SIRTUIN 5 ALLEVIATES EXCESSIVE MITOCHONDRIAL FISSION VIA DESUCCINYLATION OF ATPASE INHIBITORY FACTOR 1 IN SEPSIS-INDUCED ACUTE KIDNEY INJURY.

Sepsis-induced acute kidney injury (SAKI) poses a significant clinical challenge with high morbidity and mortality. Excessive mitochondrial fission has been identified as the central pathogenesis of sepsis-associated organ damage, which is also implicated in the early stages of SAKI. Sirtuin 5 (SIRT5) has emerged as a central regulator of cellular mitochondrial function; however, its role in the regulation of sepsis-induced excessive mitochondrial fission in kidney and the underlying mechanism remains unclear. In this study, SAKI was modeled in mice through cecal ligation and puncture, and in human renal tubular epithelial (HK-2) cells stimulated with lipopolysaccharide (LPS), to mimic the cell SAKI model. Our findings revealed that septic mice with a SIRT5 knockout exhibited shortened survival times and elevated levels of renal injury compared to wild-type mice, suggesting the significant involvement of SIRT5 in SAKI pathophysiology. Additionally, we observed that SIRT5 depletion led to increased renal mitochondrial fission, while the use of a mitochondrial fission inhibitor (Mdivi-1) reversed the detrimental effects caused by SIRT5 depletion, emphasizing the pivotal role of SIRT5 in preventing excessive mitochondrial fission. In vitro experiments demonstrated that the overexpression of SIRT5 effectively mitigated the adverse effects of LPS on HK-2 cells viability and mitochondrial fission. Conversely, downregulation of SIRT5 decreased HK-2 cells viability and exacerbated LPS-induced mitochondrial fission. Mechanistically, the protective function of SIRT5 may be in part, ascribed to its desuccinylating action on ATPase inhibitory factor 1. In conclusion, this study provides novel insights into the underlying mechanisms of SAKI, suggesting the possibility of identifying future drug targets in terms of improved mitochondrial dynamics by SIRT5.

Li J ，Yao Y ，Lei X ，Bao J ，An S ，Hu H ，Sha T ，Huang Q ，Li T ，Zeng Z ，Wang X ，Cai S ... -  《-》

ADENOSINE MONOPHOSPHATE-ACTIVATED PROTEIN KINASE PHOSPHORYLATION MEDIATED BY SIRTUIN 5 ALLEVIATES SEPTIC ACUTE KIDNEY INJURY.

Background : Our previous studies have shown that ameliorating mitochondrial damage in renal tubular epithelial cells (RTECs) can alleviate septic acute kidney injury (SAKI). It is reported that AMPK phosphorylation (p-AMPK) could ameliorate mitochondrial damage in renal tissue and Sirtuin 5 (SIRT5) overexpression significantly enhanced the level of p-AMPK in bovine preadipocytes. However, the role of SIRT5-mediated phosphorylation of AMPK in SAKI needs to be clarified. Methods : WT/SIRT5 gene knockout mouse model of cecal ligation and puncture-induced SAKI and a human kidney 2 cell model of LPS-induced SAKI were constructed. An AMPK chemical activator and SIRT5 overexpression plasmid were used. Indexes of mitochondrial structure and function, level of p-AMPK, and expression of SIRT5 protein in renal tissue and RTECs were measured. Results : After sepsis stimulation, the p-AMPK level was decreased, mitochondrial structure was disrupted, and ATP content was decreased. Notably, an AMPK activator alleviated SAKI. Sirtuin 5 gene knockout significantly aggravated SAKI, while SIRT5 overexpression alleviated mitochondrial dysfunction after LPS stimulation, as manifested by the increase of p-AMPK level, the alleviation of mitochondrial structure damage, the restoration of ATP content, the decrease of proapoptotic protein expression, as well as the reduction of reactive oxygen species generation. Conclusions : Upregulation of SIRT5 expression can attenuate mitochondrial dysfunction in RTECs and alleviate SAKI by enhancing the phosphorylation of AMPK.

Wang T ，Lin B ，Qiu W ，Yu B ，Li J ，An S ，Weng L ，Li Y ，Shi M ，Chen Z ，Zeng Z ，Lin X ，Gao Y ，Ouyang J ... -  《-》

Eriocitrin prevents Sepsis-induced acute kidney injury through anti-inflammation and anti-oxidation via modulating Nrf2/DRP1/OPA1 signaling pathway.

