High mobility group box 1 (HMGB1) is an abundant chromatin protein that acts as a cytokine when released in the extracellular milieu by necrotic and inflammatory cells. Here, we show that extracellular HMGB1 and its receptor for advanced glycation end products (RAGE) induce both migration and proliferation of vessel-associated stem cells (mesoangioblasts), and thus may play a role in muscle tissue regeneration. In vitro, HMGB1 induces migration and proliferation of both adult and embryonic mesoangioblasts, and disrupts the barrier function of endothelial monolayers. In living mice, mesoangioblasts injected into the femoral artery migrate close to HMGB1-loaded heparin-Sepharose beads implanted in healthy muscle, but are unresponsive to control beads. Interestingly, α-sarcoglycan null dystrophic muscle contains elevated levels of HMGB1; however, mesoangioblasts migrate into dystrophic muscle even if their RAGE receptor is disabled. This implies that the HMGB1–RAGE interaction is sufficient, but not necessary, for mesoangioblast homing; a different pathway might coexist. Although the role of endogenous HMGB1 in the reconstruction of dystrophic muscle remains to be clarified, injected HMGB1 may be used to promote tissue regeneration.

Abstract-High-mobility group box 1 protein (HMGB1) is a chromatin protein that is released by inflammatory and necrotic cells. Extracellular HMGB1 signals tissue damage, stimulates the secretion of proinflammatory cytokines and chemokines, and modulates stem cell function. The present study examined exogenous HMGB1 effect on mouse left-ventricular function and myocyte regeneration after infarction. Myocardial infarction was induced in C57BL/6 mice by permanent coronary artery ligation. After 4 hours animals were reoperated and 200 ng of purified HMGB1 was administered in the peri-infarcted left ventricle. This intervention resulted in the formation of new myocytes within the infarcted portion of the wall. The regenerative process involved the proliferation and differentiation of endogenous cardiac c-kit ϩ progenitor cells. Circulating c-kit ϩ cells did not significantly contribute to HMGB1-mediated cardiac regeneration. Echocardiographic and hemodynamic parameters at 1, 2, and 4 weeks demonstrated a significant recovery of cardiac performance in HMGB1-treated mice. These effects were not observed in infarcted hearts treated either with the unrelated protein glutathione S-transferase or a truncated form of HMGB1. Thus, HMGB1 appears to be a potent inducer of myocardial regeneration following myocardial infarction. (Circ Res. 2005;97:e73-e83.)

High-mobility group box 1 (HMGB1) protein is a multifunctional cytokine involved in inflammatory responses and tissue repair. In this study, it was examined whether HMGB1 plays a role in skin wound repair both in normoglycemic and diabetic mice. HMGB1 was detected in the nucleus of skin cells, and accumulated in the cytoplasm of epidermal cells in the wounded skin. Diabetic human and mouse skin showed more reduced HMGB1 levels than their normoglycemic counterparts. Topical application of HMGB1 to the wounds of diabetic mice enhanced arteriole density, granulation tissue deposition, and accelerated wound healing. In contrast, HMGB1 had no effect in normoglycemic mouse skin wounds, where endogenous HMGB1 levels may be adequate for optimal wound closure. Accordingly, inhibition of endogenous HMGB1 impaired wound healing in normal mice but had no effect in diabetic mice. Finally, HMGB1 had a chemotactic effect on skin fibroblasts and keratinoyctes in vitro. In conclusion, lower HMGB1 levels in diabetic skin may play an important role in impaired wound healing and this defect may be overcome by the topical application of HMGB1.

High mobility group box 1 protein (HMGB1) is a chromatin component leaked out by necrotic cells and actively secreted by activated myeloid cells. The extracellular protein is a potent mediator of tissue remodeling. We show here that human atherosclerotic plaques, but not normal arteries, produce extracellular HMGB1. Secreted HMGB1 originates from endothelial cells, by neointimal foam cells, and also smooth muscle cells (SMCs). SMCs are an unexpected source for secreted HMGB1, since they normally express much lower amounts of HMGB1 than other cells types, and they do not secrete it. However, cultured SMCs actively secrete HMGB1 after cholesterol loading. In turn, in response to HMGB1, SMCs proliferate, migrate, and secrete more HMGB1. Thus, SMCs are both a source and a target of HMGB1; blocking HMGB1 secretion by SMCs can be an important strategy for treatment of atherosclerotic disease and in particular restenosis.

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.

Material

No abstract

Tissue damage is usually followed by healing, as both differentiated and stem cells migrate to replace dead or damaged cells. Mesoangioblasts (vessel-associated stem cells that can repair muscles) and fibroblasts migrate toward soluble factors released by damaged tissue. Two such factors are high mobility group box 1 (HMGB1), a nuclear protein that is released by cells undergoing unscheduled death (necrosis) but not by apoptotic cells, and stromal derived factor (SDF)–1/CXCL12. We find that HMGB1 activates the canonical nuclear factor κB (NF-κB) pathway via extracellular signal-regulated kinase phosphorylation. NF-κB signaling is necessary for chemotaxis toward HMGB1 and SDF-1/CXCL12, but not toward growth factor platelet-derived growth factor, formyl-met-leu-phe (a peptide that mimics bacterial invasion), or the archetypal NF-κB–activating signal tumor necrosis factor α. In dystrophic mice, mesoangioblasts injected into the general circulation ingress inefficiently into muscles if their NF-κB signaling pathway is disabled. These findings suggest that NF-κB signaling controls tissue regeneration in addition to early events in inflammation.