Biology subjects

Khandekar, G.

Publications and source records attributed to Khandekar, G..

3 recordsLinked to original sources

bioRxiv2020

Distinct effects of different matrix proteoglycans on collagen fibrillogenesis and cell-mediated collagen reorganization

The extracellular matrix (ECM) is a complex mixture composed of fibrillar collagens as well as additional protein and carbohydrate components. Proteoglycans (PGs) contribute to the heterogeneity of the ECM and play an important role in its structure and function. While the small leucine rich proteoglycans (SLRPs), including decorin and lumican, have been studied extensively as mediators of collagen fibrillogenesis and organization, the function of large matrix PGs in collagen matrices is less well known. In this study, we showed that different matrix PGs have distinct roles in regulating collagen behaviors. We found that versican, a large chondroitin sulfate PG, promotes collagen fibrillogenesis in a turbidity assay and upregulates cell-mediated collagen compaction and reorganization, whereas aggrecan, a structurally-similar large PG, has different and often opposing effects on collagen. Compared to versican, decorin and lumican also have distinct functions in regulating collagen behaviors. The different ways in which matrix PGs interact with collagen have important implications for understanding the role of the ECM in diseases such as fibrosis and cancer, and suggest that matrix PGs are potential therapeutic targets. HighlightsO_LISmall leucine rich proteoglycans (SLRPs) and large chondroitin sulfate (CS) proteoglycans (PGs) have distinct effects on collagen fibrous network behavior. C_LIO_LIUnlike other matrix proteoglycans, versican promotes collagen fibrillogenesis in an in vitro spectrophotometric (turbidity) assay. C_LIO_LIThe versican core protein has a larger impact on collagen behavior in a fibrillogenesis assay than its glycosaminoglycan chains do. C_LIO_LIVersican increases the diameter of collagen fibers and the porosity of collagen fibrous networks, unlike aggrecan and SLRPs. C_LIO_LIThe addition of versican to collagen does not alter fibroblast contractility but leads to enhanced cell-mediated collagen reorganization and contraction. C_LI

cell biology↗

bioRxiv2019

A Bile Duct-on-a-Chip with Organ-Level Functions

Chronic cholestatic liver diseases such as primary biliary cholangitis (PBC) and primary sclerosing cholangitis (PSC) are frequently associated with damage to the barrier function of the biliary epithelium, but barrier function is difficult to study in vivo and has not been recapitulated in vitro. Here we report the development of a bile duct-on-a-chip that phenocopies not only the tubular architecture of the bile duct in three dimensions, but also its barrier functions. We demonstrated that mouse cholangiocytes in the channel of the device became polarized and formed mature tight junctions, and that the permeability of the cholangiocyte monolayer was comparable to that measured ex vivo for the rat bile duct. Permeability decreased significantly when cells formed a compacted monolayer with cell densities comparable to that seen in vivo. This device enabled independent access to the apical and basolateral surfaces of the cholangiocyte channel, allowing proof-of-concept toxicity studies with the biliary toxin biliatresone and the bile acid glycochenodeoxycholic acid. The cholangiocyte basolateral side was more vulnerable than the apical side to treatment with either agent, suggesting a protective adaptation of the apical surface that is normally exposed to bile. Further studies revealed a protective role of the cholangiocyte apical glycocalyx, wherein disruption of the glycocalyx with neuraminidase increased the permeability of the cholangiocyte monolayer after treatment with glycochenodeoxycholic acid. Conclusion: This bile duct-on-a-chip captured essential features of a simplified bile duct in structure and organ-level functions and represents a novel in vitro platform to study the pathophysiology of the bile duct using cholangiocytes from a variety of sources.

bioengineering↗

bioRxiv2019

Coordinated development of the mouse extrahepatic bile duct: implications for neonatal susceptibility to biliary injury

Background & AimsThe extrahepatic bile duct is the primary tissue initially affected by the cholangiopathy biliary atresia. Biliary atresia affects neonates exclusively and current animal models suggest that the developing bile duct is uniquely susceptible to damage. In this study, we aimed to define the anatomical and functional differences between the neonatal and adult mouse extrahepatic bile ducts.\n\nMethodsWe studied mouse passaged cholangiocytes, mouse BALB/c neonatal and adult primary cholangiocytes and isolated extrahepatic bile ducts, and a collagen reporter mouse. Methods included transmission electron microscopy, lectin staining, immunostaining, rhodamine uptake assays, bile acid toxicity assays, and in vitro modeling of the matrix.\n\nResultsThe cholangiocyte monolayer of the neonatal extrahepatic bile duct was immature, lacking the uniform apical glycocalyx and mature cell-cell junctions typical of adult cholangiocytes. Functional studies showed that the glycocalyx protected against bile acid injury and that neonatal cholangiocyte monolayers were more permeable than adult monolayers. In adult ducts, the submucosal space was filled with collagen I, elastin, hyaluronic acid, and proteoglycans. In contrast, the neonatal submucosa had little collagen I and elastin, although both increased rapidly after birth. In vitro modeling suggested that the composition of the neonatal submucosa relative to the adult submucosa led to increased diffusion of bile. A Col-GFP reporter mouse showed that cells in the neonatal but not adult submucosa were actively producing collagen.\n\nConclusionWe identified four key differences between the neonatal and adult extrahepatic bile duct. We showed that these features may have functional implications, suggesting the neonatal extrahepatic bile ducts are particularly susceptible to injury and fibrosis.\n\nLay SummaryBiliary atresia is a disease that affects newborns and is characterized by extrahepatic bile duct injury and obstruction with resulting liver injury. We identify four key differences between the epithelial and submucosal layers of the neonatal and adult extrahepatic bile duct and show that these may render the neonatal duct particularly susceptible to injury.\n\nHighlightsO_LIThe apical glycocalyx is thin and patchy in neonatal compared to adult cholangiocytes\nC_LIO_LINeonatal cholangiocytes have immature cell-cell junctions and increased permeability\nC_LIO_LIThe neonatal submucosal space has minimal collagen I or elastin\nC_LIO_LIThe neonatal submucosal space contains many actively collagen-secreting cells\nC_LI\n\nGraphical abstract\n\nO_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=95 SRC=\"FIGDIR/small/576256_ufig1.gif\" ALT=\"Figure 1\">\nView larger version (27K):\norg.highwire.dtl.DTLVardef@1685e52org.highwire.dtl.DTLVardef@1086478org.highwire.dtl.DTLVardef@1fc3f55org.highwire.dtl.DTLVardef@1a20a5f_HPS_FORMAT_FIGEXP M_FIG C_FIG

physiology↗