Evaluating side effects of nanoparticle-mediated siRNA delivery to mesenchymal stem cells using next generation...

RNA interference has immense potential to modulate cell functions. However, effective delivery of small interfering RNA (siRNA) while avoiding deleterious side effects has proven challenging. This study investigates both intended and unintended effects of diblock copolymer nanoparticle (NP) delivery of siRNA delivery to human mesenchymal stem cells (hMSC). Specifically, siRNA delivery was investigated at a range of NP-siRNA:hMSC ratios with a focus on the effects of NP-siRNA treatment on hMSC functions. Additionally, next generation RNA sequencing (RNAseq) was used with enrichment analysis to observe side effects in hMSC gene expression. Results show NP-siRNA delivery is negatively correlated with hMSC density. However, higher NP-siRNA:hMSC ratios increased cytotoxicity and decreased metabolic activity. hMSC proliferation was largely unaffected by NP-siRNA treatment, except for a threefold reduction in hMSCs seeded at 4,000 cells/cm². Flow cytometry reveals that apoptosis is a function of NP-siRNA treatment time and seeding density; ∼14% of the treated hMSCs seeded at 8,000 cells/cm² were annexin V⁺-siRNA⁺ 24 hr after treatment, while 11% of the treated population was annexin V⁺-siRNA^-. RNAseq shows that NP-siRNA treatment results in transcriptomic changes in hMSCs, while pathway analysis shows upregulation of apoptosis signaling and downregulation of metabolism, cell cycle, and DNA replication pathways, as corroborated by apoptosis, metabolism, and proliferation assays. Additionally, multiple innate immune signaling pathways such as toll-like receptor, RIG-I-like receptor, and nuclear factor-κB signaling pathways are upregulated. Furthermore, and consistent with traditional siRNA immune activation, cytokine-cytokine receptor signaling was also upregulated. Overall, this study provides insight into NP-siRNA:hMSC ratios that are favorable for siRNA delivery. Moreover, NP-siRNA delivery results in side effects across the hMSC transcriptome that suggest activation of the innate immunity that could alter MSC functions associated with their therapeutic potential.