Memory T-Cells Contribute to Calcium Release from Bones during Lactation in Mice

Area of Science:

• Endocrinology
• Immunology
• Bone Biology

Background:

• Lactation requires significant calcium, sourced from diet and maternal bone. Mammary-derived PTHrP is known to stimulate bone resorption during lactation.
• The specific impact of postpartum estrogen loss on bone metabolism and calcium homeostasis remained largely undefined.

Purpose of the Study:

• To investigate the role of estrogen loss during lactation in bone resorption and calcium release.
• To elucidate the cellular and molecular mechanisms linking estrogen deficiency, immune activation, and bone remodeling in lactating mice.

Main Methods:

• Utilized a case-control study design in a mouse model.
• Analyzed the activation of memory T-cells (T_M) and their production of cytokines (TNFα and IL-17A) in response to estrogen loss during lactation.

Main Results:

• Demonstrated that estrogen loss during lactation activates memory T-cells (T_M).
• Showed that these activated T_M cells produce TNFα and IL-17A, contributing to bone resorption and calcium release.
• Identified a novel mechanism for postpartum calcium mobilization essential for milk production.

Conclusions:

• The immune system plays a critical role in supporting calcium needs during lactation.
• This evolutionary pathway for calcium release via bone resorption during lactation may become detrimental postmenopause, contributing to osteoporosis.
• Highlighted the intricate crosstalk between the brain-bone-breast-endocrine axis and the immune system during the physiological state of lactation.