Wnt signaling and mammary stem cells

[Cuiru Keli Improves Postpartum Hypogalactia in Rats Through Secreted Frizzled-Related Protein 2-Wnt/β-catenin Signaling Pathway]

Objective

Based on the secreted frizzled-related protein 2 (SFRP2)-Wnt/β-catenin signaling pathway, this study explored the effect and mechanism of Cuiru Keli (CRKL) in the treatment of postpartum hypogalactia.

Methods

A rat model of postpartum hypogalactia was established by gavaging 2 mL of 1.6 mg/mL bromocriptine mesylate to female rats on the third day after delivery. Female rats with a delivery time difference of less than 48 hours were selected and randomly assigned to 7 groups, including a normal group (without any modeling or medication), a model group, a CRKL low-dose group of model group model rats receiving CRKL at the dose of 3 g/kg, a CRKL medium-dose group of model rats receiving CRKL at the dose of 6 g/kg, a CRKL high-dose group of model rats receiving CRKL at the dose of 9 g/kg, a positive drug group of model rats receiving domperidone at the dose of 3 mg/kg, and a negative control (NC) group of model rats receiving normal saline. Each group contained 6 rats. Except for the normal and model groups, the remaining 5 groups were continuously administered with the respective intervention drugs at the specified doses by gavage once a day for 10 days. Changes in the total litter mass of the offspring in the 7 groups within 10 days were measured, and HE staining was performed to identify pathological changes in the mammary tissue (MT). Six groups of rats (excluding the positive control group) were used to observe the pathological changes of eosinophils in pituitary tissue. ELISA was performed to determine the content of prolactin (PRL) in serum, immunohistochemical staining was used to determine the expression of prolactin receptor (PRLR) in MT, and RT-qPCR was used to determine the mRNA expression of genes related to lactation in MT. Network pharmacology and molecular docking were used to study the therapeutic effect and mechanism of CRKL on postpartum hypogalactia, particularly whether it acted through the SFRP2-Wnt/β-catenin signaling pathway. The mechanism of CRKL treatment was further validated by detecting mRNA (RT-qPCR) and protein expression (Western blot) of related pathway genes. Cell experiments were conducted using primary culture rat mammary epithelial cells (RMEC) from rat MT. RMEC were divided into four groups, including a normal group (primary culture RMEC, untreated), SFRP2 overexpression group (primary cultured RMEC treated with SFRP2 overexpression vector), SFRP2 overexpression+CRKL group (receiving treatment for SFRP2 overexpression group plus 10% drug-containing serum), and negative control group (primary culture RMEC treated with empty vector). The effect of CRKL on the expression of lactation-related genes FASN, CSN2, and GLUT1 mRNA after SFRP2 overexpression was detected by RT-qPCR.

Results

In this study, CRKL was administered at a dose of 3 g/kg in the CRKL low-dose group, 6 g/kg in the medium-dose group, and 9 g/kg in the high-dose group (P<0.05 or P<0.01). Compared with the model group, CRKL at all doses significantly increased the total litter weight gain of the offsprings within 10 days (P<0.05 or P<0.01), and effectively increased lactation (P<0.01), the area of mammary lobules, and the size and filling of acinar cavities. CRKL at all doses also increased the number of eosinophils that secreted PRL in the pituitary gland of the postpartum hypogalactia rat model, and increased the content of PRL in the serum (P<0.05 or P<0.01). CRKL promoted the secretion and expression of PRL in postpartum hypogalactic model rats. In addition, it significantly promoted the expression of genes related to milk fat, milk protein, and lactose synthesis in MT (P<0.05 or P<0.01). Network pharmacology predicted that the Wnt signaling pathway might be a key pathway for CRKL in treating postpartum hypogalactia. The molecular docking results showed that related chemical components in CRKL had good binding ability with CCND1 and SFRP2. Compared with the model group, CRKL at all doses inhibited the expression of SFRP2 gene in vivo (P<0.01) and activated the mRNA and protein expression of CCND1 and c-Myc in the Wnt/β-catenin signaling pathway in MT (P<0.05 or P<0.01). Cell experiments showed that, compared to the normal group, SFRP2 overexpression reduced the mRNA expression of milk synthesis-related genes FASN, CSN2, and GLUT1 in RMEC (P<0.01). The CCK8 results indicated that 10% of the drug-containing serum was the effective concentration administered to cells (P<0.01). After administering drug-containing serum, the expression of the lactation-related genes FASN, CSN2, and GLUT1 were up-regulated (compared with the SFRP2 overexpression group, P<0.01).

Conclusion

CRKL alleviates postpartum hypogalactia through the SFRP2-Wnt/β-catenin signaling pathway. SFRP2 might be a potential new target for the diagnosis and treatment of postpartum hypogalactia. This reveals a new mechanism of CRKL in treating postpartum hypogalactia and promotes its clinical application.

