Glycogen synthase kinase-3β and cathepsin B in diabetic endothelial progenitor cell dysfunction: an old player finds a new partner

Dapagliflozin restores diabetes-associated decline in vasculogenic capacity of endothelial progenitor cells via activating AMPK-mediated inhibition of inflammation and oxidative stress

Sodium-glucose cotransporter 2 inhibitors (SGLT2i) provide added vascular protection beyond glucose lowering to patients with type 2 diabetes mellitus (T2DM). Endothelial progenitor cells (EPCs) are an important endogenous repair mechanism for diabetic vascular complications. Yet, whether SGLT2i protect vessels in diabetic patients by improving the function of EPCs remains to be elucidated. Here we enrolled Sixty-three T2DM patients and 60 healthy participants and 15 of T2DM group took dapagliflozin for 3 months. Retinal capillary density (RCD) was examined before and after meditation. Moreover, vasculogenic capacity of EPCs cocultured with or without dapagliflozin in vitro and in vivo (hind limb ischemia model) were assessed. Mechanically, genes related to inflammation/oxidative stress, and the AMPK signaling of EPCs were determined. Our results found T2DM demonstrated a declined RCD and a decreased number of circulating EPCs compared with healthy controls. Compared with the EPCs from healthy individuals, vasculogenic capacity of T2DM EPCs was significantly impaired, which could be restored by dapagliflozin meditation or dapagliflozin coculture. Increased expression of inflammation correlative genes and decreased anti-oxidative stress related genes expression were found in EPCs form T2DM, which were accompanied with reduced phosphorylation level of AMPK. Dapagliflozin treatment activated AMPK signaling, decreased the level of inflammation and oxidative stress, and rescued vasculogenic capacity of EPCs from T2DM. Furthermore, AMPK inhibitor pretreatment diminished the enhancement vasculogenic capacity of diabetic EPCs from dapagliflozin treatment. This study demonstrates for the first time that dapagliflozin restores vasculogenic capacity of EPCs via activating AMPK-mediated inhibition of inflammation and oxidative stress in T2DM.

CircRNA-miRNA interactions in atherogenesis

Atherosclerosis is the major cause of coronary artery disease (CAD) which includes unstable angina, myocardial infarction, and heart failure. The onset of atherogenesis, a process of atherosclerotic lesion formation in the intima of arteries, is driven by lipid accumulation, a vicious cycle of reactive oxygen species (ROS)-induced oxidative stress and inflammatory reactions leading to endothelial cell (EC) dysfunction, vascular smooth muscle cell (VSMC) activation, and foam cell formation which further fuel plaque formation and destabilization. In recent years, there is a surge in the number of publications reporting the involvement of circular RNAs (circRNAs) in the pathogenesis of cardiovascular diseases, cancers, and metabolic syndromes. These studies have advanced our understanding on the biological functions of circRNAs. One of the most common mechanism of action of circRNAs reported is the sponging of microRNAs (miRNAs) by binding to the miRNAs response element (MRE), thereby indirectly increases the transcription of their target messenger RNAs (mRNAs). Individual networks of circRNA-miRNA-mRNA associated with atherogenesis have been extensively reported, however, there is a need to connect these findings for a complete overview. This review aims to provide an update on atherogenesis-related circRNAs and analyze the circRNA-miRNA-mRNA interactions in atherogenesis. The atherogenic mechanisms and clinical relevance of each atherogenesis-related circRNA were systematically discussed for better understanding of the knowledge gap in this area.

Clickable, selective, and cell-permeable activity-based probe of human cathepsin B - Minimalistic approach for enhanced selectivity

Human cathepsin B is a cysteine-dependent protease whose roles in both normal and diseased cellular states remain yet to be fully delineated. This is primarily due to overlapping substrate specificities and lack of unambiguously annotated physiological functions. In this work, a selective, cell-permeable, clickable and tagless small molecule cathepsin B probe, KDA-1, is developed and kinetically characterized. KDA-1 selectively targets active site Cys25 residue of cathepsin B for labeling and can detect active cellular cathepsin B in proteomes derived from live human MDA-MB-231 breast cancer cells and HEK293 cells. It is anticipated that KDA-1 probe will find suitable applications in functional proteomics involving human cathepsin B enzyme.

