FGF21 promotes endothelial cell angiogenesis through a dynamin-2 and Rab5 dependent pathway

The impact of adipokines on vascular networks in adipose tissue

Adipose tissue (AT) is a highly active and plastic endocrine organ. It secretes numerous soluble molecules known as adipokines, which act locally to AT control the remodel and homeostasis or exert pleiotropic functions in different peripheral organs. Aberrant production or loss of certain adipokines contributes to AT dysfunction associated with metabolic disorders, including obesity. The AT plasticity is strictly related to tissue vascularization. Angiogenesis supports the AT expansion, while regression of blood vessels is associated with AT hypoxia, which in turn mediates tissue inflammation, fibrosis and metabolic dysfunction. Several adipokines can regulate endothelial cell functions and are endowed with either pro- or anti-angiogenic properties. Here we address the role of adipokines in the regulation of angiogenesis. A better understanding of the link between adipokines and angiogenesis will open the way for novel therapeutic approaches to treat obesity and metabolic diseases.

New developments in the biology of fibroblast growth factors

The fibroblast growth factor (FGF) family is composed of 18 secreted signaling proteins consisting of canonical FGFs and endocrine FGFs that activate four receptor tyrosine kinases (FGFRs 1-4) and four intracellular proteins (intracellular FGFs or iFGFs) that primarily function to regulate the activity of voltage-gated sodium channels and other molecules. The canonical FGFs, endocrine FGFs, and iFGFs have been reviewed extensively by us and others. In this review, we briefly summarize past reviews and then focus on new developments in the FGF field since our last review in 2015. Some of the highlights in the past 6 years include the use of optogenetic tools, viral vectors, and inducible transgenes to experimentally modulate FGF signaling, the clinical use of small molecule FGFR inhibitors, an expanded understanding of endocrine FGF signaling, functions for FGF signaling in stem cell pluripotency and differentiation, roles for FGF signaling in tissue homeostasis and regeneration, a continuing elaboration of mechanisms of FGF signaling in development, and an expanding appreciation of roles for FGF signaling in neuropsychiatric diseases. This article is categorized under: Cardiovascular Diseases > Molecular and Cellular Physiology Neurological Diseases > Molecular and Cellular Physiology Congenital Diseases > Stem Cells and Development Cancer > Stem Cells and Development.

Spontaneous Browning of White Adipose Tissue Improves Angiogenesis and Reduces Macrophage Infiltration After Fat Grafting in Mice

Background: Fat grafting is a frequently used technique; however, its survival/ regeneration mechanism is not fully understood. The browning of white adipocytes, a process initiated in response to external stimuli, is the conversion of white to beige adipocytes. The physiologic significance of the browning of adipocytes following transplantation is unclear.

Methods: C57BL/6 mice received 150 mg grafts of inguinal adipose tissue, and then the transplanted fat was harvested and analyzed at different time points to assess the browning process. To verify the role of browning of adipocytes in fat grafting, the recipient mice were allocated to three groups, which were administered CL316243 or SR59230A to stimulate or suppress browning, respectively, or a control group after transplantation.

Results: Browning of the grafts was present in the center of each as early as 7 days post-transplantation. The number of beige cells peaked at day 14 and then decreased gradually until they were almost absent at day 90. The activation of browning resulted in superior angiogenesis, higher expression of the pro-angiogenic molecules vascular endothelial growth factor A (VEGF-A) and fibroblast growth factor 21 (FGF21), fewer macrophages, and ultimately better graft survival (Upregulation, 59.17% ± 6.64% vs. Control, 40.33% ± 4.03%, *p < 0.05), whereas the inhibition of browning led to poor angiogenesis, lower expression of VEGF-A, increased inflammatory macrophages, and poor transplant retention at week 10 (Downregulation, 20.67% ± 3.69% vs. Control, 40.33% ± 4.03%, *p < 0.05).

Conclusion: The browning of WAT following transplantation improves the survival of fat grafts by the promotion of angiogenesis and reducing macrophage.

