Hyaluronidase (HYAL)-2 is a weak, acid-active, hyaluronan-degrading enzyme broadly expressed in somatic tissues. Aberrant HYAL2 expression is implicated in diverse pathology. However, a significant proportion of HYAL2 is enzymatically inactive; thus the mechanisms through which HYAL2 dysregulation influences pathobiology are unclear. Recently, nonenzymatic HYAL2 functions have been described, and nuclear HYAL2 has been shown to influence mRNA splicing to prevent myofibroblast differentiation. Myofibroblasts drive fibrosis, thereby promoting progressive tissue damage and leading to multimorbidity. This study identifies a novel HYAL2 cytoplasmic function in myofibroblasts that is unrelated to its enzymatic activity. In fibroblasts and myofibroblasts, HYAL2 interacts with the GTPase-signaling small molecule ras homolog family member A (RhoA). Transforming growth factor beta 1-driven fibroblast-to-myofibroblast differentiation promotes HYAL2 cytoplasmic relocalization to bind to the actin cytoskeleton. Cytoskeletal-bound HYAL2 functions as a key regulator of downstream RhoA signaling and influences profibrotic myofibroblast functions, including myosin light-chain kinase-mediated myofibroblast contractility, myofibroblast migration, myofibroblast collagen/fibronectin deposition, as well as connective tissue growth factor and matrix metalloproteinase-2 expression. These data demonstrate that, in certain biological contexts, the nonenzymatic effects of HYAL2 are crucial in orchestrating RhoA signaling and downstream pathways that are important for full profibrotic myofibroblast functionality. In conjunction with previous data demonstrating the influence of HYAL2 on RNA splicing, these findings begin to explain the broad biological effects of HYAL2.

Progressive fibrosis leads to loss of organ function and affects many organs as a result of excessive extracellular matrix production. The ubiquitous matrix polysaccharide hyaluronan (HA) is central to this through association with its primary receptor, CD44, which exists as standard CD44 (CD44s) or multiple splice variants. Mediators such as profibrotic transforming growth factor (TGF)-β1 and proinflammatory interleukin (IL)-1β are widely associated with fibrotic progression. TGF-β1 induces myofibroblast differentiation, while IL-1β induces a proinflammatory fibroblast phenotype that promotes fibroblast binding to monocyte/macrophages. CD44 expression is essential for both responses. Potential CD44 splice variants involved, however, are unidentified. The TGF-β1-activated CD44/epidermal growth factor receptor complex induces differentiation of metastatic cells through interactions with the matrix metalloproteinase inducer, CD147. This study aimed to determine the CD44 variants involved in TGF-β1- and IL-1β-mediated responses and to investigate the potential profibrotic role of CD147. Using immunocytochemistry and quantitative PCR, standard CD44s were shown to be essential for both TGF-β1-induced fibroblast/myofibroblast differentiation and IL-1β-induced monocyte binding. Co-immunoprecipitation identified that CD147 associated with CD44s. Using CD147-siRNA and confocal microscopy, we also determined that incorporation of the myofibroblast marker, αSMA, into F-actin stress fibers was prevented in the absence of CD147 and myofibroblast-dependent collagen gel contraction was inhibited. CD147 did not associate with HA, but removal of HA prevented the association of CD44s with CD147 at points of cell-cell contact. Taken together, our data suggest that CD44s/CD147 colocalization is essential in regulating the mechanical tension required for the αSMA incorporation into F-actin stress fibers that regulates myofibroblast phenotype.

The open repair of groin hernias is often augmented with prosthetic biomaterials (mesh) as this favours a lower recurrence rate. The use of such prostheses may be associated with various complications including migration the frequency of which is unclear. A 29-year review of this complication after mesh plug hernioplasty is undertaken and technical advice described to avoid this.

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.