PKCbetaII/HuR/VEGF: A new molecular cascade in retinal pericytes for the regulation of VEGF gene expression

VEGF and ELAVL1/HuR protein levels are increased in dry and wet AMD patients. A new tile in the pathophysiologic mechanisms underlying RPE degeneration?

Age-related macular degeneration (AMD) is a common retinal pathology characterized by degeneration of macula's retinal pigment epithelium (RPE) and photoreceptors, visual impairment, or loss. Compared to wet AMD, dry AMD is more common, but lacks cures; therefore, identification of new potential therapeutic targets and treatments is urgent. Increased oxidative stress and declining antioxidant, detoxifying systems contribute to the pathophysiologic mechanisms underlying AMD. The present work shows that the Embryonic Lethal Abnormal Vision-Like 1/Human antigen R (ELAVL1/HuR) and the Vascular Endothelial Growth Factor (VEGF) protein levels are higher in the RPE of both dry and wet AMD patients compared to healthy subjects. Moreover, increased HuR protein levels are detected in the retina, and especially in the RPE layer, of a dry AMD model, the nuclear factor erythroid 2-related factor 2 (Nrf2) / peroxisome proliferator-activated receptor gamma coactivator-1α (PGC-1α) double knock-out mouse. The crosstalk among Nrf2, HuR and VEGF has been also studied in ARPE-19 cells in basal and stressful conditions related to the AMD context (i.e., oxidative stress, autophagy impairment, Nrf2 deficit), offering new evidence of the mutual influence between Nrf2 and HuR, of the dependence of VEGF expression and secretion by these two factors, and of the increased susceptibility of cells to stressful conditions in Nrf2- or HuR-impaired contexts. Overall, this study shows evidence of the interplay among Nrf2, HuR and VEGF, essential factors for RPE homeostasis, and represents an additional piece in the understanding of the complex pathophysiologic mechanisms underlying AMD.

Analysis of RNA Interference Targeted Against Human Antigen R (HuR) to Reduce Vascular Endothelial Growth Factor (VEGF) Protein Expression in Human Retinal Pigment Epithelial Cells

VEGF-A or vascular endothelial growth factor-A is an important factor in enabling neovascularization and angiogenesis. VEGF-A is regulated transcriptionally as well as post transcriptionally. Human antigen R (HuR) belonging to the embryonic lethal abnormal vision (ELAV) family is a key regulator promoting stabilization of VEGF-A mRNA. In this research we investigate, whether HuR targeted RNA interference would enable the reduction of the VEGF-A protein in human retinal pigment epithelial cells (ARPE-19) in-vitro, in normoxic conditions. Three siRNA molecules with sequences complementary to three regions of the HuR mRNA were designed. The three designed siRNA molecules were individually transfected in ARPE-19 cells using Lipofectamine™2000 reagent. Post-transfection (24 h, 48 h, 72 h), downregulation of HuR mRNA was estimated by real-time polymerase reaction, while HuR protein and VEGF-A protein levels were semi-quantitatively determined by western blotting techniques. VEGF-A protein levels were additionally quantified using ELISA techniques. All experiments were done in triplicate. The designed siRNA could successfully downregulate HuR mRNA with concomitant decreases in HuR and VEGF-A protein. The study reveals that HuR downregulation can prominently downregulate VEGF-A, making the protein a target for therapy against pathological angiogenesis conditions such as diabetic retinopathy.

Disclosing the Novel Protective Mechanisms of Ocrelizumab in Multiple Sclerosis: The Role of PKC Beta and Its Down-Stream Targets

Ocrelizumab (OCR) is a humanized anti-CD20 monoclonal antibody approved for both Relapsing and Primary Progressive forms of Multiple Sclerosis (MS) treatment. OCR is postulated to act via rapid B cell depletion; however, by analogy with other anti-CD20 agents, additional effects can be envisaged, such as on Protein Kinase C (PKC). Hence, this work aims to explore novel potential mechanisms of action of OCR in peripheral blood mononuclear cells from MS patients before and after 12 months of OCR treatment. We first assessed, up-stream, PKCβII and subsequently explored two down-stream pathways: hypoxia-inducible factor 1 alpha (HIF-1α)/vascular endothelial growth factor (VEGF), and human antigen R (HuR)/manganese-dependent superoxide dismutase (MnSOD) and heat shock proteins 70 (HSP70). At baseline, higher levels of PKCβII, HIF-1α, and VEGF were found in MS patients compared to healthy controls (HC); interestingly, the overexpression of this inflammatory cascade was counteracted by OCR treatment. Conversely, at baseline, the content of HuR, MnSOD, and HSP70 was significantly lower in MS patients compared to HC, while OCR administration induced the up-regulation of these neuroprotective pathways. These results enable us to disclose the dual positive action of OCR: anti-inflammatory and neuroprotective. Therefore, in addition to B cell depletion, the effect of OCR on these molecular cascades can contribute to counteracting disease progression.

Role of mRNA-binding proteins in retinal neovascularization

Retinal neovascularization (RNV) is a pathological process that primarily occurs in diabetic retinopathy, retinopathy of prematurity, and retinal vein occlusion. It is a common yet debilitating clinical condition that culminates in blindness. Urgent efforts are required to explore more efficient and less limiting therapeutic strategies. Key RNA-binding proteins (RBPs), crucial for post-transcriptional regulation of gene expression by binding to RNAs, are closely correlated with RNV development. RBP-RNA interactions are altered during RNV. Here, we briefly review the characteristics and functions of RBPs, and the mechanism of RNV. Then, we present insights into the role of the regulatory network of RBPs in RNV. HuR, eIF4E, LIN28B, SRSF1, METTL3, YTHDF1, Gal-1, HIWI1, and ZFR accelerate RNV progression, whereas YTHDF2 and hnRNPA2B1 hinder it. The mechanisms elucidated in this review provide a reference to guide the design of therapeutic strategies to reverse abnormal processes.

