Endothelial CD2AP Binds the Receptor ICAM-1 To Control Mechanosignaling, Leukocyte Adhesion, and the Route of Leukocyte Diapedesis In Vitro

CD2AP is Co-Expressed with Tropomyosin-Related Kinase A and Ras-Related Protein Rab-5A in Cholinergic Neurons of the Murine Basal Forebrain

Basal forebrain cholinergic neurons project to the hippocampus and cortex, are critical for learning and memory, and are central to the pathogenesis of Alzheimer's disease (AD). GWAS have consistently shown that genomic variants at the CD2AP gene locus are associated with significant increased risk of AD. GWAS studies have also shown that genetic variants in endocytosis genes, including RAB5A , significantly increase susceptibility to AD. Previous work in our lab has shown that CD2AP functions as a docking-scaffold/adaptor protein as a coordinator of nerve growth factor (NGF) and trophic signaling in neurons. We have also demonstrated that CD2AP positively regulates Rab5-mediated mechanisms of endocytosis in primary sensory neurons. The purpose of this study was to perform an in vivo characterization of CD2AP expression in cholinergic neurons of the brain regions most relevant to AD pathogenesis and to investigate the colocalization of CD2AP and Rab5 in cholinergic neurons of the murine basal forebrain. Brain tissue was perfused, harvested from ChAT BAC -eGFP transgenic mice (N=4 male, N=4 female; aged 10 mo), where cholinergic neurons (co-) express green fluorescence protein (GFP) in central and peripheral neurons that express choline acetyltransferase (ChAT). Frozen tissue sections were used to assess the specificity of the reporter in mouse brain along with localization of both CD2AP and Rab5 (co-) expression using immunofluorescence (IF) analysis of ChAT-GFP+ neurons and primary antibodies against ChAT, CD2AP and Rab5. Image J software was used to develop and optimize a colocalization assay for CD2AP and Rab5 puncta. Experiments were repeated in a follow-up cohort of aged-adult mice (N=2 male, N=2 female; aged 18 mo). IF expression of CD2AP was quantified in the basal forebrain, diagonal band of Broca (vDB), and striatal regions and compared to results from the cortical regions of the adult mouse brain. Colocalization of CD2AP was observed in the cell bodies of ChAT-GFP+ neurons of the striatum, vDB and basal forebrain regions, where CD2AP expression intensity as well as the number of cell bodies with positive signal increased incrementally. Colocalization analyses revealed near-complete overlap of CD2AP and Rab5 expression in ChAT-GFP+ cholinergic neurons of the basal forebrain region. We conclude that cholinergic neurons express CD2AP in healthy adult and aged-adult mouse brains. These data provide the first evidence of quantifiable CD2AP protein expression of cholinergic neurons specific to the diagonal band of Broca (vDB) and basal forebrain. Together with previous research from our lab, these data support a role for CD2AP in the pathogenesis of AD through orchestration of endocytosis and retrograde signaling. Ongoing studies are underway to verify these findings in a novel AD mouse model that incorporates the humanized variant of CD2AP , created by MODEL-AD, where we aim to further investigate how CD2AP variants may affect mechanistic components of Rab5 endocytosis as well as subsequent survival of cholinergic neurons in the context of known amyloid beta and Tau pathologies.

D-2-hydroxyglutarate regulates human brain vascular endothelial cell proliferation and barrier function

Gain-of-function mutations in isocitrate dehydrogenase (IDH) genes result in excessive production of (D)-2-hydroxyglutarate (D-2HG) which intrinsically modifies tumor cell epigenetics and impacts surrounding noncancerous cells through nonepigenetic pathways. However, whether D-2HG has a paracrine effect on endothelial cells in the tumor microenvironment needs further clarification. We quantified microvessel density by immunohistochemistry using tissue sections from 60 high-grade astrocytic gliomas with or without IDH mutation. Microvessel density was found to be reduced in tumors carrying an IDH mutation. Ex vivo experiments showed that D-2HG inhibited endothelial cell migration, wound healing, and tube formation by suppressing cell proliferation but not viability, possibly through reduced activation of the mTOR/STAT3 pathway. Further, D-2HG reduced fluorescent dextran permeability and decreased paracellular T-cell transendothelial migration by augmenting expression of junctional proteins thereby collectively increasing endothelial barrier function. These results indicate that D-2HG may influence the tumor vascular microenvironment by reducing the intratumoral vasculature density and by inhibiting the transport of metabolites and extravasation of circulating cells into the astrocytoma microenvironment. These observations provide a rationale for combining IDH inhibition with antitumor immunological/angiogenic approaches and suggest a molecular basis for resistance to antiangiogenic drugs in patients whose tumors express a mutant IDH allele.

