Aims: Diabetes increases oxidative stress in the retina and dysfunctions their mitochondria, accelerating capillary cell apoptosis. A 66 kDa adaptor protein, p66Shc, is considered as a sensor of oxidative stress-induced apoptosis. In the pathogenesis of diabetic retinopathy, a progressive disease, reactive oxygen species (ROS) production by activation of a small molecular weight G-protein (Ras-related C3 botulinum toxin substrate 1 [Rac1])-Nox2 signaling precedes mitochondrial damage. Rac1 activation is facilitated by guanine exchange factors (GEFs), and p66Shc increases Rac1-specific GEF activity of Son of Sevenless 1 (Sos1). p66Shc also possesses oxidoreductase activity and can directly stimulate mitochondrial ROS generation. Our aim was to investigate the role of p66Shc in the development of diabetic retinopathy and mechanism of its transcription. Results: High glucose increased p66Shc expression in human retinal endothelial cells, and elevated acetylated histone 3 lysine 9 (H3K9) levels and transcriptional factor p53 binding at its promoter. Glucose also augmented interactions between Rac1 and Sos1 and activated Rac1-Nox2. Phosphorylation of p66Shc was increased, allowing it to interact with peptidyl prolyl isomerase to facilitate its localization inside the mitochondria, culminating in mitochondrial damage. P66shc -small interfering RNA (siRNA) inhibited glucose-induced Rac1 activation and mitochondrial damage. Similar results are observed in retinal microvessels from diabetic rats. Innovation: This is the first report identifying the role of p66Shc in the development of diabetic retinopathy and implicating increased histone acetylation in its transcriptional regulation. Conclusion: Thus, p66Shc has dual role in the development of diabetic retinopathy; its regulation in the early stages of the disease should impede Rac1-ROS production and, in the later stages, prevent mitochondrial damage and initiation of a futile cycle of free radicals.

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.

Estrogen receptor–negative (ER-negative) breast cancer is thought to be more malignant and devastating than ER-positive breast cancer. ER-negative breast cancer exhibits elevated NF-κB activity, but how this abnormally high NF-κB activity is maintained is poorly understood. The importance of linear ubiquitination, which is generated by the linear ubiquitin chain assembly complex (LUBAC), is increasingly appreciated in NF-κB signaling, which regulates cell activation and death. Here, we showed that epsin proteins, a family of ubiquitin-binding endocytic adaptors, interacted with LUBAC via its ubiquitin-interacting motif and bound LUBAC’s bona fide substrate NEMO via its N-terminal homolog (ENTH) domain. Furthermore, epsins promoted NF-κB essential modulator (NEMO) linear ubiquitination and served as scaffolds for recruiting other components of the IκB kinase (IKK) complex, resulting in the heightened IKK activation and sustained NF-κB signaling essential for the development of ER-negative breast cancer. Heightened epsin levels in ER-negative human breast cancer are associated with poor relapse-free survival. We showed that transgenic and pharmacological approaches eliminating epsins potently impeded breast cancer development in both spontaneous and patient-derived xenograft breast cancer mouse models. Our findings established the pivotal role epsins played in promoting breast cancer. Thus, targeting epsins may represent a strategy to restrain NF-κB signaling and provide an important perspective into ER-negative breast cancer treatment.

Diabetes mellitus can cause impaired and delayed wound healing, leading to lower extremity amputations; however, the mechanisms underlying the regulation of vascular endothelial growth factor–dependent (VEGF-dependent) angiogenesis remain unclear. In our study, the molecular underpinnings of endothelial dysfunction in diabetes are investigated, focusing on the roles of disabled-2 (Dab2) and Forkhead box M1 (FOXM1) in VEGF receptor 2 (VEGFR2) signaling and endothelial cell function. Bulk RNA-sequencing analysis identified significant downregulation of Dab2 in high-glucose-treated primary mouse skin endothelial cells. In diabetic mice with endothelial deficiency of Dab2, in vivo and in vitro angiogenesis and wound healing were reduced when compared with wild-type diabetic mice. Restoration of Dab2 expression by injected mRNA-containing, LyP-1–conjugated lipid nanoparticles rescued impaired angiogenesis and wound healing in diabetic mice. Furthermore, FOXM1 was downregulated in skin endothelial cells under high-glucose conditions as determined by RNA-sequencing analysis. FOXM1 was found to bind to the Dab2 promoter, regulating its expression and influencing VEGFR2 signaling. The FOXM1 inhibitor FDI-6 reduced Dab2 expression and phosphorylation of VEGFR2. Our study provides evidence of the crucial roles of Dab2 and FOXM1 in diabetic endothelial dysfunction and establishes targeted delivery as a promising treatment for diabetic vascular complications.

Backgrounds/Aims: The lipid induced insulin resistance is a major pathophysiologic mechanism underlying glucose intolerance of varying severity. PPARα-agonists are proven as effective hypolipidemic agents. The aim of this study was to see if impaired glucose uptake in palmitate treated myotubes is reversed by fenofibrate. Methods: Palmitate-treated myotubes were used as a model for insulin resistance, impaired glucose uptake, fatty acid oxidation and ceramide synthesis. mRNA levels of CPT1 and CPT2 were determined by PCR array and Q-PCR. Results: The incubation of myotubes with 750 uM palmitate not only reduced glucose uptake but also impaired fatty acid oxidation and cytosolic ceramide accumulation. Palmitate upregulated CPT1b expression in L6 myotubes, while CPT2 expression level remained unchanged. The altered stoichiometric ratio between the two CPT isoforms led to reduced fatty acid oxidation (FAO), ceramide accumulation and impaired glucose uptake, whereas administration of 200 µM fenofibrate signifcantly reversed the above abnormalities by increasing CPT2 mRNA levels and restoring CPT1b to CPT2 ratio. Conclusion: Palmitate-induced alteration in the stoichiometric ratio of mitochondrial CPT isoforms leads to incomplete FAO and enhanced cytosolic ceramide accumulation that lead to insulin resistance. Fenofibrate ameliorated insulin resistance by restoring the altered stoichiometry by upregulating CPT2 and preventing, cytoplasmic ceramide accumulation.