Hsp70-Bim interaction facilitates mitophagy by recruiting parkin and TOMM20 into a complex

Prohibitin2 knockdown decreases glioma malignant phenotypes and radio-resistance by inhibiting mitophagy

PURPOSE

Prohibitin2 (PHB2), located in inner mitochondrial membrane (IMM), is an important receptor to induce mitophagy. PHB2 was identified as a cancer-promoting factor in most cancers. However, the function of PHB2 in glioma cells remains unclear. This study delved into the impact of PHB2 knockdown on the phenotype, radiosensitivity and mitophagy of glioma cells.

METHODS

PHB2 expression and its clinical relevance in glioma were investigated by western blot, quantitative reverse transcription polymerase chain reaction (qRT-PCR) and TCGA databases. The malignant phenotypes of glioma cells were analyzed in vitro using cell proliferation, cell cycle, wound healing and transwell assay. The radiosensitivity of glioma cells was detected by colony forming assay. The potential mechanism by which PHB2 regulated mitophagy was investigated by coimmunoprecipitation assay.

RESULTS

The expression of PHB2 was significantly upregulated in glioma cells and closely correlated with the malignant degree of glioma. The knockdown of PHB2 inhibited the proliferation, migration and invasion activities of glioma cells. Furthermore, PHB2 knockdown enhanced the radiosensitivity of normoxic and hypoxic glioma cells and suppressed the ionizing radiation-induced mitophagy in glioma cells. Cyanide 3-chlorophenylhydrazone (CCCP), a mitophagy agonist, could reverse the phenotypes and radiosensitivity changes elicited by PHB2 knockdown. Additionally, PHB2 regulated the expression of PGAM5 and PINK1 by directly binding to PARL.

CONCLUSIONS

Our findings revealed that PHB2 knockdown decreased glioma malignant phenotypes and radio-resistance by inhibiting mitophagy via PARL-PGAM5-PINK1-Parkin pathway. PHB2 is a promising candidate target for the development of new therapeutic strategy to enhance the efficacy of radiotherapy for glioma.

A new weapon: the application of tumor vaccines based on extracellular exosomal heat shock proteins in immunotherapy

Despite the significant advancements in cancer research, innovative approaches are still needed to reduce tumor incidence, progression, and dissemination, as well as for prolonging patient survival. Currently, the development of cancer vaccines is gaining attention as a novel preventative and therapeutic strategy. Although the concept of cancer vaccination is not new, a limited number of vaccines have received approval for tumor therapy. Heat shock protein (HSP)-based vaccination represents a promising strategy that harnesses specific tumor antigens to activate immune responses. Exosomes (Exs) are highly heterogeneous bilayer vesicles capable of transporting various types of molecules through extracellular space. Compared with conventional anticancer drugs, exosomes exhibit low toxicity and good biocompatibility, and they can stimulate the immune system either directly or indirectly. Ex-based vaccines may elicit an antitumor immune response that generates memory cells capable of recognizing cancer antigens, thereby inhibiting disease progression. This paper reviews the potential applications of HSPs and exosomes in the prevention and treatment of solid tumors. Finally, we discuss the advantages of the extracellular exosomal heat shock protein (HSP-Ex) vaccine and future research directions aimed at optimizing heat shock protein-based cancer immunotherapy strategies.

Melatonin attenuates MPP+-induced autophagy via heat shock protein in the Parkinson's disease mouse model

Background

This study investigates the protective properties of melatonin in an in vivo Parkinson's disease (PD) model, focusing on the underlying mechanisms involving heat shock proteins (HSPs).

Methods

Twelve adult male C57BL/6 mice were randomly divided into four groups (normal control, melatonin control, Parkinson's model, and melatonin treatment; n = 3 per group) and housed in a single cage. 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) was injected intraperitoneally in the Parkinson's model and treatment groups to establish a subacute PD model, while controls received saline. Limb motor ability was assessed 1 h after the final injection using behavioral tests, including the open field test to evaluate central zone entries and average movement. Dopamine transporter (DAT) expression in the striatum was analyzed by immunohistochemistry, and Western blot was used to measure autophagy proteins and HSP70 levels.

