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Mammary ductal epithelium controls cold-induced adipocyte thermogenic program

ABSTRACT: Sympathetic activation during cold exposure increases adipocyte thermogenesis via the expression of mitochondrial protein uncoupling protein 1 (UCP1)1. The propensity of adipocytes to express UCP1 is under a critical influence of the adipose microenvironment and varies between sexes and among various fat depots2-7. Here, we report that cold-induced adipocyte UCP1 expression in a female mouse subcutaneous white adipose tissue (scWAT) is regulated by mammary gland ductal epithelial cells in the adipose niche. Single-cell RNA-sequencing (scRNA-seq) shows that glandular luminal epithelium subtypes express transcripts that encode secretory factors in controlling adipocyte UCP1 expression under cold conditions. We term luminal epithelium secretory factors as “mammokines”. Using whole-tissue immunofluorescence 3D visualization, we reveal previously undescribed sympathetic nerve-ductal points of contact. We show sympathetic nerve-activated mammary ducts limit adipocyte UCP1 expression via lipocalin 2. Both in vivo and ex vivo ablation of mammary ductal epithelium enhances cold-induced scWAT adipocyte thermogenic gene program. Since the mammary duct network extends throughout most scWATs in female mice, females show markedly less scWAT UCP1 expression, fat oxidation, energy expenditure, and subcutaneous fat mass loss compared to male mice, implicating sex-specific roles of mammokines in adipose thermogenesis. These results show a previously uncharacterized role of sympathetic nerve-activated glandular epithelium in adipocyte UCP1 expression and suggest an evolutionary function of mammary duct luminal cells in defending glandular adiposity during cold exposure. Overall, our findings highlight mammary gland epithelium as a highly active metabolic cell type and implicate a broader role of mammokines in controlling female adipose metabolism, mammary gland physiology, and systemic energy homeostasis.

ORGANISM(S): Mus musculus

PROVIDER: GSE231394 | GEO | 2023/05/01

REPOSITORIES: GEO

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Project description:Non-shivering thermogenesis in adipocytes is mediated by brown adipose tissue, purportedly through the sole action of uncoupling protein 1 (UCP1). The physiological relevance of UCP1-dependent thermogenesis has primarily been inferred from the attenuation of thermogenic output of mice genetically lacking Ucp1 from birth (germline Ucp1-/-). However, germline Ucp1-/- mice harbor secondary changes within brown adipose tissue beyond UCP1, such as reduced electron transport chain abundance. We show here that these secondary changes also encompass reduced expression of genes regulating fuel liberation, changes that would attenuate the capacity of any thermogenic pathway. Therefore, the quantitative contribution of UCP1-dependent and -independent thermogenesis is not fully understood. To mitigate the potentially confounding ancillary changes to brown adipose tissue of germline Ucp1-/- mice, we constructed mice with inducible adipocyte-selective disruption of Ucp1. We find that, while germline Ucp1-/- mice succumb to cold-induced hypothermia with complete penetrance, most mice with inducible deletion of Ucp1 maintain homeothermy in the cold. However, inducible adipocyte-selective co-deletion of Ucp1 and creatine kinase B (Ckb, an effector of UCP1-independent thermogenesis) exacerbates cold-intolerance, indicative of a negative genetic interaction and thus a parallel thermogenic function. We find no evidence for impairments in insulation or non-shivering thermogenesis in skeletal muscle that would drive this phenotype. Furthermore, following UCP1 deletion or UCP1/CKB co-deletion from mature adipocytes, moderate cold exposure triggers the regeneration of mature adipocytes that coordinately restore UCP1 and CKB to brown adipose tissue, providing further evidence of their parallel thermogenic relationship. Our findings suggest that thermogenic adipocytes utilize non-paralogous protein redundancy – through UCP1 and CKB – to promote cold-induced energy dissipation.

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Mammary ductal epithelium controls cold-induced adipocyte thermogenic program

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