The study followed 12-week-old mice given subcutaneous injections of 5 × 10^5 Lewis lung carcinoma cells or phosphate-buffered solution. Separate cohorts were examined two, 2.5 and 3.5 weeks after inoculation, with blood, bone marrow, tumour, spleen and skeletal muscle collected for flow cytometry, molecular analysis and tissue measurements. EchoMRI was used to assess body composition, while laminin staining of gastrocnemius–soleus sections quantified muscle fibre cross-sectional area. Tumours grew progressively in both sexes, but only males showed the characteristic combination of substantial weight loss, reduced lean mass and smaller myofibres associated with overt cachexia. Fat mass fell in both sexes, and grip strength declined in both, showing that several physiological outcomes did not track the marked sex difference in muscle cross-sectional area.

Bone-marrow analysis indicated that the divergence began before overt wasting. In males, haematopoietic stem cells increased at two weeks and remained elevated through 3.5 weeks, while multipotent and common myeloid progenitors also expanded. Granulocyte–monocyte progenitors, which generate granulocytes and monocytes, increased in males at 2.5 weeks, together with CCR2-positive granulocyte–monocyte progenitors. This pattern was consistent with a shift toward production and potential recruitment of myeloid cells before the clear loss of muscle area seen at 3.5 weeks. Females showed a different sequence, including expansion of stem and progenitor populations around 2.5 weeks and a later increase in CCR2-positive granulocyte–monocyte progenitors at 3.5 weeks, without comparable muscle wasting during the observation period.

The bone-marrow niche, whose osteolineage, endothelial, adipocyte and stromal cells regulate stem-cell maintenance and differentiation, was also remodelled in a sex-dependent sequence. In males, osteoprogenitors and osteoblasts were elevated at two weeks, coinciding with the early rise in haematopoietic stem cells, while adipocyte progenitors decreased at 2.5 weeks. In females, endothelial progenitors and endothelial cells increased at two weeks, whereas mesenchymal stromal cells and osteolineage populations changed around the mid-point of the experiment. Trabecular marrow adipose tissue did not differ significantly across time points or sexes. The measurements therefore identified differences in cellular composition of the niche, but did not directly demonstrate that a particular niche population caused the sex-dependent changes in blood-cell production.

Cancer-associated changes in myelopoiesis did not translate into sustained accumulation of marrow-derived cells in the tumour. Plasma CCL2, a chemokine that can attract cells expressing its receptor CCR2, increased as tumours progressed. Nevertheless, several CCR2-positive populations measured within tumours declined at later time points: CCR2-positive haematopoietic stem cells and macrophages were lower at 3.5 weeks than at two weeks, while CCR2-positive megakaryocyte–erythroid progenitors declined between 2.5 and 3.5 weeks. CCR2-positive common myeloid and granulocyte–monocyte progenitors remained unchanged. These observations separate bone-marrow remodelling from a simple model in which continued overproduction of myeloid cells indefinitely supplies the tumour; the measured data instead point to a broader systemic response to cancer.

Skeletal muscle emerged as a likely destination for myeloid-lineage cells. The researchers reanalysed a previously generated single-cell RNA-sequencing dataset from male tumour-bearing muscle. Compared with sham controls, tumour-bearing animals had proportionally more neutrophils and monocytes and fewer lymphocytes. Macrophages were the main source of Ccl2 expression at two weeks, whereas by 3.5 weeks the transcript was expressed across a wider range of immune and non-immune populations. Direct measurements showed that muscle CCL2 concentrations increased at 3.5 weeks in both sexes. Neutrophil abundance in muscle also rose at that time, while persistent monocytes with a Ly6C-low, CCR2-low, CX3CR1-high phenotype had accumulated by 2.5 weeks.