Results

The PD mouse model was successfully established through MPTP stimulation. Compared to the normal control group, the model group showed a significant reduction in the frequency of entering the central zone and average movement. The number of DAT-positive cells in the brain also decreased significantly. The expression levels of HSP70 and CDK5 were significantly lower, while the expression levels of LC3 II /LC3I and p62 increased significantly. In the MT treatment group, both the frequency of entering the central zone and the average movement were significantly higher compared to the model group. DAT-positive cells in the midbrain also increased significantly. The expression levels of HSP70 and CDK5 were significantly elevated, while the expression levels of LC3 II /LC3I and p62 protein were significantly decreased.

Conclusion

Melatonin exerts a protective effect against MPP+-induced damage to dopaminergic neurons, presumably by upregulating HSP70, which inhibits neuronal autophagy.

Mitochondrial abnormalities as a target of intervention in acute myeloid leukemia

Acute myeloid leukemia (AML) is an aggressive hematological malignancy; it is the most common acute leukemia in adults. AML prognosis is often poor, and relapse often occurs after initial remission. Recurrent genetic abnormalities underlying this disease and the presence of leukemic stem cells complicate disease treatment. However, the complex metabolic reprogramming that enables the unrestrained cell growth seen in these cells may also be their Achilles' heel. In these cells, mitophagy operates as a double-edged sword. On one hand, it provides a source of building blocks for further cell division and serves as a method for removing damaged organelles, promoting cell survival. However, the profound metabolic changes to mitochondria also render these organelles more sensitive to damage and place them precariously close to excess mitophagic activation. This review discusses the dual role mitophagy plays in AML survival, the importance of targeting mitophagy to treat AML, and current progress in the area. The discovery and mechanism of action of multiple compounds that were used to inhibit or stimulate mitophagy and their effects on AML survival are also described. Further, we explore the combination strategy of mitophagy-targeting compounds with existing and/or novel chemotherapeutics to eradicate AML and discuss strategies to uncover new drug targets and novel mitochondria-targeting drugs.

Mitochondria in skeletal system-related diseases

Skeletal system-related diseases, such as osteoporosis, arthritis, osteosarcoma and sarcopenia, are becoming major public health concerns. These diseases are characterized by insidious progression, which seriously threatens patients' health and quality of life. Early diagnosis and prevention in high-risk populations can effectively prevent the deterioration of these patients. Mitochondria are essential organelles for maintaining the physiological activity of the skeletal system. Mitochondrial functions include contributing to the energy supply, modulating the Ca2+ concentration, maintaining redox balance and resisting the inflammatory response. They participate in the regulation of cellular behaviors and the responses of osteoblasts, osteoclasts, chondrocytes and myocytes to external stimuli. In this review, we describe the pathogenesis of skeletal system diseases, focusing on mitochondrial function. In addition to osteosarcoma, a characteristic of which is active mitochondrial metabolism, mitochondrial damage occurs during the development of other diseases. Impairment of mitochondria leads to an imbalance in osteogenesis and osteoclastogenesis in osteoporosis, cartilage degeneration and inflammatory infiltration in arthritis, and muscle atrophy and excitationcontraction coupling blockade in sarcopenia. Overactive mitochondrial metabolism promotes the proliferation and migration of osteosarcoma cells. The copy number of mitochondrial DNA and mitochondria-derived peptides can be potential biomarkers for the diagnosis of these disorders. High-risk factor detection combined with mitochondrial component detection contributes to the early detection of these diseases. Targeted mitochondrial intervention is an effective method for treating these patients. We analyzed skeletal system-related diseases from the perspective of mitochondria and provided new insights for their diagnosis, prevention and treatment by demonstrating the relationship between mitochondria and the skeletal system.

