Is TREM2 a Stretch: Implications of TREM2 Along Spinal Cord Circuits in Health, Aging, Injury, and Disease.

Triggering Receptor Expressed on Myeloid Cells 2 (TREM2) is a receptor found in microglia within the central nervous system (CNS) as well as in several other cell types throughout the body. TREM2 has been highlighted as a "double-edged sword" due to its contribution to anti- or pro-inflammatory signaling responses in a spatial, temporal, and disease-specific fashion. Many of the functions of TREM2 in relation to neurological disease have been elucidated in a variety of CNS pathologies, including neurodegenerative, traumatic, and vascular injuries, as well as autoimmune diseases. Less is known about the function of TREM2 in motoneurons and sensory neurons, whose cell bodies and axons span both the CNS and peripheral nervous system (PNS) and are exposed to a variety of TREM2-expressing cells and mechanisms. In this review, we provide a brief overview of TREM2 and then highlight the literature detailing the involvement of TREM2 along the spinal cord, peripheral nerves and muscles, and sensory, motor, and autonomic functions in health, aging, disease, and injury. We further discuss the current feasibility of TREM2 as a potential therapeutic target to ameliorate damage in the sensorimotor circuits of the spinal cord.