Circ-ADAM9 targeting PTEN and ATG7 promotes autophagy and apoptosis of diabetic endothelial progenitor cells by sponging mir-20a-5p

Dysfunction of endothelial progenitor cells (EPCs) is a key factor in vascular complications of diabetes mellitus. Although the roles of microRNAs and circular RNAs in regulating cell functions have been thoroughly studied, their role in regulating autophagy and apoptosis of EPCs remains to be elucidated. This study investigated the roles of mir-20a-5p and its predicted target circ-ADAM9 in EPCs treated with high glucose (30 mM) and in a diabetic mouse hind limb ischemia model. It is found that Mir-20a-5p inhibited autophagy and apoptosis of EPCs induced by high-concentration glucose. Further, mir-20a-5p could inhibit the expression of PTEN and ATG7 in EPCs, and promote the phosphorylation of AKT and mTOR proteins under high-glucose condition. Investigation of the underlying mechanism revealed that circ-ADAM9, as a miRNA sponges of mir-20a-5p, promoted autophagy and apoptosis of EPCs induced by high-concentration glucose. Circ-ADAM9 upregulated PTEN and ATG7 in interaction with mir-20a-5p, and inhibited the phosphorylation of AKT and mTOR to aggravate autophagy and apoptosis of EPCs under high glucose. In addition, silencing of circ-ADAM9 increased microvessel formation in the hind limbs of diabetic mice. Our findings disclose a novel autophagy/apoptosis-regulatory pathway that is composed of mir-20a-5p, circ-ADAM9, PTEN, and ATG7. Circ-ADAM9 is a potential novel target for regulating the function of diabetic EPCs and angiogenesis.

BODIPY-Caged Photoactivated Inhibitors of Cathepsin B Flip the Light Switch on Cancer Cell Apoptosis

Acquired resistance to apoptotic agents is a long-standing challenge in cancer treatment. Cathepsin B (CTSB) is an enzyme which, among many essential functions, promotes apoptosis during cellular stress through regulation of intracellular proteolytic networks on the minute time scale. Recent data indicate that CTSB inhibition may be a promising method to steer cells away from apoptotic death toward necrosis, a mechanism of cell death that can overcome resistance to apoptotic agents, stimulate an immune response and promote antitumor immunity. Unfortunately, rapid and selective intracellular inactivation of CTSB has not been possible. However, here we report on the synthesis and characterization of photochemical and biological properties of BODIPY-caged inhibitors of CTSB that are cell permeable, highly selective and activated rapidly upon exposure to visible light. Intriguingly, these compounds display tunable photophysical and biological properties based on substituents bound directly to boron. Me₂BODIPY-caged compound 8 displays the dual-action capability of light-accelerated CTSB inhibition and singlet oxygen production from a singular molecular entity. The dual-action capacity of 8 leads to a rapid necrotic response in MDA-MB-231 triple negative breast cancer cells with high phototherapeutic indexes (>30) and selectivity vs noncancerous cells that neither CTSB inhibition nor photosensitization gives alone. Our work confirms that singlet oxygen production and CTSB inactivation is highly synergistic and a promising method for killing cancer cells. Furthermore, this ability to trigger intracellular inactivation of CTSB with light provides researchers with a powerful photochemical tool for probing biochemical processes on short time scales.

GDF11 Improves Angiogenic Function of EPCs in Diabetic Limb Ischemia

Growth differentiation factor 11 (GDF11) has been shown to promote stem cell activity and rejuvenate the function of multiple organs in old mice, but little is known about the functions of GDF11 in the diabetic rat model of hindlimb ischemia. In this study, we found that systematic replenishment of GDF11 rescues angiogenic function of endothelial progenitor cells (EPCs) and subsequently improves vascularization and increases blood flow in diabetic rats with hindlimb ischemia. Conversely, anti-GDF11 monoclonal antibody treatment caused impairment of vascularization and thus, decreased blood flow. In vitro treatment of EPCs with recombinant GDF11 attenuated EPC dysfunction and apoptosis. Mechanistically, the GDF11-mediated positive effects could be attributed to the activation of the transforming growth factor-β/Smad2/3 and protein kinase B/hypoxia-inducible factor 1α pathways. These findings suggest that GDF11 repletion may enhance EPC resistance to diabetes-induced damage, improve angiogenesis, and thus, increase blood flow. This benefit of GDF11 may lead to a new therapeutic approach for diabetic hindlimb ischemia.

The role of cathepsin B in autophagy during obesity: A systematic review

White adipose tissue (WAT) regulates energy homeostasis by releasing adipokines and modulating cell maintenance. Nutrient excess affects adipocyte hypertrophy directly in WAT by increasing excessively the activity of autophagy systems, generating proinflammatory markers and increasing infiltration of macrophages, causing metabolic diseases such as obesity and diabetes. Evidences suggest that cathepsin B (CTSB), a papain-like cysteine peptidase protein, can modulate autophagy processes in adipocytes. This review will focus on the role of CTSB in autophagy under conditions of obesity.