Ginsentide TP1 Protects Hypoxia-Induced Dysfunction and ER Stress-Linked Apoptosis

Hypoxia-induced vascular endothelial dysfunction (VED) is a significant contributor to several severe human diseases, including heart disease, stroke, dementia, and cancer. However, current treatment options for VED are limited due to the lack of understanding of the underlying disease mechanisms and therapeutic leads. We recently discovered a heat-stable microprotein in ginseng, called ginsentide TP1, that has been shown to reduce vascular dysfunction in cardiovascular disease models. In this study, we use a combination of functional assays and quantitative pulsed SILAC proteomics to identify new proteins synthesized in hypoxia and to show that ginsentide TP1 provides protection for human endothelial cells against hypoxia and ER stress. Consistent with the reported findings, we also found that hypoxia activates various pathways related to endothelium activation and monocyte adhesion, which in turn, impairs nitric oxide (NO) synthase activity, reduces the bioavailability of NO, and increases the production of reactive oxygen species that contribute to VED. Additionally, hypoxia triggers endoplasmic reticulum stress and initiates apoptotic signaling pathways associated with cardiovascular pathology. Treatment with ginsentide TP1 reduced surface adhesion molecule expression, prevented activation of the endothelium and leukocyte adhesion, restored protein hemostasis, and reduced ER stress to protect against hypoxia-induced cell death. Ginsentide TP1 also restored NO signaling and bioavailability, reduced oxidative stress, and protected endothelial cells from endothelium dysfunction. In conclusion, this study shows that the molecular pathogenesis of VED induced by hypoxia can be mitigated by treatment with ginsentide TP1, which could be one of the key bioactive compounds responsible for the "cure-all" effect of ginseng. This research may lead to the development of new therapies for cardiovascular disorders.

Circular RNA VMA21 ameliorates lung injury in septic rat via targeting microRNA-497-5p/CD2-associated protein axis

Sepsis was characterized via an acute inflammatory response to infection, often accompanying by multiple organ failure, particularly lung damage. Circular RNA (circRNA) played an important role in the pathology of a variety of diseases. However, the role of circRNA in sepsis-induced lung injury (LI) remained unknown. This study was to explore the expression and role of circVMA21 in sepsis LI and the possible molecular mechanism. The results manifested circVMA21 and CD2-associated protein (CD2AP) were down-regulated in lung tissue and lipopolysaccharide (LPS)-treated BEAS-2B, while microRNA (miR)-497-5p was up-regulated. A large number of deaths in rats after surgery of 72 h were caused via cecal ligation-perforation surgery, W/D value and Bax positive cells were increased, LI was caused, cell apoptosis, tumor necrosis factor-α, Interleukin (IL)-1β and IL-6 expression were promoted and Bcl-2 positive cells were decreased. Overexpression of circVMA21 ameliorated these phenomena. In addition, LPS-induced apoptosis and inflammation of BEAS-2B cells was improved via overexpression of circVMA21, while overexpression of miR-497-5P was opposite. Apoptosis, inflammation, and oxidative damage of BEAS-2B cells were aggravated via knockdown of circVMA21, but it was reversed by knockdown of miR-497-5p or overexpression of CD2AP. Mechanistically, CircVMA21 mediated CD2AP expression through competitive adsorption of miR-497-5p. In conclusion, this work showed circVMA21 improved LI in sepsis rats by targeting miR-497-5p/CD2AP axis, suggesting that circVMA21 may be a novel therapeutic target for sepsis-induced LI.

