Rheumatoid arthritis and Alzheimer's disease: genetic and epigenetic links in inflammatory regulation.

Controversial data are available about the relationship between Alzheimer's disease (AD) and rheumatoid arthritis (RA). An inverse relationship between AD and RA, due to different factors, was previously described. Similarly to RA, AD pathogenesis is multifactorial and different findings support the inflammatory pathogenetic hypothesis. Several inflammatory mediators are involved in the disease onset and progression regulated by genetic and epigenetic mechanisms. Among them, inteleukin-6 (IL-6) and interleukin-1 (IL-1) as pro-inflammatory soluble factors produced by monocytes-macrophages and tumor necrosis factor alpha (TNF-α) produced by activated macrophages and mononuclear cells represent key molecules in the induction and maintenance of chronic inflammation in RA. In particular a link with the T allele of the SNP 3953 T/C in the IL-1 gene and an overexpression of miR-146a appears to be common to both RA and AD. In this review we will discuss the genetic and epigenetic regulation of the inflammatory cascade in RA and AD to find out the possible links between RA and AD onset.