ATG7 promotes autophagy in sepsis‑induced acute kidney injury and is inhibited by miR‑526b

Insights on E1-like enzyme ATG7: functional regulation and relationships with aging-related diseases

Autophagy is a dynamic self-renovation biological process that maintains cell homeostasis and is responsible for the quality control of proteins, organelles, and energy metabolism. The E1-like ubiquitin-activating enzyme autophagy-related gene 7 (ATG7) is a critical factor that initiates classic autophagy reactions by promoting the formation and extension of autophagosome membranes. Recent studies have identified the key functions of ATG7 in regulating the cell cycle, apoptosis, and metabolism associated with the occurrence and development of multiple diseases. This review summarizes how ATG7 is precisely programmed by genetic, transcriptional, and epigenetic modifications in cells and the relationship between ATG7 and aging-related diseases.

miR-506-3p induces autophagy of renal tubular epithelial cells in sepsis through targeting PI3K pathway

OBJECTIVE

To explore the effect of micro ribonucleic acid (miR)-506-3p on autophagy of renal tubular epithelial cells in sepsis and its mechanism.

METHODS

It was found through bioinformatics analysis that phosphatidylinositol 3-kinase catalytic subunit alpha (PIK3CA) was expressed at a low level in sepsis, and miR-506-3p had a targeted regulatory effect on PIK3CA. 40 8-week-old male C57BL/6 mice were randomly divided into control miR-506-3p NC group, control miR-506-3p OE group, sepsis miR-506-3p NC group, sepsis miR-506-3p OE group and sepsis miR-506-3p KD group. The pathological changes in kidney tissues of mice in each group were observed by hematoxylin-eosin (HE) staining and TUNEL staining, and mitochondria and autophagosomes were visualized by transmission electron microscopy. CCK8 assay was performed to detect the effect of miR-506-3p on the proliferation capacity of renal tubular epithelial cells. The changes in the expression of PI3K-Akt pathway proteins, mTOR and autophagy proteins were tested by Western blotting.

RESULTS

The injury and apoptotic positive cells were suppressed and decreased in miR-506-3p OE mice vs. NC group. miR-506-3p could increase the number of mitochondria and autophagosomes in kidney tissues. After introduction of exogenous miR-506-3p OE into renal tubular epithelial cells, the expressions of PI3K pathway proteins were significantly inhibited, while the expressions of autophagy proteins were significantly enhanced. After 740Y-P was added, the expressions of associated proteins had no significant changes in each group.

CONCLUSION

Overexpression of miR-506-3p can enhance the autophagy of renal tubular epithelial cells in sepsis through inhibiting the PI3K signaling pathway.

Epigenetic dysregulation of autophagy in sepsis-induced acute kidney injury: the underlying mechanisms for renoprotection

Sepsis-induced acute kidney injury (SI-AKI), a common critically ill, represents one of the leading causes of global death. Emerging evidence reveals autophagy as a pivotal modulator of SI-AKI. Autophagy affects the cellular processes of renal lesions, including cell death, inflammation, and immune responses. Herein, we conducted a systematic and comprehensive review on the topic of the proposed roles of autophagy in SI-AKI. Forty-one relevant studies were finally included and further summarized and analyzed. This review revealed that a majority of included studies (24/41, 58.5%) showed an elevation of the autophagy level during SI-AKI, while 22% and 19.5% of the included studies reported an inhibition and an elevation at the early stage but a declination of renal autophagy in SI-AKI, respectively. Multiple intracellular signaling molecules and pathways targeting autophagy (e.g. mTOR, non-coding RNA, Sirtuins family, mitophagy, AMPK, ROS, NF-Kb, and Parkin) involved in the process of SI-AKI, exerting multiple biological effects on the kidney. Multiple treatment modalities (e.g. small molecule inhibitors, temsirolimus, rapamycin, polydatin, ascorbate, recombinant human erythropoietin, stem cells, Procyanidin B2, and dexmedetomidine) have been found to improve renal function, which may be attributed to the elevation of the autophagy level in SI-AKI. Though the exact roles of autophagy in SI-AKI have not been well elucidated, it may be implicated in preventing SI-AKI through various molecular pathways. Targeting the autophagy-associated proteins and pathways may hint towards a new prospective in the treatment of critically ill patients with SI-AKI, but more preclinical studies are still warranted to validate this hypothesis.

Downregulation of miR-527 alleviates sepsis-induced acute kidney injury via targeting Beclin1

BACKGROUND

Sepsis-induced acute kidney injury (AKI) is known to result from the inflammatory responses. MiRNAs participate in the development of sepsis-induced AKI. Nevertheless, the function of miR-527 in sepsis-induced AKI remains unclear.

METHODS

Cell viability was evaluated by CCK8 assay, and TUNEL staining was applied to assess cell apoptosis. Pro-inflammatory cytokine (TNF-α, IL-6 and IL-1β) levels were evaluated by ELISA. Meanwhile, the relation among miR-527 and Beclin1 was detected by dual luciferase report assay. Western blot and RT-qPCR were used to examine the protein and mRNA levels, respectively. Furthermore, an in vivo model was constructed to assess the function of miR-527 in sepsis-induced AKI.

RESULTS

MiR-527 downregulation significantly alleviated the symptoms of sepsis-induced AKI in mice. MiR-527 level in HK-2 cells was significantly upregulated by LPS, and downregulation of miR-527 notably reversed LPS-induced inhibition of HK-2 cell viability by inhibiting apoptosis. In addition, LPS greatly increased TNF-α, IL-6 and IL-1β levels in supernatant of HK-2 cells, while miR-527 inhibitor partially restored this phenomenon. Meanwhile, Beclin1 was found to be the downstream mRNA of miR-527, and miR-527 inhibitor notably upregulated the level of LC3. MiR-527 downregulation reversed LPS-induced HK-2 cell injury through suppression of TGF-β pathway.