2,3-Difunctionalized Benzo[b]thiophene Scaffolds Possessing Potent Antiangiogenic Properties

A new class of 2-anilino-3-cyanobenzo[b]thiophenes (2,3-ACBTs) was studied for its antiangiogenic activity for the first time. One of the 2,3-ACBTs inhibited tubulogenesis in a dose-dependent manner without any toxicity. The 2,3-ACBTs significantly reduced neovascularization in both ex vivo and in vivo angiogenic assays without affecting the proliferation of endothelial cells. Neovascularization was limited through reduced phosphorylation of Akt/Src and depolymerization of f-actin and β-tubulin filaments, resulting in reduced migration of cells. In addition, the 2,3-ACBT compound disrupted the preformed angiogenic tubules, and docking/competitive binding studies showed that it binds to VEGFR2. Compound 2,3-ACBT had good stability and intramuscular profile, translating in suppressing the tumor angiogenesis induced in a xenograft model. Overall, the present study suggests that 2,3-ACBT arrests angiogenesis by regulating the Akt/Src signaling pathway and deranging cytoskeletal filaments of endothelial cells.

The role of FGF21 in the pathogenesis of cardiovascular disease

ABSTRACT

The morbidity and mortality of cardiovascular diseases (CVDs) are increasing worldwide and seriously threaten human life and health. Fibroblast growth factor 21 (FGF21), a metabolic regulator, regulates glucose and lipid metabolism and may exert beneficial effects on the cardiovascular system. In recent years, FGF21 has been found to act directly on the cardiovascular system and may be used as an early biomarker of CVDs. The present review highlights the recent progress in understanding the relationship between FGF21 and CVDs including coronary heart disease, myocardial ischemia, cardiomyopathy, and heart failure and also explores the related mechanism of the cardioprotective effect of FGF21. FGF21 plays an important role in the prediction, treatment, and improvement of prognosis in CVDs. This cardioprotective effect of FGF21 may be achieved by preventing endothelial dysfunction and lipid accumulating, inhibiting cardiomyocyte apoptosis and regulating the associated oxidative stress, inflammation and autophagy. In conclusion, FGF21 is a promising target for the treatment of CVDs, however, its clinical application requires further clarification of the precise role of FGF21 in CVDs.

rhFGF20 promotes angiogenesis and vascular repair following traumatic brain injury by regulating Wnt/β-catenin pathway

The pathology of cerebrovascular disorders takes an important role in traumatic brain injury (TBI) by increasing intracranial pressure. Fibroblast growth factor 20 (FGF20) is a brain-derived neurotrophic factor, that has been shown to play an important role in the survival of dopaminergic neurons and the treatment of Parkinson's disease (PD). However, little is known about the role of FGF20 in the treatment of TBI and its underlying mechanism. The purpose of this study was to evaluate the protective effect of recombinant human FGF20 (rhFGF20) on protecting cerebral blood vessels after TBI. In this study, we indicated that rhFGF20 could reduce brain edema, Evans blue penetration and upregulated the expression of blood-brain barrier (BBB)-related tight junction (TJ) proteins, exerting a protective effect on the BBB in vivo after TBI. In the TBI repair phase, rhFGF20 promoted angiogenesis, neurological and cognitive function recovery. In tumor necrosis factor-α (TNF-α)-induced human brain microvascular endothelial cells (hCMEC/D3), an in vitro BBB disruption model, rhFGF20 reversed the impairment in cell migration and tube formation induced by TNF-α. Moreover, in both the TBI mouse model and the in vitro model, rhFGF20 increased the expression of β-catenin and GSK3β, which are the two key regulators in the Wnt/β-catenin signaling pathway. In addition, the Wnt/β-catenin inhibitor IWR-1-endo significantly reversed the effects of rhFGF20. These results indicate that rhFGF20 may prevent vascular repair and angiogenesis through the Wnt/β-catenin pathway.

