Junction Assembly Research Articles

Myosin chaperone, UNC‐45A, is a novel regulator of intestinal epithelial barrier integrity and repair

The intestinal epithelium creates a protective barrier separating the luminal content and the immune system in the gut. Leakiness of the intestinal epithelial barrier and inefficient healing of mucosal wounds represent common manifestations of inflammatory bowel diseases (IBD). Integrity of the gut barrier is mediated by different adhesive structures, including adherens junctions (AJ), tight junctions (TJ) and focal adhesion (FA). Functions of these adhesive structures depend on their association with the cortical actin cytoskeleton and particularly, to a major actin motor protein, non‐muscle myosin II (NM‐II). While biochemical mechanisms that regulate activity of NM‐II in epithelial cells have been extensively investigated, little is known about assembly of the contractile myosin structures at the epithelial adhesion sites. In this study, we focused on UNC‐45A, a cytoskeletal chaperone that is essential for proper folding of NM‐II heavy chains and myofilament assembly. We found abundant expression of UNC‐45A in human intestinal epithelial cell (IEC) lines and in the epithelial layer of the normal human colon. Interestingly, protein levels of UNC‐45A were decreased in colonic epithelium of patients with ulcerative colitis in parallel to diminished expression of NM‐IIA and NM‐IIC isoforms. CRISPR/Cas9‐mediated knock‐out of UNC‐45A in HT‐29 and SK‐CO15 IEC disrupted epithelial barrier integrity, impaired AJ and TJ assembly, and cell migration. Consistently, decreased UNC‐45 expression increased permeability of the Drosophila gut in vivo. The mechanisms underlying barrier disruptive and anti‐migratory effects of UNC‐45A depletion involved disorganization of the actomyosin bundles at epithelial junctions and the migrating cell edge. Loss of UNC‐45A also decreased contractile forces at epithelial junctions and matrix adhesions. Expression of deletion mutants revealed roles for the myosin binding domain of UNC‐45A in controlling IEC barrier function, junctional assembly and migration. Our findings uncover a novel mechanism that regulates integrity and restitution of the intestinal epithelial barrier, which may be impaired during mucosal inflammation.

N‐cadherin signaling stabilizes occludin tight junction via PI3K p110β signaling

The blood‐brain barrier (BBB) is a specialized microvasculature integral for brain tissue‐fluid homeostasis that is comprised of brain endothelial cells (BECs) and pericytes. Disruption of the BBB and subsequent vascular leakage of protein‐rich fluids is toxic to surrounding neurons and is an underlying risk factor in neurodegenerative disorders. BECs and pericytes form adhesions through the transmembrane protein Neural (N)‐cadherin. Although BEC‐pericyte interactions are critical for maintaining the BBB, the role of N‐cadherin adhesions in regulating the BBB remain unclear. Our previous work demonstrated that mutant mice lacking Cdh2 (N‐cadherin) in ECs or pericytes exhibited a size‐dependent increase in BBB permeability without affecting vessel or pericyte coverage. These findings raise the possibility that N‐cadherin junctions activate outside‐in signaling to strengthen the BBB. Analysis of tight junction (TJ) proteins occludin and claudins 1 and 5 in microvascular BECs of the cortex demonstrated a significant reduction in the accumulation of occludin, but not claudins, at TJs of KO mice. To delineate the signaling mechanism by which N‐cadherin adhesion‐mediated signaling regulates occludin TJs, we utilize biomimetic surfaces (Ncdh‐BioS) bearing covalently linked N‐cadherin extracellular domain to induce N‐cadherin adhesion in BEC monolayers in vitro. Consistent with our observations in mice, assembly of N‐cadherin junctions induced the accumulation of occludin and ZO1 at TJs in BEC monolayers. Depletion of N‐cadherin reversed these events, suggesting that N‐cadherin adhesion‐induced signaling assembles or stabilizes occludin TJs. Analysis of occludin‐Dendra 2 kinetics revealed decreased internalization rates of occludin from TJs in BECs grown on Ncdh‐BioS as compared to collagen, suggesting that N‐cadherin signaling stabilized occludin TJs. Furthermore, formation of N‐cadherin adhesion complexes led to activation of phosphoinositide 3‐kinase (PI3K) signaling as evidenced by the spatial redistribution of Akt to the plasma membrane as well as Akt phosphorylation. Pharmacological inhibition of class I PI3K with Copanlisib or depletion of PI3K p110β, but not of other PI3K catalytic isoforms, abolished Akt activation and increased the rate of occludin internalization from TJs in BECs grown on Ncdh‐BioS. Cumulatively, these data demonstrates that N‐cadherin outside‐in signaling strengthens the BBB by stabilizing occludin TJs through PI3K p110β signaling.

