AAV-mediated expression of galactose-1-phosphate uridyltransferase corrects defects of galactose metabolism in classic galactosemia patient fibroblasts

Classic galactosemia (CG) is a rare disorder of autosomal recessive inheritance. It is caused predominantly by point mutations as well as deletions in the gene encoding the enzyme galactose-1-phosphate uridyltransferase (GALT). The majority of the more than 350 mutations identified in the GALT gene cause a significant reduction in GALT enzyme activity resulting in the toxic buildup of galactose metabolites that in turn is associated with cellular stress and injury. Consequently, developing a therapeutic strategy that reverses both the oxidative and ER stress in CG cells may be helpful in combating this disease. Recombinant adeno-associated virus (AAV)-mediated gene therapy to restore GALT activity offers the potential to address the unmet medical needs of galactosemia patients. Here, utilizing fibroblasts derived from CG patients we demonstrated that AAV-mediated augmentation of GALT protein and activity resulted in the prevention of ER and oxidative stress. We also demonstrate that these CG patient fibroblasts exhibit reduced CD109 and TGFβRII protein levels and that these effectors of cellular homeostasis could be restored following AAV-mediated expression of GALT. Finally, we show initial in vivo proof-of-concept restoration of galactose metabolism in a GALT knockout mouse model following treatment with AAV-GALT.

Assessment of galactose-1-phosphate uridyltransferase activity in cells and tissues

Galactosemias are a family of autosomal recessive genetic disorders resulting from impaired enzymes of the Leloir pathway of galactose metabolism including galactokinase, galactose uridyltransferase, and UDP-galactose 4-epimerase that are critical for conversion of galactose into glucose-6-phosphate. To better understand pathophysiological mechanisms involved in galactosemia and develop novel therapies to address the unmet need in patients, it is important to develop reliable assays to measure the activity of the Leloir pathway enzymes. Here we describe in-depth methods for indirectly measuring galacose-1-phosphate uridyltransferase activity in cell culture and animal tissues.

Epsin-mediated degradation of IP3R1 fuels atherosclerosis

The epsin family of endocytic adapter proteins are widely expressed, and interact with both proteins and lipids to regulate a variety of cell functions. However, the role of epsins in atherosclerosis is poorly understood. Here, we show that deletion of endothelial epsin proteins reduces inflammation and attenuates atherosclerosis using both cell culture and mouse models of this disease. In atherogenic cholesterol-treated murine aortic endothelial cells, epsins interact with the ubiquitinated endoplasmic reticulum protein inositol 1,4,5-trisphosphate receptor type 1 (IP3R1), which triggers proteasomal degradation of this calcium release channel. Epsins potentiate its degradation via this interaction. Genetic reduction of endothelial IP3R1 accelerates atherosclerosis, whereas deletion of endothelial epsins stabilizes IP3R1 and mitigates inflammation. Reduction of IP3R1 in epsin-deficient mice restores atherosclerotic progression. Taken together, epsin-mediated degradation of IP3R1 represents a previously undiscovered biological role for epsin proteins and may provide new therapeutic targets for the treatment of atherosclerosis and other diseases.

Endothelial cell (EC) dysfunction and inflammation contribute to plaque destabilization in atherosclerosis, increasing the risk of thrombotic events. Here, the authors show that epsin promotes EC inflammation via a mechanism involving IP3R1 degradation, and that deletion of epsin in the endothelium prevents EC dysfunctoin and atherosclerosis in mice.

Myeloid-Specific Deletion of Epsins 1 and 2 Reduces Atherosclerosis by Preventing LRP-1 Downregulation

RATIONALE

Atherosclerosis is, in part, caused by immune and inflammatory cell infiltration into the vascular wall, leading to enhanced inflammation and lipid accumulation in the aortic endothelium. Understanding the molecular mechanisms underlying this disease is critical for the development of new therapies. Our recent studies demonstrate that epsins, a family of ubiquitin-binding endocytic adaptors, are critical regulators of atherogenicity. Given the fundamental contribution lesion macrophages make to fuel atherosclerosis, whether and how myeloid-specific epsins promote atherogenesis is an open and significant question.

OBJECTIVE

We will determine the role of myeloid-specific epsins in regulating lesion macrophage function during atherosclerosis.

