High mobility group B2 is secreted by myeloid cells and has mitogenic and chemoattractant activities similar to high mobility group B1

High mobility group B box (HMGB) proteins are a family of chromatin proteins made up of two basic DNA binding domains, HMG box A and B, and a C-terminal acidic tail. HMGB have a highly conserved sequence, but different expression pattern: HMGB1 is almost ubiquitous, whereas the others are highly expressed in only a few tissues in adults. We previously demonstrated that HMGB1 is released by necrotic cells and has chemoattractant activity for inflammatory and stem cells, via binding to receptor for advanced glycation endproducts (RAGE). HMGB1 can be actively secreted by inflammatory cells. Here, we report that also HMGB2 can be secreted by THP-1 cells, and promotes proliferation and migration of endothelial cells. These functions of HMGB2 are exerted via engagement of RAGE, whose blockade completely abrogates cell responses. Since extracellular HMGB2 has been detected in the blood and other biological fluids, it might be necessary to target HMGB2 at the same time as HMGB1 for therapeutical efficacy.     

HMGB1: a signal of necrosis

When tissues are damaged, they usually heal. The cellular responses towards healing require the prior recognition that damage has occurred. High Mobility Group Box 1 protein (HMGB1) is a ubiquitous nuclear protein that is passively released by cells that have died in a traumatic, non-programmed way (necrosis). Several receptors for HMGB1 exist, and upon binding HMGB1 they alert leukocytes to extravasate from the blood into the affected tissue, trigger adaptive immunity and promote the migration and proliferation of cells (including stem cells) to repair the damaged tissue. Significantly, apoptotic cells modify their chromatin so as to bind HMGB1, which is not released. Several cell types (in particular inflammatory cells) when distressed have the ability to secrete HMGB1 actively, via a dedicated pathway, and thus produce a damage signal without dying. Because of its powerful activities, HMGB1 is involved in several disorders, including autoimmune ones.     

Circulating platelets as a source of the damage-associated molecular pattern HMGB1 in patients with systemic sclerosis

The link between platelet activation and vascular injury in Systemic Sclerosis (SSc) is poorly characterized. Here we report that platelet activation results in i) the translocation from the cytoplasm to the surface of HMGB1, a prototypical DAMP signal associated with tissue regeneration and ii) the release of platelet derived microparticles (PDμP) expressing HMGB1. Decreased HMGB1 content (334.6 ± 21.2 vs 587.1 ± 11.1 AUF, P < 0.001) and HMGB1 translocation to the outer leaflet of the plasma membrane (17.8 ± 3.5 vs 4.5 ± 0.5%, P < 0.001) characterize circulating platelets of SSc patients (n = 29) when compared with age-matched healthy controls (HC, n = 20). Conversely, a significantly higher fraction of PDμP in the blood of SSc patients, but not of HC, consistently expose (HMGB1 (MFI 62.8 ± 3.95 vs 4.3 ± 0.7). Platelet HMGB1 depletion is significantly associated in SSc patients with degranulation and with expression of P-selectin and of tissue factor as well as with fibrinogen binding to their plasma membrane. These findings indicate that platelets represent a source of HMGB1, an ancestral signal of necrosis, in the vasculature of SSc patients, possible contributing to persistent microvascular injury and endothelial cell activation.     

高迁移率族蛋白B1:从核蛋白到新的细胞因子

对高迁移率族蛋白B1（HMGB1）的认识曾长期局限于其调节基因转录的核蛋白功能。由于其作为细菌内毒素致死性的晚期介质这一重要功能不久前被发现,HMGB1新的生物学活性及其作用机制引起广泛兴趣和深入研究。HMGB1具有细胞因子的各种共同特性,包括其自分泌和旁分泌的特征、其受体依赖性以及它与其他炎症细胞因子相互诱生与协同作用的网络性。在感染性和非感染性的炎症、损伤和细胞坏死中,HMGB1介导了以巨噬细胞为主的固有免疫应答,发挥了至关重要的前炎症细胞因子和趋化因子的作用,同时还发现其对神经突触和肿瘤细胞的生长的促进作用。以HMGB1为靶子的治疗策略,包括对其产生和释放的抑制以及对其与受体（已知RAGE、TLR2和TLR4）结合的拮抗措施,在实验动物获得了可喜的成功并给临床应用带来了希望。     

