Gαi1/3 mediate Netrin-1-CD146-activated signaling and angiogenesis

Netrin-1 co-cross-linked hydrogel accelerates diabetic wound healing in situ by modulating macrophage heterogeneity and promoting angiogenesis

Diabetic wounds, characterized by prolonged inflammation and impaired vascularization, are a serious complication of diabetes. This study aimed to design a gelatin methacrylate (GelMA) hydrogel for the sustained release of netrin-1 and evaluate its potential as a scaffold to promote diabetic wound healing. The results showed that netrin-1 was highly expressed during the inflammation and proliferation phases of normal wounds, whereas it synchronously exhibited aberrantly low expression in diabetic wounds. Neutralization of netrin-1 inhibited normal wound healing, and the topical application of netrin-1 accelerated diabetic wound healing. Mechanistic studies demonstrated that netrin-1 regulated macrophage heterogeneity via the A2bR/STAT/PPARγ signaling pathway and promoted the function of endothelial cells, thus accelerating diabetic wound healing. These data suggest that netrin-1 is a potential therapeutic target for diabetic wounds.

Netrin-1-engineered endothelial cell exosomes induce the formation of pre-regenerative niche to accelerate peripheral nerve repair

The formation of vascular niche is pivotal during the early stage of peripheral nerve regeneration. Nevertheless, the mechanisms of vascular niche in the regulation of peripheral nerve repair remain unclear. Netrin-1 (NTN1) was found up-regulated in nerve stump after peripheral nerve injury (PNI). Herein, we demonstrated that NTN1-high endothelial cells (NTN1+ECs) were the critical component of vascular niche, fostering angiogenesis, axon regeneration, and repair-related phenotypes. We also found that NTN1+EC-derived exosomes (NTN1 EC-EXO) were involved in the formation of vascular niche as a critical role. Multi-omics analysis further verified that NTN1 EC-EXO carried a low-level expression of let7a-5p and activated key pathways associated with niche formation including focal adhesion, axon guidance, phosphatidylinositol 3-kinase-AKT, and mammalian target of rapamycin signaling pathway. Together, our study suggested that the construction of a pre-regenerative niche induced by NTN1 EC-EXO could establish a beneficial microenvironment for nerve repair and facilitate functional recovery after PNI.

Identification of the central role of RNA polymerase mitochondrial for angiogenesis

Mitochondria are central to endothelial cell activation and angiogenesis, with the RNA polymerase mitochondrial (POLRMT) serving as a key protein in regulating mitochondrial transcription and oxidative phosphorylation. In our study, we examined the impact of POLRMT on angiogenesis and found that its silencing or knockout (KO) in human umbilical vein endothelial cells (HUVECs) and other endothelial cells resulted in robust anti-angiogenic effects, impeding cell proliferation, migration, and capillary tube formation. Depletion of POLRMT led to impaired mitochondrial function, characterized by mitochondrial depolarization, oxidative stress, lipid oxidation, DNA damage, and reduced ATP production, along with significant apoptosis activation. Conversely, overexpressing POLRMT promoted angiogenic activity in the endothelial cells. In vivo experiments demonstrated that endothelial knockdown of POLRMT, by intravitreous injection of endothelial specific POLRMT shRNA adeno-associated virus, inhibited retinal angiogenesis. In addition, inhibiting POLRMT with a first-in-class inhibitor IMT1 exerted significant anti-angiogenic impact in vitro and in vivo. Significantly elevated expression of POLRMT was observed in the retinal tissues of streptozotocin-induced diabetic retinopathy (DR) mice. POLRMT endothelial knockdown inhibited pathological retinal angiogenesis and mitigated retinal ganglion cell (RGC) degeneration in DR mice. At last, POLRMT expression exhibited a substantial increase in the retinal proliferative membrane tissues of human DR patients. These findings collectively establish the indispensable role of POLRMT in angiogenesis, both in vitro and in vivo.

