Inhibition of Epidermal Tight Junction Function by Histamine is Mediated by H1 and H4 Receptors

RationaleAtopic Dermatitis (AD) is characterized by stratum corneum and tight junction (TJ) barrier defects. Histamine is increased in lesional AD skin. Recently, histamine has been shown to inhibit human keratinocyte (KC) terminal differentiation and promote proliferation. KC express histamine receptor 1 (H1R), H2R and H4R.MethodsCa+2-differentiated primary KC and epidermal explants were treated with histamine (100 μM) to determine the effect this had on TJ function. TJ integrity was assessed by trans-epithelial electrical resistance (TEER) and paracellular fluorescein flux. Selective antagonists were used for each receptor: H1R (Cetirizine, 10 μM), H2R (Cimetidine, 100 μM), or H4R (JNJ7777120, 10 μM). Keratinocyte differentiation was assessed by examining filaggrin, loricrin and keratin 10 protein expression by Western blot. Expression level of HRs were evaluated by PCR in skin biopsies of AD (n=6-8) and non-atopic (n=10) subjects.ResultsHistamine significantly reduced TEER, in both KC (0.6 fold, P<0.001, n=7) and ex vivo skin explants (0.7 fold, P<0.05, n=3), and enhanced fluorescein permeability flux of PHK (2.2 fold, P<0.05, n=7) and skin explants (1.3 fold, P<0.05, n=3). In KC, H1R and H4R, but not H2R, antagonists blocked histamine-mediated TEER reduction. We confirmed that histamine selectively reduced filaggrin. Only H1R antagonist was able to prevent the histamine-mediated reduction of filaggrin expression. H1R was reduced in AD skin lesional and non-lesional (P<0.01). No significant changes in H4R expression were found.ConclusionsOur studies revealed that histamine might contribute to epidermal barrier impairment observed in AD skin, by reducing TJ integrity (H1R and H4R -dependent) and filaggrin expression (H1R-dependent). RationaleAtopic Dermatitis (AD) is characterized by stratum corneum and tight junction (TJ) barrier defects. Histamine is increased in lesional AD skin. Recently, histamine has been shown to inhibit human keratinocyte (KC) terminal differentiation and promote proliferation. KC express histamine receptor 1 (H1R), H2R and H4R. Atopic Dermatitis (AD) is characterized by stratum corneum and tight junction (TJ) barrier defects. Histamine is increased in lesional AD skin. Recently, histamine has been shown to inhibit human keratinocyte (KC) terminal differentiation and promote proliferation. KC express histamine receptor 1 (H1R), H2R and H4R. MethodsCa+2-differentiated primary KC and epidermal explants were treated with histamine (100 μM) to determine the effect this had on TJ function. TJ integrity was assessed by trans-epithelial electrical resistance (TEER) and paracellular fluorescein flux. Selective antagonists were used for each receptor: H1R (Cetirizine, 10 μM), H2R (Cimetidine, 100 μM), or H4R (JNJ7777120, 10 μM). Keratinocyte differentiation was assessed by examining filaggrin, loricrin and keratin 10 protein expression by Western blot. Expression level of HRs were evaluated by PCR in skin biopsies of AD (n=6-8) and non-atopic (n=10) subjects. Ca+2-differentiated primary KC and epidermal explants were treated with histamine (100 μM) to determine the effect this had on TJ function. TJ integrity was assessed by trans-epithelial electrical resistance (TEER) and paracellular fluorescein flux. Selective antagonists were used for each receptor: H1R (Cetirizine, 10 μM), H2R (Cimetidine, 100 μM), or H4R (JNJ7777120, 10 μM). Keratinocyte differentiation was assessed by examining filaggrin, loricrin and keratin 10 protein expression by Western blot. Expression level of HRs were evaluated by PCR in skin biopsies of AD (n=6-8) and non-atopic (n=10) subjects. ResultsHistamine significantly reduced TEER, in both KC (0.6 fold, P<0.001, n=7) and ex vivo skin explants (0.7 fold, P<0.05, n=3), and enhanced fluorescein permeability flux of PHK (2.2 fold, P<0.05, n=7) and skin explants (1.3 fold, P<0.05, n=3). In KC, H1R and H4R, but not H2R, antagonists blocked histamine-mediated TEER reduction. We confirmed that histamine selectively reduced filaggrin. Only H1R antagonist was able to prevent the histamine-mediated reduction of filaggrin expression. H1R was reduced in AD skin lesional and non-lesional (P<0.01). No significant changes in H4R expression were found. Histamine significantly reduced TEER, in both KC (0.6 fold, P<0.001, n=7) and ex vivo skin explants (0.7 fold, P<0.05, n=3), and enhanced fluorescein permeability flux of PHK (2.2 fold, P<0.05, n=7) and skin explants (1.3 fold, P<0.05, n=3). In KC, H1R and H4R, but not H2R, antagonists blocked histamine-mediated TEER reduction. We confirmed that histamine selectively reduced filaggrin. Only H1R antagonist was able to prevent the histamine-mediated reduction of filaggrin expression. H1R was reduced in AD skin lesional and non-lesional (P<0.01). No significant changes in H4R expression were found. ConclusionsOur studies revealed that histamine might contribute to epidermal barrier impairment observed in AD skin, by reducing TJ integrity (H1R and H4R -dependent) and filaggrin expression (H1R-dependent). Our studies revealed that histamine might contribute to epidermal barrier impairment observed in AD skin, by reducing TJ integrity (H1R and H4R -dependent) and filaggrin expression (H1R-dependent).