In mouse hepatocytes, the gap junctional
proteins connexin32 (Cx32) and connexin26 (Cx26) are expressed in the same gap junctional plaque. Expression of the major
Cx32 protein is downregulated during liver regeneration and
cholestasis. Here we have analyzed the
acute-phase response (after experimental
inflammation) and circadian
connexin expression in Cx32-deficient and wild-type mouse liver.
Acute-phase response was triggered by
intraperitoneal injection of
lipopolysaccharide (LPS). Injection of recombinant mouse
interleukin-1beta (mIL-1beta), mIL-6 or
tumor necrosis factor alpha (mTNF-alpha) had no inflammatory effect. Northern blot analysis of positive and negative acute-phase transcripts following stimulation with
cytokine or LPS revealed no difference between Cx32-deficient livers and wild-type controls, suggesting that loss of the Cx32 gene had no effect on experimental liver
inflammation. Actin, beta-
fibrinogen and Cx26 transcripts were increased after
endotoxin stimulation. Under conditions of hepatic
acute-phase response, Cx32 transcripts were not detected in LPS-treated livers of wild-type mice. Immunoblot analysis of
proteins from inflamed wild-type livers indicated a strongly diminished amount of
Cx32 protein, whereas the level of Cx26
protein was increased. Although
intraperitoneal injection of mIL-1, mIL-6 as well as mTNF-alpha did not induce an
acute-phase response,
Cx32 protein expression was diminished, suggesting that post-transcriptional downregulation of Cx32 preceded the
acute-phase response. Northern blot hybridization of
RNA from wild-type and Cx32-deficient mouse liver revealed a similar circadian regulation of Cx26 and GAPDH transcripts with maximal expression around 2 p.m. and a minimum after midnight.