Evolution of High-Molecular-Mass Hyaluronic Acid is Associated with Subterranean Lifestyle.

Hyaluronic acid (HA) is a major component of extracellular matrix (ECM) which plays an important role in development, cellular response to injury and inflammation, cell migration, and cancer. The naked mole-rat (NMR, Heterocephalus glaber ) contains abundant high-molecular-mass HA (HMM-HA) in its tissues, which contributes to this species' cancer resistance and possibly longevity. Here we report that abundant HMM-HA is found in a wide range of subterranean mammalian species, but not in phylogenetically related aboveground species. These species accumulate abundant HMM-HA by regulating the expression of genes involved in HA degradation and synthesis and contain unique mutations in these genes. The abundant high molecular weight HA may benefit the adaptation to subterranean environment by increasing skin elasticity and protecting from oxidative stress due to hypoxic subterranean environment. HMM-HA may also be coopted to confer cancer resistance and longevity to subterranean mammals. Our work suggests that HMM-HA has evolved with subterranean lifestyle.