Mitochondrial protein CHCHD2 emerges as a guardian of the aging brain

Aging is the single greatest risk factor for neurodegenerative disease, yet the molecular events that tip an aging brain from resilience into collapse remain stubbornly opaque. A new study published in Acta Neuropathologica points to a surprising culprit and an equally surprising protector: CHCHD2, a small protein nestled in the narrow space between the two membranes of the mitochondrion. Researchers led by Teresa R. Kee, David E. Kang, and Jung-A A. Woo at Case Western Reserve University report that CHCHD2 acts as a linchpin connecting mitochondria and lysosomes, the two organelles whose coordinated decline drives Parkinson’s disease and related Lewy body disorders. When the protein fades with age, the entire waste-disposal system of the neuron begins to fail; when it is bolstered, the aging brain holds the line against inflammation, neuron loss, and protein aggregation.

The team’s starting point was a simple epidemiological observation with profound implications. Mining a published microarray dataset of 41 human frontal cortex samples spanning ages 24 to 106, they found that CHCHD2 gene expression declines steadily and significantly across the human lifespan, with a Pearson correlation coefficient of −0.63. The drop was present in both sexes but was steeper and statistically stronger in women. Because CHCHD2 levels were already known to be reduced in the brains and even the red blood cells of Parkinson’s patients, the finding suggested that the gradual erosion of this mitochondrial protein could be one of the quiet preconditions that makes an aging brain vulnerable to Lewy body pathology in the first place.

To test whether boosting CHCHD2 could counteract aging, the researchers engineered transgenic mice expressing the human wild-type protein specifically in neurons, using the same prion protein promoter strategy they had previously used to create mice carrying the Parkinson’s-linked T61I mutation. The resulting CHCHD2-WT animals expressed roughly 2.3-fold more CHCHD2 transcript than normal littermates, and the extra protein correctly localized to the mitochondrial intermembrane space, the compartment where the endogenous protein resides. Crucially, the mice appeared entirely normal: their body weights, brain morphology, synaptic protein levels, and hippocampal electrophysiology, including long-term potentiation at the CA3-CA1 synapse, were indistinguishable from wild-type controls. Whatever the extra CHCHD2 was doing, it was not disturbing normal neuronal function.

The protective effects emerged only with age, and they were striking. At 12 months of age, the CHCHD2-WT mice had significantly more tyrosine hydroxylase-positive dopaminergic neurons in the substantia nigra than wild-type littermates, the very cell population that dies in Parkinson’s disease. By 18 months, when ordinary mice show mounting neuroinflammation, the transgenic animals displayed markedly reduced immunoreactivity for Iba1 and GFAP, the standard markers of activated microglia and astrocytes. Silver staining of the substantia nigra revealed nearly twice as many degenerating axons in age-matched mice carrying the T61I mutation compared with both wild-type and CHCHD2-WT animals, and the mutant mice also accumulated conspicuous CHCHD2-positive aggregates in the midbrain that were absent from the protected animals.

Proteomics told a similar story at the level of the entire protein complement of the cortex. In 12-month-old CHCHD2-WT mice, unbiased mass spectrometry of soluble and insoluble cortical fractions showed that the vast majority of altered proteins shifted in the direction of solubility: 169 of 240 significantly changed soluble proteins were elevated, while most of the 145 altered insoluble proteins were reduced. A contingency analysis confirmed that the ratio of insoluble to soluble proteins fell significantly, with an odds ratio of 0.381. That stands in dramatic contrast to the T61I mutant brains, which the same group had previously shown to skew in the opposite direction with an odds ratio of 23.4. In other words, wild-type CHCHD2 keeps the proteome fluid and degradable, while the mutant pushes it toward the aggregated, detergent-resistant state that defines proteinopathies.