The autocrine role of FGF21 in cultured adipocytes

Exposure to cold alters glucose and lipid metabolism of white and brown adipose tissue via activation of β-adrenergic receptor (ADRB). Fibroblast growth factor 21 (FGF21) has been shown to be locally released from adipose tissue upon activation of ADRBs and FGF21 increases glucose uptake in adipocytes. Therefore, FGF21 may play an autocrine role in inducing glucose uptake after β-adrenergic stimulation. To determine the putative autocrine role of FGF21, we stimulated three different types of adipocytes in vitro with Isoprenaline (Iso), an ADRB agonist, in the presence or absence of the FGF receptor (FGFR) inhibitor PD 173074. The three cell lines represent white (3T3-L1), beige (ME3) and brown (WT-1) adipocyte phenotypes, respectively. All three cells systems expressed β-klotho (KLB) and FGFR1 after differentiation and treatment with recombinant FGF21 increased glucose uptake in 3T3-L1 and WT-1 adipocytes, while no significant effect was observed in ME3. Oppositely, all three cell lines responded to Iso treatment and an increase in glucose uptake and lipolysis were observed. Interestingly, in response to the Iso treatment only the WT-1 adipocytes showed an increase in FGF21 in the medium. This was consistent with the observation that PD 173074 decreased Iso-induced glucose uptake in the WT-1 adipocytes. This suggests that FGF21 plays an autocrine role and increases glucose uptake after β-adrenergic stimulation of cultured brown WT-1 adipocytes.

Tubulin carboxypeptidase activity of vasohibin-1 inhibits angiogenesis by interfering with endocytosis and trafficking of pro-angiogenic factor receptors

Receptor endocytosis is crucial for integrating extracellular stimuli of pro-angiogenic factors, including vascular endothelial growth factor (VEGF), into the cell via signal transduction. VEGF not only triggers various angiogenic events including endothelial cell (EC) migration, but also induces the expression of negative regulators of angiogenesis, including vasohibin-1 (VASH1). While we have previously reported that VASH1 inhibits angiogenesis in vitro and in vivo, its mode of action on EC behavior remains elusive. Recently VASH1 was shown to have tubulin carboxypeptidase (TCP) activity, mediating the post-translational modification of microtubules (MTs) by detyrosination of α-tubulin within cells. However, the role of VASH1 TCP activity in angiogenesis has not yet been clarified. Here, we showed that VASH1 detyrosinated α-tubulin in ECs and suppressed in vitro and in vivo angiogenesis. In cultured ECs, VASH1 impaired endocytosis and trafficking of VEGF receptor 2 (VEGFR2), which resulted in the decreased signal transduction and EC migration. These effects of VASH1 could be restored by tubulin tyrosine ligase (TTL) in ECs, suggesting that detyrosination of α-tubulin negatively regulates angiogenesis. Furthermore, we found that detyrosinated tubulin-rich MTs were not adequate as trafficking rails for VEGFR2 endocytosis. Consistent with these results, inhibition of TCP activity of VASH1 led to the inhibition of VASH1-mediated suppression of VEGF-induced signals, EC migration, and in vivo angiogenesis. Our results indicate a novel mechanism of VASH1-mediated inhibition of pro-angiogenic factor receptor trafficking via modification of MTs.

GIPC-Regulated IGFBP-3 Promotes HSC Migration In Vitro and Portal Hypertension In Vivo Through a β1-Integrin Pathway

BACKGROUND & AIMS

Transforming growth factor (TGF-β)-induced activation of quiescent hepatic stellate cells (HSCs) and their transformation to myofibroblasts is a key event in liver fibrosis and portal hypertension. GIPC (also referred to as synectin) is a downstream signal activation molecule of TGF-β and other receptors. In this study, we sought to identify novel genes targeted by TGF-β and GIPC and elucidate if and how they may contribute to liver fibrosis.

METHODS

We performed sequential messenger RNA sequencing analysis on TGF-β-stimulated HSCs and then on TGF-β-stimulated HSCs in the presence and absence of GIPC also referred to as synectin (GIPC) knockdown. Insulin-like growth factor binding protein-3 (IGFBP-3) transport protein emerged as a top activation target of both TGF-β and GIPC. Quantitative polymerase chain reaction, enzyme-linked immunosorbent assay, targeted chromatin immunoprecipitation, and Western blot analysis were done for further confirmation.

