Estrogen exacerbates mammary involution through neutrophil dependent and independent mechanism

Abstract

21There is strong evidence that the pro-inflammatory microenvironment during post-partum 22 mammary involution promotes parity-associated breast cancer. Estrogen exposure during 23 mammary involution drives tumour growth through the activity of neutrophils. However, how 24 estrogen and neutrophils influence mammary involution are unknown. Combined analysis of 25 transcriptomic, protein, and immunohistochemical data in Balb/c mice with and without 26 neutrophil depletion showed that estrogen promotes involution by exacerbating inflammation, 27 cell death and adipocytes repopulation through neutrophil-dependent and neutrophil-28 independent mechanisms. Remarkably, 88% of estrogen-regulated genes in mammary tissue 29 were mediated through neutrophils, which were recruited through estrogen-induced CXCL2-30 CXCR2 signalling. While neutrophils mediate estrogen-induced inflammation and adipocytes 31 repopulation, estrogen-induced mammary cell death was mediated by neutrophils-independent 32 upsurges of cathepsins and their lysosomal leakages that are critical for lysosome-mediated 33 cell death. Notably, these multifaceted effects of estrogen are unique to the phase of mammary 34 involution. These findings are important for the development of intervention strategies for 35 parity-associated breast cancer. 36 37There is strong evidence that the mammary microenvironment during the post-partum 38 mammary involution promotes mammary tumour progression. High levels of tissue fibrillar 39 collagen and elevated expression of cyclooxygenase-2 (COX-2) in the mammary gland have 40 been shown to drive tumour growth and lymph angiogenesis [1,2]. Wound healing-like tissue 41 environment associated with mammary involution is also known to promote tumour 42 development and dissemination [3]. Estrogen has been shown to stimulate the growth of 43 estrogen receptor-negative mammary tumours during mammary involution and estrogen-44 stimulated neutrophil activity plays a crucial role in fostering the pro-tumoral 45 microenvironment [4]. This suggests that estrogen exposure during post-weaning mammary 46 involution is a risk factor for parity-associated breast cancer. However, the functional roles of 47 estrogen and neutrophils in mammary biology during involution have been little studied to date. 48 Post-weaning mammary involution is a process for the lactating mammary gland to 49 return to the pre-pregnancy state. The distinctive features of mammary involution include 50 massive cell death of the secretory mammary alveoli, acute inflammation, extracellular matrix 51 remodelling and adipocyte repopulation. Involution is commonly divided into two phases. In 52 mice, the first phase is the reversible phase whereby the reintroduction of the pups within 48h 53 can re-initiate lactation [5,6]. It is typified by a decrease in milk protein synthesis and increased 54 mammary cell death resulting in the appearance of shed, dying cells within the lumen of the 55 distended alveoli [7,8]. Inflammation also occurs in the first phase with the infiltrati...

Estrogen Markedly Reduces Circulating Low-density Neutrophils and Enhances Pro-tumoral Gene Expression in Neutrophil of Tumour-bearing Mice

“…Neutrophils are known to undergo epigenetic changes during development and under mature state in response to environmental cues [31][32][33]. We have also reported that neutrophils in the post-weaning and nulliparous mammary tissue respond to estrogen differently [28]. Whether the innate immune function of neutrophils is generally compromised by tumour burden requires further investigation.…”

“…This difference in functional outcomes may be attributed to the difference in the tissue microenvironment. The pro-in ammatory microenvironment in the mammary gland of Inv mice facilitates estrogen-induced neutrophil recruitment and reprograming [15,28], leading to the release of pro-tumoral cytokines/chemokines. This is in contrast with Null mice in which, estrogen is generally anti-in ammatory in the mammary tissue [29,30].…”

The Abundance and Function of Neutrophils in the Endometriosis Systemic and Pelvic Microenvironment

“…Endometriosis is known to be estrogen-dependent, and local estradiol biosynthesis in endometriotic lesions combines with peritoneal inflammation in the peritoneal cavity to form an abnormal immune-endocrine microenvironment [1]. In breast tissue, estrogen function supports neutrophil infiltration and neutrophil-mediated adipocyte regeneration [80]. In the early phases of endometriosis, estrogen (E2) and estrogen receptor (ER) are essential for immunological regulation and angiogenesis [79], and the physiological connection between estrogen-induced modifications in neutrophil function and endometriosis pathogenesis is of particular interest.…”