BubR1 controls starvation-induced lipolysis via IMD signaling pathway in Drosophila

Lipolysis, the key process releasing fat acids to generate energy in adipose tissues, correlates with starvation resistance. Nevertheless, its detail mechanisms remain elusive. BubR1, an essential mitotic regulator, ensures proper chromosome alignment and segregation during mitosis, but its physiological functions are largely unknown. Here, we use Drosophila adult fat body, the major lipid storage organ, to study the functions of BubR1 in lipolysis. We show that both whole body- and fat body-specific BubR1 depletions increase lipid degradation and shorten the lifespan under fasting but not feeding. Relish, the conserved regulator of IMD signaling pathway, acts as the downstream target of BubR1 to control the expression level of Bmm and modulate the lipolysis upon fasting. Thus, our study reveals new functions of BubR1 in starvation-induced lipolysis and provides new insights into the molecular mechanisms of lipolysis mediated by IMD signaling pathway.

Perilipin 1 Deficiency Prompts Lipolysis in Lipid Droplets and Aggravates the Pathogenesis of Persistent Immune Activation in Drosophila

Lipid droplets (LDs) are highly dynamic intracellular organelles, which are involved in lots of biological processes. However, the dynamic morphogenesis and functions of intracellular LDs during persistent innate immune responses remain obscure. In this study, we induce long-term systemic immune activation in Drosophila through genetic manipulation. Then, the dynamic pattern of LDs is traced in the Drosophila fat body. We find that deficiency of Plin1, a key regulator of LDs' reconfiguration, blocks LDs minimization at the initial stage of immune hyperactivation but enhances LDs breakdown at the later stage of sustained immune activation via recruiting the lipase Brummer (Bmm, homologous to human ATGL). The high wasting in LDs shortens the lifespan of flies with high-energy-cost immune hyperactivation. Therefore, these results suggest a critical function of LDs during long-term immune activation and provide a potential treatment for the resolution of persistent inflammation.

Hedgehog signaling promotes lipolysis in adipose tissue through directly regulating Bmm/ATGL lipase

Hedgehog (Hh) signaling has been shown to regulate multiple developmental processes, however, it is unclear how it regulates lipid metabolism. Here, we demonstrate that Hh signaling exhibits potent activity in Drosophila fat body, which is induced by both locally expressed and midgut-derived Hh proteins. Inactivation of Hh signaling increases, whereas activation of Hh signaling decreases lipid accumulation. The major lipase Brummer (Bmm) acts downstream of Smoothened (Smo) in Hh signaling to promote lipolysis, therefore, the breakdown of triacylglycerol (TAG). We identify a critical Ci binding site in bmm promoter that is responsible to mediate Bmm expression induced by Hh signaling. Genomic mutation of the Ci binding site significantly reduces the expression of Bmm and dramatically decreases the responsiveness to Ci overexpression. Together, our findings provide a model for lipolysis to be regulated by Hh signaling, raising the possibility for Hh signaling to be involved in lipid metabolic and/or lipid storage diseases.

NF-κB Shapes Metabolic Adaptation by Attenuating Foxo-Mediated Lipolysis in Drosophila

Metabolic and innate immune signaling pathways have co-evolved to elicit coordinated responses. However, dissecting the integration of these ancient signaling mechanisms remains a challenge. Using Drosophila, we uncovered a role for the innate immune transcription factor nuclear factor κB (NF-κB)/Relish in governing lipid metabolism during metabolic adaptation to fasting. We found that Relish is required to restrain fasting-induced lipolysis, and thus conserve cellular triglyceride levels during metabolic adaptation, through specific repression of ATGL/Brummer lipase gene expression in adipose (fat body). Fasting-induced changes in Brummer expression and, consequently, triglyceride metabolism are adjusted by Relish-dependent attenuation of Foxo transcriptional activation function, a critical metabolic transcription factor. Relish limits Foxo function by influencing fasting-dependent histone deacetylation and subsequent chromatin modifications within the Bmm locus. These results highlight that the antagonism of Relish and Foxo functions are crucial in the regulation of lipid metabolism during metabolic adaptation, which may further influence the coordination of innate immune-metabolic responses.