Epithelial monolayer development and tight junction assembly on nanopillar arrays

Nanostructured materials provide an outstanding opportunity to both stimulate and measure cellular processes. In the context of tight junctions, it was previously reported that transient application of a nanotopographic surface over the apical brush border membrane of epithelial monolayers triggers redistribution of ZO‐1, claudins, and F‐actin that increases paracellular macromolecular flux. In excitable tissues, nanomaterials have been used to apply and measure electrical signals, such action potentials. As a first step towards translating these technologies for use in analysis of epithelial function, we sought to culture monolayers composed of transporting epithelia over nanopillar arrays without perturbing cellular structure or function. Madin‐Darby Canine kidney I (MDCKI) cells were cultured on collagen‐coated silicon chips with ~1.5 µm diameter nanopillar arrays. Fluorescence and scanning electron microscopy were used to assess the impact of height on nanopillar‐epithelial interactions. Monolayers formed over and were largely unaffected by short nanopillars. These nanopillars were located beneath basal epithelial surfaces and were not preferentially located within lateral intercellular spaces or beneath ZO‐1‐containing junctions. In contrast, tall nanopillars that exceeded cell height disrupted MDCK monolayer growth. Cells interacted with, encircled, and extended cytoplasm over the top of tall nanopillars, and dense ZO‐1 and F‐actin accumulations occasionally surrounded apical membranes adjacent to nanopillars. Finally, when grown over arrays composed of nanopillars 1 – 2 µm less than cell height, MDCKI grew more often between nanopillars. As a result, nanopillars were more frequently present within lateral intercellular spaces beneath junctions. Apical complex structure was intact, as assessed by fluorescence microscopy of ZO‐1, occludin, claudin‐2, F‐actin, and E‐cadherin. Apical microvilli were also unaffected. These data establish the conditions required for growth of mature, correctly assembled epithelial monolayers in which nanopillars are present within lateral intercellular spaces. This sets the stage for synthesis of functionalized nanopillar arrays for perturbation and analysis of epithelial biology.

Chitosan Oligosaccharide Ameliorates Kidney Injury by Improving Intestinal Barrier Dysfunction and Lipid Metabolism in Obese‐insulin Resistant Rats

IntroductionObesity remains a global health problem. High‐fat diet (HFD) consumption increases the risk of type 2 diabetes and initiates kidney injury. Chitosan Oligosaccharide (COS) provides anti‐obesity effects through several mechanisms. However, the effects of COS on preventing obesity‐related kidney injury in obese‐insulin resistance have not been studied. A novel action of COS in activating intestinal tight junction assembly was reported in in vitro via calcium sensing receptor‐mediated AMP‐activated protein kinase (CaSR/AMPK) activation. HFD‐induced gut dysbiosis is related with intestinal barrier dysfunction and systemic low‐grade inflammation. Therefore, AMPK activation might be a therapeutic target for preventing obesity‐related complications. Here, we explored the protective effects of COS in obesity‐induced kidney dysfunction and the involved molecular mechanisms. We hypothesized that COS might exert renoprotection against obesity‐induced kidney injury through increasing intestinal barrier integrity and lipid excretion.MethodsMale Wistar rats were fed with HFD for 16 weeks to induce obesity. Next, HFD rats were randomly divided into 4 groups: HFD, HFD treated with COS 5 or 10 mg/kg/day (COS5 or COS10) and HFD treated with metformin 30 mg/kg/day (MET). The interventions were orally treated for 8 weeks. At the end of experiment, blood, feces, intestinal and renal tissue samples were collected for further investigations.ResultsAfter 16 weeks of high‐fat diet feeding, obesity and glucose intolerance were presented in HFD compared to normal diet (ND) rats, as indicated by the significant increases in body weight (BW), plasma cholesterol and total area under the curve for glucose (TAUCg). Kidney injury were observed at week 24, as shown by elevated kidney injury score and serum creatinine. Treatment with COS5 or COS10 significantly decreased BW, hypercholesterolemia, glucose intolerance and kidney dysfunction. Interestingly, COS10 markedly increased fecal lipid excretion compared with HFD and MET. In addition, intestinal CaSR, p‐AMPK/AMPK and tight junction protein claudin‐1 expressions were downregulated in HFD which were upregulated by COS10 and MET. Renal TNFαR activation and increased proinflammatory cytokines were detected in HFD. Moreover, renal apoptosis markers, Bcl‐2‐associated X protein (Bax) and cleaved caspase‐3, were increased, along with the suppressing of anti‐apoptotic B‐cell lymphoma‐2 (Bcl‐2) in HFD. Treatment with COS10 or MET markedly alleviated renal inflammation and apoptosis.ConclusionCOS exerted renoprotection through attenuating renal inflammation and apoptosis as a result of improving intestinal barrier via CaSR/AMPK activation and lipid absorption in obese rats. Therefore, COS might be an effective new dietary supplement for treating obesity and its related complications in clinical use.