Hypoxia-Preconditioned BMSC-Derived Exosomes Induce Mitophagy via the BNIP3-ANAX2 Axis to Alleviate Intervertebral Disc Degeneration

Intervertebral disc degeneration (IVDD) is a chronic degenerative disease involving the aging and loss of proliferative capacity of nucleus pulposus cells (NPCs), processes heavily dependent on mitochondrial dynamics and autophagic flux. This study finds that the absence of BCL2/adenovirus E1B 19 kDa interacting protein 3 (BNIP3) is associated with senescence-related NPC degeneration, disrupting mitochondrial quality control. Bone marrow mesenchymal stem cells (BMSCs) have multidirectional differentiation potential and produce extracellular vesicles containing cellular activators. Therefore, in this study, BMSCs are induced under hypoxic stimulation to deliver BNIP3-rich extracellular vesicles to NPCs, thereby alleviating aging-associated mitochondrial autophagic flux, promoting damaged mitochondrial clearance, and restoring mitochondrial quality control. Mechanistically, BNIP3 is shown to interact with the membrane-bound protein annexin A2 (ANXA2), enabling the liberation of the transcription factor EB (TFEB) from the ANXA2-TFEB complex, promoting TFEB nuclear translocation, and regulating autophagy and lysosomal gene activation. Furthermore, a rat model of IVDD is established and verified the in vivo efficacy of the exosomes in repairing disc injuries, delaying NPC aging, and promoting extracellular matrix (ECM) synthesis. In summary, hypoxia-induced BMSC exosomes deliver BNIP3-rich vesicles to alleviate disc degeneration by activating the mitochondrial BNIP3/ANXA2/TFEB axis, providing a new target for IVDD treatment.

Yeast Bxi1/Ybh3 mediates conserved mitophagy and apoptosis in yeast and mammalian cells: convergence in Bcl-2 family

The process of degrading unwanted or damaged mitochondria by autophagy, called mitophagy, is essential for mitochondrial quality control together with mitochondrial apoptosis. In mammalian cells, pan-Bcl-2 family members including conical Bcl-2 members and non-conical ones are involved in and govern the two processes. We have illustrated recently the BH3 receptor Hsp70 interacts with Bim to mediate both apoptosis and mitophagy. However, whether similar pathways exist in lower eukaryotes where conical Bcl-2 members are absent remained unclear. Here, a specific inhibitor of the Hsp70-Bim PPI, S1g-10 and its analogs were used as chemical tools to explore the role of yeast Bxi1/Ybh3 in regulating mitophagy and apoptosis. Using Om45-GFP processing assay, we illustrated that yeast Ybh3 mediates a ubiquitin-related mitophagy pathway in both yeast and mammalian cells through association with Hsp70, which is in the same manner with Bim. Moreover, by using Bax/Bak double knockout MEF cells, Ybh3 was identified to induce apoptosis through forming oligomerization to trigger mitochondrial outer membrane permeabilization (MOMP) like Bax. We not only illustrated a conserved ubiquitin-related mitophagy pathway in yeast but also revealed the multi-function of Ybh3 which combines the function of BH3-only protein and multi-domain Bax protein as one.

Ectopic BH3-Only Protein Bim Associates with Hsp70 to Regulate Yeast Mitophagy

Mitophagy, a form of selective autophagy, plays an essential role to maintain a population of healthy and functional mitochondria for normal cellular metabolism. Acting mainly as one of the B-cell lymphoma 2 (Bcl-2) family pro-apoptotic members, Bim (also known as BCL2L11) was identified to be a co-chaperone of Hsp70 to promote mitophagy in mammalian cells. Herein, with the help of a specific Hsp70/Bim disruptor and Om45-GFP processing assay, we illustrated that ectopic BimEL is able to promote mitophagy through Hsp70/Bim interaction in yeast, where Bax/Bak is absent. The Hsp70/Bim-mediated mitophagy is conserved in eukaryotes, from yeast to humans.