METHODS AND RESULTS

We engineered myeloid cell-specific epsins double knockout mice (LysM-DKO) on an ApoE^-/- background. On Western diet, these mice exhibited marked decrease in atherosclerotic lesion formation, diminished immune and inflammatory cell content in aortas, and reduced necrotic core content but increased smooth muscle cell content in aortic root sections. Epsins deficiency hindered foam cell formation and suppressed proinflammatory macrophage phenotype but increased efferocytosis and anti-inflammatory macrophage phenotype in primary macrophages. Mechanistically, we show that epsin loss specifically increased total and surface levels of LRP-1 (LDLR [low-density lipoprotein receptor]-related protein 1), an efferocytosis receptor with antiatherosclerotic properties. We further show that epsin and LRP-1 interact via epsin's ubiquitin-interacting motif domain. ox-LDL (oxidized LDL) treatment increased LRP-1 ubiquitination, subsequent binding to epsin, and its internalization from the cell surface, suggesting that epsins promote the ubiquitin-dependent internalization and downregulation of LRP-1. Crossing ApoE^-/-/LysM-DKO mice onto an LRP-1 heterozygous background restored, in part, atherosclerosis, suggesting that epsin-mediated LRP-1 downregulation in macrophages plays a pivotal role in propelling atherogenesis.

CONCLUSIONS

Myeloid epsins promote atherogenesis by facilitating proinflammatory macrophage recruitment and inhibiting efferocytosis in part by downregulating LRP-1, implicating that targeting epsins in macrophages may serve as a novel therapeutic strategy to treat atherosclerosis.

Epsin deficiency promotes lymphangiogenesis through regulation of VEGFR3 degradation in diabetes

Impaired lymphangiogenesis is a complication of chronic complex diseases, including diabetes. VEGF-C/VEGFR3 signaling promotes lymphangiogenesis, but how this pathway is affected in diabetes remains poorly understood. We previously demonstrated that loss of epsins 1 and 2 in lymphatic endothelial cells (LECs) prevented VEGF-C-induced VEGFR3 from endocytosis and degradation. Here, we report that diabetes attenuated VEGF-C-induced lymphangiogenesis in corneal micropocket and Matrigel plug assays in WT mice but not in mice with inducible lymphatic-specific deficiency of epsins 1 and 2 (LEC-iDKO). Consistently, LECs isolated from diabetic LEC-iDKO mice elevated in vitro proliferation, migration, and tube formation in response to VEGF-C over diabetic WT mice. Mechanistically, ROS produced in diabetes induced c-Src-dependent but VEGF-C-independent VEGFR3 phosphorylation, and upregulated epsins through the activation of transcription factor AP-1. Augmented epsins bound to and promoted degradation of newly synthesized VEGFR3 in the Golgi, resulting in reduced availability of VEGFR3 at the cell surface. Preclinically, the loss of lymphatic-specific epsins alleviated insufficient lymphangiogenesis and accelerated the resolution of tail edema in diabetic mice. Collectively, our studies indicate that inhibiting expression of epsins in diabetes protects VEGFR3 against degradation and ameliorates diabetes-triggered inhibition of lymphangiogenesis, thereby providing a novel potential therapeutic strategy to treat diabetic complications.

Abstract 231: The Role of Epsin in Regulating SR-B1 Function and Lipid Metabolism in Atherosclerosis

Atherosclerosis is both a metabolic and inflammatory disease. Vulnerable atherosclerotic plaque forms in response to hyperlipidemia and arterial wall inflammation-associated stimuli, where macrophages represent the "Trojan horse". Owing to extreme paucity of appropriate targets that effectively block dyslipidemia and concomitantly inhibit macrophage-mediated inflammation, the battle fighting against atherosclerosis remains daunting. The discovery of new molecules and pathways that hit two birds with one stone would therefore significantly advance the development of new and more effective therapeutics to treat heart disease. In our latest study, we show that epsins 1 and 2 are upregulated in atherosclerotic plaques in apolipoprotein E deficient ApoE-/- mice fed western diet. Consequently, we show that macrophage-specific and hepatocyte-specific epsin deficiency inhibits atherosclerosis in ApoE-/- mice fed western diet. We have found that epsin interacts with and reduces the levels of anti-atherogenic SR-B1. Furthermore, given a paramount role for epsin in promoting atherosclerosis, whether targeting epsin systemically is a viable strategy to impede atheroma progression is an extremely important and medically relevant question to be addressed. Thus, our central hypothesis is that in macrophage foam cells, epsin reduces levels of SR-B1, impeding atheroma resolution; and, in liver, epsin-mediated downregulation of SR-B1 elevates cholesterol level thus facilitating atheroma progression.

