Tau and 14-3-3 in glial cytoplasmic inclusions of multiple system atrophy.

Multiple system atrophy (MSA) is a neurodegenerative disease characterized by the presence of glial cytoplasmic inclusions (GCIs), which are comprised of fibrils of the protein alpha-synuclein (alpha-syn). Increasing evidence indicate that the formation of these lesions leads to cellular dysfunction and degeneration. The events that result in the formation of GCIs remain poorly understood. It is possible that changes in the cytoplasmic milieu, perhaps the aberrant expression of alpha-syn-interacting proteins, can promote the polymerization of alpha-syn. The presence of the microtubule-binding protein, tau, in GCIs has been reported in some studies, but these findings have not been consistent, and these studies were performed prior to the availability of the more sensitive methods of detecting GCIs using anti-alpha-syn antibodies. Recently, 14-3-3 proteins, putative alpha-syn-interacting partners, have been reported in Lewy bodies, which also are pathological inclusions comprised of alpha-syn. In this study the presence of tau and 14-3-3 proteins in GCIs of 21 patients with MSA was investigated. For the majority of cases, tau and 14-3-3 proteins were detected only in a subset of GCIs. In some cases none of the GCIs contained 14-3-3 or tau. When present in GCIs, tau was in a hypophosphorylated state as demonstrated with phosphorylation-specific antibodies. Alpha-syn fibrillogenesis without 14-3-3 or tau appears to be sufficient for GCI formation, although it is possible that the accumulation of multi-functional proteins, like 14-3-3, in GCIs contribute to the disruption of cellular homeostasis.