Role of high mobility group box 1 and its signaling pathways in renal diseases

High-mobility group box 1 protein antagonizes the immunosuppressive capacity and therapeutic effect of mesenchymal stem cells in acute kidney injury

Background

Kidney ischemia reperfusion injury (IRI) is a common cause of acute kidney injury and an unavoidable consequence of kidney transplantation and still lacks specific therapeutics. Recently, mesenchymal stem cell (MSC) has been emerging as a promising cell-based therapy for IRI in the context of transplantation. MSC negatively regulates the secretion of pro-inflammatory as well as the activation of immune cells during IRI through its unique immunosuppressive property.

Methods

We employed mice kidney IRI model and MSC cell line to monitor the IRI related checkpoints. siRNAs were utilized to knock down the potential key factors for mechanistic analysis. Statistical analysis was performed by using one-way ANOVA with Tukey’s post hoc procedure by SPSS.

Results

The expression of high-mobility group box 1 protein (HMGB1) is increased in the acute phase as well as the recovery stage of IRI. Importantly, the HMGB1 upregulation is correlated with the injury severity. HMGB1 diminishes the MSC induced immunosuppressive capacity in the presence of pro-inflammatory cytokines in vitro. Toll like receptor 4 (TLR4)-mediated inducible nitric oxide synthase (iNOS) inhibition contributes to the negative effect of HMGB1 on MSCs. HMGB1-TLR4 signaling inhibition augments the therapeutic efficacy of MSCs in mice renal IRI model.

Conclusions

These findings demonstrate that HMGB1 plays a crucial role in shaping the immunoregulatory property of MSCs within the microenvironments, providing novel insights into the crosstalk between MSCs and microenvironment components, suggesting HMGB1 signals as a promising target to improve MSC-based therapy.

High mobility group box 1 as a biomarker in critically ill patients

BACKGROUND

Extracellular release of high mobility group box 1 (HMGB1) acts as a danger-associated molecular pattern, thereby "alarming" the immune system and promoting systemic inflammation. We investigated plasma HMGB1 concentrations as a potential diagnostic and prognostic biomarker in critical illness.

METHODS

Our study included 218 critically ill patients (145 with sepsis, 73 without sepsis), of whom blood samples were obtained at the time-point of admission to the medical intensive care unit (ICU).

RESULTS

High mobility group box 1 levels were significantly elevated in critically ill patients (n = 218) compared with healthy controls (n = 66). Elevated HMGB1 plasma levels were independent from the presence of sepsis. Moreover, HMGB1 was not associated with disease severity, organ failure, or mortality in the ICU. We observed a trend toward lower HMGB1 levels in ICU patients with pre-existing obesity, type 2 diabetes and end-stage renal disease patients on chronic hemodialysis.

CONCLUSION

In conclusion, our study did not reveal significant associations between HMGB1 levels at ICU admission and clinical outcomes in critically ill patients. Due to the pathogenic role of HMGB1 in the late phases of experimental sepsis, future studies might assess the potential value of HMGB1 by measuring its plasma concentrations at later time points during the course of critical illness.

HMGB1, TGF-β and NF-κB are associated with chronic allograft nephropathy

The present study aimed to investigate the association between high mobility group protein B1 (HMGB1), transforming growth factor-β1 (TGF-β1), nuclear factor-κB (NF-κB) and chronic allograft nephropathy (CAN) and to identify the clinical significance of HMGB1, TGF-β1, NF-κB on patients with CAN. Between September 2012 and November 2014, 27 patients with CAN diagnosed by biopsy were enrolled in the present study and a further 30 patients that underwent nephrectomy following trauma were selected as the control group. Immunohistochemical staining with HMGB1, TGF-β1 and NF-κB expression in the renal tissues, and western blot analysis were used to measure the relative expression of HMGB1, TGF-β1 and NF-κB. Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) was used to estimate the relative expression of HMGB1, TGF-β1 and NF-κB mRNA. Statistical analysis was used to calculate the association between HMGB1, TGF-β1 and NF-κB expression and CAN grade. Immunohistochemical staining demonstrated that HMGB1, TGF-β1 and NF-κB had markedly positive expression rates in renal tubular epithelial cell cytoplasm and membranes in CAN renal tissues, and the positive rates of HMGB1, TGF-β1 and NF-κB increased with the aggravation of CAN pathological grade (I, II and III). The results of western blot analysis indicated that the expression levels of HMGB1, TGF-β1 and NF-κB were significantly higher in the CAN group, compared with the normal group (P<0.05), and the expression levels increased with the progression of CAN grade. A positive association among HMGB1, TGF-β1 and NF-κB expression was identified. RT-qPCR analysis demonstrated that the expression of HMGB1, TGF-β1 and NF-κB mRNA in the CAN group was significantly higher than in the normal group (P<0.05), and the relative expression level of HMGB1, TGF-β1 and NF-κB mRNA not only increased with the aggravation of CAN grade, but was also positively associated with the expression of HMGB1, TGF-β1 and NF-κB, respectively. The abnormal expression of HMGB1, TGF-β1 and NF-κB is therefore, an important manifestation of CAN and the expression of HMGB1, TGF-β1 and NF-κB mRNA in the renal tissues are significantly associated with CAN pathological progression. HMGB1, TGF-β1 and NF-κB may form a signaling pathway that leads to the occurrence of CAN, which induces renal interstitial fibrosis.