Abstract 212: Endothelium-Specific Deletion of Epsins Attenuates Atherosclerosis in ApoE-deficient Mouse Model Through Stabilization of IP3 Receptor 1 and Maintaining ER Homeostasis

Background: Atherosclerosis is caused in part by endothelial dysfunction due to ER stress. Understanding the mechanisms that cause ER stress and endothelial dysfunction are essential in establishing new therapies to treat atherosclerosis. Epsins are endocytic adaptor proteins that mediate the internalization of plasma membrane receptors. However, whether epsins affect atherosclerosis remains unknown. To this end, we assessed the hypothesis that endothelial epsins play a critical role in regulating atherosclerosis.

Methods and Results: In an ApoE-deficient murine model, endothelial-specific double knockout mice (EC-iDKO/ApoE-/-) significantly attenuated atherosclerotic lesion and macrophage infiltration in the aortic root and arch compared to ApoE-/- mice fed Western diet for ten weeks. To elucidate underlying mechanisms, mass spectrometry analysis identified IP3R1 as one of major interactors of epsins upon exposure to oxLDL. We show that epsins bind IP3R1 and facilitate its degradation in the endothelium. Downregulation of IP3R1 by atherosclerosis promoting agents augmented ER stress in primary mouse aortic endothelial cells. In line with these findings from mouse studies, in human atherosclerotic lesion, IP3R1 is dramatically downregulated and decrease in IP3R1 expression is associated with increased ER stress. Conversely, loss of epsins stabilized IP3R1, attenuated ER stress, reduced expression of P-selectin, adhesion molecules, and chemoattractant MCP-1 in primary mouse aortic endothelial cells. Molecular mapping analysis revealed that epsin’s UIM domain is critical in facilitating the degradation of IP3R1. Delivery of a synthetic UIM peptide conjugated with atheroma-targeting Lyp-1 peptide significantly attenuated atherosclerosis in ApoE-/- animal models by stabilizing IP3R1 and maintaining ER homeostasis. Importantly, atherosclerotic lesion was restored in EC-iDKO/ApoE-/- mice by breeding them onto an endothelial-specific IP3R1 heterozygous background, suggesting that endothelial epsins promote atheroma progression in part by mediating IP3R1 degradation.

Conclusions: Our data identified a novel mechanism of epsins in regulating atherosclerosis and provide a potential target to treat atherosclerosis.

Eating the Dead to Keep Atherosclerosis at Bay

Atherosclerosis is the primary cause of coronary heart disease (CHD), ischemic stroke, and peripheral arterial disease. Despite effective lipid-lowering therapies and prevention programs, atherosclerosis is still the leading cause of mortality in the United States. Moreover, the prevalence of CHD in developing countries worldwide is rapidly increasing at a rate expected to overtake those of cancer and diabetes. Prominent risk factors include the hardening of arteries and high levels of cholesterol, which lead to the initiation and progression of atherosclerosis. However, cell death and efferocytosis are critical components of both atherosclerotic plaque progression and regression, yet, few currently available therapies focus on these processes. Thus, understanding the causes of cell death within the atherosclerotic plaque, the consequences of cell death, and the mechanisms of apoptotic cell clearance may enable the development of new therapies to treat cardiovascular disease. Here, we review how endoplasmic reticulum stress and cholesterol metabolism lead to cell death and inflammation, how dying cells affect plaque progression, and how autophagy and the clearance of dead cells ameliorates the inflammatory environment of the plaque. In addition, we review current research aimed at alleviating these processes and specifically targeting therapeutics to the site of the plaque.

