Mutant connexin 32 abnormally distributed in the vascular endothelial cells of X-linked Charcot-Marie-Tooth disease type 1 patients

Abstract

Objective To investigate expression distribution of mutant connexin 32 (Cx32) protein in human endothelial cells in patients with X-linked Charcot-Marie-Tooth disease type 1 ( CMTX1 ) .Methods Nerve biopsies were performed in 3 patients with CMTX1 and in 3 non-CMTX1 controls. Cx32 mutations of c. 379A ＞ T( I127F), c. 533A ＞ G(D178G) and c. 590C ＞ T(A197V) were identified in these 3 patients respectively. Immunofluorescent (IMF) staining of nerve blood vessel was processed with antibodies against Cx32, Yon Willebrand factor and Cx40. The mutant Cx32 was constructed in pEGFP-N plasmid (pEGFP-N1-Cx32) and was transfected in HeLa cells. Cx32 and GRP78, a marker of endoplasmic reticulum ( ER), were stained by IMF in HeLa cells to investigate expression of mutant Cx32. Results In 3 control cases, Cx32 was visualized by IMF staining as dots along gap junction of vascular endothelial cells,and it was coexisted with Cx40. However, immunoreactivity of Cx32 in 3 patients was predominantly decreased and was not located in endothelial gap junction. The transfection of 3 Cx32 mutants into HeLa cells demonstrated the pathogenic changes. The cells with the mutation c. 379A ＞T found Cx32 accumulations in the cytoplasm; the cells with mutation c. 533A ＞G showed few staining positive dots surrounding the nuclear and the cells with c. 590C ＞ T showed dot-like expression of Cx32 both in the cytoplasmicand cell membrane. The mutant Cx32 was not overlapped with expression of the marker of ER.ConclusionsMutant Cx32 might cause dysfunction of endothelial gap-junctions due to the abnormal expression of Cx32 in level and location in the vascular endothelial cells of CMTX1 patients. Key words: Charcot-Marie-Tooth disease; Connexins; Blood vessels; Endothelial cells