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Investigating the effect of positional variation on mid-lactation mammary gland transcriptomics in mice fed either a low-fat or high-fat diet.

ABSTRACT: Little attention has been given to the effect of positional variation of gene expression in the mammary gland. However, more research is shedding light regarding the physiological differences that mammary gland location can have on the murine mammary gland. Here we examined the differentially expressed genes between mammary gland positions under either a low-fat diet (LFD) or a high-fat diet (HFD) in the mid-lactation mammary gland (lactation day 11; L11). Three-week old WT C57BL/6 mice were randomly assigned to either a low-fat diet (LFD) or high fat diet (HFD) (n = 3/group) and either the right thoracic mammary gland (TMG) or inguinal mammary gland (IMG) was collected from each dam for a total of 12 unique glands. Within each diet, differentially expressed genes (DEGs) were first filtered by adjusted p-value (cutoff ≤ 0.05) and fold-change (FC, cutoff ≥2). Genes were further filtered by mean normalized read count with a cutoff≥10. We observed that mammary gland position had a significant impact on mammary gland gene expression with either LFD or HFD diet, with 1264 DEGs in LFD dams and 777 DEGs in HFD dams. We found that genes related to snRNP binding and translation initiation were most significantly altered between the TMG and IMG. Although we were not able to discern a molecular mechanism, many small nuclear RNAs and small nucleolar RNAs were differentially expressed between the TMG and IMG responsible for cellular functions such as splicing and ribosome biogenesis, which provides and interesting avenue for future research. Our study supports the hypothesis that collection of the mammary gland from a particular location influences mammary gland gene expression, thereby highlighting the importance for researchers to be vigilant in documenting and reporting which mammary gland they are using for their studies.

SUBMITTER: Cheng AA

PROVIDER: S-EPMC8389404 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Inflammatory breast cancer (IBC) presents as rapid-onset swelling and breast skin changes caused by tumor emboli in the breast and breast skin lymphatics. IBC has been linked with obesity and duration of breastfeeding, but how these factors affect IBC tumor progression is not clear. We modeled the simultaneous effects of diet and weaning in mice on in vivo lymphatic function; on IBC tumor growth; and on aspects of the mammary gland microenvironment before and after IBC (SUM149) xenograft inoculation. We hypothesized that weaning status and diet would have synergistic effects on lymphatic function and the breast microenvironment to enhance IBC tumor growth. Changes in lymphatic structure and function were characterized with in vivo near-infrared fluorescence (NIRF) imaging. Mice were fed either a high-fat diet (HFD; 60 kcal%) or a normal/low-fat diet (LFD; 10 kcal%), bred twice, and subjected to either normal-duration nursing (NW) or forced weaning (FW). SUM149 IBC tumors were implanted at 14 months; images were obtained before and after implantation. Multiparous mice fed HFD showed increased pre-tumor lymphatic pulsing in both the FW and NW groups relative to mice fed LFD. HFD promoted tumor growth independent of weaning time (P = 0.04). Pre-tumor lymphatic pulsing was associated with tumor volume at 8 weeks (P = 0.02) and was significantly correlated with expression of the lymphatic tracking ligand CCL21 (P = 0.05, Table 1). HFD significantly increased the numbers of monocyte-derived IBA1+, CD163+, and CD11c+ cells (P < 0.0001, P < 0.0001, P = 0.0005) in the contralateral, non-tumor-bearing mammary gland. Numbers of lymphangiogenic podoplanin+/IBA1+ macrophages were increased in the ducts of HFD and FW mice (all P < 0.003). HFD in nulliparous mice had a similar increase in lymphatic pulsing at 14 weeks (P = 0.006), indicating that this functional change was independent of parity. We conclude that HFD induced increases in mammary gland lymphatic function, assessed as pulsing rate before tumor initiation, and correlated with inflammation in the mammary gland and increased SUM149 tumor growth. The relationship between diet, lymphatic pulsing, and tumor growth warrants further investigation.

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Investigating the effect of positional variation on mid-lactation mammary gland transcriptomics in mice fed either a low-fat or high-fat diet.

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