Renal lipid accumulation and aging linked to tubular cells injury via ANGPTL4

Renal tubular epithelial cells are vulnerable to stress-induced damage, including excessive lipid accumulation and aging, with ANGPTL4 potentially playing a crucial bridging role between these factors. In this study, RNA-sequencing was used to identify a marked increase in ANGPTL4 expression in kidneys of diet-induced obese and aging mice. Overexpression and knockout of ANGPTL4 in renal tubular epithelial cells (HK-2) was used to investigate the underlying mechanism. Subsequently, ANGPTL4 expression in plasma and kidney tissues of normal young controls and elderly individuals was analyzed using ELISA and immunohistochemical techniques. RNA sequencing results showed that ANGPTL4 expression was significantly upregulated in the kidney tissue of diet-induced obesity and aging mice. In vitro experiments demonstrated that overexpression of ANGPTL4 in HK-2 cells led to increased lipid deposition and senescence. Conversely, the absence of ANGPTL4 appears to alleviate the impact of free fatty acids (FFA) on aging in HK-2 cells. Additionally, aging HK-2 cells exhibited elevated ANGPTL4 expression, and stress response markers associated with cell cycle arrest. Furthermore, our clinical evidence revealed dysregulation of ANGPTL4 expression in serum and kidney tissue samples obtained from elderly individuals compared to young subjects. Our study findings indicate a potential association between ANGPTL4 and age-related metabolic disorders, as well as injury to renal tubular epithelial cells. This suggests that targeting ANGPTL4 could be a viable strategy for the clinical treatment of renal aging.

Circular RNA circVmn2r1 acts as a miR-223-3p sponge to promote kidney aging by regulating NLRP3 expression in mice

Kidney aging accelerates the progression of various acute and chronic kidney diseases and can also induce pathological changes in other organs throughout the body. Circular RNAs (circRNAs), have been demonstrated to play a vital role in aging and age-related diseases. However, biological functions and the underlying molecular mechanism of circRNAs in kidney aging remain largely unclear. Uncovering the functions of circRNAs in kidney aging and their underlying regulatory mechanisms may shed new light on the development of novel diagnostic and therapeutic strategies for human aging. Here we report the important role of circVmn2r1 in the progression of kidney aging. We found that circVmn2r1 was one of the top expressed circRNAs in mouse kidney by RNA sequencing and was significantly upregulated in 24-month-old mouse kidney compared to 3-month-old. More importantly, we demonstrated that overexpression of circVmn2r1 promoted kidney aging in senescence-accelerated mouse prone 8 (SAMP8) mice. Cellular assays with mouse kidney tubular epithelium (TCMK-1) cells under both gain-of-function and loss-of-function conditions demonstrated that circVmn2r1 inhibited proliferation and promoted senescence, whereas miR-223-3p counteracted these effects. Mechanistic analysis demonstrated that circVmn2r1 acted as a miR-223-3p sponge to relieve the repressive effect of miR-223-3p on its target NLRP3, which we proved could inhibit proliferation and promote senescence of TCMK-1 cells. Our results indicate that circVmn2r1 promotes kidney aging through acting as a miR-223-3p sponge, consequently upregulating NLRP3 expression, and can be a valuable diagnostic marker and an important therapeutic target for kidney aging.

GLIS1 alleviates cell senescence and renal fibrosis through PGC1-α mediated mitochondrial quality control in kidney aging

Mitochondrial dysfunction is implied as a crucial factor in age-related chronic kidney disease. It is confirmed that Gli-like transcription factor 1 (GLIS1) is involved in age-related renal fibrosis, however, the correlation between mitochondrial disturbances and GLIS1-driven kidney aging are not clearly clarified. Thus, we investigated the regulatory mechanism of GLIS1 in the homeostasis of mitochondrial quality control both in vivo and in vitro. The lower expression of GLIS1 was identified in natural and accelerated kidney aged models, accompanied by the dysfunctions of mitochondrial quality control, including enhanced mitochondrial fission, reduced mitochondrial biogenesis and mitophagy, whereas, GLIS1 could maintain mitochondrial stability by interacting with peroxisome proliferator-activated receptor γ coactivator-1α (PGC1-α). Additionally, the over-expressed GLIS1 inhibited extracellular matrix accumulation and alleviated renal fibrosis while siGLIS1 inhibited PGC1-α transcription, as well as affecting its mitochondria-protective functions. Collectively, we demonstrated that GLIS1 mediated mitochondrial quality control through targeting PGC1-α in kidney aging, which might be a promising therapeutic target for attenuating cell senescence and age-related renal fibrosis.

