Hormone signaling requirements for the conversion of non-mammary mouse cells to mammary cell fate(s) in vivo

Rat Models of Hormone Receptor-Positive Breast Cancer

Hormone receptor-positive (HR+) breast cancer (BC) is the most common type of breast cancer among women worldwide, accounting for 70-80% of all invasive cases. Patients with HR+ BC are commonly treated with endocrine therapy, but intrinsic or acquired resistance is a frequent problem, making HR+ BC a focal point of intense research. Despite this, the malignancy still lacks adequate in vitro and in vivo models for the study of its initiation and progression as well as response and resistance to endocrine therapy. No mouse models that fully mimic the human disease are available, however rat mammary tumor models pose a promising alternative to overcome this limitation. Compared to mice, rats are more similar to humans in terms of mammary gland architecture, ductal origin of neoplastic lesions and hormone dependency status. Moreover, rats can develop spontaneous or induced mammary tumors that resemble human HR+ BC. To date, six different types of rat models of HR+ BC have been established. These include the spontaneous, carcinogen-induced, transplantation, hormone-induced, radiation-induced and genetically engineered rat mammary tumor models. Each model has distinct advantages, disadvantages and utility for studying HR+ BC. This review provides a comprehensive overview of all published models to date.

The Diverse Manifestations of Regeneration and Why We Need to Study Them

For hundreds of years, the question of why some organisms can regenerate missing body parts while others cannot has remained poorly understood. This has been due in great part to the inability to genetically, molecularly, and cellularly dissect this problem for most of the history of the field. It has only been in the past 20-30 years that important mechanistic advances have been made in methodologies that introduce loss and gain of gene function in animals that can regenerate. However, we still have a very incomplete understanding of how broadly regenerative abilities may be dispersed across species and whether or not such properties share a common evolutionary origin, which may have emerged independently or both. Understanding regeneration, therefore, will require rigorously practiced fundamental, curiosity-driven, discovery research. Expanding the number of research organisms used to study regeneration allows us to uncover aspects of this problem we may not yet know exist and simultaneously increases our chances of solving this long-standing problem of biology.

Adipose-derived mesenchymal stem cells formed acinar-like structure when stimulated with breast epithelial cells in three-dimensional culture

Lipotransfer has been applied in breast augmentation surgery for several years and the resident adipose-derived stem cells (ASCs) play an important role in enhancing fat graft survival. However, the interaction between ASCs and mammary epithelium is not fully understood. Many studies have shown that ASCs have a tumor-supportive effect in breast cancer. To the best of our knowledge, this is the first study on the effect of mammary epithelial cells on the human ASCs in 3D culture. ASCs were cultivated on matrigel in the conditioned medium (CM) prepared from a human breast epithelial cell line (HBL-100). The ASCs formed KRT18-positive acini-like structures after stimulation with breast epithelial cells. The expression of epithelial genes (CDH1 and KRT18) was up-regulated while the expression of mesenchymal specific genes (CDH2 and VIM) was down-regulated as determined by qRT-PCR. The stemness marker (CD29) and angiogenic factors (CD31 and VEGF) were also down-regulated as examined by immunofluorescence. In addition, the CM obtained from HBL-100 enhanced the migration and inhibited the adipogenic differentiation of ASCs. These results demonstrate that ASCs have the ability to transform into epithelial-like cells when cultured with mammary epithelial cells. Given these observations, we infer that ASCs have a positive effect on lipotransfer, not only due to their ability to secrete growth factors, but also due to their direct participation in the formation of new breast tissue.

In vivo reprogramming of non-mammary cells to an epithelial cell fate is independent of amphiregulin signaling

Amphiregulin (AREG)^-/- mice demonstrate impaired mammary development and form only rudimentary ductal epithelial trees; however, AREG^-/- glands are still capable of undergoing alveologenesis and lactogenesis during pregnancy. Transplantation of AREG^-/- mammary epithelial cells into cleared mouse mammary fat pads results in a diminished capacity for epithelial growth (∼15%) as compared to that of wild-type mammary epithelial cells. To determine whether estrogen receptor α (ERα, also known as ESR1) and/or AREG signaling were necessary for non-mammary cell redirection, we inoculated either ERα^-/- or AREG^-/- mammary cells with non-mammary progenitor cells (WAP-Cre/Rosa26LacZ+ male testicular cells or GFP-positive embryonic neuronal stem cells). ERα^-/- cells possessed a limited ability to grow or reprogram non-mammary cells in transplanted mammary fat pads. AREG^-/- mammary cells were capable of redirecting both types of non-mammary cell populations to mammary phenotypes in regenerating mammary outgrowths. Transplantation of fragments from AREG-reprogrammed chimeric outgrowths resulted in secondary outgrowths in six out of ten fat pads, demonstrating the self-renewing capacity of the redirected non-mammary cells to contribute new progeny to chimeric outgrowths. Nestin was detected at the leading edges of developing alveoli, suggesting that its expression may be essential for lobular expansion.