Neuroinflammation, Its Role in Alzheimer’s Disease and Therapeutic Strategies

Neuroinflammation precedes the clinical onset of various neurodegenerative diseases, including Alzheimer's disease (AD), by years or frequently even decades (1-3). In terms of the underlying physiology, there is a great need for understanding and controlling interactions between the central nervous system (CNS) and the immune system in an attempt to develop approaches to prevent or delay the disease's progression. Nerve cells have limited motion capability, whereas immune cells can migrate freely via circulation. This difference raises a variety of questions in the context of senile plaque formation and phagocytosis. Broad-scale unbiased genomic studies bring several genetic variants such as sialic acid binding Ig-like lectin 3 (CD33), triggering receptor expressed on myeloid cells 2 (TREM2) or complement receptor type 1 (CR1) into the focus of researchers' attention as potential risk factors for neuroinflammation. In addition, advanced proteomic analyses have been revealing links between these genetic contributors and complex, malfunctioning signaling pathways (including the upregulation of factors like tumor necrosis factor TNF-α, tumor growth factor TGF-β and interleukin IL-1α) that promote proinflammatory mechanisms via intracellular signaling and trafficking, synaptic function, and cell metabolism/ proliferation. In AD, the brain's microglia and astrocytes, which are normally responsible for maintaining the homeostasis of synaptic transmission and its remodeling by pruning, are the initiators of neuroinflammation and toxic tau and amyloid-β (Aβ) accumulation. Thus, they drive the CNS into a state of sustained or even self-accelerated deterioration. Here we aim to review the cell types and mediators involved in neuroinflammation and AD, the symptom manifestation in clinical settings, and potential candidates for improving diagnosis and treatment.