Cell-Free DNA and Mitochondria in Parkinson's Disease.

Parkinson's disease (PD) is a progressive neurodegenerative disorder marked by the gradual and irreversible loss of neurons, especially within the substantia nigra region of the midbrain. Early and accurate diagnosis remains a significant challenge in both research and clinical practice. This difficulty is further compounded by the substantial clinical and molecular heterogeneity of PD, emphasizing the urgent need for reliable biomarkers to enhance diagnostic precision and guide therapeutic strategies. One promising candidate biomarker is cell-free DNA (cfDNA), comprising short DNA fragments composed of mitochondrial (cf-mtDNA) and nucleus-derived (cf-ntDNA) DNA. cfDNA is released into body fluids through physiological or pathological processes such as apoptosis, necrosis, NETosis, or active secretion. The presence of cfDNA in human biological fluids has been utilized for years in oncology and prenatal medicine and, more recently, it has gained attention as a non-invasive diagnostic tool in the context of neurodegenerative diseases such as PD. This review article aims to provide a comprehensive overview of the current knowledge on the origin of cfDNA, highlighting the roles of the mitochondria and cf-mtDNA in PD, mitochondria quality control, and neuroinflammation in cfDNA biogenesis. The review collates available research on cfDNA types in human serum, plasma, and CSF, sequence analysis, and its potential application as a biomarker in the diagnosis and monitoring of PD, contributing to the ongoing search for non-invasive biomarkers of neurodegenerative diseases.