Role of MST1 in the regulation of autophagy and mitophagy: implications for aging-related diseases

Chinese medicine targets cellular autophagy against cardiovascular diseases: research progress and future prospects

Cardiovascular diseases (CVDs) pose a serious threat to human health and represent one of the leading causes of death worldwide. Cellular autophagy, an essential intracellular self-degradation and homeostasis maintenance mechanism, plays a pivotal role in the pathogenesis of cardiovascular diseases. Traditional Chinese Medicine (TCM), with its unique theoretical framework and therapeutic principles, has demonstrated remarkable efficacy in CVDs management, garnering increasing scientific attention. In recent years, growing research attention has focused on TCM's autophagy regulation for CVDs treatment. However, most studies remain limited to cellular and animal models, with insufficient clinical data and unclear specific metabolic pathways and targets. Therefore, it is imperative to (1) investigate autophagy mechanisms in depth (2), explore methods for autophagy balance, and (3) clarify drug interactions to establish a foundation for clinical applications. This article comprehensively summarizes relevant research findings, provides an in-depth discussion of TCM's mechanisms in autophagy regulation for CVDs treatment, reviews current research status, and outlines future development trends, aiming to offer valuable theoretical foundations and therapeutic strategies for clinical CVDs management.

Dysregulation of autophagy during photoaging reduce oxidative stress and inflammatory damage caused by UV

Photoaging, the premature aging of skin due to chronic ultraviolet (UV) exposure, is a growing concern in dermatology and cosmetic science. While UV radiation is known to induce DNA damage, oxidative stress, and inflammation in skin cells, recent research unveils a promising countermeasure: autophagy. This review explores the intricate relationship between autophagy and photoaging, highlighting how this cellular recycling process can mitigate UV-induced damage. We begin by examining the differential impacts of UVA and UVB radiation on skin cells and the role of oxidative stress in accelerating photoaging. Next, we delve into the molecular mechanisms of autophagy, including its various forms and regulatory pathways. Central to this review is the discussion of autophagy's protective functions, such as the clearance of damaged organelles and proteins, and its role in maintaining genomic integrity. Furthermore, we address the current challenges in harnessing autophagy for therapeutic purposes, including the need for selective autophagy inducers and a deeper understanding of its context-dependent effects. By synthesizing recent advancements and proposing future research directions, this review underscores the potential of autophagy modulation as a novel strategy to prevent and treat photoaging. This comprehensive analysis aims to inspire further investigation into autophagy-based interventions, offering new hope for preserving skin health in the face of environmental stressors.

Pharmacological regulators of Hippo pathway: Advances and challenges of drug development

The Hippo signaling pathway is crucial in regulating organ size, tumor progression, tissue regeneration, and bone homeostasis. Inactivation of the Hippo pathway results in the nuclear translocation and activation of YAP/TAZ. This activation not only promotes tumor progression but also enhances tissue regeneration, wound healing, and maintenance of bone stability Although its discovery occurred over two decades ago, developing effective inhibitors or activators for the Hippo pathway remains challenging. Recently, however, the pace of advancements in developing Hippo signaling-related agonists and antagonists has accelerated, with some drugs that target TEAD advancing to clinical trials and showing promise for treating related diseases. This review summarizes the progress in research on Hippo signaling-related agonists and inhibitors, offering an in-depth analysis of their regulatory mechanisms, pharmacological properties, and potential in vivo applications.

MST1, a novel therapeutic target for Alzheimer's disease, regulates mitochondrial homeostasis by mediating mitochondrial DNA transcription and the PI3K-Akt-ROS pathway

BACKGROUND

Alzheimer's disease (AD) is a prevalent irreversible neurodegenerative condition marked by gradual cognitive deterioration and neuronal loss. The mammalian Ste20-like kinase (MST1)-Hippo pathway is pivotal in regulating cell apoptosis, immune response, mitochondrial function, and oxidative stress. However, the association between MST1 and mitochondrial function in AD remains unknown. Therefore, this study investigates the effect of MST1 on neuronal damage and cognitive impairment by regulating mitochondrial homeostasis in AD.

