Distinct Ca2+signatures of leptomeningeal fibroblast subgroups in awake mouse brains in health and inflammation

The leptomeninges, composed of the arachnoid mater, and pia mater, contains distinct subgroups of fibroblasts that differ in location and transcriptomic profiles. These fibroblasts contribute to the blood–cerebrospinal fluid barrier under physiological conditions, participate in fibrosis, and support blood–brain barrier integrity during injury and disease. However, their Ca 2+ signaling profiles and underlying mechanisms in health and disease remain poorly understood. In this study, we divided leptomeningeal fibroblasts into three subgroups based on their locations: arachnoid fibroblasts, pia mater fibroblasts and perivascular fibroblasts. We employed two-photon microscopy in awake transgenic mice expressing Ca²⁺ indicators in leptomeningeal fibroblasts to investigate spontaneous and behaviorally evoked Ca²⁺ transients across different fibroblast subgroups. We found that each subgroup exhibits a distinct Ca²⁺ activity profile, with pia mater fibroblasts showing the highest-amplitude Ca²⁺ transients. Moreover, these fibroblasts displayed unique responses to both whisker air-puff stimulation and locomotion. We further demonstrated, using a chronically implanted cannula beneath the cranial window, that locomotion-associated vasodilation is followed by TRPV4 channel-mediated fibroblast Ca²⁺ elevations. Finally, systemic inflammation induced by lipopolysaccharide (LPS) reduced spontaneous Ca²⁺ transients in pia mater fibroblasts, likely due to macrophage infiltration following the inflammatory response. For the first time, this study characterizes spontaneous and behaviorally evoked Ca²⁺ dynamics in distinct leptomeningeal fibroblast subgroups in awake animals, providing novel insights into the functional roles of leptomeningeal fibroblasts in the healthy and diseased brain.