Erxleben, D. A. | Search bioRxiv

bioRxiv2026

A role for heavy chain-modification in protecting hyaluronan from free radical fragmentation during inflammation

The glycosaminoglycan hyaluronan (HA) is an essential and ubiquitous component of human tissues and biofluids. The only known covalent modification of HA entails the attachment of heavy chains (HC) from the inter-alpha-inhibitor (II) family of proteoglycans, forming stable complexes (HC*HA) that arise during inflammation. In some contexts, HC*HA is thought to contribute to pathology, whereas in others it may form part of a protective pathway. However, its exact roles are not fully understood. Here, we report that HC modifications can protect HA from fragmentation by reactive oxygen species (ROS) produced during the inflammatory cascade. Using solid-state nanopore molecular size analysis, we show that HA is highly resistant to degradation from exogenous ROS in vitro when in the context of HC*HA complexes, while the unmodified HA polymer is fragmented rapidly under the same conditions. Experiments performed with admixtures of HA and unbound antioxidant proteins - including HC-bearing components - demonstrate the necessity of covalent HC attachment to the polysaccharide for the protection. Finally, we find that HA with high-HC content from inflammatory equine synovial fluid has increased resilience to ROS damage compared to low-HC HA from a healthy joint. Collectively, these results demonstrate that covalent HC modification is an effective biological strategy for preserving HA integrity against ROS fragmentation, including in inflammatory conditions.

molecular biology↗

bioRxiv2022

Injury and a program of fetal wound healing in the fetal and neonatal extrahepatic bile duct

IntroductionBiliary atresia (BA) is an obstructive cholangiopathy that initially affects the extrahepatic bile ducts (EHBDs) of neonates. The etiology is uncertain, but evidence points to a prenatal cause; however, the response of the fetal EHBD to injury remains unknown. The objective of this study was to define the fetal response to EHBD injury and to determine whether it follows a fetal wound healing paradigm. MethodsMouse, rat, sheep, and human EHBD samples were studied at different developmental time points. Models included a fetal sheep model of prenatal hypoxia, human BA EHBD remnants and liver samples taken at the time of the Kasai procedure, EHBDs isolated from neonatal rats and mice, and spheroids and other models generated from primary neonatal mouse cholangiocytes. ResultsA wide layer of high molecular weight HA encircling the lumen was characteristic of the normal perinatal but not adult EHBD. This layer, which was surrounded by collagen, expanded in injured ducts in parallel with extensive peribiliary gland (PBG) hyperplasia, increased mucus production and elevated serum bilirubin levels. BA EHBD remnants similarly showed increased HA centered around ductular structures compared with age-appropriate controls. High molecular weight HA typical of the fetal/neonatal ducts caused increased cholangiocyte spheroid growth, whereas low molecular weight HA induced abnormal epithelial morphology; low molecular weight HA caused matrix swelling in a bile duct-on-a-chip device. ConclusionThe fetal/neonatal EHBD, including in human EHBD remnants from Kasai surgeries, demonstrated an injury response with high levels of HA typical of the regenerative, scarless program termed fetal wound healing. Although generally beneficial, the expanded peri-luminal HA layer may swell and lead to elevated bilirubin levels and obstruction of the EHBD.

physiology↗