Loss of Cingulin‐like 1 in Dahl Salt‐Sensitive Rats Leads to Reduced Renal Injury and Blood Pressure

Hypertension is both a cause and effect of chronic kidney disease (CKD) and impacts a significant proportion of patients, with a worldwide prevalence of 10‐15%. Previous genetic studies involving the Dahl salt‐sensitive (SS) rat, a model of hypertensive CKD, identified multiple genetic loci linked to kidney injury, including a region on chromosome (Chr) 8. Subsequently, an S.SHR(8) congenic (i.e. transfer of kidney injury resistant SHR genome onto the SS background) demonstrated significantly reduced proteinuria and improved renal function compared to SS control. To identify the gene/s responsible, genome sequencing and bioinformatics analysis identified cingulin‐like 1 (Cgnl1) as a putative gene linked to kidney injury on Chr. 8. Cgnl1 is known to localize to adherens and tight cell‐cell junctions, mediating junction assembly via regulating the activity of the small GTPases such as RhoA and Rac1. A SS‐Cgnl1−/− knockout (KO) was developed to test the hypothesis that loss of Cgnl1 will result in a significant attenuation of kidney injury compared to SS (WT). Both on low and high‐salt (LS=0.3% or HS=2.0% NaCl), KO animals (n=6) demonstrated reduced proteinuria compared to WT animals (n=6) for the entirety of the experiment (HS; KO= 28.7 ± 2.9 versus WT= 161.4 ± 33.1 mg/24hr at week 15, p<0.0001). To further validate Cgnl1’s effect on blood pressure and kidney injury, a temporal analysis (6‐12 weeks) using telemetry and additional renal measurements were conducted on WT and KO animals. On HS, KO animals (n=6) demonstrated reduced proteinuria compared to WT (n=6) for the entirety of the experiment (52.1 ± 7.2 versus 395.9 ± 29.8 mg/24hr at week 12, p<0.0001). While HS fed WT animals exhibited a significant increase in BP compared to LS WT (MAP=197.0 ± 5.0 versus 142.8 ± 3.5 mmHg, p<0001), KO remained unchanged (MAP= 127.6 ± 2.7 and 133.9 ± 3.7 mmHg respectively, NS). Kidney pathology measures, including glomerular and tubular injury were all significantly improved (all p<0.05) in KO compared to WT. Nephron number was measured with no significant difference between WT and KO in young animals, but HS fed WT demonstrated a significant loss of nephrons compared to KO. Bulk RNAseq of kidneys from WT and KO identified Cgnl1 as top downregulated gene with altered expression of many known genes linked with Cgnl1 compared to WT, along downregulation of genes associated with renal injury, mainly reflective of physiological differences from week12‐15. To better identify genes involved in onset of injury, single nuclei RNAseq was performed at week 4 (before physiological differences) to evaluate impact of Cgnl1 in distinct cell populations initiating injury. Additional work is also currently being done on HEK293‐ Cgnl1 knockout cell lines for more mechanistic study of Cgnl1 and pathways. In total, the molecular work, along with the physiological characterization of the SS‐Cgnl1−/−, is expected to provide insight into the role of Cgnl1 in the onset and progression of hypertensive kidney disease and identify new therapeutic targets.

Liver Proteomic Profile in Mice on a High‐Fat Diet: Modulation with Anti‐Tumor Intervention