Role of endoplasmic reticulum stress signalling in diabetic endothelial dysfunction and atherosclerosis

It is well established that diabetes mellitus accelerates atherosclerotic vascular disease. Endothelial injury has been proposed to be the initial event in the pathogenesis of atherosclerosis. Endothelium not only acts as a semi-selective barrier but also serves physiological and metabolic functions. Diabetes or high glucose in circulation triggers a series of intracellular responses and organ damage such as endothelial dysfunction and apoptosis. One such response is high glucose-induced chronic endoplasmic reticulum stress in the endothelium. The unfolded protein response is an acute reaction that enables cells to overcome endoplasmic reticulum stress. However, when chronically persistent, endoplasmic reticulum stress response could ultimately lead to endothelial dysfunction and atherosclerosis. Herein, we discuss the scientific advances in understanding endoplasmic reticulum stress-induced endothelial dysfunction, the pathogenesis of diabetes-accelerated atherosclerosis and endoplasmic reticulum stress as a potential target in therapies for diabetic atherosclerosis.

Endothelial epsins as regulators and potential therapeutic targets of tumor angiogenesis

VEGF-driven tumor angiogenesis has been validated as a central target in several tumor types deserving of continuous and further considerations to improve the efficacy and selectivity of the current therapeutic paradigms. Epsins, a family of endocytic clathrin adaptors, have been implicated in regulating endothelial cell VEGFR2 signaling, where its inactivation leads to nonproductive leaky neo-angiogenesis and, therefore, impedes tumor development and progression. Targeting endothelial epsins is of special significance due to its lack of affecting other angiogenic-signaling pathways or disrupting normal quiescent vessels, suggesting a selective modulation of tumor angiogenesis. This review highlights seminal findings on the critical role of endothelial epsins in tumor angiogenesis and their underlying molecular events, as well as strategies to prohibit the normal function of endogenous endothelial epsins that capitalize on these newly understood mechanisms.

Abstract 239: Deficiency of Macrophage Epsins Impedes Atherosclerosis by Inhibiting LRP-1 Internalization and Degradation

Background: Atherosclerosis is caused by the chronic activation of the vascular endothelium and immune and inflammatory cell infiltration of the vascular wall, leading to enhanced inflammation and lipid accumulation. Understanding the molecular mechanisms underlying this disease is critical for the development of new therapies. Epsins are a family of ubiquitin-binding endocytic adaptors. However, their role in vascular inflammation is poorly understood. Our goal is to define the novel role of epsins in regulating atherogenesis.

Methods and Results: We engineered mice with specific deletion of epsins in myeloid cells (MΦ-DKO). Strikingly, MΦ-DKO mice on an ApoE-/- background fed western diet exhibited reduced atherosclerotic lesion and foam cell accumulation, and diminished recruitment of immune or inflammatory cells to aortas by FACS analysis. In primary macrophages, epsin deficiency impaired foam cell formation by Oil Red O staining, and suppressed the pro-inflammatory M1 macrophage phenotype but increased the anti-inflammatory macrophage phenotype by gene profiling. Epsin deficiency did not alter levels of LDL scavenger receptors, or reverse cholesterol transport proteins, but did increase total and surface levels of LRP-1, a protein with anti-inflammatory and anti-atherosclerotic properties. Mechanistically, Epsin interacts with LRP-1 via epsin’s UIM domain. LPS treatment increased LRP-1 ubiquitination and subsequent binding to epsin, suggesting that epsin promotes the ubiquitin-dependent internalization and degradation of LRP-1. Accordingly, macrophages isolated from MΦ-DKO mice on LRP-1 heterozygous background restored the pro-inflammatory phenotype.

Conclusions: Epsins promote atherogenesis by facilitating pro-inflammatory macrophage recruitment and potentiating foam cell formation by downregulating LRP-1 implicating that targeting the epsin-LRP-1 interaction may serve as a novel therapeutic strategy to treat atheromas.

Abstract 257: Selective Targeting of a Novel Epsin-VEGFR2 Interaction Promotes VEGF-mediated Angiogenesis

Background: VEGF-induced binding of VEGFR2 to epsins 1 and 2 triggers VEGFR2 degradation and attenuates VEGF signaling. The epsin ubiquitin interacting motif (UIM) was shown to be required for the interaction with VEGFR2, however the molecular determinants that govern how epsin specifically interacts with and regulates VEGFR2 were unknown. The goals for the present study were (1) to identify critical molecular determinants that drive the specificity of the epsin and VEGFR2 interaction and (2) to ascertain if such determinants were critical for physiological angiogenesis in vivo .