Targeting the mitochondrial protein YME1L to inhibit osteosarcoma cell growth in vitro and in vivo

Exploring novel diagnostic and therapeutic biomarkers is extremely important for osteosarcoma. YME1 Like 1 ATPase (YME1L), locating in the mitochondrial inner membrane, is key in regulating mitochondrial plasticity and metabolic activity. Its expression and potential functions in osteosarcoma are studied in the present study. We show that YME1L mRNA and protein expression is significantly elevated in osteosarcoma tissues derived from different human patients. Moreover, its expression is upregulated in various primary and immortalized osteosarcoma cells. The Cancer Genome Atlas database results revealed that YME1L overexpression was correlated with poor overall survival and poor disease-specific survival in sarcoma patients. In primary and immortalized osteosarcoma cells, silencing of YME1L through lentiviral shRNA robustly inhibited cell viability, proliferation, and migration. Moreover, cell cycle arrest and apoptosis were detected in YME1L-silenced osteosarcoma cells. YME1L silencing impaired mitochondrial functions in osteosarcoma cells, causing mitochondrial depolarization, oxidative injury, lipid peroxidation and DNA damage as well as mitochondrial respiratory chain complex I activity inhibition and ATP depletion. Contrarily, forced YME1L overexpression exerted pro-cancerous activity and strengthened primary osteosarcoma cell proliferation and migration. YME1L is important for Akt-S6K activation in osteosarcoma cells. Phosphorylation of Akt and S6K was inhibited after YME1L silencing in primary osteosarcoma cells, but was strengthened with YME1L overexpression. Restoring Akt-mTOR activation by S473D constitutively active Akt1 mitigated YME1L shRNA-induced anti-osteosarcoma cell activity. Lastly, intratumoral injection of YME1L shRNA adeno-associated virus inhibited subcutaneous osteosarcoma xenograft growth in nude mice. YME1L depletion, mitochondrial dysfunction, oxidative injury, Akt-S6K inactivation, and apoptosis were detected in YME1L shRNA-treated osteosarcoma xenografts. Together, overexpressed YME1L promotes osteosarcoma cell growth, possibly by maintaining mitochondrial function and Akt-mTOR activation.

Targeting the postsynaptic scaffolding protein PSD-95 enhances BDNF signaling to mitigate depression-like behaviors in mice

Signaling mediated by brain-derived neurotrophic factor (BDNF), which is supported by the postsynaptic scaffolding protein PSD-95, has antidepressant effects. Conversely, clinical depression is associated with reduced BDNF signaling. We found that peptidomimetic compounds that bind to PSD-95 promoted signaling by the BDNF receptor TrkB in the hippocampus and reduced depression-like behaviors in mice. The compounds CN2097 and Syn3 both bind to the PDZ3 domain of PSD-95, and Syn3 also binds to an α-helical region of the protein. Syn3 reduced depression-like behaviors in two mouse models of stress-induced depression; CN2097 had similar but less potent effects. In hippocampal neurons, application of Syn3 enhanced the formation of TrkB-Gαi1/3-PSD-95 complexes and potentiated downstream PI3K-Akt-mTOR signaling. In mice subjected to chronic mild stress (CMS), systemic administration of Syn3 reversed the CMS-induced, depression-associated changes in PI3K-Akt-mTOR signaling, dendrite complexity, spine density, and autophagy in the hippocampus and reduced depression-like behaviors. Knocking out Gαi1/3 in hippocampal neurons prevented the therapeutic effects of Syn3, indicating dependence of these effects on the TrkB pathway. The findings suggest that compounds that induce the formation of PSD-95-TrkB complexes have therapeutic potential to alleviate depression.

Expression and functional significance of phosphoenolpyruvate carboxykinase 1 in uveal melanoma

Uveal melanoma (UVM), an uncommon yet potentially life-threatening ocular cancer, arises from melanocytes in the uveal tract of the eye. The exploration of novel oncotargets for UVM is of paramount importance. In this study, we show that PCK1 (phosphoenolpyruvate carboxykinase 1) expression is upregulated in various UVM tissues as well as in primary UVM cells and immortalized lines. Furthermore, bioinformatics studies reveal that PCK1 overexpression in UVM correlates with advanced disease stages and poor patient survival. Genetic silencing (utilizing viral shRNA) or knockout (via CRISPR/Cas9) of PCK1 significantly curtailed cell viability, proliferation, cell cycle progression, and motility, while provoking apoptosis in primary and immortalized UVM cells. Conversely, ectopic overexpression of PCK1, achieved through a viral construct, bolstered UVM cell proliferation and migration. Gαi3 expression and Akt phosphorylation were reduced following PCK1 silencing or knockout, but increased after PCK1 overexpression in UVM cells. Restoring Akt phosphorylation through a constitutively active mutant Akt1 (S473D) ameliorated the growth inhibition, migration suppression, and apoptosis induced by PCK1 silencing in UVM cells. Additionally, ectopic expression of Gαi3 restored Akt activation and counteracted the anti-UVM cell effects by PCK1 silencing. In vivo, the growth of subcutaneous xenografts of primary human UVM cells was significantly inhibited following intratumoral injection of adeno-associated virus (aav) expressing PCK1 shRNA. PCK1 depletion, Gαi3 downregulation, Akt inhibition, proliferation arrest, and apoptosis were detected in PCK1-silenced UVM xenografts. Collectively, our findings demonstrate that PCK1 promotes UVM cell growth possibly by modulating the Gαi3-Akt signaling pathway.