RNA-binding proteins potentially regulate the alternative splicing of cell cycle-associated genes in proliferative diabetic retinopathy

RNA-binding proteins (RBPs) contribute to the pathogenesis of proliferative diabetic retinopathy (PDR) by regulating gene expression through alternative splicing events (ASEs). However, the RBPs differentially expressed in PDR and the underlying mechanisms remain unclear. Thus, this study aimed to identify the differentially expressed genes in the neovascular membranes (NVM) and retinas of patients with PDR. The public transcriptome dataset GSE102485 was downloaded from the Gene Expression Omnibus database, and samples of PDR and normal retinas were analyzed. A mouse model of oxygen-induced retinopathy was used to confirm the results. The top 20 RBPs were screened for co-expression with alternative splicing genes (ASGs). A total of 403 RBPs were abnormally expressed in the NVM and retina samples. Functional analysis demonstrated that the ASGs were enriched in cell cycle pathways. Cell cycle-associated ASEs and an RBP-AS regulatory network, including 15 RBPs and their regulated ASGs, were extracted. Splicing factor proline/glutamine rich (SFPQ), microtubule-associated protein 1 B (MAP1B), heat-shock protein 90-alpha (HSP90AA1), microtubule-actin crosslinking factor 1 (MACF1), and CyclinH (CCNH) expression remarkably differed in the mouse model. This study provides novel insights into the RBP-AS interaction network in PDR and for developing screening and treatment options to prevent diabetic retinopathy-related blindness.

The Labyrinthine Landscape of APP Processing: State of the Art and Possible Novel Soluble APP-Related Molecular Players in Traumatic Brain Injury and Neurodegeneration

Amyloid Precursor Protein (APP) and its cleavage processes have been widely investigated in the past, in particular in the context of Alzheimer’s Disease (AD). Evidence of an increased expression of APP and its amyloidogenic-related cleavage enzymes, β-secretase 1 (BACE1) and γ-secretase, at the hit axon terminals following Traumatic Brain Injury (TBI), firstly suggested a correlation between TBI and AD. Indeed, mild and severe TBI have been recognised as influential risk factors for different neurodegenerative diseases, including AD. In the present work, we describe the state of the art of APP proteolytic processing, underlining the different roles of its cleavage fragments in both physiological and pathological contexts. Considering the neuroprotective role of the soluble APP alpha (sAPPα) fragment, we hypothesised that sAPPα could modulate the expression of genes of interest for AD and TBI. Hence, we present preliminary experiments addressing sAPPα-mediated regulation of BACE1, Isthmin 2 (ISM2), Tetraspanin-3 (TSPAN3) and the Vascular Endothelial Growth Factor (VEGFA), each discussed from a biological and pharmacological point of view in AD and TBI. We finally propose a neuroprotective interaction network, in which the Receptor for Activated C Kinase 1 (RACK1) and the signalling cascade of PKCβII/nELAV/VEGF play hub roles, suggesting that vasculogenic-targeting therapies could be a feasible approach for vascular-related brain injuries typical of AD and TBI.

Evidence for novel cell defense mechanisms sustained by dimethyl fumarate in multiple sclerosis patients: the HuR/SOD2 cascade

BACKGROUND

Dimethyl fumarate (DMF) is an effective treatment for relapsing remitting Multiple Sclerosis (MS) and its mechanisms of action encompass immunomodulatory and cytoprotective effects. Despite DMF is known to activate the Nrf2 pathway, Nrf2-independent mechanisms have been also reported and new insights on the underlying molecular mechanisms are still emerging including transcriptional and post-transcriptional events. At this regard, we focused on a small family of RNA-binding proteins, the ELAV-like proteins, that play a pivotal role in post-transcriptional mechanisms and are involved in the pathogenesis of several psychiatric and neurologic disorders. HuR, the ubiquitously expressed member of the family, is implicated in many cellular functions, including survival, inflammation and proper functioning of the immune system. We previously documented the potential entanglement of HuR in MS pathogenesis. In the present work, we explored HuR protein levels in peripheral blood mononuclear cells (PBMCs) from MS patients before and after DMF treatment compared to healthy controls (HC). Considering that HuR may act on various targets, playing a protective role against oxidative stress, our main goals were to evaluate whether manganese-dependent superoxide dismutase transcript (SOD2) could represent a new molecular target of HuR and to study the potential influence of DMF treatment on this interaction.

METHODS

PBMCs from 20 patients with MS and 20 frequency-matched HC by sex and age were used to evaluate HuR, MnSOD (the protein coded by SOD2) and Nrf2 protein content by Western blot, before and after 12 months of DMF treatment. Immunoprecipitation experiments coupled with RNA extraction in PBMCs were performed to explore whether SOD2 mRNA could be physically bound by HuR and whether the expression of MnSOD protein could be affected by 12 months of DMF treatment.

RESULTS

In PBMCs, HuR protein binds SOD2 transcript in HC and in MS patients naïve to disease modifying treatment. The expression of MnSOD protein is positively affected by 12 months of DMF treatment. PBMCs from MS patients have a lower HuR and MnSOD protein content compared to matched HC (HuR: p<0.01, MnSOD: p<0.01). Of interest, 12 months of DMF treatment in MS patients restores the amount of both HuR protein and MnSOD enzyme to the levels observed in HC. We also confirmed that Nrf2 is an HuR target, and we report that its levels are significantly increased in MS patients naïve to disease modifying treatment and remain elevated following DMF administration.

