Hedgehog signaling plays a conserved role in inhibiting fat formation

The Hedgehog (Hh) family of secreted signaling proteins has a broad variety of functions during metazoan development and implications in human disease. Despite Hh being modified by two lipophilic adducts, Hh migrates far from its site of synthesis and programs cellular outcomes depending on its local concentrations. Recently, lipoproteins were suggested to act as carriers to mediate Hh transport in Drosophila. Here, we examine the role of lipophorins (Lp), the Drosophila lipoproteins, in Hh signaling in the wing imaginal disk, a tissue that does not express Lp but obtains it through the hemolymph. We use the up-regulation of the Lp receptor 2 (LpR2), the main Lp receptor expressed in the imaginal disk cells, to increase Lp endocytosis and locally reduce the amount of available free extracellular Lp in the wing disk epithelium. Under this condition, secreted Hh is not stabilized in the extracellular matrix. We obtain similar results after a generalized knock-down of hemolymph Lp levels. These data suggest that Hh must be packaged with Lp in the producing cells for proper spreading. Interestingly, we also show that Patched (Ptc), the Hh receptor, is a lipoprotein receptor; Ptc actively internalizes Lp into the endocytic compartment in a Hh-independent manner and physically interacts with Lp. Ptc, as a lipoprotein receptor, can affect intracellular lipid homeostasis in imaginal disk cells. However, by using different Ptc mutants, we show that Lp internalization does not play a major role in Hh signal transduction but does in Hh gradient formation.Drosophila ͉ LDLR ͉ morphogen

Section: Results and Discusionmentioning

confidence: 99%

Patched, the receptor of Hedgehog, is a lipoprotein receptor

Callejo

Culí

Guerrero

2008

“…Triglyceride assay was performed as described with modifications (30) and is available in SI Materials and Methods.…”

Section: Methodsmentioning

confidence: 99%

“…When wg was overexpressed using the fat body-specific Dcg-Gal4 (29,30), it caused lethality at the pupal stage and severe reduction of fat body mass in the abdominal region of third instar larvae (Fig. 5D).…”

Section: The Epistatic Relationship Of Wg and Med13 In Muscle For Obementioning

confidence: 99%

Heart- and muscle-derived signaling system dependent on MED13 and Wingless controls obesity in Drosophila

Lee

Bassel‐Duby

Olson

2014

Obesity develops in response to an imbalance of energy homeostasis and whole-body metabolism. Muscle plays a central role in the control of energy homeostasis through consumption of energy and signaling to adipose tissue. We reported previously that MED13, a subunit of the Mediator complex, acts in the heart to control obesity in mice. To further explore the generality and mechanistic basis of this observation, we investigated the potential influence of MED13 expression in heart and muscle on the susceptibility of Drosophila to obesity. Here, we show that heart/muscle-specific knockdown of MED13 or MED12, another Mediator subunit, increases susceptibility to obesity in adult flies. To identify possible muscle-secreted obesity regulators, we performed an RNAi-based genetic screen of 150 genes that encode secreted proteins and found that Wingless inhibition also caused obesity. Consistent with these findings, muscle-specific inhibition of Armadillo, the downstream transcriptional effector of the Wingless pathway, also evoked an obese phenotype in flies. Epistasis experiments further demonstrated that Wingless functions downstream of MED13 within a muscle-regulatory pathway. Together, these findings reveal an intertissue signaling system in which Wingless acts as an effector of MED13 in heart and muscle and suggest that Wingless-mediated cross-talk between striated muscle and adipose tissue controls obesity in Drosophila. This signaling system appears to represent an ancestral mechanism for the control of systemic energy homeostasis.O besity is a systemic disorder caused by an energy imbalance in which energy input exceeds energy utilization, resulting in accumulation of excess body fat. Muscle plays a central role in systemic energy homeostasis by consuming nutrients and signaling in an endocrine manner to other tissues (1-3). Thus, there has been intense interest in identifying secreted factors from muscle that modulate the function of adipose tissue.Previously, we reported that cardiac deletion of MED13, a subunit of the Mediator complex, increases susceptibility to obesity in mice whereas cardiac overexpression of MED13 confers a lean phenotype (4), revealing an unforeseen function of the heart as a systemic regulator of energy homeostasis. The Mediator is a conserved multisubunit complex that mediates the interaction between RNA polymerase II and transcription factors and therefore governs transcription in all eukaryotes (5). MED13 and MED12 are among four subunits of the auxiliary kinase module, which confers additional regulatory functions to the Mediator complex (6). Expression profiling of yeast mutants or gene-depleted Drosophila cell lines revealed a close correlation between the gene-expression programs controlled by MED13 and MED12, suggesting their concerted actions in gene regulation (7,8).Drosophila provides a powerful model system for the genetic analysis of obesity (9-11). The processes that regulate energy homeostasis, such as energy storage and mobilization of fat in adipose tissue of the fat bo...

“…Wnt signaling maintains the preadipocytes in an undifferentiated state, and its inhibition is sufficient to cause spontaneous adipogenesis (19). Hh signaling also inhibits adipocyte differentiation, but unlike Wnt total repression, Hh signaling has been described to be only reduced during adipogenic differentiation with detectable levels present in mature adipocytes (20,21). This down-regulation is not sufficient to trigger adipocyte differentiation, which makes Wnt signaling a more potent regulatory pathway of adipogenesis compared to Hh signaling.…”

mentioning

confidence: 99%

Transient ciliogenesis involving Bardet-Biedl syndrome proteins is a fundamental characteristic of adipogenic differentiation

Marion

Stoetzel

Schlicht

et al. 2009

159

170

Bardet-Biedl syndrome (BBS) is an inherited ciliopathy generally associated with severe obesity, but the underlying mechanism remains hypothetical and is generally proposed to be of neuroendocrine origin. In this study, we show that while the proliferating preadipocytes or mature adipocytes are nonciliated in culture, a typical primary cilium is present in differentiating preadipocytes. This transient cilium carries receptors for Wnt and Hedgehog pathways, linking this organelle to previously described regulatory pathways of adipogenesis. We also show that the BBS10 and BBS12 proteins are located within the basal body of this primary cilium and inhibition of their expression impairs ciliogenesis, activates the glycogen synthase kinase 3 pathway, and induces peroxisome proliferator-activated receptor nuclear accumulation, hence favoring adipogenesis. Moreover, adipocytes derived from BBSpatients' dermal fibroblasts in culture exhibit higher propensity for fat accumulation when compared to controls. This strongly suggests that a peripheral primary dysfunction of adipogenesis participates to the pathogenesis of obesity in BBS.adipogenesis ͉ primary cilium ͉ ciliopathy ͉ obesity