Citations

Abstract Metabolic vulnerabilities in cancer have been targeted primarily to suppress tumor growth, but less is known about the metabolic requirements for tumor cell invasion. Here we report that lipid catabolism by cytosolic and lysosomal lipases supports pancreatic cancer cell invasion through both overlapping and distinct functional and metabolic mechanisms. Lysosomal acid lipase (LAL)-dependent lipid droplet catabolism promotes invadopodia formation and stabilization, enabling extracellular matrix degradation. In addition to modulating cellular energetics, lipidomics revealed that lipid droplet catabolism regulates cholesterol and membrane phospholipid levels. Using spatially resolved biosensors and cholesterol imaging, we found that lysosomal lipid catabolism occurs at invadopodia and sustains local ATP and membrane cholesterol. These findings identify spatially organized lipid catabolism as a mechanism that couples local energetics and membrane remodeling during the earliest steps of pancreatic cancer cell invasion.

ABSTRACT A major challenge in hematopoietic progenitor cell apheresis is determining the whole blood (WB) volume to process to achieve a CD34+ cell collection goal. We developed a web‐based calculator app that uses the Collection Efficiency 2 (CE2) model to estimate personalized WB processing volumes needed to reach a prescribed CD34+ cell collection goal. Retrospective evaluation of the app using collection data from two academic medical centers showed that actual processed WB volumes were frequently higher than the app's recommendations. The frequency of potential under‐collection events is predicted to be low had the app‐calculated volumes been utilized. Our findings suggest that using the app's recommendations may lower total WB processing volumes, reducing over‐collection and time spent on the apheresis machine, while maintaining a low under‐collection risk profile.

The interplay between intracellular and intravascular lipolysis is crucial for maintaining circulating lipid levels and systemic energy homeostasis. Adipose triglyceride lipase (ATGL) and lipoprotein lipase (LPL), the primary triglyceride (TG) lipases responsible for these two spatially separate processes, are highly expressed in adipose tissue. Yet the mechanisms underlying their coordinated regulation remain undetermined. Here, we demonstrate that genetic ablation of G0S2, a specific inhibitory protein of ATGL, completely abolished diet-induced hypertriglyceridemia and significantly attenuated atherogenesis in mice. These effects were attributable to enhanced whole-body TG clearance, not altered hepatic TG secretion. Specifically, G0S2 deletion increased circulating LPL concentration and activity, predominantly through LPL production from white adipose tissue (WAT). Strikingly, transplantation of G0S2-deficient WAT normalized plasma TG levels in mice with hypertriglyceridemia. In conjunction with improved insulin sensitivity and decreased ANGPTL4 expression, the absence of G0S2 enhanced the stability of LPL protein in adipocytes, a phenomenon that could be reversed upon ATGL inhibition. Collectively, these findings highlight the pivotal role of adipocyte G0S2 in regulating both intracellular and intravascular lipolysis, and the possibility of targeting G0S2 as a viable pharmacological approach to reducing levels of circulating TGs.