Research progress in immune microenvironment regulation of muscle atrophy induced by peripheral nerve injury

Denervated skeletal muscular atrophy is primarily characterized by loss of muscle strength and mass and an unideal functional recovery of the muscle after extended denervation. This review emphasizes the interaction between the immune system and the denervated skeletal muscle. Immune cells such as neutrophils, macrophages and T-cells are activated and migrate to denervated muscle, where they release a high concentration of cytokines and chemokines. The migration of these immune cells, the transformation of different functional immune cell subtypes, and the cytokine network in the immune microenvironment may be involved in the regulatory process of muscle atrophy or repair. However, the exact mechanisms of the interaction between these immune cells and immune molecules in skeletal muscles are unclear. In this paper, the immune microenvironment regulation of muscle atrophy induced by peripheral nerve injury is reviewed.

A Microfluidics-Based Screening Tool to Assess the Impact of Blood Plasma Factors on Microvascular Integrity

This study provides a method to assess the impact of circulating plasma factors on microvascular integrity by using a recently developed microvessel-on-a-chip platform featuring the human endothelium that is partly surrounded by the extracellular matrix. The system is high-throughput, which allows parallel analysis of organ-level microvessel pathophysiology, including vascular leakage. Ethylenediaminetetraacetic acid plasma samples are mixed with inhibitors for recalcification of the plasma samples to avoid activation of the coagulation- or complement system. Moreover, the assay is validated by spiking vascular endothelial growth factor, histamine, or tumor necrosis factor alpha to recalcified plasma and confirms their modulation of microvessel barrier function at physiologically relevant concentrations. Finally, this study shows that perfusing the microvessels with recalcified plasma samples of coronavirus disease-2019 patients, with a confirmed proinflammatory profile, results in markedly increased leakage of the microvessels. The assay provides opportunities for diagnostic screening of inflammatory or endothelial disrupting plasma factors associated with endothelial dysfunction.

From Metabolic Syndrome to Neurological Diseases: Role of Autophagy

Metabolic syndrome is not a single pathology, but a constellation of cardiovascular disease risk factors including: central and abdominal obesity, systemic hypertension, insulin resistance (or type 2 diabetes mellitus), and atherogenic dyslipidemia. The global incidence of Metabolic syndrome is estimated to be about one quarter of the world population; for this reason, it would be desirable to better understand the underlying mechanisms involved in order to develop treatments that can reduce or eliminate the damage caused. The effects of Metabolic syndrome are multiple and wide ranging; some of which have an impact on the central nervous system and cause neurological and neurodegenerative diseases. Autophagy is a catabolic intracellular process, essential for the recycling of cytoplasmic materials and for the degradation of damaged cellular organelle. Therefore, autophagy is primarily a cytoprotective mechanism; even if excessive cellular degradation can be detrimental. To date, it is known that systemic autophagic insufficiency is able to cause metabolic balance deterioration and facilitate the onset of metabolic syndrome. This review aims to highlight the current state of knowledge regarding the connection between metabolic syndrome and the onset of several neurological diseases related to it. Furthermore, since autophagy has been found to be of particular importance in metabolic disorders, the probable involvement of this degradative process is assumed to be responsible for the attenuation of neurological disorders resulting from metabolic syndrome.

Endothelial Responses in Sepsis

Endothelial cells (ECs) are vascular, nonconventional immune cells that play a major role in the systemic response after bacterial infection to limit its dissemination. Triggered by exposure to pathogens, microbial toxins, or endogenous danger signals, EC responses are polymorphous, heterogeneous, and multifaceted. During sepsis, ECs shift toward a proapoptotic, proinflammatory, proadhesive, and procoagulant phenotype. In addition, glycocalyx damage and vascular tone dysfunction impair microcirculatory blood flow, leading to organ injury and, potentially, life-threatening organ failure. This review aims to cover the current understanding of the EC adaptive or maladaptive response to acute inflammation or bacterial infection based on compelling recent basic research and therapeutic clinical trials targeting microvascular and endothelial alterations during septic shock.