The mechanistic heart of the paper lies in what happened when the researchers compared the two variants head to head. Pathway analysis of the cortical proteome revealed that the T61I mutation broadly suppresses the CLEAR signaling network, the transcriptional program that coordinates lysosomal biogenesis and function, alongside disruptions of mTOR and integrated stress response pathways. Lysosomal hydrolases, including cathepsin B, cathepsin L, and hexosaminidase A, were markedly depleted in mutant brains. Using a proximity-labeling interactome screen in which CHCHD2 variants were targeted to the mitochondrial intermembrane space fused to the BirA biotin ligase, the team discovered that T61I preferentially associates with cathepsins B and L. Proximity ligation assays and co-immunoprecipitation confirmed the interaction, and fluorometric enzyme assays showed that cathepsin B and L activities were significantly reduced in the forebrains of mutant mice, while cathepsin D was untouched.

Why does this matter for Parkinson’s disease? Cathepsin B and cathepsin L are the principal lysosomal enzymes that cleave alpha-synuclein within its amyloid-forming region, and genetic evidence links cathepsin B levels to Parkinson’s risk. When the researchers exposed cultured hippocampal neurons to sonicated alpha-synuclein pre-formed fibrils, cells expressing wild-type CHCHD2 cleared the pathological protein efficiently over 45 hours, whereas T61I-expressing cells retained significantly more of it. The mutant protein also accumulated in an insoluble form within isolated lysosomal fractions from mouse cortex, permeabilized lysosomal membranes as measured by galectin-3 puncta, and induced a greater than fourfold increase in swollen LAMP1-positive vacuoles. Recombinant T61I protein, unlike the wild-type protein, aggregated spontaneously at body temperature and resisted degradation after uptake into cells, suggesting that the misfolded mutant physically clogs and damages the very disposal machinery it is supposed to support.

Transmission electron microscopy provided the visual proof of the mitochondria-lysosome axis in action. In young wild-type mice, more than 86 percent of cortical mitochondria were classified as healthy, with elongated shapes and dense cristae, and every lysosome fell into the healthiest category. By 12 to 13 months of age, ordinary mice showed the expected deterioration: rounded mitochondria with sparse cristae and lysosomes stuffed with lipofuscin and lipid droplets. The CHCHD2-WT mice retained significantly healthier organelles on both counts, while the T61I animals fared worst of all, with no lysosomes classified as healthy and mitochondria showing severe ultrastructural abnormalities. The findings align with the human data: in postmortem frontal cortex from nine cortical Lewy body disease patients, soluble CHCHD2 was reduced by about 65 percent and cathepsin B by about 45 percent relative to controls, with the two proteins correlating significantly across all samples.

What emerges is a coherent model of how the aging brain loses its grip on protein quality control. CHCHD2, a mitochondrial intermembrane space protein, appears to sustain lysosomal health, possibly through the vesicular trafficking routes that shuttle material from mitochondria to lysosomes, and the T61I mutation corrupts this relationship by misfolding, aggregating, sequestering cathepsins, and rupturing lysosomal membranes. The authors are careful to note that the causal direction between mitochondrial and lysosomal abnormalities remains to be fully established, and the precise basis for the selectivity toward cathepsins B and L is still unclear. But the therapeutic implication is hard to miss: strategies that stabilize CHCHD2 expression, prevent its misfolding, or block the pathological interaction between mutant CHCHD2 and lysosomal cathepsins could simultaneously protect both organelles, addressing a root cause of the proteostatic failure that underlies Parkinson’s disease and perhaps brain aging more broadly. Preventing the age-associated decline of a single small mitochondrial protein, the study suggests, may be one of the most economical ways to keep an aging brain clean, functional, and resilient.

Subject of Research: Role of CHCHD2 in maintaining mitochondria-lysosome homeostasis during brain aging and Lewy body disease

Article Title: CHCHD2 mitigates age-associated proteostatic collapse by maintaining homeostasis of the mitochondria-lysosome axis

Article References: CHCHD2 mitigates age-associated proteostatic collapse by maintaining homeostasis of the mitochondria-lysosome axis. (n.d.). https://doi.org/10.1007/s00401-026-03093-4

Image Credits: AI Generated

DOI: 10.1007/s00401-026-03093-4

Keywords: CHCHD2, Parkinson's disease, Lewy body disorders, mitochondria-lysosome axis, lysosomes, cathepsin B, cathepsin L, alpha-synuclein, proteostasis, neurodegeneration, brain aging, neuroinflammation