Blocking HMGB1 signal pathway protects early radiation-induced lung injury

It has been reported that HMGB1 participated in various types of lung injury. In this study, we explored whether blocking HMGB1 has a preventive effect on the early radiation-induced lung injury and investigate the mechanism. Mice model of radiation-induced lung injury were accomplished by a single dose irradiation (15 Gy) to the whole thorax. Irradiated mice were treated with HMGB1-neutralizing antibody intraperitoneally dosed 10 μg, 50 μg, 100 μg/mouse respectively and were sacrificed after one week post-irradiation. Lung tissue slices were stained by H&E, and alveolitis was quantified by Szapiel scoring system. The level of cytokines TNF-γ in bronchoalveolar lavage fluid was detected by ELISA method. And p65NF-κB, p50NF-κB protein expression in mice lung tissues was detected by Western blot analysis. The results showed that blocking HMGB1 inhibited the inflammatory response, and thereby decreased the degree of alveolitis of irradiated lung tissue. In addition, HMGB1 antagonist can restrain the expression of type Th2 or Th17 derived inflammatory cytokines TNF-α, IL-6 and IL-17A, promote the expression of Th1 type cytokines INF-γ, and inhibit p65 NF-κB but promote p50 NF-κB activation, which promoted the resolution of the radiation-induced inflammatory response. In conclusion, blocking HMGB1 can reduce the degree of early radiation-induced lung injury, and its mechanism may be related to the promotion of p50NF-κB activation and its downstream molecules expression. Inhibiting HMGB1 may be a new target to deal with early radiation-induced lung injury.     

人HMGB1 B box蛋白的表达、鉴定及其单克隆抗体的制备

目的:表达人HMGB1 B box蛋白,制备其单克隆抗体(mAb),为进一步研究HMGB1 B box在免疫调节和抗感染免疫中的作用奠定基础。方法:将pET28-HMGB1 B box转化DH5α摇菌表达,使用His标记的蛋白纯化柱纯化、鉴定后免疫BALB/c小鼠,取免疫小鼠的脾细胞与Sp2/0细胞进行常规融合,经间接ELISA筛选阳性克隆,获得分泌人HMGB1 B box蛋白mAb的杂交瘤细胞株,通过ELISA、Western blot等方法鉴定其特性(mAb的效价、Ig类别及特异性)。结果:成功地建立了2株稳定分泌抗人HMGB1 B box的mAb细胞株,分别命名为1D2F4E3和2D4E3A2。2株mAb的免疫球蛋白类型均为IgG,Western blot显示,2株mAb均能与HMGB1 B box发生特异性反应,其滴度为1×106,mAb1 D2F4E3和2D4E3A2的A450值分别为0.324±0.093和0.296±0.085。结论:获得了2株分泌HMGB1 B box mAb的细胞株,为HMGB1 B box蛋白的生物学功能研究奠定了基础。     

HMGB1-induced autophagy in Schwann cells promotes neuroblastoma proliferation

Neuroblastoma inflicts mostly on children, and the pathogenesis remains elusive. Clinical diagnosis and therapeutic approaches are still on the incipient stage, so further understanding of the molecular and cellular mechanisms of the disease is necessary. Inflammation has been commonly regarded as a hallmark in tumorigenesis and development, and we identified a new inflammatory factor, HMGB1, is considerably increased in neuroblastoma. Our study shows that HMGB1 induces autophagy in Schwann cells through activation of TLR4, and knockdown of TLR4 obviates the HMGB1-induced autophagy. The HMGB1-induced autophagy is through classical pathway, as deficiency of Beclin 1 deprived autophagy in Schwann cells. Coculture of neuroblastoma with Schwann cells pretreated with HMGB1 promoted the proliferation of neuroblastoma cells, and if Beclin 1 is knocked down in Schwann cells, no promotion effects is observed. Taken together, our study demonstrates that HMGB1-induced autophagy in Schwann cells contributes to neuroblastoma cell proliferation, thus providing a potential therapeutic approach on neuroblastoma development.     

