# Leigh Syndrome Pathomechanism Involves Region-Specific Innate Immune Activation in Ndufs4 Knockout Mice

## TL;DR

The study finds that innate immune activation in the olfactory bulb may contribute to the progression of Leigh syndrome in mice, offering a new pathomechanism linking mitochondrial dysfunction to immune response.

## Contribution

The paper identifies region-specific innate immune activation in the olfactory bulb as a novel pathomechanism in a mouse model of Leigh syndrome.

## Key findings

- Innate immune system pathways are enriched in the olfactory bulb but not the cerebellum of Ndufs4−/− mice.
- The activation involves interferon-stimulated genes and JAK-STAT/RIG-I-like signaling pathways.
- Endogenous double-strand RNA is proposed to trigger immune signaling, recruiting leukocytes to other brain regions.

## Abstract

Although recent evidence suggests that the immune system contributes to the pathogenesis of paediatric Leigh syndrome, detailed mechanistic insights are still lacking. Here, we investigated the involvement of immune system activation and inflammation in brain tissue in Leigh syndrome, using hypothesis generating methods. We compared the transcriptomes of olfactory bulb and cerebellum from male Ndufs4−/− (knockout) mice (n = 5–6), a well-established model of paediatric Leigh syndrome. Relative to wildtype animals, knockout mice displayed enrichment of innate immune system pathways in the olfactory bulb. Unexpectedly, relative to the olfactory bulb, few pathways were enriched in the cerebellum, and none that indicated similar changes to the immune system. Innate immune system pathways in the olfactory bulb were mainly upregulated and included a large set of interferon stimulated genes, and genes involved in JAK-STAT and retinoic acid-inducible gene 1-like signalling, interleukins, interferon receptors and endogenous double strand RNA sensors. We propose that innate immune system activation starts in the olfactory bulb, is mediated by the retinoic acid-inducible gene 1-like signalling pathway in response to increased cytosolic double-strand RNA, leading to chemokines that recruit leukocytes to other brain regions to elicit an immune response. Our results fill in the gap between mitochondrial dysfunction and activation of the innate immune response, which has been reported by others. Our findings strongly suggest that immune system activation constitutes part of the Leigh syndrome pathomechanism, which is compatible with the improvement observed in mitochondrial disease patients following immune system-targeting interventions.

Enrichment of innate immune system pathways in olfactory bulb, but not cerebellum of Ndufs4−/− mice. Transcriptomic analysis of Ndufs4−/− mice brain tissues reveals enrichment of JAK-STAT and RIG-I-like receptor signalling pathways in olfactory bulb. We propose a pathomechanism of Leigh syndrome which starts with endogenous dsRNA molecules activating these signalling pathways, leading to chemokines that recruit leukocytes to other brain regions to elicit an immune response. Figure created with BioRender

Enrichment of innate immune system pathways in olfactory bulb, but not cerebellum of Ndufs4−/− mice. Transcriptomic analysis of Ndufs4−/− mice brain tissues reveals enrichment of JAK-STAT and RIG-I-like receptor signalling pathways in olfactory bulb. We propose a pathomechanism of Leigh syndrome which starts with endogenous dsRNA molecules activating these signalling pathways, leading to chemokines that recruit leukocytes to other brain regions to elicit an immune response. Figure created with BioRender

The online version contains supplementary material available at 10.1007/s10571-026-01681-2.