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Exploration of rare mitochondrial DNA mutations in lymphocyte subsets of people living with human immunodeficiency virus Caloren, Loïc


Despite advancements in Human Immunodeficiency Virus (HIV) therapy in extending lifespan and preventing AIDS, people living with HIV (PLWH) experience premature aging mainly indicated by higher prevalence and earlier onset of age-related diseases compared to HIV-negative controls. The mechanism of this aging remains unclear; however, some immune system effects observed in HIV are also characteristic of aging. Mitochondrial dysfunction, a hallmark of aging, may be linked to HIV and its treatment, which are known to affect mitochondrial DNA (mtDNA) and function. Further, mtDNA mutations are associated with aging and age-related diseases. In this regard, low frequency (<1%) mtDNA mutations have become subject to growing interest. The interplay of mtDNA mutations and immunosenescence is unknown as rare mtDNA mutations have never been characterized in lymphocyte subsets. The goal of my research was to explore rare mtDNA mutations in lymphocyte subsets of PLWH. First, I successfully adapted a unique molecular identifier (UMI)-based sequencing assay to enable sequencing of low concentration mtDNA specimens, necessary for my assaying of sorted lymphocyte specimens. I then sequenced a 264bp segment of mtDNA in the mitochondrial control region of: whole blood, CD4+ T cells, proliferative-competent (CD28+) CD8+ T cells, senescent (CD28-) CD8+ T cells, and B cells (CD19+) in 271 specimens from 48 PLWH and 41 HIV-negative controls. My analyses revealed a pattern of mtDNA variants with specific positions appearing as hotspots in the interrogated region, almost exclusively transition mutations (A↔ G, C↔ T). Total mutation burden differed slightly between lymphocyte subsets, however the distribution of mutations across genome position in each subset agreed closely with each other and with whole blood. No significant associations were observed with HIV status in any of the subsets. My research is the first to characterize rare mtDNA mutations in lymphocyte subsets, offering new insight into the composition of mtDNA mutation burden of whole blood. More research is needed to elucidate the extent of interplay between mtDNA mutations, immunosenescence and aging in HIV. Together, my findings facilitate future studies by validating a modified assay for specimens with low mtDNA concentrations and informing the use of whole blood to study mtDNA mutations.

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