BPS2026 – HYAL2 loss drives cell adhesion mode switching through the hyaluronan-rich glycocalyx

Cell division requires cells to detach, round, and then re-establish cell adhesion. During mitosis, this is hindered by the hyaluronan (HA)-rich pericellular matrix, a microns-thick brush-like layer that blocks adhesion receptors from accessing extracellular matrix (ECM) ligands. How cells navigate this glycocalyx is a long-standing conundrum. The GPI-anchored hyaluronidase HYAL2 is a prime candidate for resolving this barrier, but its ability to function in extracellular spaces has been controversial, since its enzymatic activity requires acidic pH. We examined spreading dynamics of mouse embryonic fibroblasts (MEFs) on ECM and through biomimetic HA brushes. Wild-type MEFs with or without pericellular HA exhibited indistinguishable early-time spreading, both following the classical power law R(t) ∼ t α with α ≈ 0.5, a value associated in prior work with actin-driven spreading dynamics. In contrast, HYAL2 –/– MEFs showed striking mode switching: some spread via fast bleb-driven expansion (α > 0.5), while others used slow, spiky filopodia (α < 0.5) to gain ECM substrate access. This indicates that HYAL2 loss alters the mechanical strategies cells employ, pushing them into less efficient or unstable spreading modes. In the HA brush assay, wild-type MEFs adhered more efficiently (∼60% by 1 h) than HYAL2 –/– (∼20%) or EIPA-treated (∼30%) cells, though all conditions eventually converged to ∼85% by 8 h. Importantly, inhibition of Na + /H + exchangers with EIPA phenocopied the HYAL2 –/– phenotype, supporting a model where HYAL2 colocalizes with proton pumps and CD44 to create localized acidic microdomains that enable HA digestion. These results resolve the controversy over HYAL2 function, establish that HYAL2 can act at the cell surface under physiological conditions, and reveal a mechanistic link between glycocalyx turnover, local pH regulation, and the physical strategies cells employ to overcome pericellular barriers to achieve cell adhesion.