Vagus nerve stimulation primes platelets and reduces bleeding in hemophilia A male mice

Deficiency of coagulation factor VIII in hemophilia A disrupts clotting and prolongs bleeding. While the current mainstay of therapy is infusion of factor VIII concentrates, inhibitor antibodies often render these ineffective. Because preclinical evidence shows electrical vagus nerve stimulation accelerates clotting to reduce hemorrhage without precipitating systemic thrombosis, we reasoned it might reduce bleeding in hemophilia A. Using two different male murine hemorrhage and thrombosis models, we show vagus nerve stimulation bypasses the factor VIII deficiency of hemophilia A to decrease bleeding and accelerate clotting. Vagus nerve stimulation targets acetylcholine-producing T lymphocytes in spleen and α7 nicotinic acetylcholine receptors (α7nAChR) on platelets to increase calcium uptake and enhance alpha granule release. Splenectomy or genetic deletion of T cells or α7nAChR abolishes vagal control of platelet activation, thrombus formation, and bleeding in male mice. Vagus nerve stimulation warrants clinical study as a therapy for coagulation disorders and surgical or traumatic bleeding.

MD-2 is required for disulfide HMGB1-dependent TLR4 signaling

Yang et al. show that a disulfide isoform of HMGB1, with a role in TLR4 signaling, physically interacts with and binds MD-2. MD-2 deficiency in macrophage cell lines or in primary mouse macrophages stimulated with HMGB1 implicates MD-2 in TLR4 signaling. They also identify an HGMB1 peptide inhibitor, P5779, which when administered in vivo can protect mice from acetaminophen-induced hepatoxicity, ischemia/reperfusion injury, and sepsis.

Innate immune receptors for pathogen- and damage-associated molecular patterns (PAMPs and DAMPs) orchestrate inflammatory responses to infection and injury. Secreted by activated immune cells or passively released by damaged cells, HMGB1 is subjected to redox modification that distinctly influences its extracellular functions. Previously, it was unknown how the TLR4 signalosome distinguished between HMGB1 isoforms. Here we demonstrate that the extracellular TLR4 adaptor, myeloid differentiation factor 2 (MD-2), binds specifically to the cytokine-inducing disulfide isoform of HMGB1, to the exclusion of other isoforms. Using MD-2–deficient mice, as well as MD-2 silencing in macrophages, we show a requirement for HMGB1-dependent TLR4 signaling. By screening HMGB1 peptide libraries, we identified a tetramer (FSSE, designated P5779) as a specific MD-2 antagonist preventing MD-2–HMGB1 interaction and TLR4 signaling. P5779 does not interfere with lipopolysaccharide-induced cytokine/chemokine production, thus preserving PAMP-mediated TLR4–MD-2 responses. Furthermore, P5779 can protect mice against hepatic ischemia/reperfusion injury, chemical toxicity, and sepsis. These findings reveal a novel mechanism by which innate systems selectively recognize specific HMGB1 isoforms. The results may direct toward strategies aimed at attenuating DAMP-mediated inflammation while preserving antimicrobial immune responsiveness.

HMGB1 mediates cognitive impairment in sepsis survivors

Severe sepsis, a syndrome that complicates infection and injury, affects 750,000 annually in the United States. The acute mortality rate is approximately 30%, but, strikingly, sepsis survivors have a significant disability burden: up to 25% of survivors are cognitively and physically impaired. To investigate the mechanisms underlying persistent cognitive impairment in sepsis survivors, here we developed a murine model of severe sepsis survivors following cecal ligation and puncture (CLP) to study cognitive impairments. We observed that serum levels of high mobility group box 1 (HMGB1), a critical mediator of acute sepsis pathophysiology, are increased in sepsis survivors. Significantly, these levels remain elevated for at least 4 wks after CLP. Sepsis survivors develop significant, persistent impairments in learning and memory, and anatomic changes in the hippocampus associated with a loss of synaptic plasticity. Administration of neutralizing anti-HMGB1 antibody to survivors, beginning 1 wk after onset of peritonitis, significantly improved memory impairments and brain pathology. Administration of recombinant HMGB1 to naïve mice recapitulated the memory impairments. Together, these findings indicate that elevated HMGB1 levels mediate cognitive decline in sepsis survivors, and suggest that it may be possible to prevent or reverse cognitive impairments in sepsis survivors by administration of anti-HMGB1 antibodies.

Neural signaling in the spleen controls B-cell responses to blood-borne antigen

Entry of blood-borne pathogens into the spleen elicits a series of changes in cellular architecture that culminates in the systemic release of protective antibodies. Despite an abundance of work that has characterized these processes, the regulatory mechanisms that coordinate cell trafficking and antibody production are still poorly understood. Here, marginal zone (MZ) B cells responding to streptococcus in the blood were observed to migrate along splenic nerves, arriving at the red pulp venous sinuses where they become antibody-secreting cells. Electrical stimulation of the vagus nerve, which in turn regulates the splenic nerve, arrested B-cell migration and decreased antibody secretion. Thus, neural circuits regulate the first wave of antibody production following B-cell exposure to blood-borne antigen.

Galantamine alleviates inflammation and other obesity-associated complications in high-fat diet-fed mice

Obesity, a serious and growing health threat, is associated with low-grade inflammation that plays a role in mediating its adverse consequences. Previously, we have discovered a role for neural cholinergic signaling in controlling inflammation, and demonstrated that the cholinergic agent galantamine suppresses excessive proinflammatory cytokine release. The main objective of this study was to examine the efficacy of galantamine, a clinically-approved drug, in alleviating obesity-related inflammation and associated complications. After 8 wks on a high-fat diet, C57BL/6J mice were treated with either galantamine (4 mg/kg, intraperitoneally [i.p.]) or saline for 4 wks in parallel with mice on a low-fat diet and treated with saline. Galantamine treatment of obese mice significantly reduced body weight, food intake, abdominal adiposity, plasma cytokine and adipokine levels, and significantly improved blood glucose, insulin resistance and hepatic steatosis. In addition, galantamine alleviated impaired insulin sensitivity and glucose intolerance significantly. These results indicate a previously unrecognized potential of galantamine in alleviating obesity, inflammation and other obesity-related complications in mice. These findings are of interest for studying the efficacy of this clinically-approved drug in the context of human obesity and metabolic syndrome.