Substance P and Alzheimer's Disease: Emerging Novel Roles

Alzheimer's disease (AD) is an irreversible neurodegenerative disease, clinically characterized by progressive impairments of memory and cognition. The hallmarks of AD are neurofibrillary tangles, mainly constituted by altered phosphorylated and truncated portions of tau protein, and the abnormal extracellular deposition of neurotoxic beta amyloid (A beta) peptides, derived from the proteolytic processing of amyloid precursor protein (APP). According to the amyloid hypothesis, A beta is considered to be linked to the selective neurodegeneration seen in AD. Recent evidence points to an increase in voltage-gated potassium (Kv) channel currents in the etiology of A beta-induced neuronal apoptosis. Substance P (SP) is an 11-aa neuropeptide, member of the tachykinin family, broadly distributed in the Central Nervous System where it acts as a neurotransmitter, neuromodulator, and neurotrophic factor. This peptide may play an important role in neurodegenerative disorders, since reduced levels of SP were found in brain areas and spinal fluid of AD patients. In addition to its neuroprotective properties, it was recently demonstrated that SP is able to stimulate non-amyloidogenic APP processing, thereby reducing the possibility of generation of toxic A beta peptides in the brain. Recent studies, using in vitro and in vivo models, have also shown that the neuroprotective role of SP against A beta could be related to its ability of modulate Kv channel currents. In this review, we briefly summarized the current findings on the neurotrophic and neuroprotective effects of SP, providing information about its anti-amyloidogenic and anti-A beta toxicity role.