RESULTS

IGFBP-3, an insulin growth factor transport protein, emerged as a top activation target of both TGF-β and GIPC, which was confirmed by quantitative polymerase chain reaction, enzyme-linked immunosorbent assay, and Western blot analysis. Targeted chromatin immunoprecipitation showed that GIPC increases the histone 3 lysine 27 (H3K27) acetylation activating mark and concurrently decreases the H3K27 inhibitory trimethylation (H3K27m3) mark, providing an epigenetic correlate to the gene regulation changes. In vivo, global knockout of IGFBP-3 mice resulted in attenuation of HSC activation markers and attenuation of portal pressure in response to chronic liver injury models. Analysis of serum levels from cirrhotic patients also showed an IGFBP-3 increase of more than 2-fold compared with healthy controls. Finally, in vitro mechanism studies showed that IGFBP-3 promotes HSC migration through integrin-dependent phosphorylation of protein kinase B.

CONCLUSIONS

TGF-β up-regulates IGFBP-3 through GIPC, leading to increased HSC migration in vitro and promotes portal hypertension in vivo. These studies support the role of IGFBP-3 as a potential pathophysiologic target or biomarker in chronic liver disease.

FGF21 augments autophagy in random-pattern skin flaps via AMPK signaling pathways and improves tissue survival

Random-pattern skin flap is commonly used for surgical tissue reconstruction due to its ease and lack of axial vascular limitation. However, ischemic necrosis is a common complication, especially in distal parts of skin flaps. Previous studies have shown that FGF21 can promote angiogenesis and protect against ischemic cardiovascular disease, but little is known about the effect of FGF21 on flap survival. In this study, using a rat model of random skin flaps, we found that the expression of FGF21 is significantly increased after establishment skin flaps, suggesting that FGF21 may exert a pivotal effect on flap survival. We conducted experiments to elucidate the role of FGF21 in this model. Our results showed that FGF21 directly increased the survival area of skin flaps, blood flow intensity, and mean blood vessel density through enhancing angiogenesis, inhibiting apoptosis, and reducing oxidative stress. Our studies also revealed that FGF21 administration leads to an upregulation of autophagy, and the beneficial effects of FGF21 were reversed by 3-methyladenine (3MA), which is a well-known inhibitor of autophagy, suggesting that autophagy plays a central role in FGF21’s therapeutic benefit on skin flap survival. In our mechanistic investigation, we found that FGF21-induced autophagy enhancement is mediated by the dephosphorylation and nuclear translocation of TFEB; this effect was due to activation of AMPK-FoxO3a-SPK2-CARM1 and AMPK-mTOR signaling pathways. Together, our data provides novel evidence that FGF21 is a potent modulator of autophagy capable of significantly increasing random skin flap viability, and thus may serve as a promising therapy for clinical use.

Reversal of Osteopenia in Ovariectomized Rats by Pentoxifylline: Evidence of Osteogenic and Osteo-Angiogenic Roles of the Drug

Pentoxifylline (PTX) is a non-selective phosphodiesterase inhibitor and is used for the management of intermittent claudication. We tested whether PTX has oral efficacy in stimulating new bone formation. Rat calvarial osteoblasts (RCO) were used to study the effect of PTX on osteoblast differentiation and angiogenesis. Pharmacokinetic and pharmacodynamic studies were carried out in rats to determine an oral dose of PTX. In ovariectomized (OVX) rats with osteopenia, the effect of PTX on various skeletal parameters was studied, and compared with teriparatide. Effect of PTX on angiogenic signaling was studied by immunoblotting and relevant pharmacologic inhibitors. Bone vascularity was measured by intravenous injection of polystyrene fluorospheres followed by in vivo imaging, and angiogenesis was studied in vitro by tubulogenesis of endothelial cells and in vivo by Matrigel plug assay. Effective concentration (EC₅₀) of PTX in RCO was 8.2 nM and plasma PTX level was 7 nM/mL after single oral dosing of 25 mg/kg, which was 1/6th the clinically used dose. At this dose, PTX enhanced bone regeneration at femur osteotomy site and completely restored bone mass, microarchitecture, and strength in OVX rats. Furthermore, PTX increased surface referent bone formation parameters and serum bone formation marker (PINP) without affecting the resorption marker (CTX-1). PTX increased the expression of vascular endothelial growth factor and its receptor in bones and osteoblasts. PTX also increased skeletal vascularity, tubulogenesis of endothelial cells and in vivo angiogenesis. Taken together, our study suggested that PTX at 16% of adult human oral dose completely reversed osteopenia in OVX rats by osteogenic and osteo-angiogenic mechanisms.