ntroductionNonalcoholic fatty liver disease (NAFLD) is becoming a primary cause of liver damage in Western society. Nonalcoholic steatohepatitis (NASH) is an advanced stage of NAFLD and may lead to liver cancer. Our previous long‐term murine studies have shown the beneficial role of Aquamin, a red marine algae‐derived (calcium, magnesium, additional trace element‐rich) supplement, in reducing liver injury and decreasing liver tumor incidence. The main objective of the study was to determine how manifestations and effects of NASH can be mitigated using Aquamin. We hypothesized that mice on a high‐fat Western diet (HFWD) with minerals would exhibit less liver injury than mice on a HFWD without minerals.MethodsTwo cohorts of MS‐NASH mice (8‐week‐old) were placed on a HFWD with and without minerals for 16 weeks. An additional cohort of MS‐NASH mice on the same HFWD was treated with obeticholic acid (OCA). C57BL/6 mice on a regular chow were included as a control. During the in‐life phase of the study, weight changes were assessed weekly. At termination, livers were histologically assessed for steatosis and fibrosis by using hematoxylin and eosin, and picrosirius red staining. Liver tissue samples were also subjected to tandem mass tag (TMT) mass‐spectroscopic proteomics for protein expression profile in individual mice.ResultsMice on HFWD gained more weight than mice on control diet, but there was no overall change in weight for mice on HFWD, irrespective of interventions. On histological assessment, there was no difference in steatosis between the two high‐fat groups, but mice on Aquamin showed reduced picrosirius red staining or collagen deposition as compared to placebo (on HFWD) mice. Regarding proteomic profile, there was a clear distinction among control and HFWD groups. Placebo mice were used for comparison. Aquamin intervention altered 91 proteins while OCA altered 84 proteins in liver samples with a 2‐fold change. Of these, 57 proteins were common between Aquamin and OCA. Most of the proteins were upregulated. Aquamin upregulated 39 unique pathways (with a p‐value <0.05) as assessed by the Reactome database. Some of the pathways significantly impacted by Aquamin were formation of cornified envelope; keratinization; gap junction assembly; type I hemidesmosome assembly; apoptosis‐related; plasma lipoprotein assembly, remodeling and clearance; and hedgehog “off” state pathways. Proteins downregulated by OCA are mainly involved in the synthesis of bile acids and bile salts.ConclusionThe addition of dietary minerals may play a protective role in interfering with downstream advancement from steatosis to NASH. Our studies provide mechanistic insight into how mineral supplementation may contribute to the reduction in liver injury and tumor formation (one of the most devastating consequences) of fatty liver disease in the context of HFWD‐induced steatosis.

Proteomics of lung tissue reveals differences in inflammation and alveolar-capillary barrier response between atelectasis and aerated regions

Atelectasis is a frequent clinical condition, yet knowledge is limited and controversial on its biological contribution towards lung injury. We assessed the regional proteomics of atelectatic versus normally-aerated lung tissue to test the hypothesis that immune and alveolar-capillary barrier functions are compromised by purely atelectasis and dysregulated by additional systemic inflammation (lipopolysaccharide, LPS). Without LPS, 130 proteins were differentially abundant in atelectasis versus aerated lung, mostly (n = 126) with less abundance together with negatively enriched processes in immune, endothelial and epithelial function, and Hippo signaling pathway. Instead, LPS-exposed atelectasis produced 174 differentially abundant proteins, mostly (n = 108) increased including acute lung injury marker RAGE and chemokine CCL5. Functional analysis indicated enhanced leukocyte processes and negatively enriched cell–matrix adhesion and cell junction assembly with LPS. Additionally, extracellular matrix organization and TGF-β signaling were negatively enriched in atelectasis with decreased adhesive glycoprotein THBS1 regardless of LPS. Concordance of a subset of transcriptomics and proteomics revealed overlap of leukocyte-related gene-protein pairs and processes. Together, proteomics of exclusively atelectasis indicates decreased immune response, which converts into an increased response with LPS. Alveolar-capillary barrier function-related proteomics response is down-regulated in atelectasis irrespective of LPS. Specific proteomics signatures suggest biological mechanistic and therapeutic targets for atelectasis-associated lung injury.

Regulation of Tjp1 mRNA by CPEB2 for tight junction assembly in mouse blastocyst.

Cytoplasmic polyadenylation element-binding protein 2 (CPEB2) is an mRNA-binding protein that regulates the cytoplasmic polyadenylation of mRNA and is required for tight junction (TJ) assembly in the trophectoderm epithelium during porcine preimplantation development. However, the regulatory mechanism underlying TJ assembly by CPEB2 has not been examined. The aim of this study was to elucidate how Cpeb2 regulates the subcellular localisation and stabilisation of Tjp1 mRNA for TJ biogenesis during mouse preimplantation. CPEB2 was detected in nuclei during the early stages of development and was localised at apical cell membranes from the morula stage onwards. In the Cpeb2 knockdown (KD), we observed reduced blastocyst formation with impaired TJs, defective inner cell mass development in the blastocyst outgrowth assay, and loss of pregnancy after embryo transfer. More importantly, Tjp1 mRNA was localised apically in the outer cells of control morulae but not in the Cpeb2 KD embryos, indicating that CPEB2 mediated the translocalisation of Tjp1 mRNA from the nuclei. Finally, in the control embryos, the length of the Tjp1 mRNA poly (A) tail was varied, while only a single peak was detected in the Cpeb2 KD embryos. These findings suggest that the binding of CPEB2 to the cytoplasmic polyadenylation element in the 3'-UTR can confer stability on Tjp1 mRNA and translational regulation. In summary, we demonstrated for the first time that CPEB2 mediates Tjp1 mRNA stabilisation and subcellular localisation for TJ assembly during mouse blastocyst formation.

A myosin chaperone, UNC-45A, is a novel regulator of intestinal epithelial barrier integrity and repair.

