Adverse Effects of High Temperature On Mammary Alveolar Development In Vitro

In the mammary glands during pregnancy, the alveolar buds are first branched from the mammary ducts after which they form the alveolar luminal structure for milk production postparturition. Body temperature could increase for several reasons, such as infectious disease and heat stress. We have previously reported that high temperature adversely effects on the lactation capacity of mouse mammary epithelial cells (MECs). However, it remains unclear how high temperature influences mammary morophogenesis during pregnancy. In this study, we investigated the effects of high temperature on this mammary alveolar development process using two types of culture models including embedded organoids of MECs in Matrigel; these models reproduced mammary alveolar bud induction and alveolar luminal formation. Results showed that a culture temperature of 41 °C repressed alveolar bud induction and inhibited alveolar luminal formation. In addition, the treatment at 41 °C decreased the number of proliferating mammary epithelial cells but did not affect cell migration. Levels of phosphorylated Akt, -ERK1/2, -HSP90, and -HSP27 were increased in organoids cultured at 41 °C. The specific inhibitors of HSP90 and HSP27 exacerbated the disruption of organoids at 41 °C but not at 37 °C. Furthermore, the organoids precultured at 37 and 41 °C in the alveolar luminal formation model showed differences in the expression levels of caseins and tight junction proteins, which express in MECs in lactating mammary glands, after induction of MEC differentiation by prolactin and dexamethasone treatment in vitro. These results suggest that elevated temperature directly hinders mammary alveolar development; however, heat shock proteins may mitigate the adverse effects of high temperatures.