Traumatic and Diabetic Schwann Cell Demyelination Is Triggered by a Transient Mitochondrial Calcium Release through Voltage Dependent Anion Channel 1

Mitochondrial translocator-protein ligand etifoxine reduces pain symptoms and protects against motor dysfunction development following peripheral nerve injury in rats

Peripheral nerve injury enhances mitochondrial translocator protein (TSPO) expression in the spinal cord and dorsal root ganglia (DRG), which is associated with neuroinflammation and mitochondrial dysfunction contributing to chronic pain development. Here, we investigate the effect of TSPO ligand Etifoxine, on the development of chronic pain and motor dysfunction following sciatic nerve injury. Mechanical and thermal sensitivity, as well as motor function, were measured in rats before and after sciatic nerve crush (SNC). Rats were treated with the Etifoxine (50 mg/kg, twice daily) for one week. At the end of the experiment, RT-PCR and immunohistochemistry (IHC) were performed to assess mitochondrial stress and neuroinflammation. Additionally, high-resolution respirometry (O2k) was used to evaluate mitochondrial function in the spinal cord following mitochondrial permeability transition pore (mPTP) induction by Ca2+. Etifoxine treatment post-SNC alleviated mechanical and thermal hypersensitivity, as well as motor dysfunction in rats. In addition, Etifoxine treatment modulates neuroinflammation and mitochondrial stress. Specifically, we found a significant reduction in microglia presence and the transcription of pro-inflammatory cytokines (TNFα, IL-6, IL-1β) in the DRG and spinal cord of the SNC/etifoxine-treated group. Furthermore, Etifoxine treatment prevent the decline in mitochondrial respiration, including non-phosphorylation, ATP-linked respiration, and maximal respiration, after mPTP induction by Ca2+. Our findings suggest that TSPO-ligand Etifoxine protects against motor dysfunction and the development of chronic pain by reducing neuroinflammation and apoptosis in the DRG and spinal cord. Importantly, the beneficial effects of TSPO-ligands are reflected in the restoration of the mitochondrial function under challenging conditions.

Role of Mitochondrial Dysfunction in Neuropathy

Diabetes mellitus is characterized by a state of hyperglycemia, which can lead to severe complications if left untreated or poorly managed. Diabetic peripheral neuropathy (DPN) is one common complication. This condition is characterized by damage to the nerves that supply the legs and feet as well as problems with blood vessels, the heart, or urinary tract. To alleviate pain for patients, clinicians resort to long-term treatment regimens of nerve pain medications, which are usually either anticonvulsants or antidepressants. However, little is understood about the underlying mechanisms of DPN. Many pathogenic pathways have been proposed, one of which is mitochondrial dysfunction. Mitochondrial dysfunction includes a range of possible deficiencies given the number of functions controlled by or located in mitochondria, including their core function of bioenergetics. This review focuses on mitochondrial bioenergetics, including respiration/ATP synthesis and reactive oxygen species (ROS) production, as well as calcium homeostasis and apoptosis, and their potential as targets for the effective treatment of diabetic peripheral neuropathy.

Unveiling the Role of Schwann Cell Plasticity in the Pathogenesis of Diabetic Peripheral Neuropathy

Diabetic peripheral neuropathy (DPN) is a prevalent complication of diabetes that affects a significant proportion of diabetic patients worldwide. Although the pathogenesis of DPN involves axonal atrophy and demyelination, the exact mechanisms remain elusive. Current research has predominantly focused on neuronal damage, overlooking the potential contributions of Schwann cells, which are the predominant glial cells in the peripheral nervous system. Schwann cells play a critical role in neurodevelopment, neurophysiology, and nerve regeneration. This review highlights the emerging understanding of the involvement of Schwann cells in DPN pathogenesis. This review explores the potential role of Schwann cell plasticity as an underlying cellular and molecular mechanism in the development of DPN. Understanding the interplay between Schwann cell plasticity and diabetes could reveal novel strategies for the treatment and management of DPN.

