Cell-free mitochondrial DNA in progressive multiple sclerosis

Abstract

Recent studies have linked cell-free mitochondrial DNA (ccf-mtDNA) to neurodegeneration in both Alzheimer's and Parkinson's disease, raising the possibility that the same phenomenon could be seen in other diseases which manifest a neurodegenerative component. Here, we assessed the role of circulating cell-free mitochondrial DNA (ccf-mtDNA) in end-stage progressive multiple sclerosis (PMS), where neurodegeneration is evident, contrasting both ventricular cerebral spinal fluid ccf-mtDNA abundance and integrity between PMS cases and controls, and correlating ccf-mtDNA levels to known protein markers of neurodegeneration and PMS. Our data indicate that reduced ccf-mtDNA is a component of PMS, concluding that it may indeed be a hallmark of broader neurodegeneration.

Circulating cell-free mitochondrial DNA levels in Parkinson’s disease are influenced by treatment

“…ccf-mtDNA copy number was calculated as an absolute measurement of MTND1 (minor deletion arc mitochondrial gene) and derived from a triplicated standard curve and is expressed as copies per 1 μl of CSF. As in previous work [19,33], samples with > 1 B2M copies per microliter (indicating nuclear DNA contamination) were removed from further analysis (0 months: PD patients = 81, 28% and controls = 37, 28%, and 36 months: PD patients =74, 30% and controls = 27, 23%), leaving a final cohort of 423 samples at 0 months (291 PD patients and 132 controls) and 263 samples at 36 months (176 PD patients and 87 controls).…”

“…Ccf-mtDNA quantification ccf-mtDNA was quantified using established methods [19,33]. ccf-mtDNA copy number was calculated as an absolute measurement of MTND1 (minor deletion arc mitochondrial gene) and derived from a triplicated standard curve and is expressed as copies per 1 μl of CSF.…”

“…PD and control CSF samples, biopsied at 0 and 36 months, were obtained from the Parkinson's Progression Markers Initiative (PPMI). Ccf-mtDNA was quantified by qPCR [19,33]. Statistical analysis of log [10] transformed ccf-mtDNA levels were performed using Student's t-test, ANOVA and ANCOVA, with effect sizes estimated using Cohen's d. Detailed protocols are available in the Methods Section.…”

Increased plasma levels of mitochondrial DNA and pro-inflammatory cytokines in patients with progressive multiple sclerosis

“…Recent studies have associated decreased levels of circulating cellfree mtDNA in the cerebrospinal fluid (CSF) from patients afflicted by Alzheimer's and Parkinson's disease with neurodegeneration (Podlesniy et al, 2013;Pyle et al, 2015). Similarly, reduced concentrations of circulating mtDNA were detected in the CSF of end-stage progressive MS with evidence of neurodegeneration (Lowes et al, 2019). Conversely, a significantly higher level of CSF cell-free mtDNA was found in relapsing-remitting (RR) MS patients, as well as an inverse correlation between circulating mtDNA concentration and time since disease onset, suggesting that free mtDNA level may reflect early, active inflammatory activity (Varhaug et al, 2017).…”

“…Pioneering observations reported that high mobility group box protein 1 (HMGB1, a non-histone DNA-binding protein acting as transcriptional regulator and as nucleosome stabilizer) plays a role either in MS or in experimental autoimmune encephalomyelitis (Andersson et al, 2008). Recent studies have also suggested putative associations between DAMPs arising from mitochondrial (mt) components, particularly circulating cell-free mtDNA, and MS progression (Leurs et al, 2018;Lowes et al, 2019). Such DAMPs could induce the production of cytokines and other pro-inflammatory mediators that trigger and maintain the inflammatory environment, leading to a dysregulated and imbalanced cytokine network, well described in MS patients (Kallaur et al, 2017;Khaibullin et al, 2017).…”