Association between Circulating Fibroblast Growth Factor 21 and Aggressiveness in Thyroid Cancer

Fibroblast growth factor 21 (FGF21) plays important roles in regulating glucose, lipid, and energy metabolism; however, its effects in tumors remain poorly understood. To understand the role of FGF21 in regulating tumor aggressiveness in thyroid cancer, serum levels of FGF21 were measured in healthy subjects and patients with papillary thyroid cancer (PTC), and expression levels of FGF21, FGF receptors (FGFRs), and β-klotho (KLB) were investigated in human thyroid tissues. The cell viability, migrating cells, and invading cells were measured in PTC cells after treatment with recombinant FGF21. Higher serum levels of FGF21 were found in patients with thyroid cancer than in control participants, and were significantly associated with body mass index (BMI), fasting glucose levels, triglyceride levels, tumor stage, lymphovascular invasion, and recurrence. Serum FGF21 levels were positively correlated with the BMI in patients with PTC, and significantly associated with recurrence. Recombinant FGF21 led to tumor aggressiveness via activation of the FGFR signaling axis and epithelial-to-mesenchymal transition (EMT) signaling in PTC cells, and AZD4547, an FGFR tyrosine kinase inhibitor, attenuated the effects of FGF21. Hence, FGF21 may be a new biomarker for predicting tumor progression, and targeting FGFR may be a novel therapy for the treatment of obese patients with PTC.

Fibroblast growth factor 21 enhances angiogenesis and wound healing of human brain microvascular endothelial cells by activating PPARγ

Angiogenesis of brain microvascular endothelial cells (BMECs) is required in the functional restoration of brain injury, such as traumatic brain injury (TBI) and ischemic stroke. Fibroblast growth factor 21 (FGF21) is an angiogenic molecule that functions through the formation of the FGF21/FGFR1/β-klotho complex but does not cause carcinogenic events. The current study was to determine whether recombinant human FGF21 (rhFGF21) could promote angiogenesis and scratch wound healing of human brain microvascular endothelial cells (HBMECs) and the possible underlying mechanism. rhFGF21 promoted angiogenesis and migration of HBMECs. The FGFR1 inhibitor PD173074 was applied to demonstrate that rhFGF21 functions through the formation of FGF21/FGFR1/β-klotho complexes. In addition, the specific PPARγ inhibitor GW9662 and PPARγ activator rosiglitazone were applied to determine that the role of rhFGF21 in increasing angiogenesis is through the PPARγ pathway. In addition, we revealed that the effect of rhFGF21 acts partially through upregulating eNOS expression. In conclusion, our study provides novel evidence that rhFGF21 can enhance the angiogenesis and migration of HBMECs through the formation of the FGF21/FGFR1/β-klotho complex via PPARγ activation and eNOS upregulation, indicating that FGF21 is a potential therapeutic angiogenic agent for the treatment of human brain injury.

Evolocumab, a proprotein convertase subtilisin/kexin type 9 inhibitor, promotes angiogenesis in vitro

