Active mitochondria in healthy spiny mouse fibroblasts resemble megamitochondria and remain resilient across lifespan.

Although they exhibit limited regenerative ability of some tissues and organs shortly after birth or towards the end of fetal development, humans and laboratory mammals quickly transition to producing scar tissue for tissue repair. In contrast, spiny mice exhibit complex tissue regeneration as adults and provide a blueprint for how regeneration can occur throughout adulthood in mammals. Fibroblasts are key mediators of wound healing outcomes and prior work uncovered that cells from highly regenerative mammals (spiny mice and rabbits) exhibit extreme resistance to oxidative stress compared to those from non-regenerating laboratory mice and rats. Using a battery of cellular tests in primary ear pinna fibroblasts from highly regenerative and non-regenerative mammals, we find that cells from spiny mice and rabbits exhibit a baseline preference for glycolysis supporting a lower ROS-producing basal state. Uniquely, spiny mouse fibroblasts exhibit large, spherical, depolarized mitochondria similar to megamitochondria identified in pathological tissues. The megamitochondria phenotype was present across lifespan in ear pinna fibroblasts from fetal, young and old spiny mice. While rabbit, mouse and rat fibroblasts had polarized tubular mitochondrial networks typical of adult mammalian fibroblasts, isolated rabbit and spiny mice fibroblasts shared lower oxygen consumption efficiency even in the absence of a potential gradient. Taken together, our results support that a shared metabolic signature exists in stromal cells from highly regenerative mammals, although possibly driven by different mechanisms, to converge on a ROS-resistant phenotype which ultimately helps supports tissue regeneration.