Soluble TREM1 Contributes to Aging-Related Neurodegeneration via ROBO2/ERK Pathway

Aging is recognized as the most significant risk factor for neurodegenerative diseases. Emerging evidence indicates that inflammation contributes to the progression of aging-related neurodegeneration. As a transmembrane immune receptor, triggering receptor expressed on myeloid cells 1 (TREM1) plays a crucial role in the regulation of inflammatory responses. Previously, our research group and others showed that the levels of a soluble form of TREM1 (sTREM1) were increased in the plasma or cerebrospinal fluid (CSF) of patients with Alzheimer's disease, the most common type of neurodegenerative disease among the elderly. Moreover, the elevated levels of CSF sTREM1 were closely associated with a more rapid rate of hippocampal degeneration in cognitively impaired older adults. However, the precise mechanisms by which sTREM1 contributes to aging-related neurodegeneration remain largely unclear. In this study, by utilizing senescence accelerated mouse prone 8 mice, an animal model of accelerated aging, we confirmed that serum sTREM1 levels were significantly increased during the aging process. Importantly, we demonstrated that roundabout guidance receptor 2 (ROBO2) functioned as a receptor for sTREM1 in hippocampal neurons, and its expression was also upregulated with aging. Additionally, we revealed for the first time that knockdown of neuronal ROBO2 mitigated aging-related hippocampal synaptic degeneration and cognitive impairments. Furthermore, we provided the first evidence that sTREM1 reduced the expression of synaptic proteins via the ROBO2/extracellular signal-regulated kinase pathway. These findings elucidated the mechanisms through which sTREM1 contributed to aging-related neurodegeneration and suggested that the inhibition of sTREM1-mediated signaling might represent a novel therapeutic strategy for the treatment of neurodegeneration and cognitive decline induced by aging.