Role of Ubiquilins for Brown Adipocyte Proteostasis and Thermogenesis

Single-nucleus RNA-sequencing reveals NRF1/NFE2L1 as a key factor determining the thermogenesis and cellular heterogeneity and dynamics of brown adipose tissues in mice

Brown adipose tissue (BAT) is a major site of non-shivering thermogenesis in mammals and plays an important role in energy homeostasis. Nuclear factor-erythroid 2-related factor 1 (NFE2L1, also known as Nrf1), a master regulator of cellular metabolic homeostasis and numerous stress responses, has been found to function as a critical driver in BAT thermogenic adaption to cold or obesity by providing proteometabolic quality control. Our recent studies using adipocyte-specific Nfe2l1 knockout [Nfe2l1(f)-KO] mice demonstrated that NFE2L1-dependent transcription of lipolytic genes is crucial for white adipose tissue (WAT) homeostasis and plasticity. In the present study, we found that Nfe2l1(f)-KO mice develop an age-dependent whitening and shrinking of BAT, with signatures of down-regulation of proteasome, impaired mitochondrial function, reduced thermogenesis, pro-inflammation, and elevated regulatory cell death (RCD). Mechanistic studies revealed that deficiency of Nfe2l1 in brown adipocytes (BAC) primarily results in down-regulation of lipolytic genes, which decelerates lipolysis, making BAC unable to fuel thermogenesis. These changes lead to BAC hypertrophy, inflammation-associated RCD, and consequently cold intolerance. Single-nucleus RNA-sequencing of BAT reveals that deficiency of Nfe2l1 induces significant transcriptomic changes leading to aberrant expression of a variety of genes involved in lipid metabolism, proteasome, mitochondrial stress, inflammatory responses, and inflammation-related RCD in distinct subpopulations of BAC. Taken together, our study demonstrated that NFE2L1 serves as a vital transcriptional regulator that controls the lipid metabolic homeostasis in BAC, which in turn determines the metabolic dynamics, cellular heterogeneity and subsequently cell fates in BAT.

NFE2L1-mediated proteasome function protects from ferroptosis

Objective

Ferroptosis continues to emerge as a novel modality of cell death with important therapeutic implications for a variety of diseases, most notably cancer and degenerative diseases. While susceptibility, initiation, and execution of ferroptosis have been linked to reprogramming of cellular lipid metabolism, imbalances in iron-redox homeostasis, and aberrant mitochondrial respiration, the detailed mechanisms of ferroptosis are still insufficiently well understood.

Methods and results

Here we show that diminished proteasome function is a new mechanistic feature of ferroptosis. The transcription factor nuclear factor erythroid-2, like-1 (NFE2L1) protects from ferroptosis by sustaining proteasomal activity. In cellular systems, loss of NFE2L1 reduced cellular viability after the induction of both chemically and genetically induced ferroptosis, which was linked to the regulation of proteasomal activity under these conditions. Importantly, this was reproduced in a Sedaghatian-type Spondylometaphyseal Dysplasia (SSMD) patient-derived cell line carrying mutated glutathione peroxidase-4 (GPX4), a critical regulator of ferroptosis. Also, reduced proteasomal activity was associated with ferroptosis in Gpx4-deficient mice. In a mouse model for genetic Nfe2l1 deficiency, we observed brown adipose tissue (BAT) involution, hyperubiquitination of ferroptosis regulators, including the GPX4 pathway, and other hallmarks of ferroptosis.

Conclusion

Our data highlight the relevance of the NFE2L1-proteasome pathway in ferroptosis. Manipulation of NFE2L1 activity might enhance ferroptosis-inducing cancer therapies as well as protect from aberrant ferroptosis in neurodegeneration, general metabolism, and beyond.

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Proteasome function is diminished during ferroptosis.

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NFE2L1-mediated proteasomal activity protects from ferroptosis.

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The ubiquitination of the GPX4-glutathione pathway is implicated in Nfe2l1 deficiency.

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NFE2L1 deficiency in brown fat is associated with hallmarks of ferroptosis.