Tanshinone IIA-pretreated mesenchymal stem cells alleviate neuroinflammation in 3×Tg-AD mice via the TREM2/PI3K/Akt pathway

Neuroinflammation is a key pathogenic factor for neurodegenerative diseases. Mesenchymal stem cell (MSC) transplantation, as a potential strategy for regulating neuroinflammation, has received extensive attention. Our previous research revealed that compared with ordinary MSC, MSC pretreated with tanshinone IIA (TIIA), referred to as TIIA-MSC, exhibited superior anti-neuroinflammatory activity, but the mechanism of action remains unclear. To clarify the underlying mechanism, this study integrated in vitro and in vivo experiments and evaluated the therapeutic effect of TIIA-MSC in a triple-transgenic Alzheimer's disease mouse model (3×Tg-AD mice) and explored its mechanism of action in a lipopolysaccharide (LPS)-induced BV2 microglial cell inflammation model. The results showed that TIIA-MSC could significantly improve the cognitive function of 3×Tg-AD mice, increase brain glucose metabolism levels, promote the recovery of synaptic and mitochondrial structures, and effectively alleviate neuroinflammatory responses. In vitro experiments further verified the superior inhibitory effect of TIIA-MSC on microglial cell activation and proinflammatory factor release. Mechanistic studies have indicated that the triggering receptor expressed on myeloid cells 2 (TREM2) is the key molecule that mediates this process. The knockdown of TREM2 expression significantly weakened the anti-inflammatory effect of TIIA-MSC, suggesting that TREM2 plays a central role in this process. Further analysis revealed that by activating the phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt) signaling pathway downstream of TREM2, TIIA-MSC may promote the transformation of the functional state of microglia from mainly proinflammatory to having neuroprotective and repair properties. This study systematically revealed the molecular mechanism by which TIIA-MSC regulate microglial cell phenotypic transformation through the TREM2/PI3K/Akt pathway and exert anti-neuroinflammatory effects, providing new ideas and an experimental basis for expanding the application of MSC in the treatment of neurodegenerative diseases.