H3 histamine receptor agonist inhibits biliary growth of BDL rats by downregulation of the cAMP-dependent PKA/ERK1/2/ELK-1 pathway

Abstract

Histamine regulates many functions by binding to four histamine G-coupled receptor proteins (H1R, H2R, H3R and H4R). As H3R exerts their effects by coupling to Ga i/o proteins reducing adenosine 3 0 , 5 0 -monophosphate (cAMP) levels (a key player in the modulation of cholangiocyte hyperplasia/damage), we evaluated the role of H3R in the regulation of biliary growth. We posed the following questions: (1) Do cholangiocytes express H3R? (2) Does in vivo administration of (R)-(a)-(À)-methylhistamine dihydrobromide (RAMH) (H3R agonist), thioperamide maleate (H3R antagonist) or histamine, in the absence/presence of thioperamide maleate, to bile duct ligated (BDL) rats regulate cholangiocyte proliferation? and (3) Does RAMH inhibit cholangiocyte proliferation by downregulation of cAMP-dependent phosphorylation of protein kinase A (PKA)/extracellular signal-regulated kinase 1/2 (ERK1/2)/ets-like gene-1 (Elk-1)? The expression of H3R was evaluated in liver sections by immunohistochemistry and immunofluorescence, and by real-time PCR in cholangiocyte RNA from normal and BDL rats. BDL rats (immediately after BDL) were treated daily with RAMH, thioperamide maleate or histamine in the absence/presence of thioperamide maleate for 1 week. Following in vivo treatment of BDL rats with RAMH for 1 week, and in vitro stimulation of BDL cholangiocytes with RAMH, we evaluated cholangiocyte proliferation, cAMP levels and PKA, ERK1/2 and Elk-1 phosphorylation. Cholangiocytes from normal and BDL rats express H3R. The expression of H3R mRNA increased in BDL compared to normal cholangiocytes. Histamine decreased cholangiocyte growth of BDL rats to a lower extent than that observed in BDL RAMH-treated rats; histamine-induced inhibition of cholangiocyte growth was partly blocked by thioperamide maleate. In BDL rats treated with thioperamide maleate, cholangiocyte hyperplasia was slightly higher than that of BDL rats. In vitro, RAMH inhibited the proliferation of BDL cholangiocytes. RAMH inhibition of cholangiocyte growth was associated with decreased cAMP levels and PKA/ERK1/2/Elk-1 phosphorylation. Downregulation of cAMP-dependent PKA/ERK1/2/Elk-1 phosphorylation (by activation of H3R) is important in the inhibition of cholangiocyte growth in liver diseases.

Inhibition of mast cell-derived histamine secretion by cromolyn sodium treatment decreases biliary hyperplasia in cholestatic rodents

“…As we have previously shown, 25 after BDL there is a marked increase in intrahepatic biliary mass and cholangiocyte proliferation compared with sham-operated rats. Following treatment with cromolyn sodium, IBDM was significantly decreased as shown by immunohistochemistry (quantified in the bottom left panel) and real-time PCR for CK-19 ( Figure 1).…”

“…We also evaluated the expression of CK-19 (the cholangiocyte-specific marker 25,28 ) by real-time PCR. Our cultured mast cell line expressed high levels of HDC, MAO-B, chymase, tryptase and c-kit but had virtually no expression of CK-19 ( Figure 7).…”

“…25,28 Virtually pure cholangiocytes (verified by g-glutamyltranspetidase histochemistry 29 ) were isolated as described by us 25,26 using a monoclonal antibody (a mouse IgG 2a , a gift from Dr R Faris, Brown University, Providence, RI, USA) against an unidentified antigen expressed by all rat cholangiocytes. Cell viability was evaluated using trypan blue.…”

“…Male Fisher 544 rats were subjected to sham or BDL 25,26 and congruently implanted with IP osmotic pumps to deliver saline or cromolyn sodium (inhibits mast cell histamine release, 24 mg/kg BW/day 27 ) for 7 days before killing. Animals were housed at the Scott and White Hospital Animal Facility and given free access to drinking water and standard chow.…”

Histamine receptor expression in human renal tubules: a comparative pharmacological evaluation

“…It has been largely demonstrated that H 3 R is mostly expressed in the central and, to a lesser extent, in the peripheral nervous system. Only a small number of experimental observations have showed its presence on non-neuronal cell types such as rodent fundic mucosa endocrine cells [26], cholangiocytes [37], pancreatic β-cells [38], and in the human bronchial epithelial cell line BEAS-2B [39]. Therefore, our data add a new non-neuronal localization of the H 3 R, contributing to the hypothesis that the H 3 R could also mediate nonneuronal histamine effects.…”