Methods and Results: Structural modeling uncovered two novel binding surfaces within VEGFR2 that mediate specific interactions with epsin UIM. Three glutamic acid residues in epsin UIM were found to interact with residues in VEGFR2. Further, we found that the VEGF-induced VEGFR2-epsin interaction promoted c-Cbl-mediated ubiquitination of epsin, and uncovered a previously unappreciated ubiquitin-binding surface within VEGFR2. Mutational analysis revealed that the VEGFR2-epsin interaction is supported by VEGFR2 interacting specifically with the UIM and with ubiquitinated epsin. An epsin UIM peptide, but not a mutant UIM peptide, potentiated endothelial cell proliferation, migration and angiogenic properties in vitro , increased postnatal retinal angiogenesis, and enhanced VEGF-induced physiological angiogenesis and wound healing.

Conclusions: Distinct residues in the epsin UIM and VEGFR2 mediate specific interactions between epsin and VEGFR2, in addition to UIM recognition of ubiquitin moieties on VEGFR2. These novel interactions are critical for pathophysiological angiogenesis, suggesting that these sites could be selectively targeted by therapeutics to modulate angiogenesis.

Selective Targeting of a Novel Epsin-VEGFR2 Interaction Promotes VEGF-Mediated Angiogenesis

RATIONALE

We previously reported that vascular endothelial growth factor (VEGF)-induced binding of VEGF receptor 2 (VEGFR2) to epsins 1 and 2 triggers VEGFR2 degradation and attenuates VEGF signaling. The epsin ubiquitin interacting motif (UIM) was shown to be required for the interaction with VEGFR2. However, the molecular determinants that govern how epsin specifically interacts with and regulates VEGFR2 were unknown.

OBJECTIVE

The goals for the present study were as follows: (1) to identify critical molecular determinants that drive the specificity of the epsin and VEGFR2 interaction and (2) to ascertain whether such determinants were critical for physiological angiogenesis in vivo.

METHODS AND RESULTS

Structural modeling uncovered 2 novel binding surfaces within VEGFR2 that mediate specific interactions with epsin UIM. Three glutamic acid residues in epsin UIM were found to interact with residues in VEGFR2. Furthermore, we found that the VEGF-induced VEGFR2-epsin interaction promoted casitas B-lineage lymphoma-mediated ubiquitination of epsin, and uncovered a previously unappreciated ubiquitin-binding surface within VEGFR2. Mutational analysis revealed that the VEGFR2-epsin interaction is supported by VEGFR2 interacting specifically with the UIM and with ubiquitinated epsin. An epsin UIM peptide, but not a mutant UIM peptide, potentiated endothelial cell proliferation, migration and angiogenic properties in vitro, increased postnatal retinal angiogenesis, and enhanced VEGF-induced physiological angiogenesis and wound healing.

CONCLUSIONS

Distinct residues in the epsin UIM and VEGFR2 mediate specific interactions between epsin and VEGFR2, in addition to UIM recognition of ubiquitin moieties on VEGFR2. These novel interactions are critical for pathophysiological angiogenesis, suggesting that these sites could be selectively targeted by therapeutics to modulate angiogenesis.

Motif mimetic of epsin perturbs tumor growth and metastasis

Tumor angiogenesis is critical for cancer progression. In multiple murine models, endothelium-specific epsin deficiency abrogates tumor progression by shifting the balance of VEGFR2 signaling toward uncontrolled tumor angiogenesis, resulting in dysfunctional tumor vasculature. Here, we designed a tumor endothelium-targeting chimeric peptide (UPI) for the purpose of inhibiting endogenous tumor endothelial epsins by competitively binding activated VEGFR2. We determined that the UPI peptide specifically targets tumor endothelial VEGFR2 through an unconventional binding mechanism that is driven by unique residues present only in the epsin ubiquitin-interacting motif (UIM) and the VEGFR2 kinase domain. In murine models of neoangiogenesis, UPI peptide increased VEGF-driven angiogenesis and neovascularization but spared quiescent vascular beds. Further, in tumor-bearing mice, UPI peptide markedly impaired functional tumor angiogenesis, tumor growth, and metastasis, resulting in a notable increase in survival. Coadministration of UPI peptide with cytotoxic chemotherapeutics further sustained tumor inhibition. Equipped with localized tumor endothelium-specific targeting, our UPI peptide provides potential for an effective and alternative cancer therapy.

