Small mouse cholangiocytes proliferate in response to H1 histamine receptor stimulation by activation of the IP₃/CaMK I/CREB pathway

Abstract

Cholangiopathies are characterized by the heterogeneous proliferation of different-sized cholangiocytes. Large cholangiocytes proliferate by a cAMP-dependent mechanism. The function of small cholangiocytes may depend on the activation of inositol trisphosphate (IP(3))/Ca(2+)-dependent signaling pathways; however, data supporting this speculation are lacking. Four histamine receptors exist (HRH1, HRH2, HRH3, and HRH4). In several cells: 1) activation of HRH1 increases intracellular Ca(2+) concentration levels; and 2) increased [Ca(2+)](i) levels are coupled with calmodulin-dependent stimulation of calmodulin-dependent protein kinase (CaMK) and activation of cAMP-response element binding protein (CREB). HRH1 agonists modulate small cholangiocyte proliferation by activation of IP(3)/Ca(2+)-dependent CaMK/CREB. We evaluated HRH1 expression in cholangiocytes. Small and large cholangiocytes were stimulated with histamine trifluoromethyl toluidide (HTMT dimaleate; HRH1 agonist) for 24-48 h with/without terfenadine, BAPTA/AM, or W7 before measuring proliferation. Expression of CaMK I, II, and IV was evaluated in small and large cholangiocytes. We measured IP(3), Ca(2+) and cAMP levels, phosphorylation of CaMK I, and activation of CREB (in the absence/presence of W7) in small cholangiocytes treated with HTMT dimaleate. CaMK I knockdown was performed in small cholangiocytes stimulated with HTMT dimaleate before measurement of proliferation and CREB activity. Small and large cholangiocytes express HRH1, CaMK I, and CaMK II. Small (but not large) cholangiocytes proliferate in response to HTMT dimaleate and are blocked by terfenadine (HRH1 antagonist), BAPTA/AM, and W7. In small cholangiocytes, HTMT dimaleate increased IP(3)/Ca(2+) levels, CaMK I phosphorylation, and CREB activity. Gene knockdown of CaMK I ablated the effects of HTMT dimaleate on small cholangiocyte proliferation and CREB activation. The IP(3)/Ca(2+)/CaMK I/CREB pathway is important in the regulation of small cholangiocyte function.

Stem cells in liver regeneration, fibrosis and cancer: the good, the bad and the ugly

“…Oval cells are derived from the canal of Hering, and in rodents this canal barely extends beyond the limiting plate ( Figures 4, 5); in contrast, in human liver the organization of the biliary tree is different, with the canal of Hering extending to the proximate third of the lobule [68] and so apparently requiring a name change from oval cells to 'hepatic progenitor cells' (HPCs) [69]. An enormous range of markers has been used to identify ovals cells (Table 2) [70][71][72][73][74][75][76][77][78][79][80][81][82][83] and some, such as Dlk, may signal imminent hepatocyte differentiation [71]. A popular experimental procedure to elicit an oval cell response in rats is to pre-treat the animals with 2-acetylaminofluorene (2-AAF) before performing a two-thirds PH (the 2-AAF/PH protocol).…”

“…Perhaps most significantly, inflammatory cells produce a range of cytokines and chemokines that initiate the response [82,83]; SDF-1 attracts CXCR4 + T cells, and these cells express TNF-like weak inducer of apoptosis (TWEAK), which stimulates oval cell proliferation by engaging its receptor Fn14 [80]. Other elements of the inflammatory response that may stimulate oval cells include lymphotoxin-β, IFNγ , TNFα and even histamine [81]. A resistance to the growth inhibitory effects of TGFβ has been credited with allowing oval cells to proliferate under conditions inhibitory to hepatocytes [100].…”

Physiology of Cholangiocytes

“…Based on recently published observations (90,93,171,283), we speculate that both small and large cholangiocytes have similar Ca 2+ -signaling machinery but may respond differentially to extracellular stimuli. Indeed, both small and large cholangiocytes possess the (IP 3 )/Ca2+-dependent signaling pathway but have different responses to the same agonist.…”

“…Indeed in the rat, small cholangiocytes, which are normally mitotically dormant, may proliferate in response to various stimuli (e.g., histamine, secretin, -naphthylisothiocyanate, and acute carbon tetrachloride) (90,93,105,107,165,196,207) and insults (e.g., partial hepatectomy) (9,179) and acquire functional features of large cholangiocytes (92,104,171,179). Similar proliferation and plasticity is thought to occur in human and mouse cholangiocytes (4,207,242).…”

“…Indeed, both small and large cholangiocytes possess the (IP 3 )/Ca2+-dependent signaling pathway but have different responses to the same agonist. For example, small mouse cholangiocytes proliferate in response to stimulation of the H1 histamine receptor (HRH1) by activation of the IP 3 /CaMK pathway, whereas large cholangiocytes do not proliferate in response to HRH1 activation (90). It has been also demonstrated that in diseases primarily affecting large cholangiocytes, small cholangiocytes replenish the biliary epithelium by amplification of Ca 2+ -dependent signaling and acquisition of large cholangiocyte phenotypes (4,93,171).…”