TFEB deficiency attenuates mitochondrial degradation upon brown adipose tissue whitening at thermoneutrality

Abstract

Objective Brown adipose tissue (BAT) thermogenesis offers the potential to improve metabolic health in mice and humans. However, humans predominantly live under thermoneutral conditions, leading to BAT whitening, a reduction in BAT mitochondrial content and metabolic activity. Recent studies have established mitophagy as a major driver of mitochondrial degradation in the whitening of thermogenic brite/beige adipocytes, yet the pathways mediating mitochondrial breakdown in whitening of classical BAT remain largely elusive. The transcription factor EB (TFEB), a master regulator of lysosomal biogenesis and autophagy belonging to the MiT family of transcription factors, is the only member of this family that is upregulated during whitening, pointing toward a role of TFEB in whitening-associated mitochondrial breakdown. Methods We generated brown adipocyte-specific TFEB knockout mice, and induced BAT whitening by thermoneutral housing. We characterized gene and protein expression patterns, BAT metabolic activity, systemic metabolism, and mitochondrial localization using in vivo and in vitro approaches. Results Under low thermogenic activation conditions, deletion of TFEB preserves mitochondrial mass independently of mitochondriogenesis in BAT and primary brown adipocytes. However, this does not translate into elevated thermogenic capacity or protection from diet-induced obesity. Autophagosomal/lysosomal marker levels are altered in TFEB-deficient BAT and primary adipocytes, and lysosomal markers co-localize and co-purify with mitochondria in TFEB-deficient BAT, indicating trapping of mitochondria in late stages of mitophagy. Conclusion We identify TFEB as a driver of BAT whitening, mediating mitochondrial degradation via the autophagosomal and lysosomal machinery. This study provides proof of concept that interfering with the mitochondrial degradation machinery can increase mitochondrial mass in classical BAT under human-relevant conditions. However, it must be considered that interfering with autophagy may result in accumulation of non-functional mitochondria. Future studies targeting earlier steps of mitophagy or target recognition are therefore warranted.

Impaired mitophagy in Sanfilippo a mice causes hypertriglyceridemia and brown adipose tissue activation

“…These observations are in accordance with the reported accumulation of mitochondria in BAT during whitening (at thermoneutrality) in mice with BAT-specific inactivation of Transcription Factor EB (34), the master transcriptional regulator of lysosomal and autophagosomal biogenesis (35). The increased mitochondria content in Transcription Factor EB-deficient BAT after reversing thermogenic activation was independent of mitochondria biogenesis but correlated with increased mitochondrial trapping in autophagosomes (34). Our data provide further evidence that indeed impaired autophagy and lysosomal activity in BAT associates with accumulation of mitochondria and the consequent hyperthermia and loss of adipose tissue mass.…”

“…The relevance of deficient autophagy for the mitochondrial accumulation in MPS IIIa BAT is further supported by the fact that treatment with the mTOR inhibitor, everolimus, reverted the BAT phenotype in MPS IIIa mice. These observations are in accordance with the reported accumulation of mitochondria in BAT during whitening (at thermoneutrality) in mice with BAT-specific inactivation of Transcription Factor EB ( 34 ), the master transcriptional regulator of lysosomal and autophagosomal biogenesis ( 35 ). The increased mitochondria content in Transcription Factor EB–deficient BAT after reversing thermogenic activation was independent of mitochondria biogenesis but correlated with increased mitochondrial trapping in autophagosomes ( 34 ).…”

Homeostatic feedback between lysosomal mTORC1 and mTORC2-AKT signaling controls nutrient uptake in brown adipose tissue

“…Increased mRNA levels of RagD , mucolipin1 ( MCOLN1 ), CD63 and cathepsin a (CTSa ) in LT2 AKO iBAT (Fig 3C) indicated increased transcription of these known TFEB targets, due to reduced mTORC1 activity. In line with a recent publication investigating TFEB deficiency 41 , microarray analysis failed to reveal a systemic mRNA upregulation of the coordinated lysosomal expression and regulation (CLEAR) network. Nevertheless, some CLEAR genes such as CD63 , beta-hexosaminidase subunit β , MCOLN1 , CTSa, and CTSz were significantly upregulated in the microarray analysis (data not shown).…”

Activating Parkin-dependent mitophagy alleviates oxidative stress, apoptosis, and promotes random-pattern skin flaps survival

“…TFEB is known for its ability to regulate lysosomal biogenesis and autophagy 24 , 25 . Whether TFEB participates in ML-induced mitophagy is unknown.…”