Upregulation of connexins 30 and 32 gap junctions in rat hippocampus at transcription level by chronic central injection of lipopolysaccharide

Abstract

Background: Gap junctions composed of connexins (Cx) are functional in cell defense by propagation of toxic/death molecules to neighboring cells. Hippocampus, one of the brain regions with particular vulnerability to damage, has a wide network of gap junctions. Functional response of astrocytic Cx30 and neuronal Cx32 to hippocampal damage is unknown.

Methods: We infused lipopolysaccharide (LPS) intracerebroventricularly (2.5 mug/rat) once daily for two weeks to create neuroinflammation. The mRNA and protein levels of the Cx were measured in the hippocampus after 1st, 7th and 14th injection by real-time PCR and Western-blot techniques.

Results: A significant increase in Cx32 and Cx30 gene expression was observed after 7th and 14th injection of LPS with no significant change in their protein abundance.

Conclusion: Transcriptional overexpression of hippocampal Cx30 and Cx32 could be an adaptive response to production of intracellular toxic molecules but it is not accompanied with post- transcriptional overexpression and might have no functional impact.

Fig. 1

Cx30 (A) and Cx32 (B) mRNA level in the hippocampus of the rats after daily i.c.v. injection of LPS. Connexin mRNA levels were normalized to α-tubulin and GAPDH mRNA level. Data are expressed as means ± S.E.M.  (n = 5).   P<0.001 compared to respective control group.

Fig. 2

Cx30 (A) and Cx32 (B) protein levels in the hippocampus of the rats after daily i.c.v. injection of lipopolysaccharide (LPS). (C) Immunoblots of Cx30, Cx32 and α-tubulin in LPS-treated samples. Each immunoblotting was performed in duplicate to increase the reliability of the measurements. (a), control; (b), test. Connexin protein levels were normalized to α-tubulin protein level. Data are expressed as means ± S.E.M. (n = 5).