during kidney aging and investigated the protective effects and mechanisms of short-term regimens of caloric restriction (CR) or caloric restriction mimetics (CRMs), including resveratrol and metformin. High glucose was used to induce premature senescence and EMT in human primary proximal tubular cells (PTCs) in vitro. To test the role of AMPK-mTOR signaling, siRNA was used to deplete AMPK. Cellular senescence and AMPK-mTOR signaling markers associated with EMT were detected. CR or CRMs treatment alleviated age-related EMT in aging kidneys, which was accompanied by activation of AMPK-mTOR signaling. High glucose induced premature senescence and EMT in PTCs in vitro, which was accompanied by down-regulation of AMPK/mTOR signaling. CRMs alleviated high glucose-induced senescence and EMT via stimulation of AMPK/mTOR signaling. Activation of AMPK/mTOR signaling protected PTCs from high glucose-induced EMT and cellular senescence. Short-term regimens of CR and CRMs alleviated age-related EMT via AMPK-mTOR signaling, suggesting a potential approach to reducing renal fibrosis during aging.

Hydrogen sulfide mediates the protection of dietary restriction against renal senescence in aged F344 rats.

Renal aging is always accompanied by increased oxidative stress. Hydrogen sulfide (H2S) can be up-regulated by 50% dietary restriction (DR) for 7-day and can block mitochondrial oxidative stress. H2S production exerts a critical role in yeast, worm, and fruit fly models of DR-mediated longevity. In this study, we found that renal aging could be attenuated by 30% DR for 6-month (DR-6M) and life-long (DR-LL), but not for 6-week (DR-6W). The expressions of cystathionine-γ-lyase (CGL) and cystathionine-ß- synthase (CBS) were improved by DR-6M and DR-LL. Endogenous H2S production shared the same trend with CBS and CGL, while glutathione (GSH) didn't. When comparing efficiencies of DR for different durations, more evident production of H2S was found in DR-6M and DR-LL than in DR-6W. Finally the level of oxidative stress was improved by DR-6M and DR-LL rather than by DR-6W. It concluded that aged rats had the ability to produce enough H2S on 30% DR interventions protecting against renal aging, and the effect of DR for long-term were more significant than that of DR for short-term.

Anti-Inflamm-Aging Effects of Long-Term Caloric Restriction via Overexpression of SIGIRR to Inhibit NF-κB Signaling Pathway.

BACKGROUND: Chronic inflammation is thought to be a determinant of the aging rate and longevity. Caloric restriction (CR) attenuates age-related increases in the systemic levels of several pro-inflammatory mediators, but the anti-inflammatory mechanisms of CR in the aging process remain unclear. METHODS: Fisher 344 rats in a CR group were fed an amount of food corresponding to 60% of that fed to an ad libitum-fed (AL) group for 8 months. Biochemical analyses and renal pathological grading were used to analyze physiological status. Important signaling molecules in the Toll-like receptor/nuclear factor kappa-light-chain-enhancer of activated B cells (TLR/NF-κB) pathway were also analyzed by western blotting, immunofluorescence and immunohistochemistry. RESULTS: 1) Compared with AL feeding, CR decreased aging-mediated increases in both biochemical marker levels and renal pathological grading. 2) Single immunoglobulin IL-1 (IL-1)-related receptor (SIGIRR) expression decreased with increasing age, but CR led to overexpression. 3) The expression of TLR4 was significantly higher in the CR group than in the AL group. 4) SIGIRR overexpression decreased the expression of the adaptor molecules myeloid differentiation factor 88 (MyD88), IL-1 receptor-associated kinase 4 (IRAK4) and tumor necrosis factor receptor-associated factor 6 (TRAF6). 5) The levels of the inflammatory markers phospho-IκBα and phospho-NF-κB p65 decreased in the CR group. CONCLUSIONS: The inflammatory response might be alleviated by SIGIRR via blockade of the TLR4/NF-κB signaling pathway. Therefore, CR can decrease inflammation via SIGIRR overexpression, and SIGIRR might be a new target to delay aging.

Short-term calorie restriction protects against renal senescence of aged rats by increasing autophagic activity and reducing oxidative damage.

