# 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

## TL;DR

A mutation in the HK1 gene causes CMT4G disease by disrupting its interaction with VDAC, leading to mitochondrial calcium imbalance and nerve damage.

## Contribution

This study identifies how a specific HK1 mutation in CMT4G patients disrupts mitochondrial calcium homeostasis through impaired VDAC binding.

## Key findings

- CMT4G mutation reduces interaction between HK1 and VDAC in patient cells and nerves.
- Wild-type HK1 or its N-terminal peptide reduces mitochondrial calcium release, unlike the mutated form.
- Impaired HK1-VDAC interaction disrupts mitochondrial calcium buffering, affecting myelin maintenance.

## Abstract

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.