METTL3 alleviates D-gal-induced renal tubular epithelial cellular senescence via promoting miR-181a maturation

Methyltransferase-like protein 3 (METTL3) mediated N6-Methyladenosine (m⁶A) modification has been implicated in many physiological and pathological processes. However, its function and mechanism in kidney aging are not entirely clear. Here, we investigated changes in m⁶A levels of aging kidneys and the role of METTL3 in senescent renal tubular epithelial cells and its potential mechanisms. First, we used the naturally aged mouse model and the D-galactose (D-gal)-induced aged mouse model. Dot blot and m⁶A RNA methylation quantification showed significantly decreased m⁶A levels in both models. In addition, we observed that METTL3 was down-regulated in D-gal-induced senescent human renal tubular epithelial cell line (HK-2). METTL3 reduction was associated with senescence-related phenotypes of HK-2 cells. We also found that miR-181a-5p attenuated HK-2 senescence by targeting the NF-κB pathway. Moreover, METTL3 was able to promote the maturation of miR-181a-5p and then inhibited the expression of NF-κB and IL-1α. Taken together, we demonstrate that the METTL3/miR-181a-5p/NF-κB axis counteracts HK-2 senescence. Our results suggest that METTL3 may be a novel biomarker and a potential therapy target for kidney aging.

Autophagy and kidney aging

Autophagy is a highly conserved intracellular degradation system in eukaryotes that maintains cellular and tissue homeostasis. Upon autophagy induction, cytoplasmic components are engulfed by a double-membrane organelle called the autophagosome that fuses with a lysosome to degrade its contents. In recent years, it has become clear that autophagy becomes dysregulated with aging, which leads to age-related diseases. Kidney function is particularly prone to age-related decline, and aging is the most significant risk factor for chronic kidney disease. This review first discuss the relationship between autophagy and kidney aging. Second, we describe how age-related dysregulation of autophagy occurs. Finally, we discuss the potential of autophagy-targeting drugs to ameliorate human kidney aging and the approaches necessary to discover such agents.

Peripheral Klotho protects the kidney and brain by regulating M2a/M2c macrophage polarization in d-gal-treated aged mice

In elderly individuals, aging can cause changes in the structure and function of one or more organs, increasing their susceptibility to various damage factors, especially the heart, kidney, brain and other important organs. Therefore, the incidence of cardiovascular disease, neurodegenerative diseases and chronic kidney disease in the elderly population is significantly higher than that in the general population. In our previous study, the hearts of aged mice did not express the antiaging protein Klotho (KL), but peripheral elevation of KL may significantly delay cardiac aging. The kidney and brain are the main organs that produce KL, but the effects and mechanism of peripheral KL supplementation on the kidney and hippocampus are still unclear. To study the effect and possible mechanism of KL against kidney and hippocampus aging, 60 male BALB/c mice were randomly divided into the Adult group, the KL group, the D-gal-induced Aged group, and the KL + Aged group. The results showed that KL increased anti-inflammatory M2a/M2c macrophages in the kidney and hippocampus of aging mice, significantly reduced tissue inflammation and oxidative stress, and improved organ function and aging status. More importantly, we demonstrate that despite the impermeable bloodbrain barrier in mice, peripherally administered KL surprisingly enhances M2-type microglia polarization, induces cognitive enhancement and reduces neuroinflammation. Cellular experimental results suggest that KL may play a role in delaying senescence by regulating the TLR4/Myd88/NF-κB signaling pathway to regulate macrophage polarization and reduce aging-related inflammation and oxidative stress.

KYA1797K, a Novel Small Molecule Destabilizing β-Catenin, Is Superior to ICG-001 in Protecting against Kidney Aging

INTRODUCTION

Aged kidney is characterized by mitochondrial dysfunction, cellular senescence, and fibrogenesis. The activation of Wnt/β-catenin signaling plays an important role in the initiation of kidney aging. However, the inhibiting strategies have not been discovered in detail. Here, we compared the therapeutic effects of two β-catenin inhibitors, KYA1797K and ICG-001, to assess their superiority.