CONCLUSION

SOD2 transcript is a new target of HuR protein. DMF induces an increased expression of HuR protein, which ultimately interacts more strongly with SOD2 transcript promoting the expression of this antioxidant protein. The activation of this molecular cascade can constitute an additional tool that the cells can exploit to counteract the oxidative stress associated with MS development, and can account for the multifaceted molecular mechanisms underlying DMF efficacy in MS.

RNA-binding proteins and translation control in angiogenesis

Tissue vascularization through the process of angiogenesis ensures adequate oxygen and nutrient supply during development and regeneration. The complex morphogenetic events involved in new blood vessel formation are orchestrated by a tightly regulated crosstalk between extra and intracellular factors. In this context, RNA-binding protein (RBP) activity and protein translation play fundamental roles during the cellular responses triggered by particular environmental cues. A solid body of work has demonstrated that key RBPs (such as HuR, TIS11 proteins, hnRNPs, NF90, QKIs and YB1) are implicated in both physiological and pathological angiogenesis. These RBPs are critical for the metabolism of messenger (m)RNAs encoding angiogenic modulators and, importantly, strong evidence suggests that RBP-mRNA interactions can be altered in disease. Lesser known, but not less important, the mechanistic aspects of protein synthesis can also regulate the generation of new vessels. In this review, we outline the key findings demonstrating the implications of RBP-mediated RNA regulation and translation control in angiogenesis. Furthermore, we highlight how these mechanisms of post-transcriptional control of gene expression have led to promising therapeutic strategies aimed at targeting undesired blood vessel formation.

Effect of troxerutin in counteracting hyperglycemia-induced VEGF upregulation in endothelial cells: a new option to target early stages of diabetic retinopathy?

Diabetic retinopathy (DR), one of the most common complications of diabetes mellitus, is characterized by degeneration of retinal neurons and neoangiogenesis. Until today, the pharmacological approaches for DR are limited and focused on counteracting the end-stage of this neurodegenerative disease, therefore efforts should be carried out to discover novel pharmacological targets useful to prevent DR development. Hyperglycemia is a major risk factor for endothelial dysfunction and vascular complication, which subsequently may trigger neurodegeneration. We previously demonstrated that, in the rat retina, hyperglycemia activates a new molecular cascade implicating, up-stream, protein kinase C βII (PKC βII), which in turn leads to a higher expression of vascular endothelial growth factor (VEGF), via the mRNA-binding Hu-antigen R (HuR) protein. VEGF is a pivotal mediator of neovascularization and a well-known vasopermeability factor. Blocking the increase of VEGF via modulation of this cascade can thus represent a new pharmacological option to prevent DR progression. To this aim, proper in vitro models are crucial for drug discovery, as they allow to better identify promising effective molecules. Considering that endothelial cells are key elements in DR and that hyperglycemia triggers the PKCβII/HuR/VEGF pathway, we set up two distinct in vitro models applying two different stimuli. Namely, human umbilical vein endothelial cells were exposed to phorbol 12-myristate 13-acetate, which mimics diacylglycerol whose synthesis is triggered by diabetic hyperglycemia, while human retinal endothelial cells were treated with high glucose for different times. After selecting the optimal experimental conditions able to determine an increased VEGF production, in search of molecules useful to prevent DR development, we investigated the capability of troxerutin, an antioxidant flavonoid, to counteract not only the rise of VEGF but also the activation of the PKCβII/HuR cascade in both in vitro models. The results show the capability of troxerutin to hinder the hyperglycemia-induced increase in VEGF in both models through PKCβII/HuR pathway modulation. Further, these data confirm the key engagement of this cascade as an early event triggered by hyperglycemia to promote VEGF expression. Finally, the present findings also suggest the potential use of troxerutin as a preventive treatment during the early phases of DR.

RNA-Binding Proteins: Emerging Therapeutics for Vascular Dysfunction

Vascular diseases account for a significant number of deaths worldwide, with cardiovascular diseases remaining the leading cause of mortality. This ongoing, ever-increasing burden has made the need for an effective treatment strategy a global priority. Recent advances in regenerative medicine, largely the derivation and use of induced pluripotent stem cell (iPSC) technologies as disease models, have provided powerful tools to study the different cell types that comprise the vascular system, allowing for a greater understanding of the molecular mechanisms behind vascular health. iPSC disease models consequently offer an exciting strategy to deepen our understanding of disease as well as develop new therapeutic avenues with clinical translation. Both transcriptional and post-transcriptional mechanisms are widely accepted to have fundamental roles in orchestrating responses to vascular damage. Recently, iPSC technologies have increased our understanding of RNA-binding proteins (RBPs) in controlling gene expression and cellular functions, providing an insight into the onset and progression of vascular dysfunction. Revelations of such roles within vascular disease states have therefore allowed for a greater clarification of disease mechanisms, aiding the development of novel therapeutic interventions. Here, we discuss newly discovered roles of RBPs within the cardio-vasculature aided by iPSC technologies, as well as examine their therapeutic potential, with a particular focus on the Quaking family of isoforms.

RNA-binding proteins in diabetic microangiopathy

BACKGROUND

As the most common complication of diabetes, the diabetic microangiopathy characterizes diabetic retinopathy (DR) and nephropathy (DN). Diabetic microangiopathy has always been a serious clinical problem. A wide variety of nucleic acid interacting factors called the RNA binding proteins (RBPS) take part in several crucial cellular processes.