Molecular cloning, characterization and expression profiles of CD2AP in Nile tilapia (Oreochromis niloticus) responding to Streptococcus agalactiae infection and interaction with CD2 cytoplasmic segment

The interaction between CD2-associated protein (CD2AP) and CD2 plays a vital role in lymphocyte adhesion and T cells activation in mammals. In this study, a CD2AP gene (GenBank accession number: MK579862; designated as On-CD2AP) was identified from tilapia (Oreochromis niloticus). Sequence analysis showed that On-CD2AP protein shares high similarity with mammals, including three Src homology 3 (SH3) domains, a section of poly proline motif and a coiled coil region. Transcription levels of On-CD2AP were detected in nine tissues of healthy Nile tilapia, and the highest expression levels were detected in the spleen and gill. On-CD2AP were significantly up-regulated in thymus, head kidney and brain after infected by Streptococcus agalactiae, as well as in head kidney leukocytes (HKLs) with LPS and LTA stimulation. Moreover, a section conserved pro-rich motif that are responsible for binding of CD2 to CD2AP were found in the CD2 cytoplasmic sequence of Nile tilapia (On-CD2C). A weak interaction between On-CD2AP and On-CD2C was proved by yeast two-hybrid assay. In addition, the recombinant proteins of CD2AP-His (rOn-CD2AP-His) and GST-CD2C (GST-rOn-CD2C) were obtained through prokaryotic expression system. His pull-down assay showed that rOn-CD2AP-His and GST-rOn-CD2C could bind to each other. These findings indicate that CD2AP is crucial in immune response during S.agalactiae infection, and the mechanism of interaction between CD2AP and CD2 is conservative in Nile tilapia.

The role of endothelial MERTK during the inflammatory response in lungs

As a key homeostasis regulator in mammals, the MERTK receptor tyrosine kinase is crucial for efferocytosis, a process that requires remodeling of the cell membrane and adjacent actin cytoskeleton. Membrane and cytoskeletal reorganization also occur in endothelial cells during inflammation, particularly during neutrophil transendothelial migration (TEM) and during changes in permeability. However, MERTK’s function in endothelial cells remains unclear. This study evaluated the contribution of endothelial MERTK to neutrophil TEM and endothelial barrier function. In vitro experiments using primary human pulmonary microvascular endothelial cells found that neutrophil TEM across the endothelial monolayers was enhanced when MERTK expression in endothelial cells was reduced by siRNA knockdown. Examination of endothelial barrier function revealed increased passage of dextran across the MERTK-depleted monolayers, suggesting that MERTK helps maintain endothelial barrier function. MERTK knockdown also altered adherens junction structure, decreased junction protein levels, and reduced basal Rac1 activity in endothelial cells, providing potential mechanisms of how MERTK regulates endothelial barrier function. To study MERTK’s function in vivo, inflammation in the lungs of global Mertk^-/- mice was examined during acute pneumonia. In response to P. aeruginosa, more neutrophils were recruited to the lungs of Mertk^-/- than wildtype mice. Vascular leakage of Evans blue dye into the lung tissue was also greater in Mertk^-/- mice. To analyze endothelial MERTK’s involvement in these processes, we generated inducible endothelial cell-specific (iEC) Mertk^-/- mice. When similarly challenged with P. aeruginosa, iEC Mertk^-/- mice demonstrated no difference in neutrophil TEM into the inflamed lungs or in vascular permeability compared to control mice. These results suggest that deletion of MERTK in human pulmonary microvascular endothelial cells in vitro and in all cells in vivo aggravates the inflammatory response. However, selective MERTK deletion in endothelial cells in vivo failed to replicate this response.

