Hyaluronan Synthase Isoforms Direct Distinct Patterns of Fibroblast Activation Linked to Fibrosis Progression Versus...

The stroma plays key roles in development and tissue regeneration after injury, but its expansion following injury can drive fibrosis and chronic disease. In the kidney, hyaluronan (HA) is largely absent from the healthy stroma but becomes abundant during disease. To investigate HA regulation in stromal responses, we compared HA and hyaluronan synthase (HAS) expression during kidney development, homeostasis, injury, and recovery. A rat model of ischaemia-reperfusion injury (IRI) with or without ischaemic pre-conditioning (IPC) was studied alongside embryonic and Has1/3^-/- mouse kidneys, with mechanistic studies performed in primary human fibroblasts. In healthy kidneys, stromal HA was absent, HAS1 showed limited epithelial expression, and HAS2 was undetectable. Following IRI, stromal HA accumulation and increased HAS2 expression were associated with chronic fibrosis. In contrast, during development, prominent stromal HA matrices were evident in areas of tubular generation, with strong HAS1 (not HAS2) expression. During recovery, stromal HA and HAS2 were attenuated, whereas HAS1+ stromal cells expanded but were distinct from α-SMA+ myofibroblasts. Functionally, HAS1+ fibroblasts displayed enhanced migration, fibroblast activation protein (FAP) expression and reduced profibrotic marker expression, whereas HAS2+ fibroblasts exhibited a contractile myofibroblast phenotype with high extra domain A fibronectin (EDA-FN) and type I collagen, alpha-1 subunit (COL1A1). Together, these findings identify HA as a regulator of stromal fibroblast phenotype and associate HAS1 and HAS2 in divergent fibrotic outcomes following kidney injury.