The association of extracellular vesicle (EV)-cargo miR-330-3p with postoperative delirium and a potential mechanism of tau phosphorylation and neuron toxicity

Background Postoperative delirium (POD) is a frequent and severe neurocognitive complication following cardiac surgery, associated with poor long-term outcomes. The underlying mechanisms are unclear, and objective biomarkers are urgently needed. Methods We used pre- and post-operative plasma samples from 59 patients undergoing cardiac surgery in three separate studies with rigorous delirium assessment using the Confusion Assessment Method in a case-control design. Small extracellular vesicles (sEVs) were isolated from plasma, and their miRNA cargo was profiled using RNA sequencing. Target miRNAs were validated by qRT-PCR, and digital PCR (dPCR). The functional impact of the lead candidate miRNA was investigated in vitro by assessing tau phosphorylation and cell viability in HT22 neuronal cell line. Results There were no differences in sEV morphology or numbers between patients with and without POD. While three candidate miRNAs were initially validated by qRT-PCR, subsequent dPCR analysis confirmed that only the perioperative change in plasma sEV-cargo miR-330-3p expression was significantly greater in patients who developed POD ( n = 20) compared with those who did not ( n = 20) (5.22 copies/μL plasma; 95% Confidence Interval (CI), 1.187 to 9.256; p = 0.0139). Receiver operating characteristic curve analysis for this change yielded an area under the curve of 0.745 (95% CI, 0.589 to 0.901). In vitro overexpression of miR-330-3p in a neuronal cell line significantly increased the phosphorylation of tau at Ser199 ( p < 0.0001) and Ser396 ( p < 0.001) and reduced cell viability ( p < 0.001). Conclusions Our findings suggest that sEV-bound miR-330-3p increases in patients with POD after cardiac surgery. In vitro results suggest a potential pathogenic role for miR-330-3p, linking a systemic signal to tau-related neuronal injury. Clinical Perspective What Is New? This study identifies a specific perioperative increase in small extracellular vesicle (sEV)-cargo miR-330-3p in patients with postoperative delirium (POD) following cardiac surgery. We provide the first evidence that miR-330-3p directly induces tau hyperphosphorylation and reduces neuronal viability in vitro , establishing a potential mechanistic link between systemic sEV signaling and neurodegeneration. What Are the Clinical Implications? The measurement of perioperative change in miR-330-3p could serve as an objective biological marker to assist in the early identification and risk stratification of patients at high risk for POD. The identified miR-330-3p/tau pathway represents a potential new therapeutic target; future interventions aimed at inhibiting this specific miRNA might help prevent or mitigate POD-related neuronal injury. These findings emphasize the importance of monitoring dynamic sEV-cargo changes to better understand and manage perioperative neurocognitive disorders.