Flow cytometry revealed that the muscle macrophage pool changed in composition without simply expanding in size. The overall macrophage proportion remained stable across the time course, but the fraction expressing CCR2 increased at 2.5 and 3.5 weeks, including inflammatory CD206-negative macrophages. The rise in CCR2-positive cells without a corresponding rise in total macrophages was consistent with bone-marrow-derived macrophages becoming a larger component of the existing pool. The subsets also differed between sexes: males had proportionally more CD206-positive macrophages, including CCR2-positive CD206-positive cells, whereas females had proportionally more CD206-negative macrophages. Relationships with muscle area also varied. The correlation between CCR2-positive macrophages and cross-sectional area was moderately negative in males and moderately positive in females, although neither correlation was individually significant; a statistical comparison between the sex-specific correlations was significant.

Single-cell transcriptomics in male muscle provided a possible sequence for the onset of wasting. At two weeks, before overt loss of muscle cross-sectional area, macrophages expressed higher levels of the atrophic factors Il1, Tgfb1, Tnfsf12 and Tnf. Monocytes and neutrophils increased expression of these same factors later, at 3.5 weeks. Myonuclei, the nuclei within muscle fibres, had already upregulated receptors including Il1r1, Tgfbr1, Tnfrsf1a and Tnfrsf12a at two and 3.5 weeks. Smad3 and Foxo1 signalling-associated transcripts rose earlier, followed by increased expression of the muscle-atrophy genes Trim63 and Fbxo32 at 3.5 weeks. The timing was consistent with macrophages initiating atrophic signalling before other immune-cell classes, but it did not establish a causal pathway.

That limitation was reinforced by protein measurements. Whole-muscle homogenates showed no significant changes in SMAD3, phosphorylated SMAD3, SMAD7 or TGFBR1 across the cachexia time course or between sexes, despite the cell-resolved transcriptional changes. The investigators did not directly manipulate the candidate ligands, receptors or macrophage populations to test whether they caused muscle loss, and the detailed single-cell comparison involved males only. Whole-muscle assays may also obscure signals restricted to particular cell types or fibre types. The work was conducted in a subcutaneous Lewis lung carcinoma mouse model; cachexia varies with tumour location, and these findings therefore cannot establish the same sequence or magnitude of change in people with cancer.

Overall, the experiments place aberrant myelopoiesis and haematopoietic stem-cell-niche remodelling before severe cachexia in male mice and show that the associated immune-cell dynamics are more complex than a simple increase in tumour myeloid content. Male and female animals showed different schedules of progenitor expansion and niche remodelling, while the composition and muscle-area relationships of CCR2-positive macrophages differed between sexes. The findings support aberrant myelopoiesis as an early feature of cachexia development in this preclinical model and show that similar tumour burdens can produce markedly different wasting responses. They do not establish that suppressing a particular marrow or CCR2-dependent pathway would prevent cachexia, nor do they provide evidence of clinical efficacy in patients; instead, they identify measurable events and candidate cellular signals whose roles require direct experimental testing.

Subject of Research: Sex-dependent myelopoiesis and bone-marrow niche remodelling in a mouse model of cancer cachexia

Article Title: Aberrant Myelopoiesis and Haematopoietic Stem Cell Niche Remodelling Precedes Cancer Cachexia Onset in a Sex‐Dependent Manner

Article References: Tate, A., Brown, A., Ek Orloff, L., Vanhie, J., Collao, N., Brabrook, C., Moghadam, V., Rajaković, V., Wiper‐Bergeron, N., & De Lisio, M. (2026). Aberrant Myelopoiesis and Haematopoietic Stem Cell Niche Remodelling Precedes Cancer Cachexia Onset in a Sex‐Dependent Manner. Journal of Cachexia, Sarcopenia and Muscle, 17(5), Article e70403. https://doi.org/10.1002/jcsm.70403

Image Credits: AI Generated

DOI: 10.1002/jcsm.70403

Keywords: cancer cachexia, myelopoiesis, haematopoietic stem cells, bone marrow niche, skeletal muscle, CCR2-positive macrophages, CCL2 signalling, sex differences, tumour immunology, Lewis lung carcinoma, Aberrant, Haematopoietic