Endo-lysosomal dysregulations and late-onset Alzheimer's disease: impact of genetic risk factors

Increasing evidence supports that cellular dysregulations in the degradative routes contribute to the initiation and progression of neurodegenerative diseases, including Alzheimer's disease. Autophagy and endolysosomal homeostasis need to be maintained throughout life as they are major cellular mechanisms involved in both the production of toxic amyloid peptides and the clearance of misfolded or aggregated proteins. As such, alterations in endolysosomal and autophagic flux, as a measure of degradation activity in these routes or compartments, may directly impact as well on disease-related mechanisms such as amyloid-β clearance through the blood-brain-barrier and the interneuronal spreading of amyloid-β and/or Tau seeds, affecting synaptic function, plasticity and metabolism. The emerging of several genetic risk factors for late-onset Alzheimer's disease that are functionally related to endocytic transport regulation, including cholesterol metabolism and clearance, supports the notion that in particular the autophagy/lysosomal flux might become more vulnerable during ageing thereby contributing to disease onset. In this review we discuss our current knowledge of the risk genes APOE4, BIN1, CD2AP, PICALM, PLD3 and TREM2 and their impact on endolysosomal (dys)regulations in the light of late-onset Alzheimer's disease pathology.

Neutrophil transendothelial migration: updates and new perspectives

Neutrophils represent the first line of cellular defense against invading microorganism by rapidly moving across the blood-endothelial cell (EC) barrier and exerting effector cell functions. The neutrophil recruitment cascade to inflamed tissues involves elements of neutrophil rolling, firm adhesion, and crawling onto the EC surface before extravasating by breaching the EC barrier. The interaction between neutrophils and ECs occurs via various adhesive modules and is a critical event determining the mode of neutrophil transmigration, either at the EC junction (paracellular) or directly through the EC body (transcellular). Once thought to be a homogenous entity, new evidence clearly points to the plasticity of neutrophil functions. This review will focus on recent advances in our understanding of the mechanism of the neutrophil transmigration process. It will discuss how neutrophil-EC interactions and the subsequent mode of diapedesis, junctional or nonjunctional, can be context dependent and how this plasticity may be exploited clinically.

Genetic Risk Factors for Alzheimer Disease: Emerging Roles of Microglia in Disease Pathomechanisms

The accumulation of aggregated amyloid β (Aβ) peptides in the brain is deeply involved in Alzheimer disease (AD) pathogenesis. Mutations in APP and presenilins play major roles in Aβ pathology in rare autosomal-dominant forms of AD, whereas pathomechanisms of sporadic AD, accounting for the majority of cases, remain unknown. In this chapter, we review current knowledge on genetic risk factors of AD, clarified by recent advances in genome analysis technology. Interestingly, TREM2 and many genes associated with disease risk are predominantly expressed in microglia, suggesting that these risk factors are involved in pathogenicity through common mechanisms involving microglia. Therefore, we focus on factors closely associated with microglia and discuss their possible roles in pathomechanisms of AD. Furthermore, we review current views on the pathological roles of microglia and emphasize the importance of microglial changes in response to Aβ deposition and mechanisms underlying the phenotypic changes. Importantly, functional outcomes of microglial activation can be both protective and deleterious to neurons. We further describe the involvement of microglia in tau pathology and the activation of other glial cells. Through these topics, we shed light on microglia as a promising target for drug development for AD and other neurological disorders.

BioID identifies proteins involved in the cell biology of caveolae

The mechanisms controlling the abundance and sub-cellular distribution of caveolae are not well described. A first step towards determining such mechanisms would be identification of relevant proteins that interact with known components of caveolae. Here, we applied proximity biotinylation (BioID) to identify a list of proteins that may interact with the caveolar protein cavin1. Screening of these candidates using siRNA to reduce their expression revealed that one of them, CSDE1, regulates the levels of mRNAs and protein expression for multiple components of caveolae. A second candidate, CD2AP, co-precipitated with cavin1. Caveolar proteins were observed in characteristic and previously un-described linear arrays adjacent to cell-cell junctions in both MDCK cells, and in HeLa cells overexpressing an active form of the small GTPase Rac1. CD2AP was required for the recruitment of caveolar proteins to these linear arrays. We conclude that BioID will be useful in identification of new proteins involved in the cell biology of caveolae, and that interaction between CD2AP and cavin1 may have an important role in regulating the sub-cellular distribution of caveolae.