High-mobility group box 1 inhibits HCO3- absorption in the medullary thick ascending limb through RAGE-Rho-ROCK-mediated inhibition of basolateral Na+/H+ exchange

Roles of RAGE/ROCK1 Pathway in HMGB1-Induced Early Changes in Barrier Permeability of Human Pulmonary Microvascular Endothelial Cell

Background

High mobility group box 1 (HMGB1) causes microvascular endothelial cell barrier dysfunction during acute lung injury (ALI) in sepsis, but the mechanisms have not been well understood. We studied the roles of RAGE and Rho kinase 1 (ROCK1) in HMGB1-induced human pulmonary endothelial barrier disruption.

Methods

In the present study, the recombinant human high mobility group box 1 (rhHMGB1) was used to stimulate human pulmonary microvascular endothelial cells (HPMECs). The endothelial cell (EC) barrier permeability was examined by detecting FITC-dextran flux. CCK-8 assay was used to detect cell viability under rhHMGB1 treatments. The expression of related molecules involved in RhoA/ROCK1 pathway, phosphorylation of myosin light chain (MLC), F-actin, VE-cadherin and ZO-1 of different treated groups were measured by pull-down assay, western blot and immunofluorescence. Furthermore, we studied the effects of Rho kinase inhibitor (Y-27632), ROCK1/2 siRNA, RAGE-specific blocker (FPS-ZM1) and RAGE siRNA on endothelial barrier properties to elucidate the related mechanisms.

Results

In the present study, we demonstrated that rhHMGB1 induced EC barrier hyperpermeability in a dose-dependent and time-dependent manner by measuring FITC-dextran flux, a reflection of the loss of EC barrier integrity. Moreover, rhHMGB1 induced a dose-dependent and time-dependent increases in paracellular gap formation accompanied by the development of stress fiber rearrangement and disruption of VE-cadherin and ZO-1, a phenotypic change related to increased endothelial contractility and endothelial barrier permeability. Using inhibitors and siRNAs directed against RAGE and ROCK1/2, we systematically determined that RAGE mediated the rhHMGB1-induced stress fiber reorganization via RhoA/ROCK1 signaling activation and the subsequent MLC phosphorylation in ECs.

Conclusion

HMGB1 is capable of disrupting the endothelial barrier integrity. This study demonstrates that HMGB1 activates RhoA/ROCK1 pathway via RAGE, which phosphorylates MLC inducing stress fiber formation at short time, and HMGB1/RAGE reduces AJ/TJ expression at long term independently of RhoA/ROCK1 signaling pathway.

HMGB1 in kidney diseases

High mobility group box 1 (HMGB1) is a highly conserved nucleoprotein involving in numerous biological processes, and well known to trigger immune responses as the damage-associated molecular pattern (DAMP) in the extracellular environment. The role of HMGB1 is distinct due to its multiple functions in different subcellular location. In the nucleus, HMGB1 acts as a chaperone to regulate DNA events including DNA replication, repair and nucleosome stability. While in the cytoplasm, it is engaged in regulating autophagy and apoptosis. A great deal of research has explored its function in the pathogenesis of renal diseases. This review mainly focuses on the role of HMGB1 and summarizes the pathway and treatment targeting HMGB1 in the various renal diseases which may open the windows of opportunities for the development of desirable therapeutic ends in these pathological conditions.

The SLC9A-C Mammalian Na+/H+ Exchanger Family: Molecules, Mechanisms, and Physiology

Na⁺/H⁺ exchangers play pivotal roles in the control of cell and tissue pH by mediating the electroneutral exchange of Na⁺ and H⁺ across cellular membranes. They belong to an ancient family of highly evolutionarily conserved proteins, and they play essential physiological roles in all phyla. In this review, we focus on the mammalian Na⁺/H⁺ exchangers (NHEs), the solute carrier (SLC) 9 family. This family of electroneutral transporters constitutes three branches: SLC9A, -B, and -C. Within these, each isoform exhibits distinct tissue expression profiles, regulation, and physiological roles. Some of these transporters are highly studied, with hundreds of original articles, and some are still only rudimentarily understood. In this review, we present and discuss the pioneering original work as well as the current state-of-the-art research on mammalian NHEs. We aim to provide the reader with a comprehensive view of core knowledge and recent insights into each family member, from gene organization over protein structure and regulation to physiological and pathophysiological roles. Particular attention is given to the integrated physiology of NHEs in the main organ systems. We provide several novel analyses and useful overviews, and we pinpoint main remaining enigmas, which we hope will inspire novel research on these highly versatile proteins.

Ds-HMGB1 and fr-HMGB induce depressive behavior through neuroinflammation in contrast to nonoxid-HMGB1

High mobility group box 1 (HMGB1) has been implicated as a key factor in several neuroinflammatory conditions. Our previous study suggested that the release of central HMGB1 acts as a late-phase mediator in lipopolysaccharide (LPS)-induced depression. Recent findings indicate that the redox state of HMGB1 is a critical determinant of its immunomodulatory properties. Here, we aimed to investigate the potential mechanisms that link the redox states of HMGB1 to depression in mice. Distinct redox forms of recombinant HMGB1 (rHMGB1) were used that included fully reduced HMGB (fr-HMGB1), which acted as a chemokine, and disulfide-HMGB1 (ds-HMGB1), which possessed cytokine activity. Fr-HMGB1 in vivo was partially oxidized into ds-HMGB1; thus, the mutant protein non-oxidizable chemokine-HMGB (nonoxid-HMGB1) was applied. Concurrent with depressive behavior induced by four-week stress exposure, the HMGB1 concentrations in the serum and cerebral cortex substantially increased. Therefore, a single dose of rHMGB1 (200ng/5μl/mice) or vehicle was administered to mice via intracerebroventricular (i.c.v.) injection. The receptor inhibitors of TLR4/RAGE/CXCR4 (TAK-242/FPS-ZM1/AMD3100) (3mg/kg) were intraperitoneally injected 30min prior to rHMGB1 treatment. Depressive-like behavior was measured 20h post i.c.v. injection. Administration of fr-HMGB1 prolonged the immobility duration in the tail suspension test (TST) and decreased sucrose preference. In addition to depressive behavior, the hippocampal TNF-α protein slightly increased. These depressive behaviors and upregulation of hippocampal TNF-α were alleviated or abrogated by pretreatment with the inhibitors AMD3100, FPS-ZM1, and TAK-242. Alternatively, nonoxid-HMGB1 failed to induce TNF-α protein or prolong the immobility duration. As expected, ds-HMGB1 administration substantially upregulated hippocampal TNF-α protein, increased the immobility time in the TST and decreased sucrose preference. Moreover, both glycyrrhizin and TAK-242 improved ds-HMGB1-induced depressive behavior. Furthermore, TAK-242 significantly blocked the upregulation of hippocampal TNF-α protein and protected hippocampal myelin basic protein from ds-HMGB1-induced reduction. These drugs had no effect on the total or central distance in the open field test. Collectively, this initial experiment demonstrates the role and receptor mechanisms of HMGB1 under different redox states on the induction of depressive-like behavior. Both ds-HMGB1 and fr-HMGB1 may induce depressive-like behavior in vivo mainly via neuroinflammatory response activation.