To explore the effect of short-term calorie restriction (CR) on renal aging, 8-week CR with 60% of the food intake of the ad libitum group was administered in 25-month-old male Sprague-Dawley rats. Aged rats subjected to short-term CR had lower body weight, level of triglycerides and ratio of urine protein to urine creatinine, respectively. Short-term CR blunted the increased glomerular volume, the degree of fibrosis, p16 and the positive rate of senescence-associated ß-galactosidase staining of the kidneys in old ad libitum group. Light chain 3/Atg8 as an autophagy marker exhibited a marked decline in aged kidneys, which was increased by short-term CR. The levels of p62/SQSTM1 and polyubiquitin aggregates, which were increased in older kidneys, were blunted by short-term CR. Short-term CR retarded the level of 8-hydroxydeoxyguanosine, a marker of mitochondrial DNA oxidative damage. Moreover, we found an increased level of SIRT1 and AMPK, and a decreased level of mTOR in aged kidneys after short-term CR. These results suggested that short-term CR could be considered as a potential intervention for retardation of renal senescence by increasing autophagy and subsequently reducing oxidative damage. Three master regulators of energy metabolism, SIRT1, AMPK and mTOR are associated with these effects.

Beneficial effects of short-term calorie restriction against cisplatin-induced acute renal injury in aged rats.

BACKGROUND: The therapeutic use of the antineoplastic drug cisplatin (DDP) in the elderly is limited by its nephrotoxic effects. The aim of this study was to examine the effect of short-term calorie restriction (CR) on DDP-induced nephrotoxicity in aged rats. METHODS: A group of 25-month-old male Sprague-Dawley rats were divided into two groups: ad libitum (AL) and CR, which were fed 60% of the food consumed by AL rats for 8 weeks. The two groups were each further randomly divided into two subgroups: OAL control, OAL+DDP, OCR control, and OCR+DDP. A single dose of DDP (6 mg/kg) was injected intraperitoneally. Functional and structural changes of the kidneys were evaluated quantitatively by biochemical, histopathological, and morphometric analyses. RESULTS: At the end of the 8 weeks, rats in the OCR group lost 14.8% more body mass than rats in the OAL group. Pretreatment with CR had several effects: (1) it reduced the levels of blood urea nitrogen and serum creatinine, (2) it reduced the magnitude of the renal tubular epithelial damage, and (3) it significantly reduced the incidence of activated caspase-3 and TUNEL-positive cells in kidneys injured by DDP. However, SIRT1 had the opposite trend after DDP application between the two groups. CONCLUSIONS: Short-term CR exhibits a renoprotective effect in experimental DDP-induced renal injury, the mechanism of which may involve CR antiapoptotic effects and promotion of SIRT1.

DAP5 ameliorates cisplatin-induced apoptosis of renal tubular cells.

BACKGROUND: Nephrotoxicity of cisplatin limits its clinical application. Cisplatin-induced acute renal tubular epithelial cell apoptosis is one of the major mechanisms of cisplatin nephrotoxicity. Here, the role and regulation of death-associated protein 5 (DAP5) in cisplatin-induced tubular cell apoptosis were investigated. METHODS: After upregulation of DAP5 expression by plasmid transfection and downregulation of DAP5 expression by small interfering RNA in human kidney tubular epithelial cell line (HKC) cells, the degree of cell apoptosis was assessed by flow cytometric analysis. The expression of Bax and Bcl-2 proteins was detected by Western blot analysis. The relationship between the PI3K/Akt/mTOR signaling pathway and DAP5 was also evaluated. RESULTS: During cisplatin-induced apoptosis in HKC cells, DAP5 underwent proteolytic fragmentation, yielding an 86-kDa species, DAP5/p86. Overexpression of DAP5/p97 and DAP5/p86 increased the translation of Bcl-2 and reduced the extent of cisplatin-induced apoptosis. Knockdown of DAP5 expression using small interfering RNA decreased the translation of Bcl-2 and increased the degree of apoptosis. Neither manipulation affected the expression of Bax. DAP5 expression was positively regulated by the PI3K/Akt/mTOR signaling pathway. CONCLUSION: Collectively, the results from the present study revealed a new role for DAP5 in cisplatin-induced apoptosis: DAP5/p97 and DAP5/p86 enhanced the translation of the anti-apoptotic protein Bcl-2 and inhibited cisplatin-induced apoptosis. The PI3K/Akt/mTOR signaling pathway may positively regulate the expression of DAP5.