METHODS

Over the past decade, studies have shown that RBPs have crucial part in both malignant tumors and diabetes, especially in diabetic microangiopathy. This review examined the research history of RBPS in DR and DN.

RESULTS

We reviewed the literature and found that RBPS is potentially useful as therapeutic targets, diagnostic markers, or predict disease progression.

CONCLUSION

HuR acts as a vital therapeutic targeting protein in diabetic microangiopathy. IGF2BP2, P311, TTP, YBX1, and MBNL1 have a potential role in the treatment of DN.

Altitude, Exercise, and Skeletal Muscle Angio-Adaptive Responses to Hypoxia: A Complex Story

Hypoxia, defined as a reduced oxygen availability, can be observed in many tissues in response to various physiological and pathological conditions. As a hallmark of the altitude environment, ambient hypoxia results from a drop in the oxygen pressure in the atmosphere with elevation. A hypoxic stress can also occur at the cellular level when the oxygen supply through the local microcirculation cannot match the cells’ metabolic needs. This has been suggested in contracting skeletal myofibers during physical exercise. Regardless of its origin, ambient or exercise-induced, muscle hypoxia triggers complex angio-adaptive responses in the skeletal muscle tissue. These can result in the expression of a plethora of angio-adaptive molecules, ultimately leading to the growth, stabilization, or regression of muscle capillaries. This remarkable plasticity of the capillary network is referred to as angio-adaptation. It can alter the capillary-to-myofiber interface, which represent an important determinant of skeletal muscle function. These angio-adaptive molecules can also be released in the circulation as myokines to act on distant tissues. This review addresses the respective and combined potency of ambient hypoxia and exercise to generate a cellular hypoxic stress in skeletal muscle. The major skeletal muscle angio-adaptive responses to hypoxia so far described in this context will be discussed, including existing controversies in the field. Finally, this review will highlight the molecular complexity of the skeletal muscle angio-adaptive response to hypoxia and identify current gaps of knowledges in this field of exercise and environmental physiology.

Short-and Long-Term Expression of Vegf: A Temporal Regulation of a Key Factor in Diabetic Retinopathy

To investigate the role of vascular endothelial growth factor (VEGF) at different phases of diabetic retinopathy (DR), we assessed the retinal protein expression of VEGF-A₁₆₄ (corresponding to the VEGF₁₆₅ isoform present in humans, which is the predominant member implicated in vascular hyperpermeability and proliferation), HIF-1α and PKCβ/HuR pathway in Ins2^Akita (diabetic) mice at different ages. We used C57BL6J mice (WT) at different ages as control. Retina status, in terms of tissue morphology and neovascularization, was monitored in vivo at different time points by optical coherence tomography (OCT) and fluorescein angiography (FA), respectively. The results showed that VEGF-A₁₆₄ protein expression increased along time to become significantly elevated (p < 0.05) at 9 and 46 weeks of age compared to WT mice. The HIF-1α protein level was significantly (p < 0.05) increased at 9 weeks of age, while PKCβII and HuR protein levels were increased at 46 weeks of age compared to WT mice. The thickness of retinal nerve fiber layer as measured by OCT was decreased in Ins2^Akita mice at 9 and 46 weeks of age, while no difference in the retinal vasculature were observed by FA. The present findings show that the retina of the diabetic Ins2^Akita mice, as expected for mice, does not develop proliferative retinopathy even after 46 weeks. However, diabetic Ins2^Akita mice recapitulate the same evolution of patients with DR in terms of both retinal neurodegeneration and pro-angiogenic shift, this latter indicated by the progressive protein expression of the pro-angiogenic isoform VEGF-A_164, which can be sustained by the PKCβII/HuR pathway acting at post-transcriptional level. In agreement with this last concept, this rise in VEGF-A₁₆₄ protein is not paralleled by an increment of the corresponding transcript. Nevertheless, the observed increase in HIF-1α at 9 weeks indicates that this transcription factor may favor, in the early phase of the disease, the transcription of other isoforms, possibly neuroprotective, in the attempt to counteract the neurodegenerative effects of VEGF-A_164. The time-dependent VEGF-A₁₆₄ expression in the retina of diabetic Ins2^Akita mice suggests that pharmacological intervention in DR might be chosen, among other reasons, on the basis of the specific stages of the pathology in order to pursue the best clinical outcome.

Use of dual-flow bioreactor to develop a simplified model of nervous-cardiovascular systems crosstalk: A preliminary assessment

Chronic conditions requiring long-term rehabilitation therapies, such as hypertension, stroke, or cancer, involve complex interactions between various systems/organs of the body and mutual influences, thus implicating a multiorgan approach. The dual-flow IVTech LiveBox2 bioreactor is a recently developed inter-connected dynamic cell culture model able to mimic organ crosstalk, since cells belonging to different organs can be connected and grown under flow conditions in a more physiological environment. This study aims to setup for the first time a 2-way connected culture of human neuroblastoma cells, SH-SY5Y, and Human Coronary Artery Smooth Muscle Cells, HCASMC through a dual-flow IVTech LiveBox2 bioreactor, in order to represent a simplified model of nervous-cardiovascular systems crosstalk, possibly relevant for the above-mentioned diseases. The system was tested by treating the cells with 10nM angiotensin II (AngII) inducing PKCβII/HuR/VEGF pathway activation, since AngII and PKCβII/HuR/VEGF pathway are relevant in cardiovascular and neuroscience research. Three different conditions were applied: 1- HCASMC and SH-SY5Y separately seeded in petri dishes (static condition); 2- the two cell lines separately seeded under flow (dynamic condition); 3- the two lines, seeded in dynamic conditions, connected, each maintaining its own medium, with a membrane as interface for biohumoral changes between the two mediums, and then treated. We detected that only in condition 3 there was a synergic AngII-dependent VEGF production in SH-SY5Y cells coupled to an AngII-dependent PKCβII/HuR/VEGF pathway activation in HCASMC, consistent with the observed physiological response in vivo. HCASMC response to AngII seems therefore to be generated by/derived from the reciprocal cell crosstalk under the dynamic inter-connection ensured by the dual flow LiveBox 2 bioreactor. This system can represent a useful tool for studying the crosstalk between organs, helpful for instance in rehabilitation research or when investigating chronic diseases; further, it offers the advantageous opportunity of cultivating each cell line in its own medium, thus mimicking, at least in part, distinct tissue milieu.

