The Influence of Ambient Temperature on Adipose Tissue Homeostasis, Metabolic Diseases and Cancers

Figures

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  Figure 1. Thermoregulation of mice in response to ambient temperature. In ambient temperature below their TNZ, mice need extra energy for the “heating” process to maintain their body temperature. Oppositely, mice need extra energy for “cooling” when they are housed in an environment above their TNZ. In their TNZ, mice can maintain their basal metabolism without any requirement for thermogenic activity. BMR: basal metabolic rate; ST: shivering thermogenesis; NST: non-shivering thermogenesis; TNZ: thermoneutral zone.

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  Figure 2. Phenotypes alteration of brown adipocytes in different housing temperatures. In standard animal housing (room temperature or ~21–24 °C), brown adipocytes contain multilocular lipid droplets with a high number of mitochondria. A small number of immune cells, such as macrophages, are known to reside in BAT. Housing the mice in the thermoneutrality (~28–31 °C) alters brown adipocytes phenotypes, observed by the appearance of unilocular lipid droplets and a low number of mitochondria. Higher infiltration of macrophages was also observed in BAT from mice living in the TN zone. These infiltrated macrophages reside in their activated state, reflected by the crown-like structure. Mechanisms such as autophagy-mediated mitochondria clearance and ChREBP-dependent lipid accumulation contribute to thermoneutrality-induced BAT remodeling.

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  Figure 3. TN housing alters mice’s phenotype and response to the development of diseases. TN housing induces BAT and reduces the appearance of beige adipocytes in iWAT. Upon HFD feeding, TN housing exacerbates the accumulation of immune cells in eWAT and the liver. Housing the atherosclerosis mice model in their TN zone along with western-diet feeding leads to a greater accumulation of atherogenic lesions. TN housing reduced tumor growth in mice inoculated with tumor cells. These phenotypes might be due to the higher number of CD8+ T cells and activated DC infiltrated into the tumor cells. TN housing enhances circulating pro-inflammatory cytokines resulting in higher systemic inflammation. Furthermore, TN housing also alters the circulating cholesterol profile reflected by a higher fraction of LDL. RT: room temperature; TN: thermoneutral; BAT: brown adipose tissue; DCs: dendritic cells; NAFLD: non-alcoholic fatty liver diseases; HFD: high-fat diet; LDL: low-density lipoprotein.