HMGB1/TLR4 signaling induces an inflammatory response following high-pressure renal pelvic perfusion in a porcine model

Percutaneous nephrolithotomy (PCNL) causes a rapid increase in renal pelvic pressure in the kidney, which induces an inflammatory response. High-mobility group box-1 (HMGB1) is known to trigger the recruitment of inflammatory cells and the release of proinflammatory cytokines following ischemia reperfusion injury in the kidney, but the contribution of HMGB1 to the inflammatory response following high-pressure renal pelvic perfusion has not been investigated. In this study, high-pressure renal pelvic perfusion was induced in anesthetized pigs to examine the effect of HMGB1 on the inflammatory response. HMGB1 levels in the kidney increased following high-pressure renal pelvic perfusion, together with elevated levels of inflammatory cytokines in the plasma and kidney and an accumulation of neutrophils and macrophages. Inhibition of HMGB1 alleviated this inflammatory response while perfusion with recombinant HMGB1 had an augmentative effect, confirming the involvement of HMGB1 in the inflammatory response to high-pressure renal pelvic perfusion. HMGB1 regulated the inflammatory response by activating Toll-like receptor 4 (TLR4) signaling. In conclusion, this study has demonstrated that HMGB1/TLR4 signaling contributes to the inflammatory response following high-pressure renal pelvic perfusion in a porcine model and has implications for the management of inflammation after PCNL.

Soluble Receptor for Advanced Glycation End Product Ameliorates Chronic Intermittent Hypoxia Induced Renal Injury, Inflammation, and Apoptosis via P38/JNK Signaling Pathways

Obstructive sleep apnea (OSA) associated chronic kidney disease is mainly caused by chronic intermittent hypoxia (CIH) triggered tissue damage. Receptor for advanced glycation end product (RAGE) and its ligand high mobility group box 1 (HMGB1) are expressed on renal cells and mediate inflammatory responses in OSA-related diseases. To determine their roles in CIH-induced renal injury, soluble RAGE (sRAGE), the RAGE neutralizing antibody, was intravenously administered in a CIH model. We also evaluated the effect of sRAGE on inflammation and apoptosis. Rats were divided into four groups: (1) normal air (NA), (2) CIH, (3) CIH+sRAGE, and (4) NA+sRAGE. Our results showed that CIH accelerated renal histological injury and upregulated RAGE-HMGB1 levels involving inflammatory (NF-κB, TNF-α, and IL-6), apoptotic (Bcl-2/Bax), and mitogen-activated protein kinases (phosphorylation of P38, ERK, and JNK) signal transduction pathways, which were abolished by sRAGE but p-ERK. Furthermore, sRAGE ameliorated renal dysfunction by attenuating tubular endothelial apoptosis determined by immunofluorescence staining of CD31 and TUNEL. These findings suggested that RAGE-HMGB1 activated chronic inflammatory transduction cascades that contributed to the pathogenesis of the CIH-induced renal injury. Inhibition of RAGE ligand interaction by sRAGE provided a therapeutic potential for CIH-induced renal injury, inflammation, and apoptosis through P38 and JNK pathways.