The actomyosin cytoskeleton serves as a key regulator of the integrity and remodeling of epithelial barriers by controlling assembly and functions of intercellular junctions and cell‐matrix adhesions. Although biochemical mechanisms that regulate the activity of non‐muscle myosin II (NM‐II) in epithelial cells have been extensively investigated, little is known about assembly of the contractile myosin structures at the epithelial adhesion sites. UNC‐45A is a cytoskeletal chaperone that is essential for proper folding of NM‐II heavy chains and myofilament assembly. We found abundant expression of UNC‐45A in human intestinal epithelial cell (IEC) lines and in the epithelial layer of the normal human colon. Interestingly, protein level of UNC‐45A was decreased in colonic epithelium of patients with ulcerative colitis. CRISPR/Cas9‐mediated knock‐out of UNC‐45A in HT‐29cf8 and SK‐CO15 IEC disrupted epithelial barrier integrity, impaired assembly of epithelial adherence and tight junctions and attenuated cell migration. Consistently, decreased UNC‐45 expression increased permeability of the Drosophila gut in vivo. The mechanisms underlying barrier disruptive and anti‐migratory effects of UNC‐45A depletion involved disorganization of the actomyosin bundles at epithelial junctions and the migrating cell edge. Loss of UNC‐45A also decreased contractile forces at apical junctions and matrix adhesions. Expression of deletion mutants revealed roles for the myosin binding domain of UNC‐45A in controlling IEC junctions and motility. Our findings uncover a novel mechanism that regulates integrity and restitution of the intestinal epithelial barrier, which may be impaired during mucosal inflammation.

The relation between age and airway epithelial barrier function

BackgroundThe prevalence of age-associated diseases, such as chronic obstructive pulmonary disease (COPD), is increasing as the average life expectancy increases around the world. We previously identified a gene signature for ageing in the human lung which included genes involved in apical and tight junction assembly, suggesting a role for airway epithelial barrier dysfunction with ageing.AimTo investigate the association between genes involved in epithelial barrier function and age both in silico and in vitro in the airway epithelium.MethodsWe curated a gene signature of 274 genes for epithelial barrier function and tested the association with age in two independent cohorts of bronchial brushings from healthy individuals with no respiratory disease, using linear regression analysis (FDR < 0.05). Protein–protein interactions were identified using STRING©. The barrier function of primary bronchial epithelial cells at air–liquid interface and CRISPR–Cas9-induced knock-down of target genes in human bronchial 16HBE14o-cells was assessed using Trans epithelial resistance (TER) measurement and Electric cell-surface impedance sensing (ECIS) respectively.ResultsIn bronchial brushings, we found 55 genes involved in barrier function to be significantly associated with age (FDR < 0.05). EPCAM was most significantly associated with increasing age and TRPV4 with decreasing age. Protein interaction analysis identified CDH1, that was negatively associated with higher age, as potential key regulator of age-related epithelial barrier function changes. In vitro, barrier function was lower in bronchial epithelial cells from subjects > 45 years of age and significantly reduced in CDH1-deficient 16HBE14o-cells.ConclusionThe significant association between genes involved in epithelial barrier function and age, supported by functional studies in vitro, suggest a role for epithelial barrier dysfunction in age-related airway disease.

Intestinal Epithelial AMPK Deficiency Causes Delayed Colonic Epithelial Repair in DSS-Induced Colitis.

Dysfunctions in the intestinal barrier, associated with an altered paracellular pathway, are commonly observed in inflammatory bowel disease (IBD). The AMP-activated protein kinase (AMPK), principally known as a cellular energy sensor, has also been shown to play a key role in the stabilization and assembly of tight junctions. Here, we aimed to investigate the contribution of intestinal epithelial AMPK to the initiation, progression and resolution of acute colitis. We also tested the hypothesis that protection mediated by metformin administration on intestinal epithelium damage required AMPK activation. A dextran sodium sulfate (DSS)-induced colitis model was used to assess disease progression in WT and intestinal epithelial cell (IEC)-specific AMPK KO mice. Barrier integrity was analyzed by measuring paracellular permeability following dextran-4kDa gavage and pro-inflammatory cytokines and tight junction protein expression. The deletion of intestinal epithelial AMPK delayed intestinal injury repair after DSS exposure and was associated with a slower re-epithelization of the intestinal mucosa coupled with severe ulceration and inflammation, and altered barrier function. Following intestinal injury, IEC AMPK KO mice displayed a lower goblet cell counts with concomitant decreased Muc2 gene expression, unveiling an impaired restitution of goblet cells and contribution to wound healing process. Metformin administration during the recovery phase attenuated the severity of DSS-induced colitis through improvement in intestinal repair capacity in both WT and IEC AMPK KO mice. Taken together, these findings demonstrate a critical role for IEC-expressed AMPK in regulating mucosal repair and epithelial regenerative capacity following acute colonic injury. Our studies further underscore the therapeutic potential of metformin to support repair of the injured intestinal epithelium, but this effect is conferred independently of intestinal epithelial AMPK.

