Biology subjects

Niebur, G. L.

Publications and source records attributed to Niebur, G. L..

4 recordsLinked to original sources

bioRxiv2026

Cxcr2 is required for ductal outgrowth and shapes the stromal microenvironment in postnatal mammary gland development

Mammary gland development requires coordinated signaling between epithelial and stromal compartments. While CXC chemokine receptor 2 (CXCR2) is known to regulate inflammatory and tissue remodeling processes in disease, including breast cancer, its role in mammary gland morphogenesis is not well understood. Here, we examined postnatal mammary gland development in germline Cxcr2 knockout mice. Loss of Cxcr2 resulted in delayed ductal outgrowth, reduced epithelial area, and altered stromal architecture, including decreased adipocyte size and increased collagen deposition, despite preserved branching organization. These defects occurred in the context of severe systemic immune dysregulation, marked by expansion of granulocytic populations and loss of adaptive immune cells. Together, our findings indicate that CXCR2 indirectly regulates mammary gland development through coordination between the epithelium and stroma, rather than acting through epithelial cell-intrinsic mechanisms. Because the same myeloid expansion, immune suppression, and collagen-rich stromal remodeling that CXCR2 controls during normal development are hallmarks of the pro-tumorigenic breast microenvironment, these findings establish CXCR2 as a regulator of the immune and stromal landscape of the mammary gland and provide a developmental framework for understanding its contributions to the breast tumor microenvironment.

developmental biology↗

bioRxiv2026

An immunocompetent osteoblastic model of mammary cancer bone metastasis established by syngeneic intratibial injection of PyMT mammary carcinoma cells in FVB/N mice

Osteoblastic bone metastasis, in which disseminated tumor cells drive net bone formation, is a clinically distinct and mechanistically underexplored form of skeletal disease that is enriched in hormone receptor-positive breast cancers. Preclinical models of bone metastasis from breast cancer predominantly rely on immunodeficient hosts inoculated with osteolytic human breast cancer cell lines, limiting the study of immune-dependent mechanisms of bone remodeling. Here we describe the development and characterization of an immunocompetent, syngeneic osteoblastic bone metastasis model using intratibial injection of PyMT-CK(OB), a luciferase-expressing derivative of the MMTV-PyMT mammary carcinoma cell line, in FVB/N mice. PyMT-CK(OB) cells produced detectable bioluminescent signal after intratibial injection, enabling longitudinal monitoring of tumor progression. Micro-computed tomography ({micro}CT) revealed significant increases in trabecular bone volume fraction and trabecular number at three and four weeks post-injection, consistent with osteoblastic remodeling. Histological analysis confirmed dense bone lesion formation in tumor-bearing bones. Critically, this osteoblastic phenotype was entirely absent in immunodeficient NOD SCID hosts, despite robust tumor growth, supporting a role for immune competence in tumor-induced bone formation. Loss of bioluminescent signal in immunocompetent mice reflected either immune pressure on reporter gene expression or limited space for cancer cell expansion in the bone, rather than tumor regression or hypoxia, as confirmed by hypoxia imaging and histological endpoint analysis. In contrast, a second PyMT cell subline, PyMT-CF, maintained sustained bioluminescent signal and produced predominantly osteolytic lesions, providing a complementary syngeneic model of osteolytic disease from the same parental background. In vitro hydrogel coculture experiments and protein array analysis of conditioned media revealed that the PyMT sublines have differing impact on MC3T3 osteoblast mineralization, identifying candidate mediators of divergent bone remodeling phenotypes. R7 mammary carcinoma cells derived from MMTV-RON transgenic mouse mammary tumors did not induce measurable bone remodeling under equivalent experimental conditions. Together, these models provide a validated, immunologically intact framework for studying the mechanistic basis of osteoblastic bone metastasis and evaluating therapeutic interventions targeting the tumor-bone microenvironment.

cancer biology↗

bioRxiv2025

Osteoblasts Exert a Pro-Tumorigenic Effect on Breast Cancer Spheroids Through CXCL5/CXCR2 Signaling In 2D And 3D Bone Mimetic Cultures

Bone provides a favorable niche for breast cancer colonization and metastatic progression. Breast cancer cells are attracted to the bone microenvironment where they induce bone cells to resorb bone, which enhances tumor cell proliferation in a positive feedback loop often referred to as the vicious cycle. While this phenomenon is established, the molecular interactions between cancer cells and bone cells are not well defined. CXCL5/CXCR2 signaling has recently been shown to promote breast cancer colonization to the bone. Here, we investigate the effects of osteoblasts and osteocytes on breast cancer cell proliferation in engineered two- and three-dimensional models. We observed that osteoblasts and osteocytes induce proliferative effects on cancer cells. Specifically, bone cells increase cancer proliferation in 2D culture and osteoblasts increase cancer growth more than osteocytes in 3D models. Moreover, osteocyte interaction with cancer cells in 3D models are stiffness dependent. We show that these effects depend on the CXCL5/CXCR2 signaling axis. Taken together, we demonstrate that osteoblasts drive cancer growth in a bone metastatic niche and that this effect can be rescued with CXCL5/CXCR2 inhibition.

bioengineering↗

bioRxiv2019

Mineral deposition and vascular invasion of hydroxyapatite reinforced collagen scaffolds seeded with human adipose-derived stem cells

Collagen-based scaffolds reinforced with hydroxyapatite (HA) are an attractive choice for bone tissue engineering because their composition mimics that of bone. We previously reported the development of compression-molded collagen-HA scaffolds that exhibited high porosity, interconnected pores, and mechanical properties that were well-suited for surgical handling and fixation. The objective of this study was to investigate the use of these novel collagen-HA scaffolds in combination with human adipose-derived stem cells (hASCs) as a template for bone formation in a subcutaneous athymic mouse model. Cell-seeded constructs were pre-treated with either control or osteogenic media. Cell-free and collagen-only groups were included, as was a clinically approved bone void filler as a control for the material. After 8 weeks implantation, cell-free collagen-HA scaffolds and those that were pre-seeded with osteogenically differentiated hASCs supported bone formation and vascular invasion at comparable rates. HA-reinforcement allowed collagen constructs to maintain their implanted shape, provided for improved cell-tissue-scaffold integration, and resulted in a more organized tissue when pre-treated in an osteogenic induction medium. Scaffold type and pre-treatment also determined osteoclast activity and therefore potential remodeling of the constructs. Results suggest that it may be necessary to match the scaffold with a particular cell type and cell-specific pre-treatment to achieve optimal bone formation.

bioengineering↗