Hypothesis: Age‑associated copy‑number variations that enhance immune regulation (e.g., duplications of TLR1, PLAU, or PLGRKT) reduce mitochondrial DNA heteroplasmy load in hematopoietic stem and progenitor cells (HSPCs) by lowering chronic inflammatory signaling and reactive oxygen species (ROS) production, thereby attenuating clonal expansion of mtDNA mutants.

Mechanistic rationale: Protective CNVs increase expression of innate immune receptors that promote anti‑inflammatory cytokine profiles (e.g., elevated IL‑10, reduced TNF‑α) in HSPCs. Lower inflammatory tone decreases NADPH oxidase activity and mitochondrial ROS, which are key drivers of mtDNA damage and heteroplasmy accumulation. Consequently, HSPCs carrying these CNVs experience a selective advantage for wild‑type mtDNA, slowing the age‑related rise in heteroplasmy observed after 70 years 4. This links the observed longevity benefit of immune‑regulatory CNVs in Alzheimer’s cohorts 2 to a cell‑autonomous mitigation of mitochondrial genomic instability.

Testable predictions:

1. In longitudinal blood samples from individuals >70 years, those with a protective CNV (validated by low‑pass WGS) will exhibit significantly lower mtDNA heteroplasmy fraction (measured by duplex sequencing) than CNV‑negative peers matched for age, sex, and ancestry.
2. CRISPR‑mediated introduction of a protective TLR1 duplication into human CD34⁺ HSPCs will reduce basal ROS (measured by MitoSOX) and decrease the emergence of mtDNA point mutations over 30 days in culture compared with isogenic controls.
3. Pharmacological blockade of TLR signaling (using antagonist TAK‑242) in CNV‑positive HSPCs will abolish the heteroplasmy‑protective effect, raising ROS and mtDNA mutation rates to levels seen in CNV‑negative cells.

Experimental approach: Access the UK Biobank whole‑genome sequencing dataset (~472 k participants) to identify carriers of the immune‑regulatory CNVs 1. Subset to participants with available whole‑blood mtDNA sequencing data (e.g., from the TOPMed freeze). Compare heteroplasmy burden using a linear mixed model adjusting for batch effects. Parallel in‑vitro work will use CRISPR‑Cas9 knock‑in of the CNV in primary HSPCs, followed by ROS assays, cytokine profiling (Luminex), and longitudinal mtDNA mutation tracking via duplex sequencing.

Falsifiability: If protective CNV carriers show no difference—or an increase—in mtDNA heteroplasmy relative to non‑carriers, or if engineered CNV expression fails to lower ROS and mtDNA mutation rates, the hypothesis is refuted. This would suggest that the longevity association operates through non‑hematopoietic mechanisms or that CNV‑immune effects are uncoupled from mitochondrial homeostasis.