Abstract 307: Role of Epsins in Regulating LPS-Induced Sepsis

Background: Sepsis is caused by a deleterious host response to infection, which is primarily responsible for further injury of host tissue and cause of organ dysfunction. However, the underlying regulatory mechanisms are still not fully understood. Our goal is to define the novel role of epsins in regulating sepsis.

Methods and Results: We engineered global (iDKO) and endothelial cell-specific (EC-iDKO) epsin deficient mice. When treated with lethal dose of LPS, epsin deficient mice were completely protected from LPS-induced septic death. These mice also exhibited decreased expression of tissue damage biomarkers and recruitment of neutrophils and macrophages to lungs compared to wild type (WT) suggesting that epsin deficiency mitigates sepsis induced tissue injury. Epsin deficiency further reduced expression of proinflammatory cytokines and adhesion molecules in the lungs suggesting that loss of epsin attenuates LPS-induced inflammatory responses. TAT complex production was also decreased in iDKO mice compared to WT indicating diminished coagulation and thrombin production. Knocking down of epsins in HUVECs resulted in reduced cell surface Tissue Factor (TF) expression. Loss of epsin in mice protected against loss of Thrombomodulin (TM), which is downregulated by sepsis. Mechanistically, loss of epsin inhibited LPS-induced TM internalization, while LPS treatment induced the ubiquitination of TM. Furthermore, co-IP of full length epsin 1 or epsin 1 without the UIM domain and TM demonstrated that UIM is required for the interaction between epsin 1 and TM. Collectively, we show that epsin-deficiency upregulates TM surface protein expression by preventing its internalization and subsequent degradation and inhibits heightened TF expression and activation under chronic inflammatory conditions such as that induced by LPS exposure.

Conclusions: Our findings demonstrate that epsins play a key role in regulating coagulation and provide fundamental information on the modulation of the ratio of TM/TF in various thrombotic diseases including sepsis. Furthermore, we demonstrate loss of epsin protects mice against LPS-induced sepsis, suggesting a crucial role for epsins in promoting the development of LPS-induced sepsis.

Abstract 33: Role of Epsins in Regulating LPS-Induced Sepsis

Background: Sepsis is caused by a deleterious host response to infection, which is primarily responsible for further injury of host tissue and cause of organ dysfunction. However, the underlying regulatory mechanisms are still not fully understood. Our goal is to define the novel role of epsins in regulating sepsis.

Methods and Results: We engineered global (iDKO) and endothelial cell-specific (EC-iDKO) epsin deficient mice. When treated with lethal dose of LPS, epsin deficient mice were completely protected from LPS-induced septic death. These mice also exhibited decreased expression of tissue damage biomarkers and recruitment of neutrophils and macrophages to lungs compared to wild type (WT) suggesting that epsin deficiency mitigates sepsis induced tissue injury. Epsin deficiency further reduced expression of proinflammatory cytokines and adhesion molecules in the lungs suggesting that loss of epsin attenuates LPS-induced inflammatory responses. TAT complex production was also decreased in iDKO mice compared to WT indicating diminished coagulation and thrombin production. Knocking down of epsins in HUVECs resulted in reduced cell surface Tissue Factor (TF) expression. Loss of epsin in mice protected against loss of Thrombomodulin (TM), which is downregulated by sepsis. Mechanistically, loss of epsin inhibited LPS-induced TM internalization, while LPS treatment induced the ubiquitination of TM. Furthermore, co-IP of full length epsin 1 or epsin 1 without the UIM domain and TM demonstrated that UIM is required for the interaction between epsin 1 and TM. Collectively, we show that epsin-deficiency upregulates TM surface protein expression by preventing its internalization and subsequent degradation and inhibits heightened TF expression and activation under chronic inflammatory conditions such as that induced by LPS exposure.

