Mitochondrial transplantation is under development as a class of therapy to treat aging. Mitochondrial dysfunction is a feature of aging, and evidence from animal studies suggests that lasting improvements in health result from replacement of a fraction of native mitochondria with new, functional mitochondria delivered via intravenous infusion. Cells readily take up mitochondria from their surroundings if given the chance. The biggest challenge remains scaling up manufacture, being able to harvest from cell cultures the vast numbers of mitochondria needed to produce a reasonable level of replacement in a human patient. Work has progressed to a first in human demonstration conducted recently, but a few other companies are also moving towards human trials at some pace.
One of the most interesting questions is that of how vital it is that mitochondrial DNA haplotype matches nuclear DNA haplotype. Mitochondria are the evolved descendants of ancient symbiotic bacteria, and carry their own genome, the mitochondrial DNA. There are more than 20 distinct groupings of human mitochondrial DNA haplotypes. Over evolutionary time, most mitochondrial genes migrated into nuclear DNA, so some components of the molecular machinery in a mitochondrion come from mitochondrial DNA, some from nuclear DNA. What happens when mitochondria with a different DNA haplotype are introduced into an adult individual? What if researchers construct a much better synthetic mitochondrial DNA haplotype that outperforms all natural haplotype when it comes to producing adenosine triphosphate (ATP) with a low burden of oxidative stress, and increases the efficiency of mitochondrial quality control as well? Are there roadblocks to implementing this goal?
There is some evidence to suggest that mixing and matching between haplotypes, or changing mitochondrial haplotype in an adult individual, is modestly harmful. Today's open access paper provides more data on this front, looking at outcomes on the lifespan of flies resulting from mismatches between mitochondrial genes in nuclear DNA versus mitochondrial DNA. The effect size is around a 10% reduction in median life span, which is not all that large in a species like the fruit fly, where life span is very plastic in response to circumstances. Still, it seems likely that companies developing mitochondrial transplantation therapies will choose to be cautious and match haplotype to patient.
Mitonuclear discordance modulates mitochondrial ageing dynamics in natural Drosophila populations
Mitochondria lie at the center of cellular metabolism and are key determinants of organismal ageing. Because the oxidative phosphorylation (OXPHOS) complexes are encoded by both nuclear and mitochondrial genomes, compatibility between these genomes is essential for efficient energy production and eukaryotic life. Disruption of this intergenomic coordination, via mismatches between mitonuclear genotypes, has been shown to impair metabolism with severe life-history consequences across diverse taxa. Yet, the role of mitonuclear compatibility in shaping ageing trajectories in natural populations remains poorly understood, with evidence largely limited to inbred laboratory lines.
Hormesis describes the process where mild stress can trigger protective adaptations against ensuing perturbations. In this context, mitohormetic interventions can represent a protective strategy to promote metabolic homeostasis and healthy ageing. Here, we leveraged natural genetic variation in wild Drosophila melanogaster populations to test how mitonuclear compatibility interacts with early-life metabolic stress to shape ageing phenotypes. Two mitochondrial haplotypes coexist in D. melanogaster populations along the Australian cline: "t" (most common in the north) and "m" (most common in the south), differing by 15 single-nucleotide polymorphism (SNPs) across protein-coding genes. We generated a panel of outbred populations carrying putatively coevolved ("tT," "mM") and mismatched ("mT," "tM") mitonuclear genomes.
We demonstrate that mitonuclear mismatch accelerates age-related mitochondrial decline, elevates reactive oxygen species production, and shortens lifespan. Strikingly, early-life mitochondrial stress induced by dietary modulation counteracts these effects, promoting mitochondrial homeostasis and longevity. Our findings reveal mitonuclear interactions shaping ageing trajectories in natural populations and provide unique evidence that targeted interventions can act as a buffer against the detrimental impact of genetic discordance.
View the full article at FightAging
