Adipose triglyceride lipase (ATGL) is rate-limiting in the mobilization of fatty acids from cellular triglyceride stores. This central role in lipolysis marks ATGL as interesting pharmacological target since deregulated fatty acid metabolism is closely linked to dyslipidemic and metabolic disorders. Here we report on the development and characterization of a small-molecule inhibitor of ATGL. Atglistatin is selective for ATGL and reduces fatty acid mobilization in vitro and in vivo.

Elevated circulating fatty acids (FAs) contribute to the development of obesity-associated metabolic complications such as insulin resistance (IR) and non-alcoholic fatty liver disease (NAFLD). Hence, reducing adipose tissue lipolysis to diminish the mobilization of FAs and lower their respective plasma concentrations represents a potential treatment strategy to counteract obesity-associated disorders. Here we show that specific inhibition of adipose triglyceride lipase (Atgl) with the chemical inhibitor, Atglistatin, effectively reduces adipose tissue lipolysis, weight gain, IR and NAFLD in mice fed a high-fat diet. Importantly, even long-term treatment does not lead to lipid accumulation in ectopic tissues such as the skeletal muscle or heart. Thus, the severe cardiac steatosis and cardiomyopathy that is observed in genetic models of Atgl deficiency does not occur in Atglistatin-treated mice. Our data validate the pharmacological inhibition of Atgl as a potentially powerful therapeutic strategy to treat obesity and associated metabolic disorders.

Cortical γ-aminobutyric acid (GABA)ergic interneurons in rodents originate mainly in ventrally positioned ganglionic eminences (GEs), but their origin in primates is still debated. We studied human fetal forebrains during the first half of gestation (5-23 gestational weeks, gw) for the expression of ventral transcription factors, Nkx2.1, Dlx1,2, Lhx6, and Mash1, important for development of neocortical interneurons. In embryonic (5-8 gw) human forebrain, these factors were expressed in the GE but also dorsally in the neocortical ventricular/subventricular zones (VZ/SVZ). Furthermore, their expression was retained in cells of all fetal cortical layers up to midgestation (20 gw). Nkx2.1 continued to be expressed not only in the GE but also in a subpopulation of neocortical interneurons. Moreover, proliferation marker Ki67 revealed that calretinin(+), Mash1(+), and Nkx2.1(+) cells proliferate in the neocortical VZ/SVZ at midgestation. At least some of the Mash1(+) progenitors in the neocortical SVZ could be colabeled with GABA, whereas others were oligodendrocyte progenitors, indicating a link between the 2 lineages. Taken together, these results suggest the existence of several categories of dorsal interneuronal progenitors in the human neocortical VZ/SVZ, in addition to ventrally derived cortical interneurons described in rodents. These human-specific developmental events may underlie human brain's higher complexity and capacity to process information.

The concentration of the second messenger cAMP is tightly controlled in cells by the activity of phosphodiesterases. We have previously described how the protein kinase A-anchoring protein mAKAP serves as a scaffold for the cAMP-dependent protein kinase PKA and the cAMP-specific phosphodiesterase PDE4D3 in cardiac myocytes. PKA and PDE4D3 constitute a negative feedback loop whereby PKA-catalyzed phosphorylation and activation of PDE4D3 attenuate local cAMP levels. We now show that protein phosphatase 2A (PP2A) associated with mAKAP complexes is responsible for reversing the activation of PDE4D3 by catalyzing the dephosphorylation of PDE4D3 serine residue 54. Mapping studies reveal that a C-terminal mAKAP domain (residues 2085-2319) binds PP2A. Binding to mAKAP is required for PP2A function, such that deletion of the C-terminal domain enhances both base-line and forskolin-stimulated PDE4D3 activity. Interestingly, PP2A holoenzyme associated with mAKAP complexes in the heart contains the PP2A targeting subunit B56␦. Like PDE4D3, B56␦ is a PKA substrate, and PKA phosphorylation of mAKAP-bound B56␦ enhances phosphatase activity 2-fold in the complex. Accordingly, expression of a B56␦ mutant that cannot be phosphorylated by PKA results in increased PDE4D3 phosphorylation. Taken together, our findings demonstrate that PP2A associated with mAKAP complexes promotes PDE4D3 dephosphorylation, serving both to inhibit PDE4D3 in unstimulated cells and also to mediate a cAMP-induced positive feedback loop following adenylyl cyclase activation and B56␦ phosphorylation. In general, PKA⅐PP2A⅐mAKAP complexes exemplify how protein kinases and phosphatases may participate in molecular signaling complexes to dynamically regulate localized intracellular signaling.

Background: Monoacylglycerol lipases hydrolyze monoacylglycerols into free fatty acids and glycerols.Results: Crystal structures provide the structural basis for conformational plasticity and ligand binding of a monoacylglycerol lipase.Conclusion: Hallmark features responsible for substrate binding and selectivity are conserved across species.Significance: The first structures of a monoacylglycerol lipase in complex with substrate analogs are presented.

Background: A multiprotein complex designated as lipolysome degrades intracellular triglycerides and contains proteins such as adipose triglyceride lipase (Atgl) and its co-activator Cgi-58.Results: Cgi-58 interacts with fatty acid-binding proteins (Fabps), which impact Atgl-mediated lipolysis and lipid signaling.Conclusion: Fabps modulate Atgl-mediated TG hydrolysis and link lipolysis with intracellular lipid ligand shuttling.Significance: Novel mechanistic insights into the regulation of lipid catabolism and energy homeostasis are presented.

mAKAP (muscle-selective A-kinase-anchoring protein) co-ordinates a cAMP-sensitive negative-feedback loop comprising PKA (cAMP-dependent protein kinase) and the cAMP-selective PDE4D3 (phosphodiesterase 4D3). In vitro and cellular experiments demonstrate that PKA-phosphorylation of PDE4D3 on Ser-13 increases the affinity of PDE4D3 for mAKAP. Our data suggest that activation of mAKAP-anchored PKA enhances the recruitment of PDE4D3, allowing for quicker signal termination.

Monoglyceride lipases (MGLs) are a group of α/β-hydrolases that catalyze the hydrolysis of monoglycerides (MGs) into free fatty acids and glycerol. This reaction serves different physiological functions, namely in the last step of phospholipid and triglyceride degradation, in mammalian endocannabinoid and arachidonic acid metabolism, and in detoxification processes in microbes. Previous crystal structures of MGLs from humans and bacteria revealed conformational plasticity in the cap region of this protein and gave insight into substrate binding. In this study, we present the structure of a MGL from Saccharomyces cerevisiae called Yju3p in its free form and in complex with a covalently bound substrate analog mimicking the tetrahedral intermediate of MG hydrolysis. These structures reveal a high conservation of the overall shape of the MGL cap region and also provide evidence for conformational changes in the cap of Yju3p. The complex structure reveals that, despite the high structural similarity, Yju3p seems to have an additional opening to the substrate binding pocket at a different position compared to human and bacterial MGL. Substrate specificities towards MGs with saturated and unsaturated alkyl chains of different lengths were tested and revealed highest activity towards MG containing a C18:1 fatty acid.