Extracellular vesicles improve embryo cryotolerance by maintaining the tight junction integrity during blastocoel re-expansion.

Cryopreservation is a process in which the intact living cells, tissues, or embryos are preserved at subzero temperatures for preservation. The cryopreservation process highly impacts the survival and quality of the in vitro-produced (IVP) embryos. Some studies have highlighted the use of oviduct extracellular vesicles (EVs) to improve the cryotolerance of IVP embryos but the mechanism has not been well studied. The present study unravels the role of in vitro cultured bovine oviduct epithelial cells-derived EVs in improving the re-expansion and hatching potential of thawed blastocysts (BLs). The comparison of cryotolerance between synthetic oviduct fluid (SOF) and SOF + EVs-supplemented day-7 cryopreserved BLs revealed that the embryo’s ability to re-expand critically depends on the intact paracellular sealing which facilitates increased fluid accumulation during cavity expansion after shrinkage. Our results demonstrated that BLs cultured in the SOF + EVs group had remarkably higher re-expansion (67.5 ± 4.2%) and hatching rate (84.8 ± 1.4%) compared to the SOF group (53.4 ± 3.4% and 63.9 ± 0.9%, respectively). Interestingly, EVs-supplemented BLs exhibited greater influence on the expression of core genes involved in trophectoderm (TE) maintenance, formation of tight junction (TJ) assembly, H2O channel proteins (aquaporins), and Na+/K+ ATPase alpha 1. The EVs improved the fluid flux and allowed the transport of H2O into an actively re-expanded cavity in EVs-cultured cryo-survived BLs relative to control BLs. Our findings explored the function of EVs in restoring the TE integrity, improved the cell junctional contacts and H2O movement which helps the blastocoel re-expansion after thawing the cryopreserved BLs.

WASp controls oriented migration of endothelial cells to achieve functional vascular patterning.

ABSTRACTEndothelial cell migration and proliferation are essential for the establishment of a hierarchical organization of blood vessels and optimal distribution of blood. However, how these cellular processes are quantitatively coordinated to drive vascular network morphogenesis remains unknown. Here, using the zebrafish vasculature as a model system, we demonstrate that the balanced distribution of endothelial cells, as well as the resulting regularity of vessel calibre, is a result of cell migration from veins towards arteries and cell proliferation in veins. We identify the Wiskott-Aldrich Syndrome protein (WASp) as an important molecular regulator of this process and show that loss of coordinated migration from veins to arteries upon wasb depletion results in aberrant vessel morphology and the formation of persistent arteriovenous shunts. We demonstrate that WASp achieves its function through the coordination of junctional actin assembly and PECAM1 recruitment and provide evidence that this is conserved in humans. Overall, we demonstrate that functional vascular patterning in the zebrafish trunk is established through differential cell migration regulated by junctional actin, and that interruption of differential migration may represent a pathomechanism in vascular malformations.

The Builders of the Junction: Roles of Junctophilin1 and Junctophilin2 in the Assembly of the Sarcoplasmic Reticulum-Plasma Membrane Junctions in Striated Muscle.

Contraction of striated muscle is triggered by a massive release of calcium from the sarcoplasmic reticulum (SR) into the cytoplasm. This intracellular calcium release is initiated by membrane depolarization, which is sensed by voltage-gated calcium channels CaV1.1 (in skeletal muscle) and CaV1.2 (in cardiac muscle) in the plasma membrane (PM), which in turn activate the calcium-releasing channel ryanodine receptor (RyR) embedded in the SR membrane. This cross-communication between channels in the PM and in the SR happens at specialized regions, the SR-PM junctions, where these two compartments come in close proximity. Junctophilin1 and Junctophilin2 are responsible for the formation and stabilization of SR-PM junctions in striated muscle and actively participate in the recruitment of the two essential players in intracellular calcium release, CaV and RyR. This short review focuses on the roles of junctophilins1 and 2 in the formation and organization of SR-PM junctions in skeletal and cardiac muscle and on the functional consequences of the absence or malfunction of these proteins in striated muscle in light of recently published data and recent advancements in protein structure prediction.

Programmable mismatch-fueled high-efficiency DNA signal amplifier.

