The Effects of Heat-Humidity Stress on Mammary Gland Development

Abstract

The constant rise in heat and humidity levels in the atmosphere due to climate change has been a global concern impacting various aspects of life. Studies and surveys showed that heat humidity stress can significantly impact several physiological functions in mammals, especially during pregnancy. The mammary gland could be highly susceptible to heat stress because it goes through extensive proliferation and differentiation during pregnancy and lactation in order to synthesize and secrete milk. In this study, we used a mouse model to understand the effect of heat humidity stress on mammary gland development during pregnancy and lactation. Our findings show that heat-humidity stress leads to a reduction in the overall size of the mammary glands in the mid and late stages of pregnancy. Moreover, mammary gland whole- mount and histological analysis revealed a reduction in alveolar development and epithelial content in the heat-stressed mouse mammary gland during pregnancy. Further, the immunostaining of Ki67 in mammary tissue sections showed reduced proliferation in the mammary epithelium of heat-stressed mid-pregnant mice. Furthermore, we observed that HSP70, a stress-related protein and chaperone expression, was found to be significantly upregulated in heat-stressed mouse mammary glands throughout pregnancy (early to late stages), indicating a reaction to cellular stress. These results suggest that mammary gland development is adversely affected by heat-humidity stress, which may have important implications for lactation and milk production. Although its effectiveness in diminishing the effect of heat- humidity stress on mammary development is still unknown, the elevated production of HSP70 may operate as a defence mechanism against heat-humidity stress. These findings highlight how crucial it is to consider environmental influences like heat and humidity stress when analysing the mammary glands' development and function during pregnancy. Developing approaches to sustain mammary gland function in animals under heat-humidity stress, especially in tropical countries, would require a comprehensive understanding.