Evidence from our laboratory has established a role for the G0/G1 Switch Gene 2 (G0S2) as the primary inhibitor of adipose lipolysis through inhibition of adipose triglyceride lipase (ATGL), the rate‐limiting enzyme in triglyceride hydrolysis. We have demonstrated that differential expression of G0S2 plays a crucial role in regulating hepatic lipid content during fasting and feeding. Hepatic G0S2 expression is also significantly increased in a pathological condition in mice with obesity‐induced hepatic steatosis or non‐alcoholic fatty liver disease (NAFLD), major metabolic health issues in today's society. Based on preliminary evidence we hypothesized there is a dynamic relationship between adipose lipolysis and hepatic G0S2 expression during physiological fasting, a relationship that has not been previously described. To better understand this relationship we evaluated the effect of free fatty acids (FFA) on G0S2 expression in liver. Interestingly, hepatic G0S2 expression during fasting results from increased free fatty acid (FFA) delivery to the liver from adipose tissue. Moreover, we identified that increases in hepatic FFA lead to increased G0S2 expression in a bi‐mechanistic manner. We investigated and subsequently determined that both transcriptional activation of G0S2 and inhibition of protein degradation are occurring in response to increased hepatic FFA levels. Utilizing a luciferase based reporter system and in vivo chromatin immunoprecipitation we found transcriptional activation of G0S2 in liver occurs in response to activation of liver‐X‐receptor α (LXRα). LXRα is a known regulator of pro‐lipogenic signaling in liver and plays a major role in cholesterol homeostasis. It has also been shown that LXRα can be activated in response to FAs most likely through its dimerization partner RXRα that is a known FA responsive transcription factor. We demonstrate G0S2 is a direct downstream target gene for LXRα. Additionally, the direct repeat 4 (DR4) LXR response element (LXRE) found 2kb upstream of the transcriptional start site in the G0S2 promoter is required for G0S2/ LXRα binding. This DR4 binding site is conserved between the human and mouse isoforms of G0S2 and is required in each for LXRα binding. Furthermore, we found that G0S2 is subject to ubiquitin modification and is degraded in a proteasome dependent pathway. Mutation analysis of the six‐lysine residues found in G0S2 provided key evidence that the lysine at position 25 is the prominent site for ubiquitylation. The G0S2 K25 mutant is more stable than wild‐type G0S2, which is consistent with the accompanying decrease in ubiquitylation. Additionally, fatty acids were able to abrogate G0S2 degradation and increase protein stability. These findings indicate that two mechanisms of expression regulation in combination with adipose lipolysis are functioning concomitantly to regulate hepatic G0S2 expression under physiological conditions. Additionally, aberrant G0S2 expression may contribute to the pathological setting with metabolically linked diseases including NAFLD. Support or Funding Information This work was supported by NIDDK grants DK089178 and 2R56DK089178 from the National Institutes of Health. Pre‐doctoral funding support for B.H. was generously provided by the Mayo Graduate School and Mayo Foundation for Medical Education & Research.

Adipose tissue plays a central role in the regulation of plasma triglyceride (TG) and fatty acid (FA) levels, whose elevation is associated with atherosclerotic cardiovascular disease (ASCVD). Circulating TGs are hydrolyzed by lipoprotein lipase (LPL), releasing FAs that are taken up by adipocytes. Conversely, lipolytic action of adipose tissue triglyceride lipase (ATGL) mobilizes intracellular TG storage, supplying FAs via circulation for utilization by other tissues. However, how intracellular lipolysis influences intravascular lipolysis and atherosclerotic development remains largely unknown. Herein, the current study aimed to explore the role of G0S2, a selective protein inhibitor of ATGL, in this particular context. When treated with a Western diet and antisense oligonucleotides (ASOs) targeting LDLR, mice with a global ablation of G0S2 exhibited a significantly reduced lesion formation in aorta and brachiocephalic artery than their wild type (WT) littermates. Despite of little to no impact on hypercholesterolemia, total plasma and lipoprotein-specific TG content were normalized in G0S2 -/- mice. While it did not elicit any effects on intestinal lipid adsorption and hepatic TG secretion, the G0S2 ablation resulted in considerable elevation of LPL activity and protein levels in both plasma and adipose tissue. Accordingly, these G0S2 -/- mice showed a greatly improved TG clearance upon an oral lipid challenge. Interestingly, transplantation of G0S2 -/- adipose tissue increased circulating LPL in the WD-treated WT mice, which subsequently displayed a profound reduction of plasma TG levels as well as alleviation of hepatic steatosis. By studying adipose tissue explants and primary adipocytes, we observed that the G0S2 ablation led to markedly improved insulin sensitivity, resulting in increased FOXO1 phosphorylation and decreased expression of the LPL inhibitor ANGPTL4. Together, our data indicate that in the absence of G0S2, upregulation of adipose tissue LPL plays an important role in the clearance of circulating TGs and alleviation of diet-induced hypertriglyceridemia and atherosclerosis. We thus conclude that adipocyte G0S2 acts as a critical switch of both intracellular and vascular lipolysis.