METHODS

Two-month-old male C57BL/6 mice which had undergone unilateral nephrectomy and received D-galactose (D-gal) injection were co-treated with KYA1797K or ICG-001 at 10 mg/kg/day for 4 weeks. Human proximal renal tubular cells were treated with D-gal and KYA1797K/ICG-001 to compare their effects.

RESULTS

Compared with ICG-001, which inhibits β-catenin pathway through blocking the binding of β-catenin and cAMP response element-binding protein (CREB)-binding protein (CBP), KYA1797K, a novel small molecule destabilizing β-catenin through activating Axin-GSK3β complex, possesses the superior effects on protecting against kidney aging. In D-gal-treated accelerated aging mice, KYA1797K could greatly inhibit β-catenin pathway, preserve mitochondrial homeostasis, repress cellular senescence, and retard age-related kidney fibrosis. In cultured proximal tubular cells, KYA1797K shows a better effect on inhibiting cellular senescence and could better suppress mitochondrial dysfunction and ameliorate the fibrotic changes, at the same dose as that in ICG-001.

CONCLUSION

These results show that effectively eliminating β-catenin is a necessity to target against age-related kidney injury, suggesting the multiple transcriptional regulation of β-catenin in kidney aging besides T-cell factor/lymphoid enhancer-binding factor family of transcription factors (TCF/LEF-1).

Ginsenoside Rg1 ameliorates glomerular fibrosis during kidney aging by inhibiting NOX4 and NLRP3 inflammasome activation in SAMP8 mice

Aging is closely related to the progress of renal fibrosis, which eventually results in renal dysfunction. Ginsenoside Rg1 (Rg1) has been reported to have an extensive anti-aging effect. However, the role and mechanism of Rg1 in aging-related renal fibrosis remain unclear. The present study aimed to evaluate the protective effect and mechanism of Rg1 in renal fibrosis during kidney aging in a model of SAMP8 mice. Taking SAMR1 mice as the control group, SAMP8 mice were administered Apocynin (50 mg/kg), Tempol (50 mg/kg), or Rg1 (5, 10 mg/kg) intragastrically for 9 weeks as treatment groups. The results showed that the elevated levels of blood urea nitrogen, serum creatinine and senescence-associated β-galactosidase (β-Gal) were markedly decreased, the glomerular mesangial proliferation was significantly alleviated and the increased levels of collagen IV and TGF-β1 were significantly downregulated by Rg1 in SAMP8 mice. In addition, the generation of ROS and the expression of NADHP oxidase 4 (NOX4) in the renal cortex were significantly reduced by Rg1 treatment. The expression levels of NLRP3 inflammasome-related proteins and the inflammation-related cytokine IL-1β were also inhibited by Rg1 treatment in the SAMP8 mice. These results suggested that Rg1 could delay kidney aging and inhibit aging-related glomerular fibrosis by reducing NOX4-derived ROS generation and downregulating NLRP3 inflammasome expression.

RAGE and glyoxalase in kidney disease

Glycation is an important reaction in the regulation of physiological state. When poorly controlled, however, glycation can also result in the accumulation of glycated proteins (advanced glycation endproducts; AGEs) in the body. This AGE accumulation is termed glycative stress, and is an established pathological factor: to date, glycative stress has been closely associated with not only kidney diseases, but also kidney aging. Accumulating evidence demonstrates that the progression of renal tubular damage and tubular aging are often correlated with activation of the receptor for the AGE (RAGE)-AGE pathway or decreased activity of glyoxalase 1, which is an anti-glycation enzyme to lower glycative stress. Further, glycative stress exacerbates the derangement of protein homeostasis: the posttranslationally modified proteins by glycation often lose or gain their functions. Such deranged protein homeostasis leads to endoplasmic reticulum (ER) stress, a state of ER dysfunction in which the quality control of proteins is defective, as well as to induction of its stress signal, the unfolded protein response (UPR), in the kidney. The lowering of glycative stress via modulation of RAGE-AGE axis or glyoxalase 1 activity is beneficial for tubular homeostasis and the subsequent prevention and treatment of kidney disease, suggesting the possibility of novel therapeutic approaches which target glycative stress. In this review, we focused on the impact of glycative stress in the kidney, especially the role of RAGE and glyoxalase 1. Further we also discuss the crosstalk between glycative stress and ER stress in their effect on protein homeostasis.