Blindness Caused by Sterile Inflammation, Not Energy Deficiency: Identifying the Innate Immune Pathway in Leber Hereditary Optic Neuropathy
Background
Leber hereditary optic neuropathy (LHON) is a representative hereditary ophthalmic disease characterized by vision loss due to mutations. The established scientific consensus is that mutations in mitochondrial DNA (mtDNA) impair respiratory chain complex I function, leading to rapid loss of central vision. The prevailing explanation attributes retinal ganglion cell (RGC) death to the depletion of adenosine triphosphate (ATP), the intracellular energy source, and the accumulation of reactive oxygen species (ROS).
However, many clinical challenges remain unexplained by the metabolic energy deficiency model alone. How can we understand incomplete penetrance, where carriers with the same genetic defect live their entire lives without symptoms? The extreme gender bias, with a vastly higher incidence in males, and the highly divergent disease progression among patients are cited as critical gaps in existing theories. The failure to identify the hidden regulatory axis that triggers the disease has caused the development of effective treatments to stagnate for a long time.
Key Findings
This research has identified that mitochondrial dysfunction does not stop at simple energy depletion but also triggers severe sterile inflammation. When cellular respiration fails, mitochondrial damage-associated molecular patterns (mtDAMPs) leak massively into the cytoplasm. As mitochondrial materials of bacterial origin are released, the immune system misidentifies them as a pathogen invasion. The accumulation of these dangerous molecules is further accelerated as the function of mitophagy, which removes damaged mitochondria, also fails.
The mtDNA protruding into the cytoplasm and excessive ROS stimulate three major innate immune sensors. The first is the cGAS-STING pathway, which captures cytoplasmic DNA and promotes interferon secretion. The second is the Toll-like receptor 9 (TLR9) signaling, which responds sensitively to unmethylated sequences. The third is the activation of the NLRP3 inflammasome, which releases large amounts of the inflammatory cytokine interleukin-1 beta (IL-1β).
The triggered innate immune response results in the uncontrollable excitation of microglia and astrocytes. Analysis suggests that toxic factors secreted during the activation of inflammatory pathways are the primary cause of severe secondary neuronal injury to retinal ganglion cells. The cause of intraocular inflammation occurring during Adeno-associated virus (AAV) treatment, aimed at correcting defective genes, is also closely linked to the hypersensitivity of the innate immune system.
Significance and Outlook
This study provides an academic turning point by redefining LHON from a simple energy metabolic disorder to a neuroinflammatory disease. It provides clues to explain the long-standing mysteries of incomplete penetrance and male predominance through the difference in individual patients' immune response thresholds. The interpretation is that blindness becomes apparent only when sterile innate immune activation triggers the potential vulnerability of respiratory defects.
The direction of therapeutic strategies also requires fundamental expansion. Moving beyond the existing framework of merely supplementing mitochondrial respiratory complexes, a new pathway for combining immunomodulatory drugs that block cGAS-STING or NLRP3 has emerged. Plans are underway to develop biomarkers capable of predicting the risk of acute vision loss by quantitatively analyzing mtDAMPs in blood or aqueous humor.
Engineering vectors and optimizing combination therapies to manage intraocular inflammation arising during AAV gene therapy remains a challenge. The key to future practical application will be finding the balance of targeting only neuronal damage while avoiding the risk of tissue infection that may occur when intraocular immunity is excessively suppressed.
Leber hereditary optic neuropathy (LHON) is a mitochondrial disease caused primarily by pathogenic mitochondrial DNA (mtDNA) variants that impair respiratory chain complex I function. Although bioenergetic failure, oxidative stress, and retinal ganglion cell degeneration are central features of disease pathogenesis, these mechanisms do not fully explain the incomplete penetrance, male predominance, and marked clinical heterogeneity observed in LHON. Emerging evidence suggests that mitochondrial dysfunction can also trigger sterile inflammatory responses through the release of mitochondrial damage-associated molecular patterns (DAMPs), including mtDNA and reactive oxygen species, and through impaired mitophagic clearance. These signals activate innate immune pathways, including cGAS-STING, TLR9, and the NLRP3 inflammasome, potentially contributing to neuroinflammation, glial activation, and secondary neuronal injury. The relevance of immune signaling has gained further attention with the development of AAV-based gene therapies for LHON, where treatment-associated ocular inflammation has emerged as a clinically important challenge. In this review, we examine the evidence linking mitochondrial dysfunction to innate immune activation in LHON, discuss the immunological mechanisms underlying disease progression and gene therapy-associated inflammation, and highlight emerging opportunities for biomarker development, immunomodulatory intervention, and improved therapeutic design. We propose that LHON should be viewed not only as a disorder of mitochondrial bioenergetics but also as a neuroinflammatory disease shaped by the interplay between mitochondrial stress and immune signaling.
In clinical settings, this can be used as a tool for early screening of the risk of onset in asymptomatic carriers who possess the genetic mutation but have not yet begun to experience vision loss. The scenario involves regularly checking the concentration of circulating mitochondrial DNA in aqueous humor or serum and levels of pro-inflammatory cytokines; if signs of innate immune activation are detected, anti-inflammatory intervention can begin before optic nerve damage spreads.
The therapeutic development industry gains an opportunity to establish a combination therapy pipeline to overcome the limitations of monotherapy. The strategy involves combining cGAS inhibitors or NLRP3 inflammasome inhibitors with gene replacement therapies or metabolic modulators currently on the market or under development to suppress neuroinflammation. It is also expected to serve as a direct guideline for the design of improved capsids and optimal anti-inflammatory combination therapies to reduce the intraocular inflammation side effects commonly reported after AAV vector administration.