Ginsenoside Rg5 Inhibits Succinate-Associated Lipolysis in Adipose Tissue and Prevents Muscle Insulin Resistance

Endoplasmic reticulum (ER) stress, inflammation, and lipolysis occur simultaneously in adipose dysfunction and contribute to insulin resistance. This study was designed to investigate whether ginsenoside Rg5 could ameliorate adipose dysfunction and prevent muscle insulin resistance. Short-term high-fat diet (HFD) feeding induced hypoxia with ER stress in adipose tissue, leading to succinate accumulation due to the reversal of succinate dehydrogenase (SDH) activity. Rg5 treatment reduced cellular energy charge, suppressed ER stress and then prevented succinate accumulation in adipose tissue. Succinate promoted IL-1β production through NLRP3 inflammasome activation and then increased cAMP accumulation by impairing PDE3B expression, leading to increased lipolysis. Ginsenoside Rg5 treatment suppressed NLRP3 inflammasome activation, preserved PDE3B expression and then reduced cAMP accumulation, contributing to inhibition of lipolysis. Adipose lipolysis increased FFAs trafficking from adipose tissue to muscle. Rg5 reduced diacylglycerol (DAG) and ceramides accumulation, inhibited protein kinase Cθ translocation, and prevented insulin resistance in muscle. In conclusion, succinate accumulation in hypoxic adipose tissue acts as a metabolic signaling to link ER stress, inflammation and cAMP/PKA activation, contributing to lipolysis and insulin resistance. These findings establish a previously unrecognized role of ginsenosides in the regulation of lipid and glucose homeostasis and suggest that adipose succinate-associated NLRP3 inflammasome activation might be targeted therapeutically to prevent lipolysis and insulin resistance.

Elevating CXCR7 Improves Angiogenic Function of EPCs via Akt/GSK-3β/Fyn-Mediated Nrf2 Activation in Diabetic Limb Ischemia

RATIONALE

Endothelial progenitor cells (EPCs) respond to stromal cell-derived factor 1 (SDF-1) through chemokine receptors CXCR7 and CXCR4. Whether SDF-1 receptors involves in diabetes mellitus-induced EPCs dysfunction remains unknown.

OBJECTIVE

To determine the role of SDF-1 receptors in diabetic EPCs dysfunction.

METHODS AND RESULTS

CXCR7 expression, but not CXCR4 was reduced in EPCs from db/db mice, which coincided with impaired tube formation. Knockdown of CXCR7 impaired tube formation of EPCs from normal mice, whereas upregulation of CXCR7 rescued angiogenic function of EPCs from db/db mice. In normal EPCs treated with oxidized low-density lipoprotein or high glucose also reduced CXCR7 expression, impaired tube formation, and increased oxidative stress and apoptosis. The damaging effects of oxidized low-density lipoprotein or high glucose were markedly reduced by SDF-1 pretreatment in EPCs transduced with CXCR7 lentivirus but not in EPCs transduced with control lentivirus. Most importantly, EPCs transduced with CXCR7 lentivirus were superior to EPCs transduced with control lentivirus for therapy of ischemic limbs in db/db mice. Mechanistic studies demonstrated that oxidized low-density lipoprotein or high glucose inhibited protein kinase B and glycogen synthase kinase-3β phosphorylation, nuclear export of Fyn and nuclear localization of nuclear factor (erythroid-derived 2)-like 2 (Nrf2), blunting Nrf2 downstream target genes heme oxygenase-1, NAD(P)H dehydrogenase (quinone 1) and catalase, and inducing an increase in EPC oxidative stress. This destructive cascade was blocked by SDF-1 treatment in EPCs transduced with CXCR7 lentivirus. Furthermore, inhibition of phosphatidylinositol 3-kinase/protein kinase B prevented SDF-1/CXCR7-mediated Nrf2 activation and blocked angiogenic repair. Moreover, Nrf2 knockdown almost completely abolished the protective effects of SDF-1/CXCR7 on EPC function in vitro and in vivo.

CONCLUSIONS

Elevated expression of CXCR7 enhances EPC resistance to diabetes mellitus-induced oxidative damage and improves therapeutic efficacy of EPCs in treating diabetic limb ischemia. The benefits of CXCR7 are mediated predominantly by a protein kinase B/glycogen synthase kinase-3β/Fyn pathway via increased activity of Nrf2.

Progenitor Cells for Arterial Repair: Incremental Advancements towards Therapeutic Reality

Coronary revascularization remains the standard treatment for obstructive coronary artery disease and can be accomplished by either percutaneous coronary intervention (PCI) or coronary artery bypass graft surgery. Considerable advances have rendered PCI the most common form of revascularization and improved clinical outcomes. However, numerous challenges to modern PCI remain, namely, in-stent restenosis and stent thrombosis, underscoring the importance of understanding the vessel wall response to injury to identify targets for intervention. Among recent promising discoveries, endothelial progenitor cells (EPCs) have garnered considerable interest given an increasing appreciation of their role in vascular homeostasis and their ability to promote vascular repair after stent placement. Circulating EPC numbers have been inversely correlated with cardiovascular risk, while administration of EPCs in humans has demonstrated improved clinical outcomes. Despite these encouraging results, however, advancing EPCs as a therapeutic modality has been hampered by a fundamental roadblock: what constitutes an EPC? We review current definitions and sources of EPCs as well as the proposed mechanisms of EPC-mediated vascular repair. Additionally, we discuss the current state of EPCs as therapeutic agents, focusing on endogenous augmentation and transplantation.