3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase (HMGCR) protects hair cells from cisplatin-induced ototoxicity in vitro: possible relation to the activities of p38 MAPK signaling pathway

Metformin Attenuates Myocardial Ischemia-Reperfusion Injury through the AMPK-HMGCR-ROS Signaling Axis

OBJECTIVE

To explore the role and mechanism of metformin (MET) in regulating myocardial injury caused by cardiac ischemia-reperfusion.

MATERIAL AND METHODS

A rat model of myocardial ischemia-reperfusion injury was established by ligation of the anterior descending branch of the left coronary artery. The myocardial area at risk and the infarction size were measured by Evans blue and 2,3,5‑triphenyltetrazole chloride (TTC) staining, respectively. Terminal Deoxynucleotidyl Transferase-Mediated dUTP Nick End Labeling (TUNEL) staining was used to detect apoptosis of cardiomyocytes. The expression of 4‑hydroxynonenal (4‑HNE) was detected by immunohistochemical staining. Real-time quantitative polymerase chain reaction (RT-PCR) and Western blot were used to detect mRNA and expression of the Adenosine 5'-monophosphate-activated protein kinase (AMPK) - 3‑hydroxy-3‑methylglutaryl-CoA reductase (HMGCR) signaling pathway, respectively.

RESULTS

MET treatment decreased the infarct size and the activity of the myocardial enzyme profile, thus demonstrating protection of ischemic myocardium. The number of TUNEL positive cells significantly decreased. Immunohistochemical results showed that MET decreased the expression of 4‑HNE in myocardial tissue and the content of malondialdehyde (MDA) in myocardial cells. Further experimental results showed that MET decreased HMGCR transcription and protein expression, and increased AMPK phosphorylation. In the model of hypoxia and reoxygenation injury of cardiomyocytes, MET increased the viability of cardiomyocytes, decreased the activity of lactic dehydrogenase (LDH), decreased malondialdehyde content and intracellular reactive oxygen species (ROS) concentrations, and regulate the AMPK-HMGCR signaling pathway through coenzyme C (ComC).

CONCLUSION

MET inhibits the expression of HMGCR by activating AMPK, reduces oxidative damage and apoptosis of cardiomyocytes, and alleviates myocardial ischemia-reperfusion injury.

Potential role of modulating autophagy levels in sensorineural hearing loss

In recent years, extensive research has been conducted on the pathogenesis of sensorineural hearing loss (SNHL). Apoptosis and necrosis have been identified to play important roles in hearing loss, but they cannot account for all hearing loss. Autophagy, a cellular process responsible for cell self-degradation and reutilization, has emerged as a significant factor contributing to hearing loss, particularly in cases of autophagy deficiency. Autophagy plays a crucial role in maintaining cell health by exerting cytoprotective and metabolically homeostatic effects in organisms. Consequently, modulating autophagy levels can profoundly impact the survival, death, and regeneration of cells in the inner ear, including hair cells (HCs) and spiral ganglion neurons (SGNs). Abnormal mitochondrial autophagy has been demonstrated in animal models of SNHL. These findings indicate the profound significance of comprehending autophagy while suggesting that our perspective on this cellular process holds promise for advancing the treatment of SNHL. Thus, this review aims to clarify the pathogenic mechanisms of SNHL and the role of autophagy in the developmental processes of various cochlear structures, including the greater epithelial ridge (GER), SGNs, and the ribbon synapse. The pathogenic mechanisms of age-related hearing loss (ARHL), also known as presbycusis, and the latest research on autophagy are also discussed. Furthermore, we underscore recent findings on the modulation of autophagy in SNHL induced by ototoxic drugs. Additionally, we suggest further research that might illuminate the complete potential of autophagy in addressing SNHL, ultimately leading to the formulation of pioneering therapeutic strategies and approaches for the treatment of deafness.

AdipoRon reduces cisplatin-induced ototoxicity in hair cells:possible relation to the regulation of mitochondrial biogenesis

AdipoRon (AR) can exert antidiabetic and anti-inflammatory effects by maintaining mitochondrial structure and function. The present study was designed to explore whether AR protects the auditory cells from cisplatin-induced damage and, if so, to probe the possible mechanisms underlying its action on this type of cells. Cell viability and apoptosis in House Ear Institute-Organization of Corti 1 (HEI-OC1 cells) and mouse cochlea hair cells (HCs) were detected by CCK8 and immunofluorescence. The expressions of apoptosis-related proteins (cleaved caspase-3 and Bcl-2), adiponectin receptor 1 (AdipoR 1) and the key factors relevant to mitochondrial biogenesis（SIRT1 and TFAM）were determined by Western blot and immunofluorescence. Changes in apoptotic rate and expression of SIRT1 and TFAM after silencing of AdipoR 1 (AdipoR 1-siRNA) in HEI-OC1 cells were measured by flow cytometry and Western blot. The levels of reactive oxygen species (ROS) were evaluated by MitoSox red staining. We found that 30 μM cisplatin exposure induced severe cellular damage, which resulted from activation of the mitochondrial apoptotic pathway. Cisplatin decreased the expression of AdipoR 1, SIRT1, and TFAM proteins, leading to impaired mitochondrial biogenesis and increased mitochondrial ROS production. 10 μM AR pre-treatment enhanced mitochondrial biogenesis, decreased mitochondrial ROS levels, alleviated imbalances in the mitochondrial apoptotic pathway, thus reducing cisplatin-induced apoptosis. Taken together, this work reveals that AR exerts anti-apoptotic effects, possibly via regulating mitochondrial biogenesis and function. Interestingly, AR might possess the promising potential to be a novel drug for the prevention and/ or treatment of cisplatin-induced ototoxicity.