Pathogenic variants of Valosin-containing protein induce lysosomal damage and transcriptional activation of autophagy regulators in neuronal cells

Valosin-containing protein acts as a target and mediator of S-nitrosylation in the heart through distinct mechanisms

S-nitrosylation (SNO) is an emerging paradigm of redox signaling protecting cells against oxidative stress in the heart. Our previous studies demonstrated that valosin-containing protein (VCP), an ATPase-associated protein, is a vital mediator protecting the heart against cardiac stress and ischemic injury. However, the molecular regulations conferred by VCP in the heart are not fully understood. In this study, we explored the potential role of VCP in cardiac protein SNO using multiple cardiac-specific genetically modified mouse models and various analytical techniques including biotin switch assay, liquid chromatography, mass spectrometry, and western blotting. Our results showed that cardiac-specific overexpression of VCP led to an overall increase in the levels of SNO-modified cardiac proteins in the transgenic (TG) vs. wild-type (WT) mice. Mass spectrometry analysis identified mitochondrial proteins involved in respiration, metabolism, and detoxification as primary targets of SNO modification in VCP-overexpressing mouse hearts. Particularly, we found that VCP itself underwent SNO modification at a specific cysteine residue in its N-domain. Additionally, our study demonstrated that glyceraldehyde 3-phosphate dehydrogenase (GAPDH), a key enzyme in glycolysis, also experienced increased SNO in response to VCP overexpression. While deletion of inducible nitric oxide synthase (iNOS) in VCP TG mice did not affect VCP SNO, it did abolish SNO modification in mitochondrial complex proteins, suggesting a dual mechanism of regulation involving both iNOS-dependent and independent pathways. Overall, our findings shed light on post-translational modification of VCP in the heart, unveiling a previously unrecognized role for VCP in regulating cardiac protein SNO and offering new insights into its function in cardiac protection.

ALS-related p97 R155H mutation disrupts lysophagy in iPSC-derived motor neurons

Mutations in the AAA+ ATPase p97 cause multisystem proteinopathy 1, which includes amyotrophic lateral sclerosis; however, the pathogenic mechanisms that contribute to motor neuron loss remain obscure. Here, we use two induced pluripotent stem cell models differentiated into spinal motor neurons to investigate how p97 mutations perturb the motor neuron proteome. Using quantitative proteomics, we find that motor neurons harboring the p97 R155H mutation have deficits in the selective autophagy of lysosomes (lysophagy). p97 R155H motor neurons are unable to clear damaged lysosomes and have reduced viability. Lysosomes in mutant motor neurons have increased pH compared with wild-type cells. The clearance of damaged lysosomes involves UBXD1-p97 interaction, which is disrupted in mutant motor neurons. Finally, inhibition of the ATPase activity of p97 using the inhibitor CB-5083 rescues lysophagy defects in mutant motor neurons. These results add to the evidence that endo-lysosomal dysfunction is a key aspect of disease pathogenesis in p97-related disorders.

Valosin containing protein (VCP): initiator, modifier, and potential drug target for neurodegenerative diseases

The AAA+ ATPase valosin containing protein (VCP) is essential for cell and organ homeostasis, especially in cells of the nervous system. As part of a large network, VCP collaborates with many cofactors to ensure proteostasis under normal, stress, and disease conditions. A large number of mutations have revealed the importance of VCP for human health. In particular, VCP facilitates the dismantling of protein aggregates and the removal of dysfunctional organelles. These are critical events to prevent malfunction of the brain and other parts of the nervous system. In line with this idea, VCP mutants are linked to the onset and progression of neurodegeneration and other diseases. The intricate molecular mechanisms that connect VCP mutations to distinct brain pathologies continue to be uncovered. Emerging evidence supports the model that VCP controls cellular functions on multiple levels and in a cell type specific fashion. Accordingly, VCP mutants derail cellular homeostasis through several mechanisms that can instigate disease. Our review focuses on the association between VCP malfunction and neurodegeneration. We discuss the latest insights in the field, emphasize open questions, and speculate on the potential of VCP as a drug target for some of the most devastating forms of neurodegeneration.

Genetic disruption of mammalian endoplasmic reticulum-associated protein degradation: Human phenotypes and animal and cellular disease models

Endoplasmic reticulum-associated protein degradation (ERAD) is a stringent quality control mechanism through which misfolded, unassembled and some native proteins are targeted for degradation to maintain appropriate cellular and organelle homeostasis. Several in vitro and in vivo ERAD-related studies have provided mechanistic insights into ERAD pathway activation and its consequent events; however, a majority of these have investigated the effect of ERAD substrates and their consequent diseases affecting the degradation process. In this review, we present all reported human single-gene disorders caused by genetic variation in genes that encode ERAD components rather than their substrates. Additionally, after extensive literature survey, we present various genetically manipulated higher cellular and mammalian animal models that lack specific components involved in various stages of the ERAD pathway.

Elamipretide alleviates pyroptosis in traumatically injured spinal cord by inhibiting cPLA2-induced lysosomal membrane permeabilization

Spinal cord injury (SCI) is a devastating injury that may result in permanent motor impairment. The active ingredients of medications are unable to reach the affected area due to the blood‒brain barrier. Elamipretide (SS-31) is a new and innovative aromatic cationic peptide. Because of its alternating aromatic and cationic groups, it freely crosses the blood‒brain barrier. It is also believed to decrease inflammation and protect against a variety of neurological illnesses. This study explored the therapeutic value of SS-31 in functional recovery after SCI and its possible underlying mechanism. A spinal cord contusion injury model as well as the Basso Mouse Scale, footprint assessment, and inclined plane test were employed to assess how well individuals could function following SCI. The area of glial scarring, the number of dendrites, and the number of synapses after SCI were confirmed by HE, Masson, MAP2, and Syn staining. Western blotting, immunofluorescence, and enzyme-linked immunosorbent assays were employed to examine the expression levels of pyroptosis-, autophagy-, lysosomal membrane permeabilization (LMP)- and MAPK signalling-related proteins. The outcomes showed that SS-31 inhibited pyroptosis, enhanced autophagy and attenuated LMP in SCI. Mechanistically, we applied AAV vectors to upregulate Pla2g4A in vivo and found that SS-31 enhanced autophagy and attenuated pyroptosis and LMP by inhibiting phosphorylation of cPLA2. Ultimately, we applied asiatic acid (a p38-MAPK agonist) to test whether SS-31 regulated cPLA2 partially through the MAPK-P38 signalling pathway. Our group is the first to suggest that SS-31 promotes functional recovery partially by inhibiting cPLA2-mediated autophagy impairment and preventing LMP and pyroptosis after SCI, which may have potential clinical application value.