ADAM17 Inhibition Protects Cognition in Intermittent Hypoxia: The Role of TREM2.

Purpose: The triggering receptor expressed on myeloid cells 2 (TREM2) is a new therapeutic target in Alzheimer's disease. However, its role in obstructive sleep apnea (OSA)-related cognitive impairment is still unclear. This study aimed to investigate the effect and regulatory mechanism of TREM2 on cognitive impairment related to OSA.

Methods: Since intermittent hypoxia (IH) is the primary pathophysiologic characteristic of OSA, we conducted IH animal and BV2 cell model to investigate the mechanism. Trem2 knockdown and Trem2 overexpression cells were created by Lentivirus transfection. A disintegrin and metalloprotease 17 (ADAM17) is the primary enzyme for TREM2 shedding, we used TAPI-1 to inhibit its activity. Morris water maze, Nissl staining, real-time PCR, immunofluorescence, Western blotting, fluorometric assay kit, and enzyme-linked immunosorbent assay were used to explore the molecular mechanism.

Results: The TREM2 levels were decreased in BV2 cells exposed to IH for 24 hours. IH elevated the levels of IL-1β, TNF-α and CD86 in BV2 cells, as well as the levels of p-Tau in conditioned media-cultured HT-22 cells. Conversely, IH reduced the levels of IL-10 and CD206 in BV2 cells. However, these effects were exacerbated in BV2 cells with Trem2 knockdown, whereas they were mitigated in those with Trem2 overexpression. Additionally, the ADAM17 activity and soluble TREM2 (sTREM2) levels were increased in BV2 cells subjected to IH. Treatment with TAPI-1, suppressed ADAM17 activity and restored TREM2 expression both in vitro and in vivo. Inhibition of ADAM17 led to a reduction in the expression of CD86, IL-1β, TNF-α and p-Tau levels, while enhancing the expression of CD206, IL10 and cognitive functions.

Conclusion: TREM2 played a protective role in IH-induced neuroinflammation and neuronal injury by promoting microglia M2 polarization. IH caused excessive activation of ADAM17 and resulted in augmented degradation of TREM2. Restoring TREM2 expression by inhibiting ADAM17 indicates a potentially promising therapeutic strategy for cognitive impairment in OSA.