The requirement of the mitochondrial protein NDUFS8 for angiogenesis

Mitochondria are important for the activation of endothelial cells and the process of angiogenesis. NDUFS8 (NADH:ubiquinone oxidoreductase core subunit S8) is a protein that plays a critical role in the function of mitochondrial Complex I. We aimed to investigate the potential involvement of NDUFS8 in angiogenesis. In human umbilical vein endothelial cells (HUVECs) and other endothelial cell types, we employed viral shRNA to silence NDUFS8 or employed the CRISPR/Cas9 method to knockout (KO) it, resulting in impaired mitochondrial functions in the endothelial cells, causing reduction in mitochondrial oxygen consumption and Complex I activity, decreased ATP production, mitochondrial depolarization, increased oxidative stress and reactive oxygen species (ROS) production, and enhanced lipid oxidation. Significantly, NDUFS8 silencing or KO hindered cell proliferation, migration, and capillary tube formation in cultured endothelial cells. In addition, there was a moderate increase in apoptosis within NDUFS8-depleted endothelial cells. Conversely, ectopic overexpression of NDUFS8 demonstrated a pro-angiogenic impact, enhancing cell proliferation, migration, and capillary tube formation in HUVECs and other endothelial cells. NDUFS8 is pivotal for Akt-mTOR cascade activation in endothelial cells. Depleting NDUFS8 inhibited Akt-mTOR activation, reversible with exogenous ATP in HUVECs. Conversely, NDUFS8 overexpression boosted Akt-mTOR activation. Furthermore, the inhibitory effects of NDUFS8 knockdown on cell proliferation, migration, and capillary tube formation were rescued by Akt re-activation via a constitutively-active Akt1. In vivo experiments using an endothelial-specific NDUFS8 shRNA adeno-associated virus (AAV), administered via intravitreous injection, revealed that endothelial knockdown of NDUFS8 inhibited retinal angiogenesis. ATP reduction, oxidative stress, and enhanced lipid oxidation were detected in mouse retinal tissues with endothelial knockdown of NDUFS8. Lastly, we observed an increase in NDUFS8 expression in retinal proliferative membrane tissues obtained from human patients with proliferative diabetic retinopathy. Our findings underscore the essential role of the mitochondrial protein NDUFS8 in regulating endothelial cell activation and angiogenesis.

Insights from the neural guidance factor Netrin-1 into neurodegeneration and other diseases

Netrin-1 was initially discovered as a neuronal growth cue for axonal guidance, and its functions have later been identified in inflammation, tumorigenesis, neurodegeneration, and other disorders. We have recently found its alterations in the brains with Alzheimer's disease, which might provide important clues to the mechanisms of some unique pathologies. To provide better understanding of this promising molecule, we here summarize research progresses in genetics, pathology, biochemistry, cell biology and other studies of Netrin-1 about its mechanistic roles and biomarker potentials with an emphasis on clinical neurodegenerative disorders in order to expand understanding of this promising molecular player in human diseases.

