Background
Circulating cell-free mitochondrial DNA (ccf-mtDNA) fragments are released into the bloodstream following cell death, can activate the innate immune system, and have been associated with aging-related outcomes, including frailty, in the general population. Data on ccf-mtDNA levels during both acute and chronic phases of HIV infection remain limited. We hypothesized that HIV infection is associated with higher ccf-mtDNA.
Methods
We measured ccf-mtDNA levels in the AIDS Linked to the Intravenous Experience (ALIVE) (N=890) and Multicenter AIDS Cohort Study (MACS)(N=427). Using ultrasensitive digital PCR, we quantified short and long ccf-mtDNA fragments in serum samples. Measurements were taken at intervals of 1, 3, or 5 years. Levels of ccf-mtDNA were compared by HIV serostatus and CD4 T-cell counts (<350 vs. ≥350 cells/mm³), using mixed-effect linear regression models that controlled for demographics, BMI, active injection drug use, and alcohol use. We also measured ccf-mtDNA levels in non-human primates (n=6) before and after SIV infection and following antiretroviral therapy (ART) initiation. Samples were drawn at baseline, peak viremia (2 weeks post-infection), pre-ART (5 weeks post-infection), and 3- and 6-months post-ART initiation.
Results
: In both cohorts, PWH had significantly lower levels of both short and long ccf-mtDNA fragments compared to HIV-negative individuals. The difference was more pronounced in the ALIVE cohort (0.119 log scale units lower) than in the MACS cohort (0.094 units lower) (both p<0.05). Furthermore, individuals with lower CD4 T-cell counts (<350 cells/mm³) exhibited further reductions in ccf-mtDNA levels, with significant reductions in both short and long fragments in the ALIVE cohort and short fragments in the MACS cohort (Figure Panel A). In nonhuman primates, short ccf-mtDNA levels increased shortly after infection, peaking just before ART initiation (p=0.001), and subsequently declined, reaching levels below baseline after 6 months on ART. Long fragments remained stable during the early post-ART phase but declined significantly by 6 months (p=0.02, Figure Panel B).
Conclusions
Contrary to the initial hypothesis, ART-suppressed HIV infection is associated with lower levels of both short and long ccf-mtDNA fragments, following an initial increase during acute infection. These findings underscore the need for further investigation into the mechanisms regulating ccf-mtDNA in people living with HIV and its potential role in aging-related diseases.