Dimethyl-2-oxoglutarate improves redox balance and mitochondrial function in muscle pericytes of individuals with diabetes mellitus

AIMS/HYPOTHESIS

Treatment of vascular complications of diabetes remains inadequate. We reported that muscle pericytes (MPs) from limb muscles of vascular patients with diabetes mellitus display elevated levels of oxidative stress causing a dysfunctional phenotype. Here, we investigated whether treatment with dimethyl-2-oxoglutarate (DM-2OG), a tricarboxylic acid cycle metabolite with antioxidant properties, can restore a healthy metabolic and functional phenotype.

METHODS

MPs were isolated from limb muscles of diabetes patients with vascular disease (D-MPs) and from non-diabetic control participants (ND-MPs). Metabolic status was assessed in untreated and DM-2OG-treated (1 mmol/l) cells using an extracellular flux analyser and anion-exchange chromatography-mass spectrometry (IC-MS/MS). Redox status was measured using commercial kits and IC-MS/MS, with antioxidant and metabolic enzyme expression assessed by quantitative RT-PCR and western blotting. Myogenic differentiation and proliferation and pericyte-endothelial interaction were assessed as functional readouts.

RESULTS

D-MPs showed mitochondrial dysfunction, suppressed glycolytic activity and reduced reactive oxygen species-buffering capacity, but no suppression of antioxidant systems when compared with ND-MP controls. DM-2OG supplementation improved redox balance and mitochondrial function, without affecting glycolysis or antioxidant systems. Nonetheless, this was not enough for treated D-MPs to regain the level of proliferation and myogenic differentiation of ND-MPs. Interestingly, DM-2OG exerted a positive effect on pericyte-endothelial cell interaction in the co-culture angiogenesis assay, independent of the diabetic status.

CONCLUSIONS/INTERPRETATION

These novel findings support the concept of using DM-2OG supplementation to improve pericyte redox balance and mitochondrial function, while concurrently allowing for enhanced pericyte-endothelial crosstalk. Such effects may help to prevent or slow down vasculopathy in skeletal muscles of people with diabetes. Graphical abstract.

Emerging roles for RNA-binding proteins as effectors and regulators of cardiovascular disease

The cardiovascular system comprises multiple cell types that possess the capacity to modulate their phenotype in response to acute or chronic injury. Transcriptional and post-transcriptional mechanisms play a key role in the regulation of remodelling and regenerative responses to damaged cardiovascular tissues. Simultaneously, insufficient regulation of cellular phenotype is tightly coupled with the persistence and exacerbation of cardiovascular disease. Recently, RNA-binding proteins such as Quaking, HuR, Muscleblind, and SRSF1 have emerged as pivotal regulators of these functional adaptations in the cardiovascular system by guiding a wide-ranging number of post-transcriptional events that dramatically impact RNA fate, including alternative splicing, stability, localization and translation. Moreover, homozygous disruption of RNA-binding protein genes is commonly associated with cardiac- and/or vascular complications. Here, we summarize the current knowledge on the versatile role of RNA-binding proteins in regulating the transcriptome during phenotype switching in cardiovascular health and disease. We also detail existing and potential DNA- and RNA-based therapeutic approaches that could impact the treatment of cardiovascular disease in the future.

Autophagy Stimulus Promotes Early HuR Protein Activation and p62/SQSTM1 Protein Synthesis in ARPE-19 Cells by Triggering Erk1/2, p38MAPK, and JNK Kinase Pathways

RNA-binding protein dysregulation and altered expression of proteins involved in the autophagy/proteasome pathway play a role in many neurodegenerative disease onset/progression, including age-related macular degeneration (AMD). HuR/ELAVL1 is a master regulator of gene expression in human physiopathology. In ARPE-19 cells exposed to the proteasomal inhibitor MG132, HuR positively affects at posttranscriptional level p62 expression, a stress response gene involved in protein aggregate clearance with a role in AMD. Here, we studied the early effects of the proautophagy AICAR + MG132 cotreatment on the HuR-p62 pathway. We treated ARPE-19 cells with Erk1/2, AMPK, p38^MAPK, PKC, and JNK kinase inhibitors in the presence of AICAR + MG132 and evaluated HuR localization/phosphorylation and p62 expression. Two-hour AICAR + MG132 induces both HuR cytoplasmic translocation and threonine phosphorylation via the Erk1/2 pathway. In these conditions, p62 mRNA is loaded on polysomes and its translation in de novo protein is favored. Additionally, for the first time, we report that JNK can phosphorylate HuR, however, without modulating its localization. Our study supports HuR's role as an upstream regulator of p62 expression in ARPE-19 cells, helps to understand better the early events in response to a proautophagy stimulus, and suggests that modulation of the autophagy-regulating kinases as potential therapeutic targets for AMD may be relevant.