The Role of High Mobility Group Box 1 in Innate Immunity

With growing accounts of inflammatory diseases such as sepsis, greater understanding the immune system and the mechanisms of cellular immunity have become primary objectives in immunology studies. High mobility group box 1 (HMGB1) is a ubiquitous nuclear protein that is implicated in various aspects of the innate immune system as a damage-associated molecular pattern molecule and a late mediator of inflammation, as well as in principal cellular processes, such as autophagy and apoptosis. HMGB1 functions in the nucleus as a DNA chaperone; however, it exhibits cytokine-like activity when secreted by injurious or infectious stimuli. Extracellular HMGB1 acts through specific receptors to promote activation of the NF-κB signaling pathway, leading to production of cytokines and chemokines. These findings further implicate HMGB1 in lethal inflammatory diseases as a crucial regulator of inflammatory, injurious, and infectious responses. In this paper, we summarize the role of HMGB1 in inflammatory and non-inflammatory states and assess potential therapeutic approaches targeting HMGB1 in inflammatory diseases.     

人高迁移率族B1的表达及其多克隆抗体的制备与鉴定

目的以原核表达的人高迁移率族B1(High mobihty group box 1,HMGB1)蛋白为免疫原免疫日本大耳白兔,制备其兔多克隆抗体并进行鉴定。方法将人HMGB1 cDNA克隆于原核表达载体pQE-80L并转化大肠杆菌DH5α,经异丙基-β-D-硫代半乳糖苷(IPTG)诱导HMGB1表达,Ni^2 -NTA层析纯化后,用其免疫兔。以ELISA检测抗体效价,Western blot鉴定抗体特异性。结果成功表达并纯化了人HMGB1蛋白,纯化后纯度可达96％;ELISA法测定抗体效价为1：25600;Western blot结果显示所制备的抗体可特异性与人HMGB1蛋白结合。结论成功制备了兔抗人HMGB1多克隆抗体,为进一步研究HMGB1与相关疾病的关系打下了基础。     

HMGB1 blockade differentially impacts pulmonary inflammation and defense responses in poly(I:C)/LPS-exposed heart transplant mice

A large number of recipients are in a compromised immune defense condition because of the routine application of immunosuppressive regimens after heart transplantation. Our previous work demonstrated that blockade of high-mobility group box 1 (HMGB1) prolongs the graft survival. Whether and how HMGB1 blockade impacts respiratory responses against pathogen-like challenge in organ transplant recipients when it improves cardiac graft are not elucidated. At the present study, after abdominal heterotopic heart transplantation, the recipient mice were treated with HMGB1 mAb, and then challenged with poly(I:C) or LPS intratracheally on day 7 post transplantation. We found that the level of bronchoalveolar lavage (BAL) HMGB1 was elevated after heart transplantation, and aggravated responses to respiratory tract poly(I:C)/LPS challenge were observed. HMGB1 neutralizing mAb treatment in poly(I:C)-challenged recipient mice alleviated pulmonary histopathological changes, neutrophil infiltration and inflammatory cytokine release, but unaffected the level of IFN-β, the distribution of CD11b⁺CD27⁺/CD11b⁺CD27⁻ NK cell subsets, and CD8⁺ T cell responses. In LPS-exposed recipient mice, HMGB1 mAb treatment ameliorated pulmonary inflammatory damage and enhanced the phagocytosis of phagocytic cells. Thus, this study may establish a basis for the application of HMGB1 blockade to improve the outcomes of heart transplant recipients because HMGB1 inhibition ameliorates pulmonary inflammation, but maintains defense-associated responses.     

