Sterile innate immune mechanisms in neurodegenerative diseases

Neurodegenerative diseases are characterized by the dysfunction and death of susceptible neuronal populations. Increasing evidence has demonstrated that sustained neuroinflammation and activation of innate immune complexes underlie neurodegeneration, worsening disease progression and outcomes. Sterile inflammation (which occurs in the absence of infection) can be triggered by neurodegenerative disease-associated misfolded proteins. These studies highlight the need to decipher the complexities of innate immune signaling mechanisms and their contribution to neuropathology. In this review, we focus on major neurodegenerative diseases that have a well-documented neuroinflammatory component: Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, multiple sclerosis, and frontotemporal dementia. In the context of these diseases, we discuss recent advances in innate-immune mechanisms that have been demonstrated to partake in disease progression and neurodegeneration. These include evolutionarily conserved innate-immune signaling complexes whose uncontrolled activation amplifies neurodegeneration, damaging lipid droplets that accumulate within myeloid cells and prevent their ability to clear toxic protein aggregates, as well as genome-wide studies-implicated genes/proteins. The individual and/or concerted actions of these pathways could be leveraged to rationally target the pathogenesis or progression of neurodegenerative diseases.