Novel reliable real-time PCR for differential detection of MSRV env and syncytin-1 in RNA and DNA from patients with multiple sclerosis

Abstract

Two components of the HERV-W family of human endogenous retroviruses are activated during multiple sclerosis (MS) and proposed immunopathogenic co-factors: MSRV (MS-associated retrovirus), and ERVWE1 (whose env protein, syncytin-1, reaches the plasma membrane). MSRV env and syncytin-1 are closely related, and difficult to distinguish each other. The sequences of extracellular MSRV env and of syncytin-1 available in GenBank were compared with those found in MS patients and controls of the cohort under study. With respect to syncytin-1, MSRV env sequences have a 12-nucleotide insertion in the trans-membrane moiety. Based on this insertion, discriminatory real-time PCR assays were developed, that can amplify selectively either MSRV env or syncytin-1. The data of MS patients and controls indicated that MSRV and ERVWE1 are both expressed in the brain of MS patients, while only MSRV is present in the blood; MSRV was released in culture by PBMCs of MSRV-producer individuals. These cells expressed the complete MSRV env gene in the absence of syncytin-1 expression, up to the final, fully glycosylated envelope protein product, since western blot staining with anti-HERV-Wenv antibody detected two bands of the same molecular weight (73 and 61 kDa) of the fully glycosylated and partially glycosylated HERV-Wenv uncleaved proteins. Beyond MSRV env DNA copy numbers were more abundant in MS patients than in healthy humans, while syncytin-1 were unchanged. These findings reinforce the link between MSRV and MS.