Elevated HMGB1-related interleukin-6 is associated with dynamic responses of monocytes in patients with active pulmonary tuberculosis

There were limited studies assessing the role of HMGB1 in TB infection. In this prospective study, we aimed to assess the levels of HMGB1 in plasma or sputum from active pulmonary tuberculosis (APTB) patients positive for Mtb culture test, and to evaluate its relationship with inflammatory cytokines and innate immune cells. A total of 36 sputum Mtb culture positive APTB patients and 32 healthy volunteers (HV) were included. Differentiated THP-1 cells were treated for 6, 12 and 24 hrs with BCG at a multiplicity of infection of 10. The absolute values and percentages of white blood cells (WBC), neutrophils, lymphocytes, and monocytes were detected by an automatic blood analyzer. Levels of HMGB1, IL-6, IL-10 and TNF-α in plasma, sputum, or cell culture supernatant were measured by ELISA. The blood levels of HMGB1, IL-6, IL-10 and TNF-α, the absolute values of WBC, monocytes and neutrophils, and the percentage of monocytes were significant higher in APTB patients than those in HV groups (P<0.05). The sputum levels of HMGB1, IL-10, and TNF-α were also significantly higher in APTB patients than those in HV groups (P<0.05). Meanwhile, plasma level of HMGB1, IL-6, and IL-10 in APTB patients were positively correlated with those in sputum (P<0.05), respectively. IL-6 was positively correlated with HMGB1 both in plasma and sputum of APTB patients (P<0.05). HMGB1 and IL-6 is positively correlated with the absolute number of monocytes in APTB patients (P<0.05). BCG induced HMGB1, IL-6, IL-10 and TNF-α production effectively in PMA-treated THP-1 cells. HMGB1 may be used as an attractive biomarker for APTB diagnosis and prognosis and may reflect the inflammatory status of monocytes in patients with APTB.     

HMGB1 blockade attenuates experimental autoimmune myocarditis and suppresses Th17-cell expansion

High-mobility group box 1 (HMGB1), a non-histone nuclear protein, has been implicated in cardiovascular diseases. Dilated cardiomyopathy (DCM), one of the leading causes of heart failure, is often caused by coxsackievirus B3-triggered myocarditis and promoted by the post-infectious autoimmune process. Th17 cells, a novel CD4(+) T subset, may be important in the pathogenesis of autoimmune myocarditis. In the present study, we attempted to block HMGB1 function with a monoclonal antibody specific for HMGB1 B box and investigated the effects of the blockade on Th17 cells and experimental autoimmune myocarditis (EAM). After induction of EAM, HMGB1 protein levels were significantly elevated both in the heart and blood. Administration of an anti-HMGB1 B box mAb attenuated cardiac pathological changes and reduced the number of infiltrating inflammatory cells in the heart during EAM. These protective effects of HMGB1 blockade correlated with a reduced number of Th17 cells in local tissues and lower levels of IL-17 in the serum. Furthermore, in vitro, studies demonstrated that HMGB1 promoted Th17-cell expansion. Therefore, we speculate that HMGB1 blockade ameliorates cardiac pathological changes in EAM by suppressing Th17 cells.     

Requirement of HMGB1 and RAGE for the maturation of human plasmacytoid dendritic cells

Dendritic cells (DC) are key components of innate and adaptive immune responses. Plasmacytoid DC (PDC) are a specialized DC subset that produce high amounts of type I interferons in response to microbes. High mobility group box 1 protein (HMGB1) is an abundant nuclear protein, which acts as a potent pro-inflammatory factor when released extracellularly. We show that HMGB1 leaves the nucleus of maturing PDC following TLR9 activation, and that PDC express on the plasma membrane the best-characterized receptor for HMGB1, RAGE. Maturation and type I IFN secretion of PDC is hindered when the HMGB1/RAGE pathway is disrupted. These results reveal HMGB1 and RAGE as the first known autocrine loop modulating the maturation of PDC, and suggest that antagonists of HMGB1/RAGE might have therapeutic potential for the treatment of systemic human diseases.     

外源性HMGB1的研究进展

胞内HMGB1可以主动或被动释放到胞外,外源性HMGB1被认为是重要的晚期炎症因子,在炎症的发生发展中起重要作用.胞外HMGB1能与很多因子形成复合物,通过不同的受体通路影响转录因子NF-κB的活性,发挥不同的生物学效应.除发挥炎症因子的作用外,HMGB1在组织的修复和重建中的作用也不容小觑.另外,HMGB1预处理可以诱导产生免疫耐受,可能与脓毒症末期免疫功能低下有一定关系.