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Central nervous system (CNS) injury transforms naive astrocytes into reactive astrocytes, which eventually become scar-forming astrocytes that can impair axonal regeneration and functional recovery. This sequential phenotypic change, known as reactive astrogliosis, has long been considered unidirectional and irreversible. However, we report here that reactive astrocytes isolated from injured spinal cord reverted in retrograde to naive astrocytes when transplanted into a naive spinal cord, whereas they formed astrocytic scars when transplanted into injured spinal cord, indicating the environment-dependent plasticity of reactive astrogliosis. We also found that type I collagen was highly expressed in the spinal cord during the scar-forming phase and induced astrocytic scar formation via the integrin-N-cadherin pathway. In a mouse model of spinal cord injury, pharmacological blockade of reactive astrocyte-type I collagen interaction prevented astrocytic scar formation, thereby leading to improved axonal regrowth and better functional outcomes. Our findings reveal environmental cues regulating astrocytic fate decisions, thereby providing a potential therapeutic target for CNS injury.

Metastatic seeding by disseminated cancer cells principally occurs in perivascular niches. Here, we show that mechanotransduction signalling triggered by the pericyte-like spreading of disseminated cancer cells on host tissue capillaries is critical for metastatic colonization. Disseminated cancer cells employ L1CAM (cell adhesion molecule L1) to spread on capillaries and activate the mechanotransduction effectors YAP (Yes-associated protein) and MRTF (myocardin-related transcription factor). This spreading is robust enough to displace resident pericytes, which also use L1CAM for perivascular spreading. L1CAM activates YAP by engaging β integrin and ILK (integrin-linked kinase). L1CAM and YAP signalling enables the outgrowth of metastasis-initiating cells both immediately following their infiltration of target organs and after they exit from a period of latency. Our results identify an important step in the initiation of metastatic colonization, define its molecular constituents and provide an explanation for the widespread association of L1CAM with metastatic relapse in the clinic.

A robust nanopillar platform with increased spatial resolution reveals that perinuclear forces, originating from stress fibres spanning the nucleus of fibroblasts, are significantly higher on these nanostructured substrates than the forces acting on peripheral adhesions. Many perinuclear adhesions embrace several nanopillars at once, pulling them into β1-integrin- and zyxin-rich clusters, which are able to translocate in the direction of cell motion without losing their tensile strength. The high perinuclear forces are greatly reduced upon inhibition of cell contractility or actin polymerization and disruption of the actin cap by KASH dominant-negative mutant expression. LMNA null fibroblasts have higher peripheral versus perinuclear forces, impaired perinuclear β -integrin recruitment, as well as YAP nuclear translocation, functional alterations that can be rescued by lamin A expression. These highly tensed actin-cap fibres are required for YAP nuclear signalling and thus play far more important roles in sensing nanotopographies and mechanochemical signal conversion than previously thought.

Cell migration is a stepwise process that coordinates multiple molecular machineries. Using in vitro angiogenesis screens with short interfering RNA and chemical inhibitors, we define here a MAP4K4-moesin-talin-β1-integrin molecular pathway that promotes efficient plasma membrane retraction during endothelial cell migration. Loss of MAP4K4 decreased membrane dynamics, slowed endothelial cell migration, and impaired angiogenesis in vitro and in vivo. In migrating endothelial cells, MAP4K4 phosphorylates moesin in retracting membranes at sites of focal adhesion disassembly. Epistasis analyses indicated that moesin functions downstream of MAP4K4 to inactivate integrin by competing with talin for binding to β1-integrin intracellular domain. Consequently, loss of moesin (encoded by the MSN gene) or MAP4K4 reduced adhesion disassembly rate in endothelial cells. Additionally, α5β1-integrin blockade reversed the membrane retraction defects associated with loss of Map4k4 in vitro and in vivo. Our study uncovers a novel aspect of endothelial cell migration. Finally, loss of MAP4K4 function suppressed pathological angiogenesis in disease models, identifying MAP4K4 as a potential therapeutic target.

Focal adhesions are mechanosensitive elements that enable mechanical communication between cells and the extracellular matrix. Here, we demonstrate a major mechanosensitive pathway in which α-actinin triggers adhesion maturation by linking integrins to actin in nascent adhesions. We show that depletion of the focal adhesion protein α-actinin enhances force generation in initial adhesions on fibronectin, but impairs mechanotransduction in a subsequent step, preventing adhesion maturation. Expression of an α-actinin fragment containing the integrin binding domain, however, dramatically reduces force generation in depleted cells. This behavior can be explained by a competition between talin (which mediates initial adhesion and force generation) and α-actinin for integrin binding. Indeed, we show in an in vitro assay that talin and α-actinin compete for binding to β ₃ integrins, but cooperate in binding to β ₁ integrins. Consistently, we find opposite effects of α-actinin depletion and expression of mutants on substrates that bind β ₃ integrins (fibronectin and vitronectin) versus substrates that only bind β ₁ integrins (collagen). We thus suggest that nascent adhesions composed of β ₃ integrins are initially linked to the actin cytoskeleton by talin, and then α-actinin competes with talin to bind β ₃ integrins. Force transmitted through α-actinin then triggers adhesion maturation. Once adhesions have matured, α-actinin recruitment correlates with force generation, suggesting that α-actinin is the main link transmitting force between integrins and the cytoskeleton in mature adhesions. Such a multistep process enables cells to adjust forces on matrices, unveiling a role of α-actinin that is different from its well-studied function as an actin cross-linker.

