Inflammatory Pathways and Emerging Biomarkers in Single Large-Scale Mitochondrial DNA Deletions and Mitochondrial Depletion Syndrome: Implications for Disease Mechanisms and Therapeutic Targeting

Mitochondrial diseases (MDs) are considered the most common inborn errors of metabolism causing dysfunction in the energy metabolism, due to mutations in both mitochondrial DNA (mtDNA) or nuclear genes. Their high clinical and genetic heterogeneity makes difficult the diagnosis and the therapeutic approach. Recent research highlights the critical interplay between mitochondrial dysfunction and immune dysregulation, with both innate and adapative immune. Defects in mtDNA replication and maintenance, mediated by proteins such as DNA polymerase γ, Twinkle helicase, and mitochondrial single-stranded DNA-binding protein, result in primary mitochondrial disease as mtDNA depletion, multiple deletions, or point mutations, leading to impaired energy production and cellular dysfunction. Therefore, the surveillance of mtDNA integrity and functioning is essential in the maintenance of cellular health, even because the mtDNA release into the cytosol, acts as a source of damage-associated molecular patterns (DAMPs) that, among others, has been shown to induce a pro-inflammatory state, through Tolllike receptor 9 and the cyclic GMP-AMP (cGAMP) synthase (cGAS), stimulating type 1 interferon response, which contribute to systemic inflammation and may exacerbate disease progression. However, only few studies addressed the link between innate immune response and mitochondrial function in primary MDs. Therefore, we propose to explore the effect of mtDNA instability on the inflammatory status and interferon-mediate response and their possible impact on the clinical evolution of patients with primary MDs. To this purpose, we will evaluate markers related to interferon-regulated pathways in blood and fibroblasts in two cohort of patients, first affected by Single Large Scale Mitochondrial DNA Deletions (SLSMDs) and a second cohort with Mitochondria Depletion Syndrome (MDS). In the SLSMDs cohort we also investigate the effect of anti-interferon drugs, MMF to test novel therapeutic strategies based on this new mechanism of action involved in disease pathogenesis. With this project we intend to elucidate novel relevant pathogenic pathways and to identify new potential biomarkers and therapeutic strategies to be tested in controlled clinical tria