METHODS

In this study, 4- and 7-month-old 5xFAD mice were selected to simulate the early and middle stages of AD, respectively; age-matched wild-type mice served as controls for comparative analysis. Adeno-associated virus (AAV) was injected into the hippocampus of mice. Four weeks post-injection, cognitive function, neuronal damage indicators, and mitochondrial morphology, dynamics, oxidative stress, ATP, and apoptosis-related indicators were evaluated. Additionally, RNA-sequencing was performed on the hippocampal tissue of 5xFAD mice and MST1-knockdown 5xFAD mice. Subsequently, Gene Ontology (GO) enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses were performed on differentially expressed genes to elucidate the potential mechanism of MST1. In vitro studies were performed to investigate the effects of MST1 on SH-SY5Y model cell viability and mitochondrial function and validate the potential underlying molecular mechanisms.

RESULTS

MST1 overexpression accelerated neuronal degeneration and cognitive deficits in vivo while promoting oxidative stress and mitochondrial damage. Similarly, in vitro, MST1 overexpression facilitated apoptosis and mitochondrial dysfunction. MST1 knockdown and chemical inactivation reduced cognitive decline, mitochondrial dysfunction, and neuronal degeneration. Mechanistically, MST1 regulated the transcription of mitochondrial genes, including MT-ND4L, MT-ATP6, and MT-CO2, by binding to PGC1α. Moreover, MST1 influenced cellular oxidative stress through the PI3K-Akt-ROS pathway, ultimately disrupting mitochondrial homeostasis and mediating cell damage.

CONCLUSIONS

Cumulatively, these results suggest that MST1 primarily regulates mitochondrial DNA transcription levels by interacting with PGC1α and modulates cellular oxidative stress through the PI3K-Akt-ROS pathway, disrupting mitochondrial homeostasis. This discovery can be exploited to potentially enhance mitochondrial energy metabolism pathways by targeting MST1, offering novel potential therapeutic targets for treating AD.

Inhibiting endothelial cell Mst1 attenuates acute lung injury in mice

Lung endothelium plays a pivotal role in the orchestration of inflammatory responses to acute pulmonary insults. Mammalian sterile 20-like kinase 1 (Mst1) is a serine/threonine kinase that has been shown to play an important role in the regulation of apoptosis, stress responses, and organ growth. This study investigated the role of Mst1 in lung endothelial activation and acute lung injury (ALI). We found that Mst1 was significantly activated in inflamed lung endothelial cells (ECs) and mouse lung tissues. Overexpression of Mst1 promoted nuclear factor κ-B (NF-κB) activation through promoting JNK and p38 activation in lung ECs. Inhibition of Mst1 by either its dominant negative form (DN-Mst1) or its pharmacological inhibitor markedly attenuated cytokine-induced expression of cytokines, chemokines, and adhesion molecules in lung ECs. Importantly, in a mouse model of lipopolysaccharide-induced (LPS-induced) ALI, both deletion of Mst1 in lung endothelium and treatment of WT mice with a pharmacological Mst1 inhibitor significantly protected mice from LPS-induced ALI. Together, our findings identified Mst1 kinase as a key regulator in controlling lung EC activation and suggest that therapeutic strategies aimed at inhibiting Mst1 activation might be effective in the prevention and treatment of inflammatory lung diseases.

