Skin capillary endothelial cells form a network of spatiotemporally conserved Ca2+ activity

Ca2+ signaling and its regulation are important for endothelial cell (EC) functions, including local blood flow control, mechanotransduction, and barrier function. Yet the spatiotemporal organization of Ca2+ activity and its regulation across a vascular plexus is poorly understood in an in vivo mammalian context, largely due to technical barriers. To overcome this gap in knowledge, we developed an approach to resolve Ca2+ activity with single cell resolution in the skin vasculature of live adult mice by multi-photon imaging. Here, we tracked thousands of Ca2+ events in the skin capillary plexus during homeostasis and observed signaling heterogeneity between ECs, with just over half displaying Ca2+ activity over minutes. Longitudinal tracking of the same mice revealed that the same ECs maintain Ca2+ activity over days to weeks. Interestingly, activity dynamics, such as frequency and event duration, are not conserved at a single cell level but at an EC population level. To identify the molecular underpinning of this spatiotemporal Ca2+ activity, we conditionally deleted in ECs the most expressed gap junction protein - Connexin 43 (Cx43). We found that loss of Cx43 initially causes a subset of ECs to display sustained Ca2+ activity and biases the dynamics of the whole network towards chronically persistent activity over time. Lastly, through pharmacological targeting of a small panel of known Ca2+ mediators, we showed that inhibition of L-type Voltage Gated Ca2+ channels largely restores physiological Ca2+ activity after loss of Cx43, but has no effect on signaling dynamics in homeostatic settings. Significance StatementCa2+ signaling in mammalian endothelial cells (ECs) locally regulates blood flow, force sensing, and vessel permeability. In periods of vascular development and repair, there is a need for large-scale coordination in each of those functions. To understand what mechanisms drive collective Ca2+ activity during vascular remodeling, we must first address the open question of how tissue-level Ca2+ is spatiotemporally organized and regulated during homeostasis. Intravital imaging in skin vasculature of live mice reveals that a conserved set of cells orchestrates tissue-wide Ca2+ from minutes to days to weeks. How this network maintains itself over time requires long-range communication through a gap junction protein, Connexin 43 (Cx43). Cx43 dysregulation subsequently recruits L-type Voltage Gated Ca2+ channels to reshape the EC Ca2+ landscape.