Mutant huntingtin disrupts mitochondrial proteostasis by interacting with TIM23

Abstract

Mutant huntingtin (mHTT), the causative protein in Huntington’s disease (HD), associates with the translocase of mitochondrial inner membrane 23 (TIM23) complex, resulting in inhibition of synaptic mitochondrial protein import first detected in presymptomatic HD mice. The early timing of this event suggests that it is a relevant and direct pathophysiologic consequence of mHTT expression. We show that, of the 4 TIM23 complex proteins, mHTT specifically binds to the TIM23 subunit and that full-length wild-type huntingtin (wtHTT) and mHTT reside in the mitochondrial intermembrane space. We investigated differences in mitochondrial proteome between wtHTT and mHTT cells and found numerous proteomic disparities between mHTT and wtHTT mitochondria. We validated these data by quantitative immunoblotting in striatal cell lines and human HD brain tissue. The level of soluble matrix mitochondrial proteins imported through the TIM23 complex is lower in mHTT-expressing cell lines and brain tissues of HD patients compared with controls. In mHTT-expressing cell lines, membrane-bound TIM23-imported proteins have lower intramitochondrial levels, whereas inner membrane multispan proteins that are imported via the TIM22 pathway and proteins integrated into the outer membrane generally remain unchanged. In summary, we show that, in mitochondria, huntingtin is located in the intermembrane space, that mHTT binds with high-affinity to TIM23, and that mitochondria from mHTT-expressing cells and brain tissues of HD patients have reduced levels of nuclearly encoded proteins imported through TIM23. These data demonstrate the mechanism and biological significance of mHTT-mediated inhibition of mitochondrial protein import, a mechanism likely broadly relevant to other neurodegenerative diseases.

Melatonin inhibits cytosolic mitochondrial DNA–induced neuroinflammatory signaling in accelerated aging and neurodegeneration

“…Huntington's disease (HD) is caused by mutant huntingtin (mHTT) (26), a protein with an expanded polyglutamine region which binds to the TIM23 mitochondrial protein import complex and inhibits protein import (27,28). Impaired mitochondrial protein import increased mitochondrial oxidative stress.…”

Mitochondrial protein import dysfunction: mitochondrial disease, neurodegenerative disease and cancer

“…Both wild type and mutant HTT have been found in the mitochondrial inter-membrane space where the mHTT protein binds specifically to Tim23 (Fig. 2C) [182,183]. The binding of mHTT to Tim23 has been shown to reduce import of nuclear encoded mitochondrial proteins as suggested by reduced levels of matrix localised proteins in cells expressing mHTT and in HD patient brain tissue [182,183].…”

Interaction of Oxidative Stress and Misfolded Proteins in the Mechanism of Neurodegeneration

“…It has been reported that mHtt fragments bind to the translocase of the inner mitochondrial membrane 23 (TIM23) complex and inhibit the mitochondrial protein import by altering the mitochondrial proteome, leading to mitochondrial dysfunction [ 94 , 95 ].…”