Herein, by introducing mismatches, a high-efficiency mismatch-fueled catalytic multiple-arm DNA junction assembly (M-CMDJA) with high-reactivity and a high-threshold is developed as a programmable DNA signal amplifier for rapid detection and ultrasensitive intracellular imaging of miRNA. Compared with traditional nucleic acid signal amplification (NASA) with a perfect complement, the M-CMDJA possesses larger kinetic and thermodynamic favorability owing to the more negative reaction standard free energy (ΔG) as driving force, resulting in much higher efficiency and rates. Once traces of the input initiator react with the mismatched substrate DNA, it could be converted into amounts of output multiple-arm DNA junctions via the M-CMDJA as the functional DNA conversion nanodevice. Impressively, the mismatch-fueled catalytic four-arm DNA junction assembly (M-CFDJA) exhibits high conversion efficiency up to 1.05 × 108 in 30 min, which is almost ten times more than those of conventional methods. Therefore, the M-CMDJA could easily address the challenges of traditional methods: slow rates and low efficiency. In application, the M-CFDJA as a DNA signal amplifier was successfully used to develop a biosensing platform for rapid miRNA detection with a LOD of 6.11 aM and the ultrasensitive intracellular imaging of miRNA, providing a basis for the next-generation of versatile DNA signal amplification methods for ultimate applications in DNA nanobiotechnology, biosensing assay, and clinical diagnoses.

First Responders to Hyperosmotic Stress in Murine Astrocytes: Connexin 43 Gap Junctions Are Subject to an Immediate Ultrastructural Reorganization.

Simple SummaryGap junctions are intercellular channels that provide the means for direct transport of small molecules, ions, and water between connected cells. With these functions, gap junctions are essential for the maintenance of astrocytic homeostasis and of particular importance in the context of pathophysiological disbalances. These include the hyperosmolar hyperglycemic syndrome or the pathology after brain trauma. We demonstrate that short-term hyperosmolarity reduces intercellular communication via gap junctions. These functional changes coincide with the transformation of gap junction ultrastructure as evidenced by freeze-fracture replica immunolabeling and transmission electron microscopy. The hyperosmolarity-induced immediate changes in the ultrastructural assembly of connexons, the protein constituents of gap junction channels, have not been described in astrocytes before and are revealing the coherence of structure and function in gap junctions. Phosphorylation of Connexin 43, the main gap junction protein in astrocytes, at amino acid 368 (Serine) might link the two.In a short-term model of hyperosmotic stress, primary murine astrocytes were stimulated with a hyperosmolar sucrose solution for five minutes. Astrocytic gap junctions, which are mainly composed of Connexin (Cx) 43, displayed immediate ultrastructural changes, demonstrated by freeze–fracture replica immunogold labeling: their area, perimeter, and distance of intramembrane particles increased, whereas particle numbers per area decreased. Ultrastructural changes were, however, not accompanied by changes in Cx43 mRNA expression. In contrast, transcription of the gap junction regulator zonula occludens (ZO) protein 1 significantly increased, whereas its protein expression was unaffected. Phosphorylation of Serine (S) 368 of the Cx43 C–terminus has previously been associated with gap junction disassembly and reduction in gap junction communication. Hyperosmolar sucrose treatment led to enhanced phosphorylation of Cx43S368 and was accompanied by inhibition of gap junctional intercellular communication, demonstrated by a scrape loading-dye transfer assay. Taken together, Cx43 gap junctions are fast reacting elements in response to hyperosmolar challenges and can therefore be considered as one of the first responders to hyperosmolarity. In this process, phosphorylation of Cx43S368 was associated with disassembly of gap junctions and inhibition of their function. Thus, modulation of the gap junction assembly might represent a target in the treatment of brain edema or trauma.

CAMP controls a trafficking mechanism that maintains the neuron specificity and subcellular placement of electrical synapses.

Electrical synapses are established between specific neurons and within distinct subcellular compartments, but the mechanisms that direct gap junction assembly in the nervous system are largely unknown. Here, we show that a developmental program tunes cAMP signaling to direct the neuron-specific assembly and placement of electrical synapses in the C.elegans motor circuit. We use live-cell imaging to visualize electrical synapses invivo and an optogenetic assay to confirm that they are functional. In ventral A class (VA) motor neurons, the UNC-4 transcription factor blocks expression of cAMP antagonists that promote gap junction miswiring. In unc-4 mutants, VA electrical synapses are established with an alternative synaptic partner and are repositioned from the VA axon to soma. cAMP counters these effects by driving gap junction trafficking into the VA axon for electrical synapse assembly. Thus, our experiments establish that cAMP regulates gap junction trafficking for the biogenesis of functional electrical synapses.

Effects of valerate on intestinal barrier function in cultured Caco-2 epithelial cell monolayers.

