Fatty acids (FAs) are stored safely in the form of triacylglycerol (TAG) in lipid droplet (LD) organelles by professional storage cells called adipocytes. These lipids are mobilized during adipocyte lipolysis, the fundamental process of hydrolyzing TAG to FAs for internal or systemic energy use. Our understanding of adipocyte lipolysis has greatly increased over the past 50 years from a basic enzymatic process to a dynamic regulatory one, involving the assembly and disassembly of protein complexes on the surface of LDs. These dynamic interactions are regulated by hormonal signals such as catecholamines and insulin which have opposing effects on lipolysis. Upon stimulation, patatin-like phospholipase domain containing 2 (PNPLA2)/adipocyte triglyceride lipase (ATGL), the rate limiting enzyme for TAG hydrolysis, is activated by the interaction with its co-activator, alpha/beta hydrolase domain-containing protein 5 (ABHD5), which is normally bound to perilipin 1 (PLIN1). Recently identified negative regulators of lipolysis include G0/G1 switch gene 2 (G0S2) and PNPLA3 which interact with PNPLA2 and ABHD5, respectively. This review focuses on the dynamic protein–protein interactions involved in lipolysis and discusses some of the emerging concepts in the control of lipolysis that include allosteric regulation and protein turnover. Furthermore, recent research demonstrates that many of the proteins involved in adipocyte lipolysis are multifunctional enzymes and that lipolysis can mediate homeostatic metabolic signals at both the cellular and whole-body level to promote inter-organ communication. Finally, adipocyte lipolysis is involved in various diseases such as cancer, type 2 diabetes and fatty liver disease, and targeting adipocyte lipolysis is of therapeutic interest.

Patatin-Like Phospholipase Domain Containing 2 (PNPLA2)/Adipose Triglyceride Lipase (ATGL) and PNPLA3/Adiponutrin are close paralogs that appear to have opposite functions on triacylglycerol (TAG) mobilization and storage. PNPLA2/ATGL is a major triglyceride lipase in adipose tissue and liver, whereas a common human variant of PNPLA3, I148M, greatly increases risk of hepatosteatosis. Nonetheless, the function of PNPLA3 and the mechanism by which the I148M variant promotes TAG accumulation are poorly understood. Here we demonstrate that PNPLA3 strongly interacts with α/β hydrolase domain-containing 5 (ABHD5/CGI-58), an essential co-activator of PNPLA2/ATGL. Molecular imaging experiments demonstrate that PNPLA3 effectively competes with PNPLA2/ATGL for ABHD5, and that PNPLA3 I148M is more effective in this regard. Inducible overexpression of PNPLA3 I148M greatly suppressed PNPLA2/ATGL-dependent lipolysis and triggered massive TAG accumulation in brown adipocytes, and these effects were dependent on ABHD5. The interaction of PNPLA3 and ABHD5 can be regulated by fatty acid supplementation and synthetic ABHD5 ligands, raising the possibility that this interaction might be targeted for treatment of fatty liver disease.

Many species of bacteria can spread over a moist surface via a particular form of collective motion known as "surface swarming". This form of motility is typically studied by inoculating bacteria on a gel formed by 0.4-1.5% agar, which contains essential nutrients for their growth and proliferation. Using Pseudomonas aeruginosa and its pili-less mutant, ΔPilA, we investigate physical factors that either facilitate or restrict the swarming motility, measured by the rate of increase in area covered by a spreading bacterial colony, i.e., a swarm. The wild-type colony spreads over the agar surface in highly branched structures. The pili-less mutant fills up the area more fully as it spreads, but it also produces numerous and fragmented branches, or tendrils, at the swarm front. Whereas additional surfactants enhance swarming, increasing the agar percentage, adding extra salt or sugar or incorporating viscous agents in the agar matrix all decrease swarming, supporting the conclusion that swarming motility is restricted by the surface tension at the swarm front and swarm growth is limited by the rate of water supply from within the agar gel. The physical basis elaborated through this study provides a useful framework for understanding the swarming behavior of numerous species of bacteria.

eneralized pustular psoriasis (GPP) is an orphan disease characterized by the rapid appearance of sterile pustules and generalized erythema. Patients are often systemically ill and may experience severe organ dysfunction and rarely death. The genetic risk factors for pustular psoriasis are different from other types of psoriasis. To date, variations have been identified in the following genes: IL36RN (interleukin-36 receptor antagonist), CARD14 (caspase recruitment domain family member 14), AP1S3 (adapter related protein complex 1 subunit sigma 3), SERPINA3 (serpin family A member 3), and MPO (myeloperoxidase); however, the majority of patients do not have a known genetic variant. 1 Owing to the rarity of GPP, there is limited information about the natural disease course. The only epidemiological data from the United States is a report of 63 patients seen over 29 years at a single institution. 2 The objective of this study is to describe the clinical characteristics, natural disease course, treatments, and health care utilization of patients with GPP across the United States. Methods Study Design and PopulationThis is a retrospective, longitudinal case series of adults (≥18 years) with a diagnosis of GPP confirmed by a dermatologist (January 1, 2007-December 31, 2018) (Table 1). Up to 5 potential cases were identified from each of 20 participating sites' electronic health records or site-specific databases, starting with cases seen most recently. All diagnoses were confirmed by the principal investigator at each site at the time of data entry. Only patients who met the European Rare and Severe Psoriasis Expert Network (ERASPEN) consensus definition of GPP with documentation of "primary, sterile, macroscopically visible pustules on nonacral skin, excluding cases where pustulation is restricted to psoriatic plaques" 3 and had had a dermatology encounter with active pustular disease during the study period were included.IMPORTANCE Generalized pustular psoriasis (GPP) is a chronic, orphan disease with limited epidemiological data.OBJECTIVE To describe the clinical characteristics, treatments, longitudinal disease course, and disease-specific health care utilization among patients with GPP across the United States. DESIGN, SETTING, AND PARTICIPANTSA retrospective longitudinal case series involving 95 adults who met the European Rare and Severe Psoriasis Expert Network consensus definition for GPP and were treated at 20 US academic dermatology practices between January 1, 2007, and December 31, 2018. MAIN OUTCOMES AND MEASURESThe primary outcome is to describe the patient characteristics, associated medical comorbidities, treatment patterns complications, and GPP-specific health care utilization.RESULTS Sixty-seven of 95 patients (70.5%) were women (mean age, 50.3 years [SD, 16.1 years]). In the initial encounter, 35 patients (36.8%) were hospitalized and 64 (67.4%) were treated with systemic therapies. In total, more than 20 different systemic therapies were tried. During the follow-up period, 19 patients (35.8%) rep...