Polystyrene nanoplastics impair mitochondrial function, quality control, and ER-mitochondria crosstalk in HeLa cells

Polystyrene nanoplastics (PS-NPs) represent persistent environmental contaminants derived from the degradation of plastic debris and are increasingly detected in biological systems, raising concerns regarding their potential effects on human health. Emerging evidence suggests that, following cellular internalization, PS-NPs can induce intracellular stress responses and interfere with mitochondrial homeostasis, highlighting mitochondria as key targets of nanoplastic-induced cellular dysfunction. This study aimed to investigate the effects of PS-NPs on mitochondrial function in HeLa cells. Particular attention was devoted to Mitochondrial Quality Control (MQC) pathways, including the mitochondrial Unfolded Protein Response (UPR^mt), a stress-adaptive mechanism that remains poorly characterized in response to nanoplastic exposure in human cellular model. In addition, the study examined the functional crosstalk between the Endoplasmic Reticulum and mitochondria.

HeLa cells were exposed to PS-NPs, and mitochondrial bioenergetics, oxidative stress, mitochondrial membrane potential, cellular ATP levels, extracellular lactate levels, and calcium homeostasis were assessed using functional assays. MQC-related pathways, including UPR^mt, mitochondrial biogenesis, dynamics, autophagy/mitophagy, and ER stress responses, were evaluated through biochemical, molecular, and imaging approaches.

Our results demonstrate that PS-NP exposure induces mitochondrial dysfunction, characterized by impaired mitochondrial coupling, mitochondrial membrane depolarization, increased H₂O₂ levels in cell lysates, and altered cellular redox homeostasis. Moreover, PS-NPs disrupt MQC processes, leading to an imbalance in the mechanisms that maintain mitochondrial homeostasis, including modulation of UPR^mt-associated proteins and dysregulation of ER-mitochondria communication via Mitochondria-Associated Membranes (MAMs).

Collectively, these data advance our understanding of PS-NP toxicity by identifying alterations in MQC systems and ER-mitochondria crosstalk as key events in nanoplastic-induced cellular stress. These findings provide novel mechanistic insights into nanoplastic toxicity and highlight the potential impact of environmental PS-NP exposure on cellular homeostasis and human health.