Severe inflammation and oxidative stress are characteristics of sepsis-associated kidney injury with high morbidity and mortality. Eriocitrin (ERI) has shown promise in suppressing sepsis-associated kidney injury and LPS-induced periodontal disease, however, its efficacy in alleviating SAKI remains unexplored. This study aimed to investigate the therapeutic potential of ERI on SAKI through in vivo and in vitro experiments, elucidating its underlying mechanism. The therapeutic effects of ERI against SAKI were evaluated by survival rate, changes of serum creatinine (Scr) and blood urea nitrogen (BUN) and statistic of renal histological score in a Cecal ligation and puncture (CLP)-induced septic mice. Impactions about anti-coagulation, anti-inflammation, anti-oxidative stress and improvement of mitochondrial damage and mitochondrial morphology were further assayed. In vitro, HUVECs upon stimulation of LPS with or without different dosage of ERI, followed by evaluating changes in inflammation, mitochondrial dynamic equilibrium and signaling pathways. ERI demonstrated ameliorative effects on SAKI by attenuating inflammation, oxidative stress and coagulation evidenced by the improved survival rate, alleviated kidney histological injury, declined BUN and Scr in serum and diminished levels of inflammation cytokines, and coagulation factors. Mechanistically, ERI suppressed DRP1-regulated mitochondrial fission and promoted OPA1-modulated mitochondrial fusion by activating Nrf2 in septic mice and LPS-stimulated HUVECs, which maintained mitochondrial dynamic equilibrium, improved mitochondrial morphology, assured integrity of mitochondrial function, decreased oxidative stress, impeded overwhelming inflammation, and thus, played a pivotal role in ERI's protection against SAKI. Our data confirmed the therapeutic potential of ERI in mitigating SAKI，suggesting its viability as a pharmacological agent in clinic settings.

Wu M ，Huang Z ，Akuetteh PDP ，Huang Y ，Pan J ... -  《-》

p53 Deacetylation Alleviates Sepsis-Induced Acute Kidney Injury by Promoting Autophagy.

Recent studies have shown that autophagy upregulation can attenuate sepsis-induced acute kidney injury (SAKI). The tumor suppressor p53 has emerged as an autophagy regulator in various forms of acute kidney injury (AKI). Our previous studies showed that p53 acetylation exacerbated hemorrhagic shock-induced AKI and lipopolysaccharide (LPS)-induced endothelial barrier dysfunction. However, the role of p53-regulated autophagy in SAKI has not been examined and requires clarification. In this study, we observed the dynamic changes of autophagy in renal tubular epithelial cells (RTECs) and verified the protective effects of autophagy activation on SAKI. We also examined the changes in the protein expression, intracellular distribution (nuclear and cytoplasmic), and acetylation/deacetylation levels of p53 during SAKI following cecal ligation and puncture (CLP) or LPS treatment in mice and in a LPS-challenged human RTEC cell line (HK-2 cells). After sepsis stimulation, the autophagy levels of RTECs increased temporarily, followed by a sharp decrease. Autophagy inhibition was accompanied by an increased renal tubular injury score. By contrast, autophagy agonists could reduce renal tubular damage following sepsis. Surprisingly, the expression of p53 protein in both the renal cortex and HK-2 cells did not significantly change following sepsis stimulation. However, the translocation of p53 from the nucleus to the cytoplasm increased, and the acetylation of p53 was enhanced. In the mechanistic study, we found that the induction of p53 deacetylation, due to either the resveratrol/quercetin -induced activation of the deacetylase Sirtuin 1 (Sirt1) or the mutation of the acetylated lysine site in p53, promoted RTEC autophagy and alleviated SAKI. In addition, we found that acetylated p53 was easier to bind with Beclin1 and accelerated its ubiquitination-mediated degradation. Our study underscores the importance of deacetylated p53-mediated RTEC autophagy in future SAKI treatments.

Sun M ，Li J ，Mao L ，Wu J ，Deng Z ，He M ，An S ，Zeng Z ，Huang Q ，Chen Z ... -  《Frontiers in Immunology》

Disturbance of mitochondrial dynamics and mitophagy in sepsis-induced acute kidney injury.

The renal tubule cells require a large number of mitochondria to supply ATP due to their high-energy demand during reabsorption and secretion against chemical gradients and result in mitochondria susceptible to disorder and injury during stress conditions. Injured mitochondria are eventually degraded by mitophagy, and disturbances in mitophagy are associated with the pathogenesis of acute kidney injury (AKI) such as diabetic nephropathy and glomerulosclerosis. However, whether a disturbance in mitophagy has occurred and the role it plays in (SAKI) is still unclear. Therefore, the aim of this study was to investigate the key features of mitophagy and mitochondrial dynamics in sepsis-induced acute kidney injury (SAKI). In this study, a murine septic AKI model induced by cecal ligation and puncture (CLP) was built; mitophagy and mitochondrial dynamics were measured in mice kidney in different time point. The results showed that mitochondrial dynamics were characterized by fission/fusion aberrant, however more inclined to fission, and mitochondrial associated apoptosis was elevated over-time during SAKI. Furthermore, mitophagy was impaired in the later phase of SAKI, although elevated in early stage of SAKI. The results indicate that the underlying mechanisms of impaired mitophagy may associate with the cleavage of Parkin via caspases activated by NLRP3, at least partly. It is conceivable that this selective autophagic process and quality control machinery was impaired, leading to the accumulation of damaged mitochondria, oxidative stress, and cell death. Therefore, a targeted approach, by enhancing mitophagy during SAKI, may be a promising therapeutic strategy.

Liu JX ，Yang C ，Zhang WH ，Su HY ，Liu ZJ ，Pan Q ，Liu HF ... -  《-》