Nanosystems based on siRNA silencing HuR expression counteract diabetic retinopathy in rat

We evaluated whether specifically and directly targeting human antigen R (HuR), a member of embryonic lethal abnormal vision (ELAV) proteins family, may represent a new potential therapeutic strategy to manage diabetic retinopathy. Nanosystems loaded with siRNA silencing HuR expression (lipoplexes), consisting of solid lipid nanoparticles (SLN) and liposomes (SUV) were prepared. Photon correlation spectroscopy analysis, Zeta potential measurement and atomic force microscopy (AFM) studies were carried out to characterize the complexation of siRNA with the lipid nanocarriers. Nanosystems were evaluated by using AFM and scanning electron microscopy. The lipoplexes were injected into the eye of streptozotocin (STZ)-induced diabetic rats. Retinal HuR and VEGF levels were detected by Western blot and ELISA, respectively. Retinal histology was also carried out. The results demonstrated that retinal HuR and VEGF are significantly increased in STZ-rats and are blunted by HuR siRNA treatment. Lipoplexes with a weak positive surface charge and with a 4:1 N/P (cationic lipid nitrogen to siRNA phosphate) ratio exert a better transfection efficiency, significantly dumping retinal HuR and VEGF levels. In conclusion, we demonstrated that siRNA can be efficiently delivered into the rat retina using lipid-based nanocarriers, and some of the lipoplexes loaded with siRNA silencing HuR expression are potential candidates to manage retinal diseases.

Molecular Markers of Diabetic Retinopathy: Potential Screening Tool of the Future?

Diabetic retinopathy (DR) is among the leading causes of new onset blindness in adults. Effective treatment may delay the onset and progression of this disease provided it is diagnosed early. At present retinopathy can only be diagnosed via formal examination of the eye by a trained specialist, which limits the population that can be effectively screened. An easily accessible, reliable screening biomarker of diabetic retinopathy would be of tremendous benefit in detecting the population in need of further assessment and treatment. This review highlights specific biomarkers that show promise as screening markers to detect early diabetic retinopathy or even to detect patients at increased risk of DR at the time of diagnosis of diabetes. The pathobiology of DR is complex and multifactorial giving rise to a wide array of potential biomarkers. This review provides an overview of these pathways and looks at older markers such as advanced glycation end products (AGEs), inflammatory markers, vascular endothelial growth factor (VEGF) as well as other newer proteins with a role in the pathogenesis of DR including neuroprotective factors such as brain derived neurotrophic factor (BDNF) and Pigment Epithelium Derived Factor (PEDF); SA100A12, pentraxin 3, brain natriuretic peptide, apelin 3, and chemerin as well as various metabolites such as lipoprotein A, folate, and homocysteine. We also consider the possible role of proteins identified through proteomics work whose levels are altered in the sera of patients with DR as screening markers though their role in pathophysiology remains to be characterized. The role of microRNA as a promising new screening marker is also discussed.

Protein Kinase C Activation as a Potential Therapeutic Strategy in Alzheimer's Disease: Is there a Role for Embryonic Lethal Abnormal Vision-like Proteins?

Alzheimer's disease (AD), the most common cause of dementia, is an irreversible and progressive neurodegenerative disorder. It affects predominantly brain areas that are critical for memory and learning and is characterized by two main pathological hallmarks: extracellular amyloid plaques and intracellular neurofibrillary tangles. Protein kinase C (PKC) has been classified as one of the cognitive kinases controlling memory and learning. By regulating several signalling pathways involved in amyloid and tau pathologies, it also plays an inhibitory role in AD pathophysiology. Among downstream targets of PKC are the embryonic lethal abnormal vision (ELAV)-like RNA-binding proteins that modulate the stability and the translation of specific target mRNAs involved in synaptic remodelling linked to cognitive processes. This MiniReview summarizes the current evidence on the role of PKC and ELAV-like proteins in learning and memory, highlighting how their derangement can contribute to AD pathophysiology. This last aspect emphasizes the potential of pharmacological activation of PKC as a promising therapeutic strategy for the treatment of AD.

Feedback Regulation of Kinase Signaling Pathways by AREs and GREs

In response to environmental signals, kinases phosphorylate numerous proteins, including RNA-binding proteins such as the AU-rich element (ARE) binding proteins, and the GU-rich element (GRE) binding proteins. Posttranslational modifications of these proteins lead to a significant changes in the abundance of target mRNAs, and affect gene expression during cellular activation, proliferation, and stress responses. In this review, we summarize the effect of phosphorylation on the function of ARE-binding proteins ZFP36 and ELAVL1 and the GRE-binding protein CELF1. The networks of target mRNAs that these proteins bind and regulate include transcripts encoding kinases and kinase signaling pathways (KSP) components. Thus, kinase signaling pathways are involved in feedback regulation, whereby kinases regulate RNA-binding proteins that subsequently regulate mRNA stability of ARE- or GRE-containing transcripts that encode components of KSP.

