# Chromogen-based double immunohistochemical detection of mitochondrial respiratory chain deficiencies in human brain tissue

## TL;DR

A new staining method allows researchers to study mitochondrial function in brain tissue with greater precision and using less sample.

## Contribution

A dual-antigen, chromogen-based immunohistochemical method for simultaneous detection of MRC complexes and mitochondrial mass in human brain tissue.

## Key findings

- The new method reliably detects mitochondrial respiratory chain deficiencies in neurons.
- The approach preserves tissue morphology and requires less tissue than traditional methods.
- It enables precise identification of mitochondrial dysfunction in brain samples from patients with POLG mutations.

## Abstract

Studies of the mitochondrial respiratory chain (MRC) have given important insights into the pathology of mitochondrial and neurodegenerative disorders. Immunohistochemical methods for staining MRC complexes are particularly valuable for assessing quantitative changes in situ, especially in complex tissues with cellular heterogeneity, such as the brain. However, traditional approaches have notable limitations. Chromogen-based staining, while preserving tissue morphology, has been restricted to a single antigen per section, preventing co-assessment of MRC complexes and mitochondrial mass on the same section. Immunofluorescence, which allows multiplex staining of multiple targets, partially addresses this limitation but compromises tissue morphology and can be highly variable in postmortem brain samples. To address these challenges, we have established a dual-antigen, chromogen-based immunohistochemical method that allows simultaneous assessment of each MRC complex and the mitochondrial marker voltage-dependent anion channel 1 (VDAC1) on the same section. As proof of concept, we apply this method on brain tissue from patients with neurological disease caused by mutations in the mitochondrial DNA polymerase gamma (POLG). Our findings demonstrate that this approach is both reliable and robust. Moreover, this method enables more precise identification of MRC deficiencies in neurons and significantly reduces the amount of tissue required for analysis, a critical advantage when working with scarce human brain samples.