Abstract
The conservation of mammary gland physiology by maintaining the maximum number of mammary epithelial cells (MECs) is of the utmost importance for the optimum amount of milk production. In a state of negative energy balance, palmitic acid (PA) reduces the number of bovine MECs. However, there is no effective strategy against PA-induced apoptosis of MECs. In the present study, 5-aminolevulinic acid (5-ALA) was established as a remedial agent against PA-induced apoptosis of MAC-T cells (an established line of bovine MECs). In PA-treated cells, the apoptosis-related genes BCL2 and BAX were down- and upregulated, respectively. The elevated expression of major genes of the unfolded protein response (UPR), such as CHOP, a proapoptotic marker (C/EBP homologous protein), reduced the viability of PA-treated MAC-T cells. In contrast, 5-ALA pretreatment increased and decreased BCL2 and BAX expression, respectively. Moreover, cleaved caspase-3 protein expression was significantly reduced in the 5-ALA-pretreated group in comparison with the PA group. The downregulation of major UPR-related genes, including CHOP, extended the viability of MAC-T cells pretreated with 5-ALA and also reduced the enhanced intensity of the PA-induced expression of phospho-protein kinase R-like ER kinase. Moreover, the enhanced expression of HO-1 (antioxidant gene heme oxygenase) by 5-ALA reduced PA-induced oxidative stress (OxS). HO-1 is not only protective against OxS but also effective against ER stress. Collectively, these findings offer new insights into the protective effects of 5-ALA against PA-induced apoptosis of bovine MECs.
Highlights
Dairy cows synthesize copious amounts of milk over the lactation period
We previously reported that palmitic acid (PA) induced severe endoplasmic reticulum (ER) stress and reduced the viability of bovine mammary epithelial cells (MECs) [7]
The data from our current study indicated that PA reduced viability by 20% and caused 13.71% apoptosis of MAC-T cells, while pretreatment with different doses of 5-aminolevulinic acid (5-ALA) enhanced viability, consistent with the findings of previous studies [10]
Summary
Dairy cows synthesize copious amounts of milk over the lactation period. Milk production is largely determined by the number of mammary epithelial cells (MECs) [1]. These cells are the structural and functional unit of the mammary gland and are indispensable for the synthesis and storage of milk before secretion from the udder. In the early lactation period, a negative energy balance (NEB) occurs in dairy cows when there is a discrepancy in the increase in nutrient requirements while the dry matter intake is decreased (up to 40%), due to fetal growth and hormonal change [4,5,6], which results in the mobilization of body fat and elevated circulating concentrations of nonesterified fatty acids to maintain energy requirements [7,8,9]
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