CONCLUSION

Downregulation of miR-527 alleviated sepsis-induced AKI via targeting Beclin1. Thus, miR-527 might act as a vital mediator in sepsis-induced AKI.

Non-Coding RNAs in Sepsis-Associated Acute Kidney Injury

Sepsis is a systemic inflammatory response caused by a severe infection that leads to multiple organ damage, including acute kidney injury (AKI). In intensive care units (ICU), the morbidity and mortality associated with sepsis-associated AKI (SA-AKI) are gradually increasing due to lack of effective and early detection, as well as proper treatment. Non-coding RNAs (ncRNAs) exert a regulatory function in gene transcription, RNA processing, post-transcriptional translation, and epigenetic regulation of gene expression. Evidence indicated that miRNAs are involved in inflammation and programmed cell death during the development of sepsis-associated AKI (SA-AKI). Moreover, lncRNAs and circRNAs appear to be an essential regulatory mechanism in SA-AKI. In this review, we summarized the molecular mechanism of ncRNAs in SA-AKI and discussed their potential in clinical diagnosis and treatment.

Regulatory Role of Non-Coding RNAs on Immune Responses During Sepsis

Sepsis is resulted from a systemic inflammatory response to bacterial, viral, or fungal agents. The induced inflammatory response by these microorganisms can lead to multiple organ system failure with devastating consequences. Recent studies have shown altered expressions of several non-coding RNAs such as long non-coding RNAs (lncRNAs), microRNAs (miRNAs) and circular RNAs (circRNAs) during sepsis. These transcripts have also been found to participate in the pathogenesis of multiple organ system failure through different mechanisms. NEAT1, MALAT1, THRIL, XIST, MIAT and TUG1 are among lncRNAs that participate in the pathoetiology of sepsis-related complications. miR-21, miR-155, miR-15a-5p, miR-494-3p, miR-218, miR-122, miR-208a-5p, miR-328 and miR-218 are examples of miRNAs participating in these complications. Finally, tens of circRNAs such as circC3P1, hsa_circRNA_104484, hsa_circRNA_104670 and circVMA21 and circ-PRKCI have been found to affect pathogenesis of sepsis. In the current review, we describe the role of these three classes of noncoding RNAs in the pathoetiology of sepsis-related complications.

SIRT1 attenuates sepsis-induced acute kidney injury via Beclin1 deacetylation-mediated autophagy activation

Our previous studies showed that silent mating-type information regulation 2 homologue-1 (SIRT1, a deacetylase) upregulation could attenuate sepsis-induced acute kidney injury (SAKI). Upregulated SIRT1 can deacetylate certain autophagy-related proteins (Beclin1, Atg5, Atg7 and LC3) in vitro. However, it remains unclear whether the beneficial effect of SIRT1 is related to autophagy induction and the underlying mechanism of this effect is also unknown. In the present study, caecal ligation and puncture (CLP)-induced mice, and an LPS-challenged HK-2 cell line were established to mimic a SAKI animal model and a SAKI cell model, respectively. Our results demonstrated that SIRT1 activation promoted autophagy and attenuated SAKI. SIRT1 deacetylated only Beclin1 but not the other autophagy-related proteins in SAKI. SIRT1-induced autophagy and its protective effect against SAKI were mediated by the deacetylation of Beclin1 at K430 and K437. Moreover, two SIRT1 activators, resveratrol and polydatin, attenuated SAKI in CLP-induced septic mice. Our study was the first to demonstrate the important role of SIRT1-induced Beclin1 deacetylation in autophagy and its protective effect against SAKI. These findings suggest that pharmacologic induction of autophagy via SIRT1-mediated Beclin1 deacetylation may be a promising therapeutic approach for future SAKI treatment.

Overexpression of SP1 restores autophagy to alleviate acute renal injury induced by ischemia-reperfusion through the miR-205/PTEN/Akt pathway

Background

Acute kidney injury (AKI) is a major kidney disease with poor clinical outcome. SP1, a well-known transcription factor, plays a critical role in AKI and subsequent kidney repair through the regulation of various cell biologic processes. However, the underlying mechanism of SP1 in these pathological processes remain largely unknown.

Methods

An in vitro HK-2 cells with anoxia-reoxygenation injury model (In vitro simulated ischemic injury disease) and an in vivo rat renal ischemia-reperfusion injury model were used in this study. The expression levels of SP1, miR-205 and PTEN were detected by RT-qPCR, and the protein expression levels of SP1, p62, PTEN, AKT, p-AKT, LC3II, LC3I and Beclin-1 were assayed by western blot. Cell proliferation was assessed by MTT assay, and the cell apoptosis was detected by flow cytometry. The secretions of IL-6 and TNF-α were detected by ELISA. The targeted relationship between miR-205 and PTEN was confirmed by dual luciferase report assay. The expression and positioning of LC-3 were observed by immunofluorescence staining. TUNEL staining was used to detect cell apoptosis and immunohistochemical analysis was used to evaluate the expression of SP1 in renal tissue after ischemia-reperfusion injury in rats.

Results

The expression of PTEN was upregulated while SP1 and miR-205 were downregulated in renal ischemia-reperfusion injury. Overexpression of SP1 protected renal tubule cell against injury induced by ischemia-reperfusion via miR-205/PTEN/Akt pathway mediated autophagy. Overexpression of SP1 attenuated renal ischemia-reperfusion injury in rats.

Conclusions

SP1 overexpression restored autophagy to alleviate acute renal injury induced by ischemia-reperfusion through the miR-205/PTEN/Akt pathway.