The proprotein convertases family is involved in several physiological processes such as cell growth, migration, and angiogenesis, and also in different pathological conditions. Evolocumab, an inhibitor of proprotein convertase subtilisin/kexin type 9 (PCSK9), has recently been approved for treatment of hypercholesterolemia. This study aimed to investigate the effect of evolocumab on angiogenesis in human umbilical vein endothelial cells (HUVECs). Cell proliferation and migration were evaluated using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide and Transwell methods. In vitro angiogenesis was assessed by tube formation assay. Vascular endothelial growth factor (VEGF) secretion by HUVECs was also determined using an enzyme-linked immunosorbent assay kit. Evolocumab significantly increased HUVECs viability at 100 μg/mL. Significant enhancement in cell migration, and mean tubules length and size was observed at the concentrations of 10 and 100 μg/mL and also in mean number of junctions at the concentration of 100 μg/mL. Administration of evolocumab at the concentration of 10 μg/mL increased VEGF release into supernatants of HUVECs. Findings of this investigation provided in vitro evidence for pro-angiogenic activity of evolocumab through promoting cell proliferation, migration, tubulogenesis, and VEGF secretion in HUVECs.

FGF21 trafficking in intact human cells revealed by cryo-electron tomography with gold nanoparticles

The fibroblast growth factor FGF21 was labeled with molecularly defined gold nanoparticles (AuNPs), applied to human adipocytes, and imaged by cryo-electron tomography (cryo-ET). Most AuNPs were in pairs about 80 Å apart, on the outer cell surface. Pairs of AuNPs were also abundant inside the cells in clathrin-coated vesicles and endosomes. AuNPs were present but no longer paired in multivesicular bodies. FGF21 could thus be tracked along the endocytotic pathway. The methods developed here to visualize signaling coupled to endocytosis can be applied to a wide variety of cargo and may be extended to studies of other intracellular transactions.

MiRNA-575 suppresses angiogenesis by targeting Rab5-MEK-ERK pathway in endothelial cells

Hypertension is a major risk factor for the development of atherosclerosis. Increased carotid intima-media thickness (CIMT) is generally considered as an early marker of atherosclerosis. Recently, circulating miRNAs have been implicated both as sensitive biomarkers and key regulators in the development of atherosclerosis. However, the biological functions and molecular regulatory mechanisms for miR-575 on angiogenesis remain unknown. In our study, we first identified up-regulation of circulating miR-575 in plasma of essential hypertensive patients with increased CIMT (iCIMT) compared with those patients with normal CIMT (nCIMT). Furthermore, the overexpression of miR-575 in human umbilical vein endothelial cells (HUVECs) by its mimics significantly inhibited migration and proliferation as well as induction of apoptosis of HUVECs. Inhibition of miR-575 performed the reverse effects of HUVECs. We further suggested Rab5B was the downstream target of miR-575 and knockdown of Rab5B significantly inhibited migration and proliferation of HUVECs. Overexpression of Rab5B largely rescued the miR-575-mediated impairment of angiogenesis processes including: cell proliferation, migration, and apoptosis as well as activation of mitogen-activated protein kinase/extracellular signal-regulated kinase (MEK-ERK) signaling. Therefore, our results uncover a novel role of miR-575 in endothelial cells, implying a potential biomarker and clinical target for atherosclerosis in hypertensive patients.

A2A Receptor Activation Attenuates Hypertensive Cardiac Remodeling via Promoting Brown Adipose Tissue-Derived FGF21

Adipocytes play important roles in regulating cardiovascular health and disease. However, the molecular mechanism underlying the endocrine role of brown adipose tissue (BAT) in pathological cardiac remodeling remains unknown. Herein we show that adenosine A_2A receptor (A_2AR) knockout (A_2ARKO) causes interscapular BAT (iBAT) dysfunction, leading to accelerated cardiac remodeling in hypertension compared with wild-type (WT) mice. Surgical iBAT depletion induces dramatic cardiac remodeling in WT but not in A_2ARKO hypertensive mice. AMPK/PGC1α signaling-induced fibroblast growth factor 21 (FGF21) in brown adipocytes is required for A_2AR-mediated inhibition of hypertensive cardiac remodeling. Recombinant FGF21 administration improves cardiac remodeling in iBAT-depleted hypertensive mice. More importantly, brown adipocyte-specific A_2ARKO inhibits FGF21 production and accelerates cardiac damage in hypertension. Consistently, brown adipocyte-specific FGF21 knockout abolishes the effects of A_2AR agonism in attenuating hypertensive cardiac remodeling. Our findings reveal a distinctive endocrine role of BAT in hypertensive cardiac remodeling via activating A_2AR/FGF21 pathway.