Induction of VEGFA mRNA translation by CoCl2 mediated by HuR

Vascular endothelial growth factor (VEGF) A is a master regulator of neovascularization and angiogenesis. VEGFA is potently induced by hypoxia and by pathological conditions including diabetic retinopathy and tumorigenesis. Fine-tuning of VEGFA expression by different stimuli is important for maintaining tissue vascularization and organ homeostasis. Here, we tested the effect of the hypoxia mimetic cobalt chloride (CoCl2) on VEGFA expression in human cervical carcinoma HeLa cells. We found that CoCl2 increased the levels of VEGFA mRNA and VEGFA protein without affecting VEGFA mRNA stability. Biotin pulldown analysis to capture the RNA-binding proteins (RBPs) bound to VEGFA mRNA followed by mass spectrometry analysis revealed that the RBP HuR [human antigen R, a member of the embryonic lethal abnormal vision (ELAV) family of proteins], interacts with VEGFA mRNA. VEGFA mRNA-tagging experiments showed that exposure to CoCl2 increases the interaction of HuR with VEGFA mRNA and promoted the colocalization of HuR and the distal part of the VEGFA 3'-untranslated region (UTR) in the cytoplasm. We propose that under hypoxia-like conditions, HuR enhances VEGFA mRNA translation.

Diabetic macular edema: new concepts in patho-physiology and treatment

Diabetic macular edema (DME), a serious eye complication caused primarily by hyperglycemia, is one of the major causes of blindness. DME, which is characterized by cystic retinal thickening or lipid deposition, is prone to relapse after successful treatment. DME is a complex pathological process caused by multiple factors, including breakdown of the inner and outer blood-retinal barriers, oxidative stress, and elevated levels of vascular endothelial growth factor which have been demonstrated in both preclinical and clinical studies. Starling's law theory explains many of the features of DME. Early detection and treatment of DME can prevent vision loss. Current effective interventions for DME include treatment of systemic risk factors, such as elevated blood glucose, blood pressure and dyslipidemia. Ophthalmic treatments include laser photocoagulation, surgery and intraocular pharmacotherapy. New drugs, which are given by intraocular injection, have emerged in recent years to become first line treatment for DME that affects the central macula with loss of vision. Laser photocoagulation is still the gold standard of treatment for DME which does not involve the central macular. This review outlines these new treatments with particular emphasis on the optimal timing of how they are given.

Novel pharmacological approaches to the treatment of type 2 diabetes

The huge increase in type 2 diabetes is a burden worldwide. Many marketed compounds do not address relevant aspects of the disease; they may already compensate for defects in insulin secretion and insulin action, but loss of secreting cells (β-cell destruction), hyperglucagonemia, gastric emptying, enzyme activation/inhibition in insulin-sensitive cells, substitution or antagonizing of physiological hormones and pathways, finally leading to secondary complications of diabetes, are not sufficiently addressed. In addition, side effects for established therapies such as hypoglycemias and weight gain have to be diminished. At present, nearly 1000 compounds have been described, and approximately 180 of these are going to be developed (already in clinical studies), some of them directly influencing enzyme activity, influencing pathophysiological pathways, and some using G-protein-coupled receptors. In addition, immunological approaches and antisense strategies are going to be developed. Many compounds are derived from physiological compounds (hormones) aiming at improving their kinetics and selectivity, and others are chemical compounds that were obtained by screening for a newly identified target in the physiological or pathophysiological machinery. In some areas, great progress is observed (e.g., incretin area); in others, no great progress is obvious (e.g., glucokinase activators), and other areas are not recommended for further research. For all scientific areas, conclusions with respect to their impact on diabetes are given. Potential targets for which no chemical compound has yet been identified as a ligand (agonist or antagonist) are also described.

ELAV-GAP43 pathway activation following combined exposure to cocaine and stress

RATIONALE

An increasing body of evidence suggests that drug addiction engages circuits also associated with memory processes. In particular, in the hippocampus, a substantial similarity seems to exist between the changes yielded by drugs of abuse and those induced by hippocampal-dependent learning.

OBJECTIVES

Considering the key involvement of neuronal Embryonic Lethal Abnormal Vision (nELAV) proteins in memory processes occurring within the hippocampus and the critical role of stress for compulsive drug use and relapse, we investigated the effect of cocaine and stress challenges on the activation of the nELAV cascade.

MATERIALS AND METHODS

Rats were treated subcutaneously with vehicle or cocaine hydrochloride (20 mg/kg, once a day for 2 weeks). Three days later, half of them were also subjected to a single stress exposure. Western blotting and real-time polymerase chain reaction (PCR) experiments were performed on the hippocampi.

RESULTS

Our results show that the combination of repeated exposure to cocaine and acute stress significantly enhances nELAV expression and phosphorylation in the hippocampus with a concomitant increase of GAP43 expression (a specific nELAV target), an effect that seems to involve, upstream, protein kinase C alpha (PKCα). The activation of this pathway occurs independently from widespread neuronal activation since no alterations were observed in the expression of the immediate early gene Arc (a widely established index of neuronal activity), suggesting that the activation of the nELAV-GAP43 cascade reflects a targeting of specific processes rather than a global interference with hippocampal homeostasis.

CONCLUSIONS

Based on our results, we speculate that cocaine and stress may recruit such a pathway, crucial for physiological learning, potentially contributing to the aberrant engagement of learning mechanisms observed in drug addiction behavior.

Stanniocalcin-1 promotes tumor angiogenesis through up-regulation of VEGF in gastric cancer cells

BACKGROUND

Stanniocalcin-1(STC-1) is up-regulated in several cancers including gastric cancer. Evidences suggest that STC-1 is associated with carcinogenesis and angiogenic process. However, it is unclear on the exact role for STC-1 in inducing angiogenesis and tumorigeneisis.

METHOD

BGC/STC cells (high-expression of STC-1) and BGC/shSTC cells (low- expression of STC-1) were constructed to investigate the effect of STC-1 on the xenograft tumor growth and angiogenesis in vitro and in vivo. ELISA assay was used to detect the expression of vascular endothelial growth factor (VEGF) in the supernatants. Neutralizing antibody was used to inhibit VEGF expression in supernatants. The expression of phosphorylated -PKCβII, phosphorylated -ERK1/2 and phosphorylated -P38 in the BGC treated with STC-1protein was detected by western blot.

