Cytotoxic impact of non-structural protein 9 on tonsil-derived mesenchymal stem cells: mitochondrial metabolism disruption in upper respiratory system

Severe acute respiratory syndrome coronavirus (SARS-CoV) possesses a higher replicative capacity and pathogenicity compared to classical coronaviruses. Among its non-structural proteins, non-structural proteins 9 (NSP9) is believed to play a pivotal role in viral RNA synthesis. This study aims to investigate the cytotoxic effects of the NSP9 on the upper respiratory system, specifically its impact on mitochondrial function and cell proliferation.

In this study, we examined the effect of NSP9 on the human upper respiratory system using Tonsil-derived mononuclear mesenchymal stem cells (TMSCs) were treated with varying concentrations of NSP9 (0.01, 0.05, 0.2, 0.4, and 0.8 μg/ml) for 4 h. Cell viability, mitochondrial respiration, and protein expression changes were examined using the CCK-8 assay, LIVE/DEAD assay, oxygen consumption rate (OCR) measurement, and western blot analysis.

NSP9 exhibited significant cytotoxicity at 0.2 μg/ml, impairing mitochondrial metabolic efficiency and cell proliferation. Mitochondrial activity was further analyzed using real-time OCR measurements, revealing substantial reductions. To further elucidate the effect of NSP9 on cell proliferation, the expression of phosphoinositide 3-kinase (PI3K) and phosphorylated AKT protein markers were analyzed. Protein expression results confirmed that NSP9 treatment led to reduced phosphorylation of key cell proliferation markers, including PI3K and AKT.

These findings demonstrate that NSP9 induces significant cytotoxic effects in TMSCs by disrupting mitochondrial respiration, reducing ATP production, and impairing cell proliferation. Collectively, possessing toxicity of NSP9 to TMSCs can adversely affect to upper respiratory system by inhibiting cell proliferation and disrupting mitochondria-related metabolic activity.