Conclusions: Our findings demonstrate that epsins play a key role in regulating coagulation and provide fundamental information on the modulation of the ratio of TM/TF in various thrombotic diseases including sepsis. Furthermore, we demonstrate loss of epsin protects mice against LPS-induced sepsis, suggesting a crucial role for epsins in promoting the development of LPS-induced sepsis.

Abstract 141: The Role of Macrophage Epsins in the Regulation of LRP-1 in Atherosclerosis

Background: Epsins are a family of ubiquitin-binding endocytic clathrin adaptors. We recently published that endothelial epsins function as critical regulators of tumor angiogenesis by controlling VEGF signaling (JCI, 2012; ATVB, 2013). Our goal is to define the novel role of epsins in macrophages in regulating atherogenesis.

Methods and Results: We engineered mice with specific deletion of epsins in myeloid cells (MΦ-DKO). Strikingly, MΦ-DKO mice on ApoE-/- background fed western diet significantly reduced atherosclerotic lesion formation and foam cell accumulation. In macrophages, epsin deficiency did not alter LDL scavenger receptors, CD36, Lox1 or SRB1, or reverse cholesterol transport proteins, ABCA1 or ABCG1, but did significantly reduce Lucifer Yellow pinocytosis, indicating a major defect in lipid uptake. Epsin deficiency did decrease total and surface protein levels of LRP-1, a protein with anti-inflammatory and anti-atherosclerotic properties. Oil Red O staining of isolated ApoE-/-/M[[Unable to Display Character: Ф]]-DKO macrophages showed little lipid accumulation, suggesting a mechanism in which epsin deficiency impairs foam cell formation. In addition, epsin 1 and LRP-1 interact in macrophages. Furthermore, this interaction is abolished in the absence of epsin’s UIM domain and LPS treatment increases LRP-1 ubiquitination, suggesting that epsin promotes the ubiquitin-dependent internalization of LRP-1. Epsin deficiency also significantly suppressed the pro-inflammatory M1 macrophage phenotype found in plaques and increased the anti-inflammatory macrophage phenotype, thus suggesting an important pro-inflammatory role for epsins in macrophages. Our finding implicates epsin as a potential therapeutic target for atherosclerosis treatment.

Conclusions: We demonstrate epsins promote atherogenesis by potentiating foam cell formation and maintaining pro-inflammatory macrophages within the atherosclerotic plaque, thus suggesting epsins as a novel therapeutic target to combat atherogenesis.

Epsin is required for Dishevelled stability and Wnt signalling activation in colon cancer development

Uncontrolled canonical Wnt signalling supports colon epithelial tumour expansion and malignant transformation. Understanding the regulatory mechanisms involved is crucial for elucidating the pathogenesis of and will provide new therapeutic targets for colon cancer. Epsins are ubiquitin-binding adaptor proteins upregulated in several human cancers; however, the involvement of epsins in colon cancer is unknown. Here we show that loss of intestinal epithelial epsins protects against colon cancer by significantly reducing the stability of the crucial Wnt signalling effector, dishevelled (Dvl2), and impairing Wnt signalling. Consistently, epsins and Dvl2 are correspondingly upregulated in colon cancer. Mechanistically, epsin binds Dvl2 via its epsin N-terminal homology domain and ubiquitin-interacting motifs and prohibits Dvl2 polyubiquitination and degradation. Our findings reveal an unconventional role for epsins in stabilizing Dvl2 and potentiating Wnt signalling in colon cancer cells to ensure robust colon cancer progression. The pro-carcinogenic role of Epsins suggests that they are potential therapeutic targets to combat colon cancer.

Temporal and spatial regulation of epsin abundance and VEGFR3 signaling are required for lymphatic valve formation and function