G protein subunit alpha i2's pivotal role in angiogenesis

Here we explored the potential role of Gαi2 (G protein subunit alpha i2) in endothelial cell function and angiogenesis. Methods: Genetic methodologies such as shRNA, CRISPR/Cas9, dominant negative mutation, and overexpression were utilized to modify Gαi2 expression or regulate its function. Their effects on endothelial cell functions were assessed in vitro. In vivo, the endothelial-specific Gαi2 shRNA adeno-associated virus (AAV) was utilized to silence Gαi2 expression. The impact of this suppression on retinal angiogenesis in control mice and streptozotocin (STZ)-induced diabetic retinopathy (DR) mice was analyzed. Results: Analysis of single-cell RNA sequencing data revealed Gαi2 (GNAI2) was predominantly expressed in retinal endothelial cells and expression was increased in retinal endothelial cells following oxygen-induced retinopathy (OIR) in mice. Moreover, transcriptome analysis linking Gαi2 to angiogenesis-related processes/pathways, supported by increased Gαi2 expression in experimental OIR mouse retinas, highlighted its possible role in angiogenesis. In various endothelial cell types, shRNA-induced silencing and CRISPR/Cas9-mediated knockout (KO) of Gαi2 resulted in substantial reductions in cell proliferation, migration, invasion, and capillary tube formation. Conversely, Gαi2 over-expression in endothelial cells induced pro-angiogenic activities, enhancing cell proliferation, migration, invasion, and capillary tube formation. Furthermore, our investigation revealed a crucial role of Gαi2 in NFAT (nuclear factor of activated T cells) activation, as evidenced by the down-regulation of NFAT-luciferase reporter activity and pro-angiogenesis NFAT-targeted genes (Egr3, CXCR7, and RND1) in Gαi2-silenced or -KO HUVECs, which were up-regulated in Gαi2-overexpressing endothelial cells. Expression of a dominant negative Gαi2 mutation (S48C) also down-regulated NFAT-targeted genes, slowing proliferation, migration, invasion, and capillary tube formation in HUVECs. Importantly, in vivo experiments revealed that endothelial Gαi2 knockdown inhibited retinal angiogenesis in mice, with a concomitant down-regulation of NFAT-targeted genes in mouse retinal tissue. In contrast, Gαi2 over-expression in endothelial cells enhanced retinal angiogenesis in mice. Single-cell RNA sequencing data confirmed increased levels of Gαi2 specifically in retinal endothelial cells of mice with streptozotocin (STZ)-induced diabetic retinopathy (DR). Importantly, endothelial Gαi2 silencing ameliorated retinal pathological angiogenesis in DR mice. Conclusion: Our study highlights a critical role for Gαi2 in NFAT activation, endothelial cell activation and angiogenesis, offering valuable insights into potential therapeutic strategies for modulating these processes.

Non-canonical G protein signaling

The original paradigm of classical - also referred to as canonical - cellular signal transduction of heterotrimeric G proteins (G protein) is defined by a hierarchical, orthograde interaction of three players: the agonist-activated G protein-coupled receptor (GPCR), which activates the transducing G protein, that in turn regulates its intracellular effectors. This receptor-transducer-effector concept was extended by the identification of regulators and adapters such as the regulators of G protein signaling (RGS), receptor kinases like βARK, or GPCR-interacting arrestin adapters that are integrated into this canonical signaling process at different levels to enable fine-tuning. Finally, the identification of atypical signaling mechanisms of classical regulators, together with the discovery of novel modulators, added a new and fascinating dimension to the cellular G protein signal transduction. This heterogeneous group of accessory G protein modulators was coined "activators of G protein signaling" (AGS) proteins and plays distinct roles in canonical and non-canonical G protein signaling pathways. AGS proteins contribute to the control of essential cellular functions such as cell development and division, intracellular transport processes, secretion, autophagy or cell movements. As such, they are involved in numerous biological processes that are crucial for diseases, like diabetes mellitus, cancer, and stroke, which represent major health burdens. Although the identification of a large number of non-canonical G protein signaling pathways has broadened the spectrum of this cellular communication system, their underlying mechanisms, functions, and biological effects are poorly understood. In this review, we highlight and discuss atypical G protein-dependent signaling mechanisms with a focus on inhibitory G proteins (Gi) involved in canonical and non-canonical signal transduction, review recent developments and open questions, address the potential of new approaches for targeted pharmacological interventions.

Emerging role of extracellular vesicles in diabetic retinopathy

Diabetic retinopathy (DR), a complex complication of diabetes mellitus (DM), is a leading cause of adult blindness. Hyperglycemia triggers DR, resulting in microvascular damage, glial apoptosis, and neuronal degeneration. Inflammation and oxidative stress play crucial roles during this process. Current clinical treatments for DR primarily target the advanced retinal disorder but offer limited benefits with inevitable side effects. Extracellular vesicles (EVs) exhibit unique morphological features, contents, and biological properties and can be found in cell culture supernatants, various body fluids, and tissues. In DR, EVs with specific cargo composition would induce the reaction of receptor cell once internalized, mediating cellular communication and disease progression. Increasing evidence indicates that monitoring changes in EV quantity and content in DR can aid in disease diagnosis and prognosis. Furthermore, extensive research is investigating the potential of these nanoparticles as effective therapeutic agents in preclinical models of DR. This review explores the current understanding of the pathological effects of EVs in DR development, discusses their potential as biomarkers and therapeutic strategies, and paves the way for further research and therapeutic advancements.

