Central Texas Veterans Health Care System, TX, USA.
Hepatology. 2011 Feb;53(2):628-39. doi: 10.1002/hep.24041. Epub 2011 Jan 3.
Small cholangiocytes proliferate via activation of calcium (Ca(2+) )-dependent signaling in response to pathological conditions that trigger the damage of large cyclic adenosine monophosphate-dependent cholangiocytes. Although our previous studies suggest that small cholangiocyte proliferation is regulated by the activation of Ca(2+) -dependent signaling, the intracellular mechanisms regulating small cholangiocyte proliferation are undefined. Therefore, we sought to address the role and mechanisms of action by which phenylephrine, an α(1) -adrenergic agonist stimulating intracellular D-myo-inositol-1,4,5-triphosphate (IP(3) )/Ca(2+) levels, regulates small cholangiocyte proliferation. Small and large bile ducts and cholangiocytes expressed all AR receptor subtypes. Small (but not large) cholangiocytes respond to phenylephrine with increased proliferation via the activation of IP(3) /Ca(2+) -dependent signaling. Phenylephrine stimulated the production of intracellular IP(3) . The Ca(2+) -dependent transcription factors, nuclear factor of activated T cells 2 (NFAT2) and NFAT4, were predominantly expressed by small bile ducts and small cholangiocytes. Phenylephrine stimulated the Ca(2+) -dependent DNA-binding activities of NFAT2, NFAT4, and Sp1 (but not Sp3) and the nuclear translocation of NFAT2 and NFAT4 in small cholangiocytes. To determine the relative roles of NFAT2, NFAT4, or Sp1, we knocked down the expression of these transcription factors with small hairpin RNA. We observed an inhibition of phenylephrine-induced proliferation in small cholangiocytes lacking the expression of NFAT2 or Sp1. Phenylephrine stimulated small cholangiocyte proliferation is regulated by Ca(2+) -dependent activation of NFAT2 and Sp1.
Selective stimulation of Ca(2+) -dependent small cholangiocyte proliferation may be key to promote the repopulation of the biliary epithelium when large bile ducts are damaged during cholestasis or by toxins.
在触发大环腺苷单磷酸依赖性胆管细胞损伤的病理条件下，小胆管细胞通过激活钙（Ca(2+) ）依赖性信号而增殖。虽然我们之前的研究表明小胆管细胞增殖受 Ca(2+) 依赖性信号的激活调控，但调节小胆管细胞增殖的细胞内机制尚不清楚。因此，我们试图确定苯肾上腺素（一种刺激细胞内 D-肌醇-1,4,5-三磷酸（IP(3) ）/Ca(2+) 水平的α(1) -肾上腺素能激动剂）通过何种作用机制和发挥何种作用来调节小胆管细胞增殖。小胆管和大胆管以及胆管细胞均表达所有 AR 受体亚型。小（而非大）胆管细胞通过激活 IP(3) /Ca(2+) 依赖性信号对苯肾上腺素作出反应而增加增殖。苯肾上腺素刺激细胞内 IP(3) 的产生。钙依赖性转录因子活化 T 细胞核因子 2（NFAT2）和 NFAT4 主要由小胆管和小胆管细胞表达。苯肾上腺素刺激 NFAT2、NFAT4 和 Sp1（而非 Sp3）的 Ca(2+) 依赖性 DNA 结合活性以及 NFAT2 和 NFAT4 在小胆管细胞中的核易位。为了确定 NFAT2、NFAT4 或 Sp1 的相对作用，我们用小发夹 RNA 敲低这些转录因子的表达。我们观察到在缺乏 NFAT2 或 Sp1 表达的小胆管细胞中，苯肾上腺素诱导的增殖受到抑制。苯肾上腺素刺激小胆管细胞增殖是通过 NFAT2 和 Sp1 的 Ca(2+) 依赖性激活来调节的。
在胆流阻滞或毒素作用下大胆管受损时，选择性刺激 Ca(2+) 依赖性小胆管细胞增殖可能是促进胆管上皮细胞再增殖的关键。