FGF21 Administration Suppresses Retinal and Choroidal Neovascularization in Mice

Pathological neovascularization, a leading cause of blindness, is seen in retinopathy of prematurity, diabetic retinopathy, and age-related macular degeneration. Using a mouse model of hypoxia-driven retinal neovascularization, we find that fibroblast growth factor 21 (FGF21) administration suppresses, and FGF21 deficiency worsens, retinal neovessel growth. The protective effect of FGF21 against neovessel growth was abolished in adiponectin (APN)-deficient mice. FGF21 administration also decreased neovascular lesions in two models of neovascular age-related macular degeneration: very-low-density lipoprotein-receptor-deficient mice with retinal angiomatous proliferation and laser-induced choroidal neovascularization. FGF21 inhibited tumor necrosis α (TNF-α) expression but did not alter Vegfa expression in neovascular eyes. These data suggest that FGF21 may be a therapeutic target for pathologic vessel growth in patients with neovascular eye diseases, including retinopathy of prematurity, diabetic retinopathy, and age-related macular degeneration.

Hepatic Stellate Cell Selective Disruption of Dynamin-2 GTPase Increases Murine Fibrogenesis through Up-Regulation of Sphingosine-1 Phosphate-Induced Cell Migration

Dynamin-2 (Dyn2) is implicated in endocytosis of receptor tyrosine kinases, which contribute to hepatic stellate cell (HSC) activation and liver fibrosis. A point mutation converting lysine 44 of Dyn2 to alanine (Dyn2K44A) disrupts its GTPase activity. We hypothesized that Dyn2K44A expression in HSCs would decrease HSC activation and fibrogenesis in vivo by disrupting receptor tyrosine kinase endocytosis and signaling. Dyn2K44A^fl/fl mice were crossed with Collagen1-Cre (Col1^Cre) mice to generate offspring with HSC selective expression of Dyn2K44A (Col1^Cre/Dyn2K44A^fl/fl). Contrary to our hypothesis, Col1^Cre/Dyn2K44A^fl/fl mice showed increased hepatic fibrosis in response to liver injury. To elucidate mechanisms, we conducted in vitro experiments with HSCs infected with adenoviral vectors encoding LacZ, Dyn2K44A, or Dyn2WT. HSC-expressing Dyn2K44A displayed increased mRNA and protein levels of sphingosine kinase-1 (SK1), an enzyme previously implicated in the pathogenesis of fibrosis. To study the functional effects of Dyn2K44A regulation of SK1, we examined effects of AKT signaling and migration in HSCs. Dyn2K44A promoted both AKT phosphorylation and HSC migration in an SK1-dependent manner. Genetic disruption of Dyn2 GTPase activity selectively in HSC enhances fibrogenesis, driven at least in part through up-regulation of the SK1 pathway and cell migration in HSCs.

Valproic Acid and Other HDAC Inhibitors Upregulate FGF21 Gene Expression and Promote Process Elongation in Glia by Inhibiting HDAC2 and 3

BACKGROUND

Fibroblast growth factor 21, a novel regulator of glucose and lipid metabolism, has robust protective properties in neurons. However, its expression and function in glia are unknown. Valproic acid, a mood stabilizer and anticonvulsant, is a histone deacetylase inhibitor and a dynamic gene regulator. We investigated whether histone deacetylase inhibition by valproic acid and other inhibitors upregulates fibroblast growth factor 21 expression and, if so, sought to identify the histone deacetylase isoform(s) involved and their role in altering glial cell morphology.

METHODS

C6 glioma or primary cortical glial cultures were treated with histone deacetylase inhibitors, and fibroblast growth factor 21 levels and length of cell processes were subsequently measured. Histone deacetylase 1, 2, or 3 was also knocked down to detect which isoform was involved in regulating fibroblast growth factor 21 mRNA levels. Finally, knockdown and overexpression of fibroblast growth factor 21 were performed to determine whether it played a role in regulating cell process length.

