This preprint examines how dietary vitamin D deficiency affects skeletal invasion by mammary cancer cells in a murine model. The investigators used tibial injection of MMTV‑PyMT mammary tumor cells in non‑immunodeficient FVB mice to assess bone invasion under conditions of dietary‑induced vitamin D deficiency. The work builds on prior observations from the same model in which vitamin D deficiency accelerated primary mammary carcinogenesis and spontaneous lung metastasis. The current study focuses specifically on mechanisms that could account for enhanced skeletal invasion when vitamin D is lacking.
The authors emphasize that the report is a preprint and has not undergone peer review. Experimental details and supplementary material are provided in the source document.
A central finding reported is that vitamin D deficiency increased pro‑inflammatory cytokine levels within bone compartments. The increased inflammatory milieu was detected at internal bone surfaces and within marrow. Alongside the cytokine changes, the authors observed increased expression of nestin on the internal bone surface and in marrow. The co‑occurrence of elevated pro‑inflammatory cytokines and higher nestin expression is presented as a mechanistic link between vitamin D deficiency and an environment permissive for tumor cell invasion of bone.
The study frames these observations within the broader concept that inflammation is a hallmark of cancer and can facilitate invasion and metastatic colonization of distant tissues, including the skeleton.
The authors report that vitamin D deficiency promoted epithelial‑to‑mesenchymal transition (EMT) in the mammary tumor cells, identifying the transcription factor Zeb1 as a mediator of this effect. Increased EMT is proposed to contribute to the enhanced invasive phenotype observed in bone in the vitamin D–deficient animals. The manuscript connects elevated inflammation in bone with upregulation of EMT programs via Zeb1, suggesting a pathway by which vitamin D status can influence cellular plasticity and invasive behavior.
To probe upstream regulators of Zeb1, the authors examined the effect of the chemokine CXCL12 on MMTV‑PyMT tumor cells in vitro. They report that CXCL12 stimulated Zeb1 expression in these cells. Importantly, treatment with the biologically active form of vitamin D, 1,25(OH)2D, efficiently countered the CXCL12‑induced increase in Zeb1. This in vitro result supports a model in which vitamin D signalling can directly oppose pro‑invasive transcriptional programs driven by chemokine signalling.
The authors assessed cytokine production by MMTV‑PyMT tumor cells treated in vitro and report that 1,25(OH)2D treatment significantly reduced levels of multiple pro‑inflammatory cytokines. The list of cytokines reported to be reduced includes GM‑CSF, ICAM‑1, IL‑1ra, IP‑10, JE, MCP‑5, MIP‑1α, MIP‑1β, MIP‑2, RANTES and CXCL12. The manuscript presents this observation as a crucial link between vitamin D signalling and modulation of the inflammatory tumor microenvironment, which may in turn limit signals that promote EMT and invasion.
These in vitro cytokine reductions provide mechanistic support for the in vivo finding that vitamin D deficiency is associated with a pro‑inflammatory bone environment that coincides with greater invasion.
The report notes an association between vitamin D repleteness and very high expression of Socs1 (suppressor of cytokine signalling 1). Socs1 is a negative regulator of the JAK/STAT pathway and functions to restrain excessive inflammatory signalling. The authors interpret high Socs1 expression in the vitamin D‑replete state as a mechanism by which vitamin D limits inflammatory responses and exerts tumor‑suppressive effects, thereby reducing the propensity for inflammation‑driven bone invasion.
Based on the mechanistic data, the authors suggest that maintaining vitamin D repleteness in breast cancer patients could reduce inflammation‑driven skeletal invasion and potentially enhance the efficacy of therapies intended to prevent bone metastasis. They link vitamin D’s suppression of pro‑inflammatory cytokines, inhibition of CXCL12‑driven Zeb1 induction, and upregulation of Socs1 to reduced EMT and invasion.
It is important to note that these findings derive from a preclinical model and in vitro assays; the manuscript is a preprint and has not been peer reviewed. The source reports experimental observations in the MMTV‑PyMT model and related cell assays, but translation to human disease and clinical recommendations would require additional validation in peer‑reviewed studies and clinical trials.
Authors and funding: The preprint lists Jiarong Li, Aimee‑Lee Luco, Anne Camirand and Richard Kremer (Research Institute of the MUHC) as authors, and acknowledges funding from the Canadian Institutes of Health Research. The authors declared no competing interests.