Contact sites of endoplasmic reticulum (ER) and mitochondria locally convey calcium signals between the IP 3 receptors (IP3R) and the mitochondrial calcium uniporter, and are central to cell survival. It remains unclear whether IP3Rs also have a structural role in contact formation and whether the different IP3R isoforms have redundant functions. Using an IP3R-deficient cell model rescued with each of the three IP3R isoforms and an array of super-resolution and ultrastructural approaches we demonstrate that IP3Rs are required for maintaining ER-mitochondrial contacts. This role is independent of calcium fluxes. We also show that, while each isoform can support contacts, type 2 IP3R is the most effective in delivering calcium to the mitochondria. Thus, these studies reveal a non-canonical, structural role for the IP3Rs and direct attention towards the type 2 IP3R that was previously neglected in the context of ER-mitochondrial calcium signaling.

Endoplasmic reticulum-mitochondria contacts (ERMCs) are restructured in response to changes in cell state. While this restructuring has been implicated as a cause or consequence of pathology in numerous systems, the underlying molecular dynamics are poorly understood. Here, we show means to visualize the capture of motile IP3 receptors (IP3Rs) at ERMCs and document the immediate consequences for calcium signaling and metabolism. IP3Rs are of particular interest because their presence provides a scaffold for ERMCs that mediate local calcium signaling, and their function outside of ERMCs depends on their motility. Unexpectedly, in a cell model with little ERMC Ca2+ coupling, IP3Rs captured at mitochondria promptly mediate Ca2+ transfer, stimulating mitochondrial oxidative metabolism. The Ca2+ transfer does not require linkage with a pore-forming protein in the outer mitochondrial membrane. Thus, motile IP3Rs can traffic in and out of ERMCs, and, when ‘parked’, mediate calcium signal propagation to the mitochondria, creating a dynamic arrangement that supports local communication.

No abstract

Resistance arteries and arterioles evolved as specialized blood vessels serving two important functions: ( a) regulating peripheral vascular resistance and blood pressure and ( b) matching oxygen and nutrient delivery to metabolic demands of organs. These functions require control of vessel lumen cross-sectional area (vascular tone) via coordinated vascular cell responses governed by precise spatial-temporal communication between intracellular signaling pathways. Herein, we provide a contemporary overview of the significant roles that redox switches play in calcium signaling for orchestrated endothelial, smooth muscle, and red blood cell control of arterial vascular tone. Three interrelated themes are the focus: ( a) smooth muscle to endothelial communication for vasoconstriction, ( b) endothelial to smooth muscle cell cross talk for vasodilation, and ( c) oxygen and red blood cell interregulation of vascular tone and blood flow. We intend for this thematic framework to highlight gaps in our current knowledge and potentially spark interest for cross-disciplinary studies moving forward.

mechanism, specifically human NaDC3. With~30% identity between the vcINDY and hNaDC3, we hypothesized that a similar mechanism could be responsible for the functioning of hNADC3. Homology modeling with vcINDY suggested that several pairs of residues are brought into proximity upon substrate translocation. We prepared a series of double mutants introducing cysteines at positions predicted to be brought together in the outward-facing state of the protein and expressed them in Xenopus laevis oocytes. Using two-electrode voltage clamp and disulfide crosslinking, we investigated whether inhibition of transport activity observed upon formation of disulfides is consistent with the proposed mechanism of transport.