MST1 knockdown inhibits osteoarthritis progression through Parkin-mediated mitophagy and Nrf2/NF-κB signalling pathway

Osteoarthritis (OA) is a complicated disease that involves apoptosis and mitophagy. MST1 is a pro-apoptotic factor. Hence, decreasing its expression plays an anti-apoptotic effect. This study aims to investigate the protective effect of MST1 inhibition on OA and the underlying processes. Immunofluorescence (IF) was used to detect MST1 expression in cartilage tissue. Western Blot, ELISA and IF were used to analyse the expression of inflammation, extracellular matrix (ECM) degradation, apoptosis and mitophagy-associated proteins. MST1 expression in chondrocytes was inhibited using siRNA and shRNA in vitro and in vivo. Haematoxylin-Eosin, Safranin O-Fast Green and alcian blue staining were used to evaluate the therapeutic effect of inhibiting MST1. This study discovered that the expression of MST1 was higher in OA patients. Inhibition of MST1 reduced inflammation, ECM degradation and apoptosis and enhanced mitophagy in vitro. MST1 inhibition slows OA progression in vivo. Inhibiting MST1 suppressed apoptosis, inflammation and ECM degradation via promoting Parkin-mediated mitophagy and the Nrf2-NF-κB axis. The results suggest that MST1 is a possible therapeutic target for the treatment of osteoarthritis as its inhibition delays the progression of OA through the Nrf2-NF-κB axis and mitophagy.

The structure and function of FUN14 domain-containing protein 1 and its contribution to cardioprotection by mediating mitophagy

Cardiovascular disease (CVD) is a serious public health risk, and prevention and treatment efforts are urgently needed. Effective preventive and therapeutic programs for cardiovascular disease are still lacking, as the causes of CVD are varied and may be the result of a multifactorial combination. Mitophagy is a form of cell-selective autophagy, and there is increasing evidence that mitophagy is involved in cardioprotective processes. Recently, many studies have shown that FUN14 domain-containing protein 1 (FUNDC1) levels and phosphorylation status are highly associated with many diseases, including heart disease. Here, we review the structure and functions of FUNDC1 and the path-ways of its mediated mitophagy, and show that mitophagy can be effectively activated by dephosphorylation of Ser13 and Tyr18 sites, phosphorylation of Ser17 site and ubiquitination of Lys119 site in FUNDC1. By effectively activating or inhibiting excessive mitophagy, the quality of mitochondria can be effectively controlled. The main reason is that, on the one hand, improper clearance of mitochondria and accumulation of damaged mitochondria are avoided, and on the other hand, excessive mitophagy causing apoptosis is avoided, both serving to protect the heart. In addition, we explore the possible mechanisms by which FUNDC1-mediated mitophagy is involved in exercise preconditioning (EP) for cardioprotection. Finally, we also point out unresolved issues in FUNDC1 and its mediated mitophagy and give directions where further research may be needed.

The Mst1/2-BNIP3 axis is required for mitophagy induction and neuronal viability under mitochondrial stress

Mitophagy induction upon mitochondrial stress is critical for maintaining mitochondrial homeostasis and cellular function. Here, we found that Mst1/2 (Stk3/4), key regulators of the Hippo pathway, are required for the induction of mitophagy under various mitochondrial stress conditions. Knockdown of Mst1/2 or pharmacological inhibition by XMU-MP-1 treatment led to impaired mitophagy induction upon CCCP and DFP treatment. Mechanistically, Mst1/2 induces mitophagy independently of the PINK1-Parkin pathway and the canonical Hippo pathway. Moreover, our results suggest the essential involvement of BNIP3 in Mst1/2-mediated mitophagy induction upon mitochondrial stress. Notably, Mst1/2 knockdown diminishes mitophagy induction, exacerbates mitochondrial dysfunction, and reduces cellular survival upon neurotoxic stress in both SH-SY5Y cells and Drosophila models. Conversely, Mst1 and Mst2 expression enhances mitophagy induction and cell survival. In addition, AAV-mediated Mst1 expression reduced the loss of TH-positive neurons, ameliorated behavioral deficits, and improved mitochondrial function in an MPTP-induced Parkinson's disease mouse model. Our findings reveal the Mst1/2-BNIP3 regulatory axis as a novel mediator of mitophagy induction under conditions of mitochondrial stress and suggest that Mst1/2 play a pivotal role in maintaining mitochondrial function and neuronal viability in response to neurotoxic treatment.

