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

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). MSRVenv and syncytin-1 are closely
related, and difficult to distinguish each other. The sequences of extracellular
MSRVenv 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,
MSRVenv 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 MSRVenv 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 MSRVenv
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 61kDa) of the
fully glycosylated and partially glycosylated HERV-Wenv uncleaved proteins.
Beyond MSRVenv 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.