Functional ProTracer identifies patterns of cell proliferation in tissues and underlying regulatory mechanisms

A genetic system, ProTracer, has been recently developed to record cell proliferation in vivo. However, the ProTracer is initiated by an infrequently used recombinase Dre, which limits its broad application for functional studies employing floxed gene alleles. Here we generated Cre-activated functional ProTracer (fProTracer) mice, which enable simultaneous recording of cell proliferation and tissue-specific gene deletion, facilitating broad functional analysis of cell proliferation by any Cre driver.

Lithium Chloride Promotes Milk Protein and Fat Synthesis in Bovine Mammary Epithelial Cells via HIF-1α and β-Catenin Signaling Pathways

Lithium is one of the trace elements with many physiological properties, such as being anti-cancer, anti-viral, and anti-inflammatory. However, little is known about its effect on milk synthesis during lactation. Therefore, we selected different concentrations (5 mM, 10 mM, and 20 mM) of lithium chloride (LiCl) and assessed the effect of LiCl on bovine mammary epithelial (MAC-T) cells that underwent 4 days of differentiation induction. Moreover, we analyzed the effect of LiCl on the expression of genes related to milk fat and milk protein synthesis. Herein, LiCl (5-20 mM) significantly increased the expression of β-casein, promoted mRNA expression and phosphorylated protein expression of the signal transduction molecule and activator of transcription 5β (STAT5-β), and inhibited mRNA and protein expression of suppressor of cytokine signaling 2 (SOCS2). In contrast, 5 and 10 mM LiCl significantly inhibited expression of SOCS3. LiCl at concentration of 5-20 mM enhanced phosphorylation level of mTOR protein; at 10 mM and 20 mM, LiCl significantly promoted expression and phosphorylation of downstream ribosomal protein S6 kinase beta-1 (S6K1) protein. Considering milk fat synthesis, mRNA expression of acetyl CoA carboxylase (ACC) and lipoprotein lipase (LPL) genes was considerably increased in the presence of LiCl (5-20 mM). Additionally, increased protein expression levels of stearoyl-CoA desaturase (SCD), peroxisome proliferator-activated receptor-γ (PPARγ), and sterol regulatory element-binding protein 1 (SREBP1) were observed at all LiCl concentrations tested. Subsequently, LiCl (5-20 mM) significantly promoted protein expression and phosphorylation of β-catenin, while 10 mM and 20 mM of LiCl significantly promoted protein expression of hypoxia-inducible factor-1α (HIF-1α). Collectively, it has been shown that 10 mM LiCl can effectively activate HIF-1α, β-catenin, and β-catenin downstream signaling pathways. Conversely, at 10 mM, LiCl inhibited SOCS2 and SOCS3 protein expression through JAK2/STAT5, mTOR, and SREBP1 signaling pathways, improving synthesis of milk protein and fat. Therefore, LiCl can be used as a potential nutrient to regulate milk synthesis in dairy cows.

R-spondin-3 is an oncogenic driver of poorly differentiated invasive breast cancer

R-spondins (RSPOs) are influential signaling molecules that promote the Wnt/β-catenin pathway and self-renewal of stem cells. Currently, RSPOs are emerging as clinically relevant oncogenes, being linked to cancer development in multiple organs. Although this has instigated the rapid development and testing of therapeutic antibodies targeting RSPOs, functional evidence that RSPO causally drives cancer has focused primarily on the intestinal tract. Here, we assess the oncogenic capacity of RSPO in breast cancer in a direct fashion by generating and characterizing a novel mouse model with conditional Rspo3 expression in the mammary gland. We also address the prevalence of RSPO gene alterations in breast cancer patients. We found that a quarter of breast cancer patients harbor RSPO2/RSPO3 copy number amplifications, which are associated with lack of steroid hormone receptor expression and reduced patient survival. Foremost, we demonstrate the causal oncogenic capacity of RSPO3 in the breast, as conditional Rspo3 overexpression consistently drives the development of mammary adenocarcinomas in our novel Rspo3 breast cancer model. RSPO3-driven mammary tumors typically show poor differentiation, areas of epithelial-to-mesenchymal transition, and metastatic potential. Given the reported interplay in the Wnt/β-catenin pathway, we comparatively analyzed RSPO3-driven mouse mammary tumors versus classical WNT1-driven analogues. This revealed that RSPO3-driven tumors are distinct, as the poorly differentiated tumor morphology and metastatic potential were observed in RSPO3-driven tumorigenesis exclusively, further substantiated by differentiating gene expression profiles. Co-expression of Rspo3 and Wnt1 transduced mammary tumors with a mixed phenotype harboring morphological features characteristic of both transgenes. In summary, we report that a quarter of breast cancer patients harbor RSPO2/RSPO3 copy number gains, and these patients have a worse prognosis, whilst providing in vivo evidence that RSPO3 drives poorly differentiated invasive breast cancer in mice. Herewith, we establish RSPO3 as a driver of breast cancer with clinical relevance, proposing RSPO3 as a novel candidate target for therapy in breast cancer. © 2022 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.