PIEZO1 and PECAM1 interact at cell-cell junctions and partner in endothelial force sensing

Two prominent concepts for the sensing of shear stress by endothelium are the PIEZO1 channel as a mediator of mechanically activated calcium ion entry and the PECAM1 cell adhesion molecule as the apex of a triad with CDH5 and VGFR2. Here, we investigated if there is a relationship. By inserting a non-disruptive tag in native PIEZO1 of mice, we reveal in situ overlap of PIEZO1 with PECAM1. Through reconstitution and high resolution microscopy studies we show that PECAM1 interacts with PIEZO1 and directs it to cell-cell junctions. PECAM1 extracellular N-terminus is critical in this, but a C-terminal intracellular domain linked to shear stress also contributes. CDH5 similarly drives PIEZO1 to junctions but unlike PECAM1 its interaction with PIEZO1 is dynamic, increasing with shear stress. PIEZO1 does not interact with VGFR2. PIEZO1 is required in Ca2+-dependent formation of adherens junctions and associated cytoskeleton, consistent with it conferring force-dependent Ca2+ entry for junctional remodelling. The data suggest a pool of PIEZO1 at cell junctions, the coming together of PIEZO1 and PECAM1 mechanisms and intimate cooperation of PIEZO1 and adhesion molecules in tailoring junctional structure to mechanical requirement.

Global PIEZO1 Gain-of-Function Mutation Causes Cardiac Hypertrophy and Fibrosis in Mice

PIEZO1 is a subunit of mechanically-activated, nonselective cation channels. Gain-of-function PIEZO1 mutations are associated with dehydrated hereditary stomatocytosis (DHS), a type of anaemia, due to abnormal red blood cell function. Here, we hypothesised additional effects on the heart. Consistent with this hypothesis, mice engineered to contain the M2241R mutation in PIEZO1 to mimic a DHS mutation had increased cardiac mass and interventricular septum thickness at 8–12 weeks of age, without altered cardiac contractility. Myocyte size was greater and there was increased expression of genes associated with cardiac hypertrophy (Anp, Acta1 and β-MHC). There was also cardiac fibrosis, increased expression of Col3a1 (a gene associated with fibrosis) and increased responses of isolated cardiac fibroblasts to PIEZO1 agonism. The data suggest detrimental effects of excess PIEZO1 activity on the heart, mediated in part by amplified PIEZO1 function in cardiac fibroblasts.

Endothelial Piezo1 sustains muscle capillary density and contributes to physical activity

Piezo1 forms mechanically activated nonselective cation channels that contribute to endothelial response to fluid flow. Here we reveal an important role in the control of capillary density. Conditional endothelial cell-specific deletion of Piezo1 in adult mice depressed physical performance. Muscle microvascular endothelial cell apoptosis and capillary rarefaction were evident and sufficient to account for the effect on performance. There was selective upregulation of thrombospondin-2 (TSP2), an inducer of endothelial cell apoptosis, with no effect on TSP1, a related important player in muscle physiology. TSP2 was poorly expressed in muscle endothelial cells but robustly expressed in muscle pericytes, in which nitric oxide (NO) repressed the Tsp2 gene without an effect on Tsp1. In endothelial cells, Piezo1 was required for normal expression of endothelial NO synthase. The data suggest an endothelial cell-pericyte partnership of muscle in which endothelial Piezo1 senses blood flow to sustain capillary density and thereby maintain physical capability.

DogCatcher allows loop-friendly protein-protein ligation

There are many efficient ways to connect proteins at termini. However, connecting at a loop is difficult because of lower flexibility and variable environment. Here, we have developed DogCatcher, a protein that forms a spontaneous isopeptide bond with DogTag peptide. DogTag/DogCatcher was generated initially by splitting a Streptococcus pneumoniae adhesin. We optimized DogTag/DogCatcher through rational design and evolution, increasing reaction rate by 250-fold and establishing millimolar solubility of DogCatcher. When fused to a protein terminus, DogTag/DogCatcher reacts slower than SpyTag003/SpyCatcher003. However, inserted in loops of a fluorescent protein or enzyme, DogTag reacts much faster than SpyTag003. Like many membrane proteins, the ion channel TRPC5 has no surface-exposed termini. DogTag in a TRPC5 extracellular loop allowed normal calcium flux and specific covalent labeling on cells in 1 min. DogTag/DogCatcher reacts under diverse conditions, at nanomolar concentrations, and to 98% conversion. Loop-friendly ligation should expand the toolbox for creating protein architectures.

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Spontaneous transamidation at internal sites harnessing a DogTag/DogCatcher pair

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DogCatcher is designed and bred for high solubility and rapid reaction

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Within protein loops DogTag can clamp on its partner faster than SpyTag003

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Fast and faithful fluorescent labeling of an ion channel at the cell surface via DogTag

Kv1.3 voltage-gated potassium channels link cellular respiration to proliferation through a non-conducting mechanism

Cellular energy metabolism is fundamental for all biological functions. Cellular proliferation requires extensive metabolic reprogramming and has a high energy demand. The Kv1.3 voltage-gated potassium channel drives cellular proliferation. Kv1.3 channels localise to mitochondria. Using high-resolution respirometry, we show Kv1.3 channels increase oxidative phosphorylation, independently of redox balance, mitochondrial membrane potential or calcium signalling. Kv1.3-induced respiration increased reactive oxygen species production. Reducing reactive oxygen concentrations inhibited Kv1.3-induced proliferation. Selective Kv1.3 mutation identified that channel-induced respiration required an intact voltage sensor and C-terminal ERK1/2 phosphorylation site, but is channel pore independent. We show Kv1.3 channels regulate respiration through a non-conducting mechanism to generate reactive oxygen species which drive proliferation. This study identifies a Kv1.3-mediated mechanism underlying the metabolic regulation of proliferation, which may provide a therapeutic target for diseases characterised by dysfunctional proliferation and cell growth.

Xanthine-based photoaffinity probes allow assessment of ligand engagement by TRPC5 channels

Diazirine-containing photoaffinity probes, based on the potent and selective TRPC1/4/5 channel inhibitor Pico145, allowed the development of an assay to probe cellular interactions between TRPC5 protein and xanthine-based TRPC5 channel modulators.

KHS101 disrupts energy metabolism in human glioblastoma cells and reduces tumor growth in mice

Pharmacological inhibition of uncontrolled cell growth with small-molecule inhibitors is a potential strategy for treating glioblastoma multiforme (GBM), the most malignant primary brain cancer. We showed that the synthetic small-molecule KHS101 promoted tumor cell death in diverse GBM cell models, independent of their tumor subtype, and without affecting the viability of noncancerous brain cell lines. KHS101 exerted cytotoxic effects by disrupting the mitochondrial chaperone heat shock protein family D member 1 (HSPD1). In GBM cells, KHS101 promoted aggregation of proteins regulating mitochondrial integrity and energy metabolism. Mitochondrial bioenergetic capacity and glycolytic activity were selectively impaired in KHS101-treated GBM cells. In two intracranial patient-derived xenograft tumor models in mice, systemic administration of KHS101 reduced tumor growth and increased survival without discernible side effects. These findings suggest that targeting of HSPD1-dependent metabolic pathways might be an effective strategy for treating GBM.