Overexpressed Gαi1 exerts pro-tumorigenic activity in nasopharyngeal carcinoma

The current study tested the expression and potential functions of Gαi1 in nasopharyngeal carcinoma (NPC). The Cancer Genome Atlas (TCGA) database results demonstrate that Gαi1 transcripts' number in NPC tissues is significantly higher than that in the normal nasal epithelial tissues. Its overexpression correlates with poor survival in certain NPC patients. Moreover, Gαi1 is significantly upregulated in NPC tissues of local primary patients and in different primary human NPC cells. Whereas its expression is relatively low in cancer-surrounding normal tissues and in primary nasal epithelial cells. Genetic silencing (via shRNA strategy) or knockout (via CRISPR-sgRNA method) of Gαi1 substantially suppressed viability, proliferation, cell cycle progression, and migration in primary NPC cells, causing significant caspase-apoptosis activation. Contrarily, ectopic Gαi1 expression exerted pro-tumorigenic activity and strengthened cell proliferation and migration in primary NPC cells. Gαi1 is important for Akt-mTOR activation in NPC cells. Akt-S6K phosphorylation was downregulated after Gαi1 shRNA or KO in primary NPC cells, but strengthened following Gαi1 overexpression. In Gαi1-silenced primary NPC cells, a S473D constitutively-active mutant Akt1 (caAkt1) restored Akt-S6K phosphorylation and ameliorated Gαi1 shRNA-induced proliferation inhibition, migration reduction and apoptosis. Bioinformatics analyses proposed zinc finger protein 384 (ZNF384) as a potential transcription factor of Gαi1. In primary NPC cells, ZNF384 shRNA or knockout (via CRISPR-sgRNA method) decreased Gαi1 mRNA and protein expression, whereas ZNF384 overexpression upregulated it. Importantly, there was an increased binding between ZNF384 protein and the Gαi1 promoter in human NPC tissues and different NPC cells. In vivo studies showed that intratumoral injection of Gαi1-shRNA-expressing adeno-associated virus (AAV) impeded subcutaneous NPC xenograft growth in nude mice. Gαi1 downregulation, Akt-mTOR inactivation, and apoptosis induction were detected in Gαi1-silenced NPC xenograft tissues. Gαi1 KO also effectively inhibited the growth of NPC xenografts in nude mice. Together, overexpressed Gαi1 exerts pro-tumorigenic activity in NPC possibly by promoting Akt-mTOR activation.

Endothelial cell-derived RSPO3 activates Gαi1/3-Erk signaling and protects neurons from ischemia/reperfusion injury

The current study explores the potential function and the underlying mechanisms of endothelial cell-derived R-spondin 3 (RSPO3) neuroprotection against ischemia/reperfusion-induced neuronal cell injury. In both neuronal cells (Neuro-2a) and primary murine cortical neurons, pretreatment with RSPO3 ameliorated oxygen and glucose deprivation (OGD)/re-oxygenation (OGD/R)-induced neuronal cell death and oxidative injury. In neurons RSPO3 activated the Akt, Erk and β-Catenin signaling cascade, but only Erk inhibitors reversed RSPO3-induced neuroprotection against OGD/R. In mouse embryonic fibroblasts (MEFs) and neuronal cells, RSPO3-induced LGR4-Gab1-Gαi1/3 association was required for Erk activation, and either silencing or knockout of Gαi1 and Gαi3 abolished RSPO3-induced neuroprotection. In mice, middle cerebral artery occlusion (MCAO) increased RSPO3 expression and Erk activation in ischemic penumbra brain tissues. Endothelial knockdown or knockout of RSPO3 inhibited Erk activation in the ischemic penumbra brain tissues and increased MCAO-induced cerebral ischemic injury in mice. Conversely, endothelial overexpression of RSPO3 ameliorated MCAO-induced cerebral ischemic injury. We conclude that RSPO3 activates Gαi1/3-Erk signaling to protect neuronal cells from ischemia/reperfusion injury.