Short-chain fatty acids (SCFAs) are a group of microbial metabolites of undigested dietary fiber, protein and unabsorbed amino acids in the colon, well-known for their gut health promoting benefits. A relatively high intestinal level of valerate was found in the healthy human subjects. However, the intestinal protection effects and the underlying mechanism of valerate are waiting to be verified and elucidated. In the present study, valerate, a SCFAs mainly converted from proteins or amino acids, was demonstrated to promote intestinal barrier function at its physiological concentrations of 0-4 mM in the Caco-2 cell monolayer model of intestinal barrier using transepithelial electrical resistance (TEER) assay and paracellular permeability assay. Valerate achieved the maximum increase in the TEER at 2 mM and reduced the paracellular permeability. Its intestinal barrier function promoting activity is similar to that of butyrate, with a broader range of effective concentrations than the later. Through western blot analysis, this activity is linked to the valerate-induced AMPK activation and tight junctions (TJs) assembly, but not to the reinforced expression of TJs related proteins. It provides direct experimental evidence supporting valerate's function in intestinal health, implying the once under-valued function of valerate and its amino acid precursors. The valerate's role in regulating intestine homeostasis and its possible synergetic effects with other SCFAs warranted to be further investigated.

Abstract 13476: ROR2 Deficiency is Associated With Endothelial Dysfunction and Reduced Angiogenesis in Pulmonary Arterial Hypertension

Introduction: Pulmonary arterial hypertension (PAH) is characterized by endothelial dysfunction and progressive loss of lung microvessels. Our group has shown that Wnt pathways are critical for pulmonary angiogenesis but the role of the Wnt/planar cell polarity specific receptor ROR2 in lung endothelial angiogenic responses is unknown. Hypothesis: We hypothesized that ROR2 is required for proper angiogenic responses in pulmonary microvascular endothelial cells (PMVECs) and its loss contributes to endothelial dysfunction in PAH. Methods and Results: Analysis of PAH lung tissues demonstrated reduced ROR2 expression within vascular lesions and in explanted PMVECs. ROR2 deficiency was associated with reduced proliferation and tube formation in response to VEGF-A, a major inducer of angiogenesis. We found that ROR2 promotes VEGF receptor 2 activation via direct phosphorylation of cytoplasmic residues (Y1175/Y951) and that restoring ROR2 expression in PAH PMVECs led to improved angiogenic responses. Besides angiogenic sprouting, we found that ROR2 is required for lung endothelial barrier formation by promoting the assembly of mature focal adhesions and adherens junctions through activation of Src and focal adhesion kinase (FAK). Compared to wild-type controls, endothelial-specific ROR2 knockout (ROR2 ECKO) mice demonstrated more severe hemodynamics, small vessel loss, and muscularization in chronic hypoxia. Moreover, ROR2 ECKO demonstrated severe RV dysfunction associated with reduced capillary density. We validated these findings in samples of decompensated RV tissue from PAH patients, monocrotaline, and Sugen-hypoxia rats which also demonstrated a significant reduction of ROR2 expression that correlated with RV capillary loss. Conclusion: ROR2 plays a protective role in the pulmonary and RV circulations and its loss prevents vessel repair in PAH. Targeting ROR2 could promote recovery of small vessel loss and RV adaptation in PAH.

Discovery of new intracellular junctions: The calcium entry units (CEUs)

In 2017, Boncompagni, Michelucci et al. demonstrated that during exercise the sarcotubular system of extensor digitorum longus (EDL) fibers undergoes a profound remodeling that leads to the assembly of new junctions between T-tubule extensions at the I band and sarcoplasmic reticulum (SR) stacks. As these junctions contain colocalized STIM1 and Orai1 and enhance store-operated Ca2+ entry (SOCE), they have been named Ca2+ entry units (CEUs). In addition, it has been more recently shown that (1) CEUs disassemble following recovery, with T-tubules retraction from the I band faster than SR stacks disassembly, and (2) lack of calsequestrin-1 (CASQ1) induces a constitutive assembly of CEUs, resulting in enhanced SOCE that counteracts the SR Ca2+ depletion. We have now analyzed (1) CEUs during postnatal maturation (at 2 wk of age) and (2) whether CEUs form in slow-twitch fibers (soleus). (a) Compared with adult (4 mo) EDL fibers of resting WT mice, at 2 wk of age we found a greater longitudinal disposition of T-tubules associated to SR membranes forming junctions virtually identical to CEUs in adult EDLs of exercised WT mice, which promote increased STIM1/Orai1-mediated SOCE. (b) We also compared structure and function of soleus (which also express the cardiac isoform CASQ2) from WT mice and from mice lacking either CASQ1 (CASQ1-null) or CASQ1/2 (dCASQ-null). In soleus from both genotypes, CEUs are constitutively assembled although they appear structurally smaller than those described previously in exercised WT or CASQ1-null EDLs. A detailed EM quantitative analysis revealed that CEUs were more abundant in dCASQ-null than CASQ1-null mice. The amount of CEUs strictly correlated with the ability of soleus fibers to recover extracellular Ca2+ via SOCE to support contractility during high-frequency stimulation. These data were supported by molecular analysis of Western blots, showing that Orai1 expression was enhanced following ablation of CASQ.