ABSTRACT G0S2 and HIG2 are two selective inhibitors of ATGL (also known as PNPLA2), the key enzyme for intracellular lipolysis. Whereas G0S2 regulates triglyceride (TG) mobilization in adipocytes and hepatocytes, HIG2 functions to enhance intracellular TG accumulation under hypoxic conditions. A homologous hydrophobic domain (HD) is shared by G0S2 and HIG2 (also known as HILPDA) for binding to ATGL. However, the determinants of their lipid droplet (LD) localization are unknown. Here, we study how G0S2 and HIG2 are targeted to LDs, and identify both ATGL-independent and -dependent mechanisms. Structural prediction and studies in cells reveal that ATGL-independent localization of G0S2 to both the endoplasmic reticulum (ER) and LDs is mediated by a hairpin structure consisting of two hydrophobic sequences. Positively charged residues in the hinge region play a crucial role in sorting G0S2, which initially localizes to ER, to LDs. Interestingly, the role of these positive charges becomes dispensable when ATGL is co-expressed. In comparison, HIG2, which lacks a similar hairpin structure, is dependent on ATGL for its full LD targeting. Thus, our studies identify specific structural features and mechanisms for mediating accumulation of these two ATGL inhibitors on LDs.

Integrins are heterodimeric (α/β) membrane proteins that play fundamental roles in many biological processes, e.g. cell adhesion and spreading, which are important for platelet function and hemostasis. Integrin function is modulated by bi-directional transmembrane signaling: inside-out and outside-in, which is mediated through the interactions between integrin cytoplasmic tails and intracellular, regulatory proteins. Here, we show that VPS33B, a member of the Sec1/Munc18 (SM) family and component of the Class C core of the CORVET/HOPS sorting complexes, binds directly to the β subunit. Overexpression of VPS33B in CHO cells potentiated α IIb β 3 outside-in signaling but not inside-out signaling. Platelets, from megakaryocyte- and platelet-specific VPS33B conditional knockout mice we generated, had normal morphology yet their spreading on fibrinogen was impaired and they failed to support clot retraction. Platelet aggregation and ATP secretion in response to low-dose thrombin were reduced in the VPS33B knockout mice. α IIb β 3 -mediated endocytosis of fibrinogen was also defective. Tail bleeding times were prolonged in the VPS33B knockout mice. Furthermore, VPS33B acted upstream of the RhoA-ROCK-MLC and Rac1 dependent pathways that leads to clot retraction and cell spreading, respectively. Our work demonstrates that vesicular trafficking complexes are a novel class of modifiers of integrin function and in hemostasis. Our data also provide insights into the molecular mechanism and treatment of ARC syndrome.

Introduction: The relative performance of carotid artery stenting (CAS) and carotid endarterectomy (CEA) among Medicare beneficiaries in routine clinical practice has not been established. Objective: To compare the performance of CAS relative to CEA among Medicare beneficiaries. Methods: We linked Medicare data (2000-2009) to the Society for Vascular Surgery’s Vascular Registry (SVS-VR; 2005-2008) and to the NCDR® Carotid Artery Revascularization and Endarterectomy Registry (CARE; 2006-2008/9). Medicare patients aged ≥66 years undergoing CAS or CEA were followed from the procedure date for the outcomes of death, stroke/transient ischemic attack (TIA), peri-procedural myocardial infarction (MI) or a composite endpoint for these outcomes. We derived high-dimensional propensity scores using registry and Medicare data to control for patient-level factors and adjusted for provider-level factors including past-year CAS/CEA physician and hospital volume, hospital ownership, teaching affiliation, and hospital size in a Cox regression model comparing CAS to CEA. Results: Among 5,254 SVS-VR (1,999 CAS and 3,255 CEA) and 4,055 CARE (2,824 CAS and 1,231 CEA) patients, CAS patients were more often at higher surgical risk (SVS-VR: 96.7% vs. 44.5%; CARE: 71.3% vs. 44.7%) and had a higher comorbidity burden. Crude outcome risks for death and stroke/TIA were lower for CEA. Adjusting for patient-level factors drove estimates downwards for CAS relative to CEA but only after further adjustment for provider-level factors did the performance of CAS and CEA become comparable on all outcomes (figure 1). Conclusion: Performance of CAS and CEA among Medicare beneficiaries was comparable after accounting for patient- and provider-level factors, which is consistent with landmark trials. Further studies are needed to understand the role of heterogeneity in provider-level characteristics.