HYALURONAN DEPLETION DISRUPTS EXTRACELLULAR MATRIX INTEGRITY AND REVERSIBLY ALTERS GLIAL–VASCULAR INTERACTIONS IN THE ADULT RAT CORTEX

Hyaluronan (HA) is the principal backbone of the brain extracellular matrix (ECM), yet its physiological modulation in the adult cortex remains poorly understood. Here we asked how reversible inhibition of HA synthesis affects extracellular space properties, glial morphology and cerebrovascular organisation in healthy adult rats. Female Wistar rats received a 4‑methylumbelliferone (4‑MU; 2.5% w/w) supplemented diet or control chow for 10 weeks, with an additional 10‑week washout subgroup. We performed quantitative confocal morphometry of perineuronal nets (PNNs), astrocytes, microglia and cortical microvasculature.
4‑MU treatment significantly reduced Wisteria floribunda agglutinin labelled PNN intensity and compacted single‑net architecture, and these changes fully reversed after washout. Microglia shifted toward a more highly ramified, homeostatic morphology with increased cell area, branching, junction number and fractal dimension, which returned to baseline after recovery. Vascular network analysis showed increased cortical capillary length, surface area, area fraction and branching complexity in 4‑MU treated animals, consistent with angiogenic remodelling; these effects were lost after washout.
These data indicate that pharmacological HA depletion can reversibly reorganise ECM geometry, microglial state and microvascular topology without disruption of astrocytic polarity or impairment of blood–brain barrier integrity. HA dynamics therefore act as an important regulator of neuro‑glial‑vascular coupling and provide a useful handle to probe ECM‑driven plasticity in the adult brain.
This work was supported by JPND WesternND, APVV‑23‑0436 and VEGA 2/0158/25.