TFEB/3 Govern Repair Schwann Cell Generation and Function Following Peripheral Nerve Injury

TFEB and TFE3 (TFEB/3), key regulators of lysosomal biogenesis and autophagy, play diverse roles depending on cell type. This study highlights a hitherto unrecognized role of TFEB/3 crucial for peripheral nerve repair. Specifically, they promote the generation of progenitor-like repair Schwann cells after axonal injury. In Schwann cell-specific TFEB/3 double knock-out mice of either sex, the TFEB/3 loss disrupts the transcriptomic reprogramming that is essential for the formation of repair Schwann cells. Consequently, mutant mice fail to populate the injured nerve with repair Schwann cells and exhibit defects in axon regrowth, target reinnervation, and functional recovery. TFEB/3 deficiency inhibits the expression of injury-responsive repair Schwann cell genes, despite the continued expression of c-jun, a previously identified regulator of repair Schwann cell function. TFEB/3 binding motifs are enriched in the enhancer regions of injury-responsive genes, suggesting their role in repair gene activation. Autophagy-dependent myelin breakdown is not impaired despite TFEB/3 deficiency. These findings underscore a unique role of TFEB/3 in adult Schwann cells that is required for proper peripheral nerve regeneration.

The Hexokinase 1 5'-UTR Mutation in Charcot-Marie-Tooth 4G Disease Alters Hexokinase 1 Binding to Voltage-Dependent Anion Channel-1 and Leads to Dysfunctional Mitochondrial Calcium Buffering

Demyelinating Charcot-Marie-Tooth 4G (CMT4G) results from a recessive mutation in the 5'UTR region of the Hexokinase 1 (HK1) gene. HK participates in mitochondrial calcium homeostasis by binding to the Voltage-Dependent Anion Channel (VDAC), through its N-terminal porin-binding domain. Our hypothesis is that CMT4G mutation results in a broken interaction between mutant HK1 and VDAC, disturbing mitochondrial calcium homeostasis. We studied a cohort of 25 CMT4G patients recruited in the French gypsy population. The disease was characterized by a childhood onset, an intermediate demyelinating pattern, and a significant phenotype leading to becoming wheelchair-bound by the fifth decade of life. Co-IP and PLA studies indicated a strong decreased interaction between VDAC and HK1 in the patients' PBMCs and sural nerve. We observed that either wild-type HK1 expression or a peptide comprising the 15 aa of the N-terminal wild-type HK1 administration decreased mitochondrial calcium release in HEK293 cells. However, mutated CMT4G HK1 or the 15 aa of the mutated HK1 was unable to block mitochondrial calcium release. Taken together, these data show that the CMT4G-induced modification of the HK1 N-terminus disrupts HK1-VDAC interaction. This alters mitochondrial calcium buffering that has been shown to be critical for myelin sheath maintenance.

Cell metabolism pathways involved in the pathophysiological changes of diabetic peripheral neuropathy

Diabetic peripheral neuropathy is a common complication of diabetes mellitus. Elucidating the pathophysiological metabolic mechanism impels the generation of ideal therapies. However, existing limited treatments for diabetic peripheral neuropathy expose the urgent need for cell metabolism research. Given the lack of comprehensive understanding of energy metabolism changes and related signaling pathways in diabetic peripheral neuropathy, it is essential to explore energy changes and metabolic changes in diabetic peripheral neuropathy to develop suitable treatment methods. This review summarizes the pathophysiological mechanism of diabetic peripheral neuropathy from the perspective of cellular metabolism and the specific interventions for different metabolic pathways to develop effective treatment methods. Various metabolic mechanisms (e.g., polyol, hexosamine, protein kinase C pathway) are associated with diabetic peripheral neuropathy, and researchers are looking for more effective treatments through these pathways.

Mapping the N-Terminal Hexokinase-I Binding Site onto Voltage-Dependent Anion Channel-1 To Block Peripheral Nerve Demyelination

The voltage-dependent anion channel (VDAC), the most abundant protein on the outer mitochondrial membrane, is implicated in ATP, ion and metabolite exchange with cell compartments. In particular, the VDAC participates in cytoplasmic and mitochondrial Ca²⁺ homeostasis. Notably, the Ca²⁺ efflux out of Schwann cell mitochondria is involved in peripheral nerve demyelination that underlies most peripheral neuropathies. Hexokinase (HK) isoforms I and II, the main ligands of the VDAC, possess a hydrophobic N-terminal structured in α-helix (NHKI) that is necessary for the binding to the VDAC. To gain further insight into the molecular basis of HK binding to the VDAC, we developed and optimized peptides based on the NHKI sequence. These modifications lead to an increase of the peptide hydrophobicity and helical content that enhanced their ability to prevent peripheral nerve demyelination. Our results provide new insights into the molecular basis of VDAC/HK interaction that could lead to the development of therapeutic compounds for demyelinating peripheral neuropathies.