Uncoupling protein 1 (UCP1) is highly expressed in brown adipose tissue, where it generates heat by uncoupling electron transport from ATP production. UCP1 is also found outside classical brown adipose tissue depots, in adipocytes that are termed 'brite' (brown-in-white) or 'beige'. In humans, the presence of brite or beige (brite/beige) adipocytes is correlated with a lean, metabolically healthy phenotype, but whether a causal relationship exists is not clear. Here we report that human brite/beige adipocyte progenitors proliferate in response to pro-angiogenic factors, in association with expanding capillary networks. Adipocytes formed from these progenitors transform in response to adenylate cyclase activation from being UCP1 negative to being UCP1 positive, which is a defining feature of the beige/brite phenotype, while displaying uncoupled respiration. When implanted into normal chow-fed, or into high-fat diet (HFD)-fed, glucose-intolerant NOD-scid IL2rg(null) (NSG) mice, brite/beige adipocytes activated in vitro enhance systemic glucose tolerance. These adipocytes express neuroendocrine and secreted factors, including the pro-protein convertase PCSK1, which is strongly associated with human obesity. Pro-angiogenic conditions therefore drive the proliferation of human beige/brite adipocyte progenitors, and activated beige/brite adipocytes can affect systemic glucose homeostasis, potentially through a neuroendocrine mechanism.

Angiopoietins regulate vascular homeostasis via the endothelial Tie receptor tyrosine kinases. Angiopoietin-1 (Ang1) supports endothelial stabilization via Tie2 activation. Angiopoietin-2 (Ang2) functions as a context-dependent Tie2 agonist/antagonist promoting pathological angiogenesis, vascular permeability and inflammation. Elucidating Ang2-dependent mechanisms of vascular destablization is critical for rational design of angiopoietin antagonists that have demonstrated therapeutic efficacy in cancer trials. Here, we report that Ang2, but not Ang1, activates β1-integrin, leading to endothelial destablization. Autocrine Ang2 signalling upon Tie2 silencing, or in Ang2 transgenic mice, promotes β1-integrin-positive elongated matrix adhesions and actin stress fibres, regulating vascular endothelial-cadherin-containing cell-cell junctions. The Tie2-silenced monolayer integrity is rescued by β1-integrin, phosphoinositide-3 kinase or Rho kinase inhibition, and by re-expression of a membrane-bound Tie2 ectodomain. Furthermore, Tie2 silencing increases, whereas Ang2 blocking inhibits transendothelial tumour cell migration in vitro. These results establish Ang2-mediated β1-integrin activation as a promoter of endothelial destablization, explaining the controversial vascular functions of Ang1 and Ang2.

How different integrins that bind to the same type of extracellular matrix protein mediate specific functions is unclear. We report the functional analysis of β1- and αv-class integrins expressed in pan-integrin-null fibroblasts seeded on fibronectin. Reconstitution with β1-class integrins promotes myosin-II-independent formation of small peripheral adhesions and cell protrusions, whereas expression of αv-class integrins induces the formation of large focal adhesions. Co-expression of both integrin classes leads to full myosin activation and traction-force development on stiff fibronectin-coated substrates, with αv-class integrins accumulating in adhesion areas exposed to high traction forces. Quantitative proteomics linked αv-class integrins to a GEF-H1-RhoA pathway coupled to the formin mDia1 but not myosin II, and α5β1 integrins to a RhoA-Rock-myosin II pathway. Our study assigns specific functions to distinct fibronectin-binding integrins, demonstrating that α5β1integrins accomplish force generation, whereas αv-class integrins mediate the structural adaptations to forces, which cooperatively enable cells to sense the rigidity of fibronectin-based microenvironments.

Integrin-containing focal adhesions transmit extracellular signals across the plasma membrane to modulate cell adhesion, signalling and survival. Although integrins are known to undergo continuous endo/exocytic traffic, the potential impact of endocytic traffic on integrin-induced signals is unknown. Here, we demonstrate that integrin signalling is not restricted to cell-ECM adhesions and identify an endosomal signalling platform that supports integrin signalling away from the plasma membrane. We show that active focal adhesion kinase (FAK), an established marker of integrin-ECM downstream signalling, localizes with active integrins on endosomes. Integrin endocytosis positively regulates adhesion-induced FAK activation, which is early endosome antigen-1 and small GTPase Rab21 dependent. FAK binds directly to purified endosomes and becomes activated on them, suggesting a role for endocytosis in enhancing distinct integrin downstream signalling events. Finally, endosomal integrin signalling contributes to cancer-related processes such as anoikis resistance, anchorage independence and metastasis.

Tumor metastasis is a hallmark of cancer. Metastatic cancer cells often reside in distal tissues and organs in their dormant state. Mechanisms underlying the pre-metastatic niche formation are poorly understood. Here we show that in a colorectal cancer (CRC) model, primary tumors release integrin beta-like 1 (ITGBL1)-rich extracellular vesicles (EVs) to the circulation to activate resident fibroblasts in remote organs. The activated fibroblasts induce the pre-metastatic niche formation and promote metastatic cancer growth by secreting pro-inflammatory cytokine, such as IL-6 and IL-8. Mechanistically, the primary CRC-derived ITGBL1-enriched EVs stimulate the TNFAIP3-mediated NF-κB signaling pathway to activate fibroblasts. Consequently, the activated fibroblasts produce high levels of pro-inflammatory cytokines to promote metastatic cancer growth. These findings uncover a tumor-stromal interaction in the metastatic tumor microenvironment and an intimate signaling communication between primary tumors and metastases through the ITGBL1-loaded EVs. Targeting the EVs-ITGBL1-CAFs-TNFAIP3-NF-κB signaling axis provides an attractive approach for treating metastatic diseases.