Endothelial histamine H1 receptor signaling reduces blood–brain barrier permeability and susceptibility to autoimmune encephalomyelitis

Disruption of the blood–brain barrier (BBB) underlies the development of experimental autoimmune encephalomyelitis (EAE) and multiple sclerosis. Environmental factors, such as Bordetella pertussis, are thought to sensitize central endothelium to biogenic amines like histamine, thereby leading to increased BBB permeability. B. pertussis-induced histamine sensitization (Bphs) is a monogenic intermediate phenotype of EAE controlled by histamine H1 receptor (Hrh1/H1R). Here, we transgenically overexpressed H1R in endothelial cells of Hrh1-KO (H1RKO) mice to test the role of endothelial H1R directly in Bphs and EAE. Unexpectedly, transgenic H1RKO mice expressing endothelial H1R under control of the von Willebrand factor promoter (H1RKO-vWFH1R Tg) were Bphs-resistant. Moreover, H1RKO-vWFH1R Tg mice exhibited decreased BBB permeability and enhanced protection from EAE compared with H1RKO mice. Thus, contrary to prevailing assumptions, our results show that endothelial H1R expression reduces BBB permeability, suggesting that endothelial H1R signaling may be important in the maintenance of cerebrovascular integrity

Central histamine H3 receptor signaling negatively regulates susceptibility to autoimmune inflammatory disease of the CNS

Histamine (HA), a biogenic amine with a broad spectrum of activities in both physiological and pathological settings, plays a key regulatory role in experimental allergic encephalomyelitis, the autoimmune model of multiple sclerosis. HA exerts its effect through four G protein-coupled receptors designated HA receptor H1, H2, H3, and H4. We report here that, compared with wild-type animals, mice with a disrupted HA H3 receptor (H3RKO), the expression of which is normally confined to cells of the nervous system, develop more severe disease and neuroinflammation. We show that this effect is associated with dysregulation of blood–brain barrier permeability and increased expression of MIP-2, IP-10, and CXCR3 by peripheral T cells. Our data suggest that pharmacological targeting of the H3R may be useful in preventing the development and formation of new lesions in multiple sclerosis, thereby significantly limiting the progression of the disease