Abstract P5-06-11: Secreted frizzled related protein 1: From lobular involution to breast osteoimmunological disorder
Authors: Clemenceau Alisson , Lacouture Aurélie , Bherer Juliette , Étienne Audet-Walsh , Diorio Caroline , Durocher Francine 
Published: March 2022

Abstract
Breast cancer is the leading cause of cancer-related death in women worldwide. Our group previously performed a human transcriptome array on normal tissue, atypical ductal hyperplasia, ductal carcinoma in situ and estrogen receptor-α positive invasive ductal carcinoma. Among the transcripts down-regulated during carcinogenesis: Secreted Frizzled-Related Protein 1 (SFRP1), a Wnt signaling pathway antagonist inversely associated with age-related lobular involution has been identified.Interestingly, SFRP1 expression is higher in presence of hydroxyapatite microcalcifications in non-tumoral breast tissue. SFRP1 is also known to be involved in the increase of bone resorption, notably by downregulating osteoblastic differentiation. This suggests that the lack of SFRP1 could be involved in both osteoblast-like phenotype acquisition and early breast carcinogenesis. Unfortunately, data on the mechanism of microcalcifications formation and their impacts on breast carcinogenesis are still lacking.We hypothesize that loss of SFRP1 is responsible for microcalcifications accumulation and early breast carcinogenesis. Our objectives are:1. To define the impact of microcalcifications on SFRP1 expression in non-tumoral mammary gland and 2. to decipher the causal role of SFRP1 in microcalcifications formation. Organoid culture using freshly purified epithelial cells from nulliparous and multiparous mice mammary glands, in presence or in absence of hydroxyapatite crystals has been performed. Organoids number and phenotype have been studied (aim 1). We also have modulated SFRP1 expression in mammary cell lines by lentiviral transduction and performed proliferation, migration and alizarin assays to assess the tumoral aggressivity and cells abilities to produce calcium deposits in vitro (aim 2). SFRP1 and markers of osteoblastic differentiation (Runt-related transcription factor 2, RUNX2) and bone formation (Alkaline Phosphatase, ALPL; Osteopontin, SPP1; Periostin, POSTN) will also be quantified by quantitative PCR in both mice organoids and human mammary cell lines (aims 1 and 2). 1. The ratio between the mammary gland and body weight obtained from nulliparous mice (n = 12) is significantly lower compared with multiparous mice (n = 12; fold-change = 1.84; p-value &lt; 0.001). Hydroxyapatite crystals induced an increase in the proportion of organoids with lumen and branching compared with the control without hydroxyapatite specifically in organoids obtained from nulliparous mice. Organoid’s size and gene expression profiles are still to be assessed. 2. SFRP1 downregulation in a non-tumoral atypical ductal hyperplasia cell line (MCF10AT1) induced an increase in proliferative and migratory cells abilities. It was also responsible for an increase in estrogen receptor 1 (ESR1) expression, suggesting that SFRP1 is related to luminal carcinogenesis. Results also demonstrate that decreasing SFRP1 in MCF10AT1 induced a profile similar to growth stage in bone tissue, which notably means an increase of expression of the osteoblastic transcription factor RUNX2 and the marker of mineralization SPP1, also involved in lactation-related pink adipose tissue formation. We also observed an increase of POSTN expression, known to be involved in decreased bone mineral density during lactation.SFRP1 upregulation in the invasive luminal A cell line MCF7 reduced cell migration and ESR1 expression. Likewise, it increased MCF7 proliferation compared to control. In addition, it induced an increase of RUNX2 and SPP1 expression, similar to what is reported in matrix mineralization profile in bone. These results support our hypothesis that SFRP1 has a causal role in the acquisition of a malignant phenotype but also in osteoblast-like phenotype in mammary epithelial cells. The cause of SFRP1 downregulation in women remains to be explored.
Citation Format: Alisson Clemenceau, Aurélie Lacouture, Juliette Bherer, Audet-Walsh Étienne, Caroline Diorio, Francine Durocher. Secreted frizzled related protein 1: From lobular involution to breast osteoimmunological disorder [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P5-06-11.