Lymphatic valves prevent the backflow of the lymph fluid and ensure proper lymphatic drainage throughout the body. Local accumulation of lymphatic fluid in tissues, a condition called lymphedema, is common in individuals with malformed lymphatic valves. The vascular endothelial growth factor receptor 3 (VEGFR3) is required for the development of lymphatic vascular system. The abundance of VEGFR3 in collecting lymphatic trunks is high before valve formation and, except at valve regions, decreases after valve formation. We found that in mesenteric lymphatics, the abundance of epsin 1 and 2, which are ubiquitin-binding adaptor proteins involved in endocytosis, was low at early stages of development. After lymphatic valve formation, the initiation of steady shear flow was associated with an increase in the abundance of epsin 1 and 2 in collecting lymphatic trunks, but not in valve regions. Epsin 1 and 2 bound to VEGFR3 and mediated the internalization and degradation of VEGFR3, resulting in termination of VEGFR3 signaling. Mice with lymphatic endothelial cell-specific deficiency of epsin 1 and 2 had dilated lymphatic capillaries, abnormally high VEGFR3 abundance in collecting lymphatics, immature lymphatic valves, and defective lymph drainage. Deletion of a single Vegfr3 allele or pharmacological suppression of VEGFR3 signaling restored normal lymphatic valve development and lymph drainage in epsin-deficient mice. Our findings establish a critical role for epsins in the temporal and spatial regulation of VEGFR3 abundance and signaling in collecting lymphatic trunks during lymphatic valve formation.

Abstract P1-05-21: The role of epsin in promoting Epithelial-Mesenchymal Transition and metastasis by activating NF-kB signaling in breast cancer

Background: Breast Cancer progression and metastasis are multi-step processes that involve local tumor growth and invasion followed by tumor dissemination to and re-establishment at distant sites. The ability of a tumor to metastasize is the major determinant of the mortality of cancer patients. Thus, elucidating the molecular pathways essential for tumor metastasis is of high priority in cancer biology. We have previously demonstrated that deficiency of epsins, a family of endocytic clathrin adaptor proteins, decreases tumor growth by enhancing VEGF signaling in vascular endothelial cells and subsequently promoting dysfunctional tumor angiogenesis.

Research Objective: Our immediate aim in the current research is to determine the role of epsin in regulating breast cancer growth and metastasis by activating NF-κB signaling. Our ultimate goal is to seek better treatment for breast cancer patients.

Rationale: Our preliminary data demonstrate that epsins are overexpressed in human cancers, including breast cancer. Knockdown of epsins in human breast cancer cell line MDA-MB-231 inhibits in vitro cell proliferation and migration. Xenograft or tail-vein injection of epsin-deficient breast cancer cells reveals marked reduction in in vivo tumorigenesis and lung metastasis. Moreover, E-cadherin is increased and vimentin decreased in epsin-deficient MDA-MB-231 and in tumors derived from epsin-deficient MDA-MB-231 tumor models. Conversely, overexpression of epsin in breast epithelial cell line MCF10A and MDA-MB-231 results in decreased E-cadherin and increased vimentin expression.

Hypothesis: We hypothesize that epsin regulates EMT through modulating NF-κB signaling.

Methods: we use combined techniques of western blot, confocal immunofluorescence and RT-PCR to examine NF-κB activation.

Results: NF-κB phosphorylation, nuclear translocation and NF-κB target gene snail/slug expression is downregulated in epsin-deficient MDA-MB-231. Epsin overexpression in MDA-MB-231 increases NF-κB phosphorylation. Mechanistically, we show that epsin co-immunoprecipitates with components of TNF Receptor Signaling Complex (TNFR-SC) including TNFR1, TRADD, RIP, TRAF2 and NEMO in MDA-MB-231, which can be enhanced by TNFα stimulation. Conversely, recruitment of NEMO and TRAF2 to TNFR1 is impaired in epsin-deficient MDA-MB-231 compared to control upon TNFα treatment. Given that ubiquitin-interacting motifs (UIM) of epsin is important for its interaction with ubiquitinated proteins, we show that wild type (WT) but not a UIM-deficient mutant epsin (epsin ΔUIM) coprecipitates with TNFR1 in 293T cells. Overexpression of epsin ΔUIM inhibits NF-κB activation in MDA-MB-231 and 293T cells compared to WT. In addition, UIM of epsin and polyubquitination of RIP are required for the interaction of epsin with RIP in 293T cells response to TNFα.

Conclusion: epsin promotes breast cancer growth and metastasis by upregulating NF-kB signaling and EMT. Epsin serves as scaffolding protein through UIM-polyubiquitin chain interaction to stabilize TNFR1 signaling complex (TNFR-SC) and subsequently enhance NF-kB signaling in breast cancer cells. Our study provides a basis for novel therapeutic targets for the development of anti-metastatic cancer treatments.

Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P1-05-21.