Roles of Semaphorins in Neurodegenerative Diseases

Abstract

Semaphorins are secreted and transmembrane proteins that bind plexin/ neuropilin or integrin receptors, providing paracrine axonal guidance signals and ultimately leading to a functional and developed neuronal network. Following semaphorin’s initial discovery, their relevance in the central nervous system (CNS) soon intrigued researchers about the possible links between semaphorins, their receptors and signaling mechanisms and different neurodegenerative diseases. Here, we explore the current knowledge of semaphorin’s function and signaling in Alzheimer’s disease (AD), Parkinson’s disease (PD), Charcot-Marie-Tooth disease (CMT), amyotrophic lateral sclerosis (ALS), multiple sclerosis (MS), and Human T-cell lymphotropic virus type 1 (HTLV-1)-associated myelopathy/tropical spastic paraparesis (HAM/TSP). We focus on the effects of the most known semaphorin subclasses 3A and 4D, yet extending our discussion to other semaphorins that have been found involved in specific neuropathologies and the potential effect of semaphorins modulating the immune system in disorders with inflammatory components. Molecular, cellular, and genetic evidences are reviewed, highlighting the relevance of semaphorins on each disease etiology, pathophysiology, and progression. The newly discovered semaphorin functions in neurological disorders even suggest alternative therapies that may be highly valuable in diseases that have no current cure.