RESULTS

STC-1 could promote angiogenesis in vitro and in vivo, and the angiogenesis was consistent with VEGF expression in vitro. Inhibition of VEGF expression in supernatants with neutralizing antibody markedly abolished angiogenesis induced by STC-1 in vitro. The process of STC-1-regulated VEGF expression was mediated via PKCβII and ERK1/2.

CONCLUSIONS

STC-1 promotes the expression of VEGF depended on the activation of PKCβII and ERK1/2 pathways. VEGF subsequently enhances tumor angiogenesis which in turn promotes the gastric tumor growth.

The PKCbeta/HuR/VEGF pathway in diabetic retinopathy

We investigated whether the diabetes-related PKCbeta activation affects VEGF expression through the mRNA-stabilizing human embryonic lethal abnormal vision (ELAV) protein, HuR, in the retina of streptozotocin (STZ)-induced diabetic rats. Diabetes was induced in rats by STZ injection. Retinal tissues were processed to detect PKCbetaI, PKCbetaII, VEGF and HuR contents, as well as HuR phosphorylation. Immunoprecipitation coupled to RT-PCR was employed to evaluate HuR binding to VEGF mRNA in RiboNucleoProteic (RNP) complexes. Statistical analysis was performed by ANOVA followed by an appropriate post hoc comparison test. Following experimental diabetes PKCbetaI and PKCbetaII levels were increased compared to sham; there was also a PKC-mediated phosphorylation/activation of HuR. These effects were blunted by the in vivo co-administration of a selective PKCbeta inhibitor. A specific binding between the HuR protein and the VEGF mRNA was also detected. The PKCbeta/HuR activation was accompanied by enhanced VEGF protein expression that was, again, blunted by the PKCbeta inhibitor. These findings first demonstrate the activation, in the retina, of the PKCbeta/HuR/VEGF pathway following experimental diabetes and disclose a new potential pharmacological target to counteract pathologies implicating VEGF deregulation, such as diabetic retinopathy.

Involvement of Ca2+-dependent PKCs in the adaptive changes of mu-opioid pathways to sympathetic denervation in the guinea pig colon

In the guinea pig colon, chronic sympathetic denervation entails supersensitivity to inhibitory mu-opioid agents modulating cholinergic neurons. The mechanism underlying such adaptive change has not yet been unravelled, although protein kinase C (PKC) may be involved. A previous study indirectly demonstrated that activation of mu-opioid receptors on myenteric neurons facilitates PKC activity. Such coupling may counteract the inhibitory action of mu-opioid agents on acetylcholine overflow, since PKC, per se, increases this parameter. After chronic sympathetic denervation such restraint abates, representing a possible mechanism for development of supersensitivity to mu-opioid agents. In the present study, this hypothesis was further investigated. After chronic sympathetic denervation, Ca(2+)-dependent PKC activity was reduced in colonic myenteric plexus synaptosomes. The mu-opioid agent, DAMGO, increased Ca(2+)-dependent PKC activity in synaptosomes obtained from normal, but not from denervated animals. In myenteric synaptosomes obtained from this experimental group, protein levels of Ca(2+)-dependent PKC isoforms betaI, betaII and gamma decreased, whereas alpha levels increased. In whole-mount preparations, the four Ca(2+)-dependent PKC isoforms co-localized with mu-opioid receptors on subpopulations of colonic myenteric neurons. The percentage of neurons staining for PKCbetaII, as well as the number of mu-opioid receptor-positive neurons staining for PKCbetaII, decreased in denervated preparations. The same parameters related to PKCalpha, betaI or gamma remained unchanged. Overall, the present data strengthen the concept that mu-opioid receptors located on myenteric neurons are coupled to Ca(2+)-dependent PKCs. After chronic sympathetic denervation, a reduced efficiency of this coupling may predominantly involve PKCbetaII, although also PKCbetaI and gamma, but not PKCalpha, may be implicated.

Oxidative stress and diabetic retinopathy: pathophysiological mechanisms and treatment perspectives

Retinopathy is one of the most severe ocular complications of diabetes and is a leading cause of acquired blindness in young adults. The cellular components of the retina are highly coordinated but very susceptible to the hyperglycemic environment. The microvasculature of the retina responds to hyperglycemic milieu through a number of biochemical changes, including increased oxidative stress and polyol pathway, PKC activation and advanced glycation end product formation. Oxidative stress is considered as one of the crucial contributors in the pathogenesis of diabetic retinopathy, but oxidative stress appears to be highly interrelated with other biochemical imbalances that lead to structural and functional changes and accelerated loss of capillary cells in the retinal microvasculature and, ultimately, pathological evidence of the disease. One such potential connection that links oxidative stress to metabolic alterations is gyceraldehyde-3-phosphate dehydrogenase whose activity is impaired in diabetes, and that results in activation of other major pathways implicated in the pathogenesis of diabetic retinopathy. Alterations associated with oxidative stress offer many potential therapeutic targets making this an area of great interest to the development of safe and effective treatments for diabetic retinopathy. Animal models of diabetic retinopathy have shown beneficial effects of antioxidants on the development of retinopathy, but clinical trials (though very limited in numbers) have provided somewhat ambiguous results. Although antioxidants are being used for other chronic diseases, controlled clinical trials are warranted to investigate potential beneficial effects of antioxidants in the development of retinopathy in diabetic patients.