Inhibiting endothelial cell Mst1 attenuates acute lung injury in mice

Background

Lung endothelium plays a pivotal role in the orchestration of inflammatory and injury responses to acute pulmonary insults. Mammalian sterile 20-like kinase 1 (Mst1), a mammalian homolog of Hippo, is a serine/threonine kinase that is ubiquitously expressed in many tissues and has been shown to play an important role in the regulation of apoptosis, inflammation, stress responses, and organ growth. While Mst1 exhibits high expression in the lung, its involvement in the endothelial response to pulmonary insults remains largely unexplored.

Methods

Mst1 activity was assessed in lung endothelium by western blot. Mst1 endothelial specific knockout mice and a pharmacological inhibitor were employed to assess the effects of Mst1 on homeostatic and lipopolysaccharide (LPS)-induced endothelial responses. Readouts for these studies included various assays, including NF-κB activation and levels of various inflammatory cytokines and adhesion molecules. The role of Mst1 in lung injury was evaluated in a LPS-induced murine model of acute lung injury (ALI).

Results

Mst1 phosphorylation was significantly increased in lung endothelial cells after exposure to tumor necrosis factor (TNF)-alpha (TNF-α) and mouse lung tissues after LPS exposure. Overexpression of full length Mst1 or its kinase domain promoted nuclear factor kappaB (NF-κB) activation through promoting JNK and p38 activation, whereas dominant negative forms of Mst1 (DN-Mst1) attenuated endothelial responses to TNF-α and interleukin-1β. Consistent with this, targeted deletion of Mst1 in lung endothelium reduced lung injury to LPS in mice. Similarly, wild-type mice were protected from LPS-induced lung injury following treatment with a pharmacological inhibitor of Mst1/2.

Conclusions

Our findings identified Mst1 kinase as a key regulator in the control of lung EC activation and suggest that therapeutic strategies aimed at inhibiting Mst1 activation might be effective in the prevention and treatment of lung injury to inflammatory insults.

Denosumab Attenuates Glucolipotoxicity-Induced β-Cell Dysfunction and Apoptosis by Attenuating RANK/RANKL Signals

Obesity is strongly associated with insulin sensitivity in type 2 diabetes (T2D), mainly because free fatty acids (FFAs) are released from excess fat tissue. Long-term exposure to high levels of FFAs and glucose leads to glucolipotoxicity, causing damage to pancreatic β-cells, thus accelerating the progression of T2D. Therefore, the prevention of β-cell dysfunction and apoptosis is essential to prevent the development of T2D. Unfortunately, there are currently no specific clinical strategies for protecting β-cells, highlighting the need for effective therapies or preventive approaches to improve the survival of β-cells in T2D. Interestingly, recent studies have shown that the monoclonal antibody denosumab (DMB), used in osteoporosis, displays a positive effect on blood glucose regulation in patients with T2D. DMB acts as an osteoprotegerin (OPG) by inhibiting the receptor activator of the NF-κB ligand (RANKL), preventing the maturation and function of osteoclasts. However, the exact mechanism by which the RANK/RANKL signal affects glucose homeostasis has not been fully explained. The present study used human 1.4 × 10⁷ β-cells to simulate the T2D metabolic condition of high glucose and free fatty acids (FFAs), and it investigated the ability of DMB to protect β-cells from glucolipotoxicity. Our results show that DMB effectively attenuated the cell dysfunction and apoptosis caused by high glucose and FFAs in β-cells. This may be caused by blocking the RANK/RANKL pathway that reduced mammalian sterile 20-like kinase 1 (MST1) activation and indirectly increased pancreatic and duodenal homeobox 1 (PDX-1) expression. Furthermore, the increase in inflammatory cytokines and ROS caused by the RANK/RANKL signal also played an important role in glucolipotoxicity-induced cytotoxicity, and DMB can also protect β-cells by reducing the mechanisms mentioned above. These findings provide detailed molecular mechanisms for the future development of DMB as a potential protective agent of β-cells.