Parkinson's disease (PD) is second most common neurodegenerative diseases in worldwide (Pringsheim et al., 2014). People living with Parkinson's disease were rapidly increased throughout the world in the past two decades (Bloem et al., 2021), which cause a huge burden for the caregivers and society (Dorsey et al., 2007). The major underlying pathogenesis of PD is synuclein deposition and progressive loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc) of the midbrain (Bloem et al., 2021; Ben-Shlomo et al., 2024), which caused by complicated factors including genetic risk factors and environmental factors (Tysnes and Storstein, 2017).

Microglia are the major immune cells resident in the brain and play an important role in the maintenance of brain homeostasis (Antignano et al., 2023; Yu et al., 2023), the dysfunction of microglia was confirmed to be a major cause of PD (Kam et al., 2020). It was reported that increased ameboid microglia (activated state) existed in the nigral of patients with Parkinson's disease (Smajic et al., 2022), and chronic neuroinflammation mediated by microglia activation could cause apoptosis of dopaminergic neurons (Isik et al., 2023), suppression of microglia activation could reduce the neuronal loss and improve the motor deficit of PD rat models (Zhang et al., 2023a). Therefore, microglia became a promising target in the treatment of PD.

Adipose derived stem cells (ADSCs) are a kind of mesenchymal stem cells (MSCs) which are isolated from adipose tissue (Wang et al., 2024). Similar with MSCs from other tissues, ADSCs possess immunosuppressive properties and have anti-inflammatory effects on inflammatory response (Al-Ghadban and Bunnell, 2020). Administration of ADSCs could reduce the activation of microglia and increase the survival of dopaminergic neurons in PD model (Choi et al., 2015; Munoz et al., 2019). Thus, ADSCs are a potential treatment for PD. Recently, several studies declared that ADSCs mainly functioned by the delivery of small extracellular vesicles (sEVs) (Munoz et al., 2019; Jeon et al., 2023), a type of extracellular vesicle with a diameter of 30-200 nm and played an important role in physiological and pathological processes (Guo et al., 2021). These ADSC derived sEVs (ADSC-sEVs) possessed similar properties with ADSCs and displayed amazing effect in immune modulation, tissue repair or wound healing (Munoz et al., 2019; Jeon et al., 2023; Li et al., 2022a). Thus, ADSC-sEVs may be a promising substitute of ADSCs for its easy access and convenient to use in clinic applications. Chen et al. observed that ADSC-sEVs could suppress the activation of microglia and decrease the secretion of inflammatory factors, which caused neuronal apoptosis (Chen et al., 2020a). In previous study, we also observed a similar result, that is, rat ADSC-sEVs could protect neurons from microglia-mediated injury by inhibiting microglia activation (Feng et al., 2019). However, whether ADSC-sEVs have protective effect on Parkinson's disease in vivo remains unknown, and the underlying mechanisms of ADSC-sEVs in blocking microglia inflammatory activation need further investigation.

In the present study, PD mouse model was established by unilateral stereotaxic injection of Lipopolysaccharide (LPS) into substantia nigra of midbrain. ADSC-sEVs were delivered by tail intravenous injection to detect the in vivo effect of ADSC-sEVs on microglia activation in the substantia nigra of PD mouse model, and explore whether ADSC-sEVs influence the progression of PD. Next, RNA sequencing (RNA-seq) was used to detect the microRNA profile of ADSCs and ADSC-sEVs, and the top enriched microRNAs were obtained. MiR-100-5p, a microRNA that possesses anti-inflammatory effect was found to be enriched both in ADSCs and ADSC-sEVs. Then, the effect of miR-100-5p on microglia activation and whether ADSC-sEVs functioned through miR-100-5p was explored, the target genes of miR-100-5p were predicted by TargetScan for sequence alignment and Deltex E3 ubiquitin ligase 3 L (DTX3L) was chosen for further study. Finally, the potential mechanism that whether miR-100-5p suppressed microglia activation via DTX3L/Signal Transducers and Activators of Transcription 1 (STAT1) signal pathway was further investigated. Verification of the effect of ADSC-sEVs on PD and the investigation of underlying mechanisms will provide new therapy as well as new thought for the treatment and drug development of PD.