TLR4-mediated inflammation is a key pathogenic event leading to kidney damage and fibrosis in cyclosporine nephrotoxicity

Cyclosporine A (CsA) successfully prevents allograft rejection, but nephrotoxicity is still a dose-limiting adverse effect. TLR4 activation promotes kidney damage but whether this innate immunity receptor mediates CsA nephrotoxicity is unknown. The in vivo role of TLR4 during CsA nephrotoxicity was studied in mice co-treated with CsA and the TLR4 inhibitor TAK242 and also in TLR4^-/- mice. CsA-induced renal TLR4 expression in wild-type mice. Pharmacological or genetic targeting of TLR4 reduced the activation of proinflammatory signaling, including JNK/c-jun, JAK2/STAT3, IRE1α and NF-κB and the expression of Fn14. Expression of proinflammatory factors and cytokines was also decreased, and kidney monocyte and lymphocyte influx was prevented. TLR4 inhibition also reduced tubular damage and drastically prevented the development of kidney fibrosis. In vivo and in vitro CsA promoted secretion of the TLR ligand HMGB1 by tubular cells upstream of TLR4 activation, and prevention of HMGB1 secretion significantly reduced CsA-induced synthesis of MCP-1, suggesting that HMGB1 may be one of the mediators of CsA-induced TLR4 activation. These results suggest that TLR4 is a potential pharmacological target in CsA nephrotoxicity.

The Role of HMGB1 Signaling Pathway in the Development and Progression of Hepatocellular Carcinoma: A Review

The story of high mobility group protein B1 (HMGB1) in cancer is complicated and the function of HMGB1 in different cancers is uncertain. This review aims to retrieve literature regarding HMGB1 from English electronic resources, analyze and summarize the role of the HMGB1 signaling pathway in hepatocellular carcinoma (HCC), and provide useful information for carcinogenesis and progression of HCC. Results showed that HMGB1 could induce cell proliferation, differentiation, cell death, angiogenesis, metastasis, inflammation, and enhance immunofunction in in vitro and in vivo HCC models. HMGB1 and its downstream receptors RAGE, TLRs and TREM-1 may be potential anticancer targets. In conclusion, HMGB1 plays an important role in oncogenesis and represents a novel therapeutic target, which deserves further study.

microRNA-218 suppresses the proliferation, invasion and promotes apoptosis of pancreatic cancer cells by targeting HMGB1

OBJECTIVE

To detect the expression profiles of microRNA-218 (miR-218) in human pancreatic cancer tissue (PCT) and cells and their effects on the biological features of human pancreatic cancer cell line PANC-1 and observe the effect of miR-218 on the expression of the target gene high mobility group box 1 (HMGB1), with an attempt to provide new treatment methods and strategies for pancreatic cancer.

METHODS

The expressions of miR-218 in PCT and normal pancreas tissue as well as in various pancreatic cancer cell lines including AsPC-1, BxPC-3, and PANC-1 were determined with quantitative real-time reverse transcription polymerase chain reaction (qRT-PCR). The change of miR-218 expression in PANC-1 cells was detected using qRT-PCT after the transfection of miR-218 mimic for 48 h. Cell Counting Kit-8 (CCK-8) was applied for detecting the effect of miR-218 on the activity of PANC-1 cells. The effects of miR-218 on the proliferation and apoptosis of PANC-1 cells were analyzed using the flow cytometry. The effect of miR-218 on the migration of PANC-1 cells was detected using the Trans-well migration assay. The HMGB1 was found to be a target gene of miR-218 by luciferase reporter assay, and the effect of miR-218 on the expression of HMGB1 protein in cells were determined using Western blotting.

RESULTS

As shown by qRT-PCR, the expressions of miR-218 in PCT and in pancreatic cancer cell line significantly decreased when compared with the normal pancreatic tissue (NPT) (P<0.01). Compared with the control group, the miR-218 expression significantly increased in the PANC-1 group after the transfection of miR-218 mimic for 48 h (P<0.01). Growth curve showed that the cell viability significantly dropped after the overexpression of miR-218 in the PANC-1 cells for two days (P<0.05). Flow cytometry showed that the S-phase fraction significantly dropped after the overexpression of miR-218 (P<0.01) and the percentage of apoptotic cells significantly increased (P<0.01). As shown by the Trans-well migration assay, the enhanced miR-218 expression was associated with a significantly lower number of cells that passed through a Transwell chamber (P<0.01). Luciferase reporter assay showed that, compared with the control group, the relative luciferase activity significantly decreased in the miR-218 mimic group (P<0.01). As shown by the Western blotting, compared with the control group, the HMGB1 protein expression significantly decreased in the PANC-1 group after the transfection of miR-218 mimic for 48 h (P<0.01).

CONCLUSIONS

The miR-218 expression decreases in human PCT and cell lines. miR-218 can negatively regulate the HMGB1 protein expression and inhibit the proliferation and invasion of pancreatic cancer cells. A treatment strategy by enhancing the miR-218 expression may benefit the patients with pancreatic cancer.