Antagonism of histamine H3 receptor promotes angiogenesis following focal cerebral ischemia

Novel insights on the biology and immunologic effects of histamine: A road map for allergists and mast cell biologists

Histamine (C5H9N3, molecular weight 111.15 g/mol) is a well-studied endogenous biogenic amine composed of an imidazole ring attached to an ethylamine side chain. It has a limited half-life of a few minutes within tissues and in circulation. Several cell types including mast cells (MCs), basophils, platelets, histaminergic neurons, and enterochromaffin cells produce varying amounts of histamine using histidine decarboxylase. However, only MCs and basophils have complex mechanisms to pack and store histamine in granules along with other mediators using serglycin and its carried glycosaminoglycan side chains. Relatively low granule pH (∼5.5) supports the binding of stored histamine to heparin, whereas exposure to neutral pH after degranulation weakens the binding and histamine becomes liberated. Histamine exerts multifaceted regulatory biofunctions by engaging its 4 types of heptahelical G protein-coupled receptors (H1R-H4R), which have different expression profiles and functions. MCs express H1R, H2R, and H4R, which gives them a dual role in histamine biology as producers and responsive target cells. Histamine plays a role in a variety of physiologic and pathologic processes such as cell proliferation, differentiation, hematopoiesis, vascular permeability, embryogenesis, tissue regeneration, and wound healing. The emergence of histamine receptor-deficient mouse models and the development of multiple histamine receptor agonists and antagonists have helped researchers better understand these physiologic and pathogenic functions of histamine. We review the biology of histamine with a focus on immunologic aspects and the role of histamine in allergy and MC biology.

Inhibition of histamine receptor 3 alleviates sevoflurane-induced hypomyelination and neurobehavioral deficits

BACKGROUND

Inhalational anesthetic sevoflurane can cause myelination damage in developing brain. This study examines the effects of histamine receptor 3 (H3) antagonist thioperamide on sevoflurane-induced hypomyelination and neurobehavioral deficits.

METHODS

Neonatal C57BL/6 mice were exposed to sevoflurane for consecutive three days and treated with H3 receptor antagonist thioperamide. Myelination was assessed in the hippocampus and corpus callosum. The neurobehavioral functions were also examined. Primary oligodendrocyte progenitor cells (OPCs) were used for in vitro experiments and the underlying mechanism.

RESULTS

Inhibition of H3 receptor with thioperamide significantly alleviated sevoflurane-induced impairments in myelination and neurobehavioral functions. In vitro experiments showed that thioperamide reversed the effects of sevoflurane on OPCs migration, proliferation and differentiation into mature oligodendrocytes. Mechanistically, thioperamide improved sevoflurane-induced hypomyelination may through H3 receptor-mediated GSK-3β/β-catenin pathway.

CONCLUSION

H3 receptor antogonist thioperamide could protect developing brain against hypomyelination and neurobehavioral deficits after repeated sevoflurane exposure. Therefore H3 receptor is a potential target for preventing anesthetic-induced developmental neurotoxicity.

Choroid plexus mast cells drive tumor-associated hydrocephalus

Tumor-associated hydrocephalus (TAH) is a common and lethal complication of brain metastases. Although other factors beyond mechanical obstructions have been suggested, the exact mechanisms are unknown. Using single-nucleus RNA sequencing and spatial transcriptomics, we find that a distinct population of mast cells locate in the choroid plexus and dramatically increase during TAH. Genetic fate tracing and intracranial mast-cell-specific tryptase knockout showed that choroid plexus mast cells (CPMCs) disrupt cilia of choroid plexus epithelia via the tryptase-PAR2-FoxJ1 pathway and consequently increase cerebrospinal fluid production. Mast cells are also found in the human choroid plexus. Levels of tryptase in cerebrospinal fluid are closely associated with clinical severity of TAH. BMS-262084, an inhibitor of tryptase, can cross the blood-brain barrier, inhibit TAH in vivo, and alleviate mast-cell-induced damage of epithelial cilia in a human pluripotent stem-cell-derived choroid plexus organoid model. Collectively, we uncover the function of CPMCs and provide an attractive therapy for TAH.

Signaling pathways in brain ischemia: Mechanisms and therapeutic implications

Ischemic stroke occurs when the arteries supplying blood to the brain are narrowed or blocked, inducing damage to brain tissue due to a lack of blood supply. One effective way to reduce brain damage and alleviate symptoms is to reopen blocked blood vessels in a timely manner and reduce neuronal damage. To achieve this, researchers have focused on identifying key cellular signaling pathways that can be targeted with drugs. These pathways include oxidative/nitrosative stress, excitatory amino acids and their receptors, inflammatory signaling molecules, metabolic pathways, ion channels, and other molecular events involved in stroke pathology. However, evidence suggests that solely focusing on protecting neurons may not yield satisfactory clinical results. Instead, researchers should consider the multifactorial and complex mechanisms underlying stroke pathology, including the interactions between different components of the neurovascular unit. Such an approach is more representative of the actual pathological process observed in clinical settings. This review summarizes recent research on the multiple molecular mechanisms and drug targets in ischemic stroke, as well as recent advances in novel therapeutic strategies. Finally, we discuss the challenges and future prospects of new strategies based on the biological characteristics of stroke.

Angiogenesis after ischemic stroke

Owing to its high disability and mortality rates, stroke has been the second leading cause of death worldwide. Since the pathological mechanisms of stroke are not fully understood, there are few clinical treatment strategies available with an exception of tissue plasminogen activator (tPA), the only FDA-approved drug for the treatment of ischemic stroke. Angiogenesis is an important protective mechanism that promotes neural regeneration and functional recovery during the pathophysiological process of stroke. Thus, inducing angiogenesis in the peri-infarct area could effectively improve hemodynamics, and promote vascular remodeling and recovery of neurovascular function after ischemic stroke. In this review, we summarize the cellular and molecular mechanisms affecting angiogenesis after cerebral ischemia registered in PubMed, and provide pro-angiogenic strategies for exploring the treatment of ischemic stroke, including endothelial progenitor cells, mesenchymal stem cells, growth factors, cytokines, non-coding RNAs, etc.