Energy metabolism disorders and oxidative stress in the SH-SY5Y cells following PM_2.5 air pollution exposure

Highlights

• The alteration of the molecular processes of energy metabolism induced by ambient PM_2.5 is proposed.

• Cellular mitochondrial respiration is more sensitive to PM_2.5 treatment, while glycolysis only shows damage at high doses and prolonged treatment time.

• BHA significantly recovered the effects of PM_2.5 on mitochondrial respiration.

Abstract

Studies have shown that PM_2.5 exposure can induce neuronal apoptosis and neurobehavioral changes in animal experiments due partly to the mitochondria-mediated oxidative damage. How does it affect the mitochondrial energy metabolism as well as the neuronal damage, however, remain unclear. This study aimed to investigate the molecular processes of energy metabolism and oxidative damage induced by ambient PM_2.5 exposure in SH-SY5Y cells. SH-SY5Y cells were treated with PM_2.5 to establish a cytotoxicity model. A Seahorse Extracellular Flux Analyzer (XFp) was performed to evaluate the cellular mitochondrial respiratory and glycolysis after exposure to PM_2.5. The dose- and time-dependent effects of PM_2.5 on oxidative damage and apoptosis were analyzed. To further explore the relationship among oxidative damage, energy metabolism and apoptosis, SH-SY5Y cells were co-cultured with BHA and PM_2.5 for 24 h. The results demonstrated that the basic respiration and ATP production, the typical index of mitochondrial respiration as well as glycolysis, significantly reduced in SH-SY5Y cells with dose and time dependent. At the same time, the PM_2.5 could significantly decrease the cell viability and Mn-SOD activity, and increase the ROS levels and apoptosis rate as the escalation of dose and the extension of time. Importantly, the application of BHA could synchronously recover the PM_2.5 induced cell energy metabolism disorder, oxidative damage, and apoptosis. It seems that the abnormal cellular energy metabolism may be caused by oxidative damage following fine particles exposure, and further led to apoptosis.

Introduction

Ambient fine particulate matter pollution has become a major public health issue around the world and PM levels of most cities in the world were above the WHO standards(Lelieveld et al., 2015; Mukherjee and Agrawal, 2018). Studies have revealed that air pollution are associated with various human disorders, including lung cancer, cerebrovascular disease and neuropsychiatric disorders (Lelieveld et al., 2015; Hahad et al., 2020). Strikingly, recent epidemiological investigations indicate that PM_2.5 exposure increased the incidence of elderly Alzheimer’s disease (AD), Parkinson’s disease (PD), as well as other neurodegenerative diseases (Jung et al., 2015, Kioumourtzoglou et al., 2016, Ritz et al., 2016). For example, some studies demonstrated that long-term exposure to fine particles increased odds of depression, anxiety disorders, suicidal behaviors and psychoses(Braithwaite et al., 2019; Fan et al., 2020). Likewise, selective memory and behavioral alteration and locomotor dysfunction were found in mice after ambient ultrafine particle matter exposure(Allen et al., 2014; Jew et al., 2019). The mechanism studies, from both animal and cell experiments, indicate that mitochondrial dysfunction and oxidative stress are involved into the pathogenesis of air pollution-induced disorders, such as brain dysfunction, neuron damage and loss, as well as neuro inflammation (Hahad 2020). Neuronal loss is the most damaging consequence and is related to cognitive dysfunction. Studies in mice have disclosed that neuronal loss by apoptosis is one of the pathological hallmarks of neurodegeneration(Okouchi et al., 2007; Cavallucci and D'Amelio, 2011). The induction of intrinsic apoptosis in neurons seems to center on control of Bax signaling in mitochondria. PM_2.5 could induce neurotoxicity by causing mitochondrial-dependent apoptosis.

Mitochondria is the major site of oxidative stress as well as energy metabolism. Pioneered by Mitchell (1961), mitochondria was found to play a pivotal role in producing adenosine triphosphate via oxidative phosphorylation. Further studies have demonstrated that PM_2.5 triggered the alterations of the mitochondrial structure and function in vivo and in vitro models and generally associated with oxidative stress and apoptosis activation(Guo et al., 2017; Chew et al., 2020; Sotty et al., 2020). Oxidative damage and mitochondrial dysfunction in response to PM_2.5 exposure might lead to energy depletion, accumulation of inflammatory cytokine(Bourgeois and Owens, 2014), autophagy (Wei et al., 2018) and apoptosis. And abnormal energy metabolism in response to PM_2.5 stimuli may be implicated in the regulation of neurotoxicity and even neurological disorders. PM_2.5 inducing energy metabolism has been widely debated (Ning et al., 2019, Zhang et al., 2020), thus the particular detail of fine particles regulating the energy metabolism warrants continued investigation.

In this study, PM_2.5 induced cytotoxicity model were established using SH-SY5Y cells. Mitochondrial respiratory function and glycolysis of cells were assessed by Seahorse Extracellular Flux Analyzer (XFp), which could detect the energy metabolism in living cells. The details of PM_2.5 induced energy metabolism disorders on cytotoxicity of SH-SY5Y cells were presented which provides a novel insight for the effects of airborne particles in damaging energy metabolism in SH-SY5Y cell.