Aim: Uncoupling protein 1 (UCP1) is the crucial protein for non-shivering thermogenesis in placental mammals, but the molecular mechanism of thermogenic proton transport is still unknown. Its histidine pair motif (H145 and H147) has been claimed as a critical element for proton translocation, leading to the paradigmatic “cofactor model” of the UCP1 thermogenic mechanism. The histidine pair motif is mutated (H145Q) in the naked mole-rat (NMR, Heterocephalus glaber) UCP1, suggesting disrupted thermogenic function in line with NMR's poor thermoregulatory abilities. Here, we investigated the functionality NMR versus mouse UCP1 to scrutinized the importance of the histidine pair motif. Methods: Respiratory analyses for UCP1 function were performed in isolated brown adipose tissue mitochondria from NMR and mouse. The histidine pair motif of NMR UCP1 was manipulated through mutations, ectopically overexpressed in HEK293 cells and subjected to plate-based respirometry for functional comparison. Results: Isolated BAT mitochondria of NMRs display guanosine diphosphate-sensitive respiration, indicative of thermogenically competent UCP1. Overexpressed wildtype NMR UCP1 demonstrates proton leak activity comparable to mouse UCP1. Neither restoration of the histidine pair motif nor full ablation of the motif through a double mutation affects UCP1-dependent respiration. Conclusions: The UCP1 variant of the NMR, a warm-adapted fossorial species, excludes the histidine pair motif as crucial for UCP1 thermogenic function. Collectively, we show that functional investigation into natural sequence variation of UCP1 not only casts new light on the thermophysiology of NMRs but also represents a powerful tool to delineate structure-function relationships underlying the enigmatic thermogenic proton transport of UCP1.

Brown adipose tissue (BAT) is a heater organ that expresses thermogenic uncoupling protein 1 (UCP1) to maintain high body temperatures during cold stress. BAT thermogenesis is considered an overarching mammalian trait, but its evolutionary origin is unknown. We show that adipose tissue of marsupials, which diverged from eutherian mammals ~150 million years ago, expresses a nonthermogenic UCP1 variant governed by a partial transcriptomic BAT signature similar to that found in eutherian beige adipose tissue. We found that the reconstructed UCP1 sequence of the common eutherian ancestor displayed typical thermogenic activity, whereas therian ancestor UCP1 is nonthermogenic. Thus, mammalian adipose tissue thermogenesis may have evolved in two distinct stages, with a prethermogenic stage in the common therian ancestor linking UCP1 expression to adipose tissue and thermal stress. We propose that in a second stage, UCP1 acquired its thermogenic function specifically in eutherians, such that the onset of mammalian BAT thermogenesis occurred only after the divergence from marsupials. 

Increasing energy expenditure through uncoupling protein 1 (UCP1) activity in thermogenic adipose tissue is widely investigated to correct diet-induced obesity (DIO). Paradoxically, UCP1-deficient male mice are resistant to DIO at room temperature. Recently, we uncovered a key role for fibroblast growth factor 21 (FGF21), a promising drug target for treatment of metabolic disease, in this phenomenon. As the metabolic action of FGF21 is so far understudied in females, we aim to investigate potential sexual dimorphisms. Here, we confirm that male UCP1 KO mice display resistance to DIO in mild cold, without significant changes in metabolic parameters. Surprisingly, females gained the same amount of body fat as WT controls. Molecular regulation was similar between UCP1 KO males and females, with an upregulation of serum FGF21, coinciding with beiging of inguinal white adipose tissue and induced lipid metabolism. While energy expenditure did not display significant differences, UCP1 KO females significantly increased their food intake. Altogether, our results indicate that hyperphagia is likely counteracting the beneficial effects of FGF21 in female mice. This underlines the importance of sex-specific studies in (pre)clinical research for personalized drug development.

Background & Aims: The existence of different subtypes of pancreatic ductal adenocarcinoma (PDAC) and their correlation with patient outcome have shifted the emphasis on patient classification for better decision-making algorithms and personalized therapy. The contribution of mechanisms regulating the cancer stem cell (CSC) population in different subtypes remains unknown.

Methods: Using RNA-seq, we identified B-cell CLL/lymphoma 3 (BCL3), an atypical nf-κb signaling member, as differing in pancreatic CSCs. To determine the biological consequences of BCL3 silencing in vivo and in vitro, we generated bcl3-deficient preclinical mouse models as well as murine cell lines and correlated our findings with human cell lines, PDX models, and 2 independent patient cohorts. We assessed the correlation of bcl3 expression pattern with clinical parameters and subtypes.

Results: Bcl3 was significantly down-regulated in human CSCs. Recapitulating this phenotype in preclinical mouse models of PDAC via BCL3 genetic knockout enhanced tumor burden, metastasis, epithelial to mesenchymal transition, and reduced overall survival. Fluorescence-activated cell sorting analyses, together with oxygen consumption, sphere formation, and tumorigenicity assays, all indicated that BCL3 loss resulted in CSC compartment expansion promoting cellular dedifferentiation. Overexpression of BCL3 in human PDXs diminished tumor growth by significantly reducing the CSC population and promoting differentiation. Human PDACs with low BCL3 expression correlated with increased metastasis, and BCL3-negative tumors correlated with lower survival and nonclassical subtypes.

Conclusions: We demonstrate that bcl3 impacts pancreatic carcinogenesis by restraining CSC expansion and by curtailing an aggressive and metastatic tumor burden in PDAC across species. Levels of BCL3 expression are a useful stratification marker for predicting subtype characterization in PDAC, thereby allowing for personalized therapeutic approaches.