β‑Carotene Ameliorates LPS-Induced Endoplasmic\nReticulum Stress and Mitochondrial Disorder by Targeting ORAI1 in\nBovine Mammary Epithelial Cells

Ca<sup>2+</sup> is an important regulator of endoplasmic reticulum\n(ER) and mitochondrial function. Store-operated calcium entry (SOCE)\nserves as the predominant pathway for the influx of extracellular\nCa<sup>2+</sup> into the cell. ORAI1, ORAI2, and ORAI3 are the main\nproteins of SOCE. Ca<sup>2+</sup> disturbance leads to ER stress and\nmitochondrial damage. β-Carotene (β-C) is a precursor\nof vitamin A and has anti-inflammatory and antioxidant effects. However,\nit remains unclear if β-C mitigates ER stress and mitochondrial\ndysfunction triggered by LPS and its underlying molecular mechanisms\nhave not been fully elucidated in bovine mammary epithelial cells\n(BMECs). Therefore, the experiment aimed to explore the protective\nmechanism of β-C. Results showed that LPS increased the ORAI1\nexpression, and caused ER stress by upregulating the expression of\nER stress-related genes and proteins in BMECs. LPS also caused mitochondrial\ndysfunction by decreasing mitochondrial fusion proteins and increasing\nmitochondrial division and apoptosis proteins. Silencing ORAI1 mitigated\nER stress and mitochondrial impairment caused by LPS. Conversely,\nelevated ORAI1 levels induced similar stress and damage in BMECs.\nβ-C pretreatment resulted in diminished ORAI1 expression and\na reduction in ER stress and mitochondrial dysfunction triggered by\nLPS. However, ORAI1 overexpression blocked the protective effects\nof β-C. In conclusion, β-C alleviated the LPS-induced\nER stress and mitochondria dysfunction in an ORAI1-dependent manner.\nOur findings provide a mechanistic basis for further exploration of\nthe regulatory effects of β-C on mammary injuries.