RESULTS

Treatment of C6 cells or primary glial cultures with valproic acid elevated fibroblast growth factor 21 mRNA levels, extended cell process length, and markedly increased acetylated histone-H3 levels. Other histone deacetylase inhibitors including pan- and class I-specific inhibitors, or selective knockdown of histone deacetylase 2 or 3 isoform produced similar effects. Knockdown or overexpression of fibroblast growth factor 21 significantly decreased or increased C6 cell process length, respectively.

CONCLUSIONS

In glial cell line and primary glia, using pharmacological inhibition and selective gene silencing of histone deacetylases to boost fibroblast growth factor 21 mRNA levels results in elongation of cell processes. Our study provides a new mechanism via which histone deacetylase 2 and 3 participate in upregulating fibroblast growth factor 21 transcription and extending process outgrowth in glia.

Fibroblast Growth Factor 21 As an Emerging Therapeutic Target for Type 2 Diabetes Mellitus

Fibroblast growth factor (FGF) 21 is a distinctive member of the FGF family that functions as an endocrine factor. It is expressed predominantly in the liver, but is also found in adipose tissue and the pancreas. Pharmacological studies have shown that FGF21 normalizes glucose and lipid homeostasis, thereby preventing the development of metabolic disorders, such as obesity and diabetes. Despite growing evidence for the therapeutic potential of FGF21, paradoxical increases of FGF21 in different disease conditions point to the existence of FGF21 resistance. In this review, we give a critical appraisal of recent advances in the understanding of the regulation of FGF21 production under various physiological conditions, its antidiabetic actions, and the clinical implications. We also discuss recent preclinical and clinical trials using engineered FGF21 analogs in the management of diabetes, as well as the potential side effects of FGF21 therapy.

The emerging role of fibroblast growth factor 21 in diabetic nephropathy

Diabetic nephropathy (DN), an important cause of end-stage renal diseases, brings about great social and economic burden. Due to the variable pathological changes and clinical course, the prognosis of DN is very difficult to predict. DN is also usually associated with enhanced genomic damage and cellular injury. Fibroblast growth factor 21 (FGF21), a nutritionally regulated hormone secreted mainly by the liver, plays a critical role in metabolism. Administration of FGF21 decreases blood glucose, triglyceride, and cholesterol levels, and improves insulin sensitivity, which is closely associated with the development and progression of glomerular diseases. In addition, FGF21 level was associated with renal function. However, the precise role of FGF21 in DN remains unclear. This review will give a comprehensive understanding of the underlying role of FGF21 and its possible interaction with other molecules in DN.

Exosome Adherence and Internalization by Hepatic Stellate Cells Triggers Sphingosine 1-Phosphate-dependent Migration

Exosomes are cell-derived extracellular vesicles thought to promote intercellular communication by delivering specific content to target cells. The aim of this study was to determine whether endothelial cell (EC)-derived exosomes could regulate the phenotype of hepatic stellate cells (HSCs). Initial microarray studies showed that fibroblast growth factor 2 induced a 2.4-fold increase in mRNA levels of sphingosine kinase 1 (SK1). Exosomes derived from an SK1-overexpressing EC line increased HSC migration 3.2-fold. Migration was not conferred by the dominant negative SK1 exosome. Incubation of HSCs with exosomes was also associated with an 8.3-fold increase in phosphorylation of AKT and 2.5-fold increase in migration. Exosomes were found to express the matrix protein and integrin ligand fibronectin (FN) by Western blot analysis and transmission electron microscopy. Blockade of the FN-integrin interaction with a CD29 neutralizing antibody or the RGD peptide attenuated exosome-induced HSC AKT phosphorylation and migration. Inhibition of endocytosis with transfection of dynamin siRNA, the dominant negative dynamin GTPase construct Dyn2K44A, or the pharmacological inhibitor Dynasore significantly attenuated exosome-induced AKT phosphorylation. SK1 levels were increased in serum exosomes derived from mice with experimental liver fibrosis, and SK1 mRNA levels were up-regulated 2.5-fold in human liver cirrhosis patient samples. Finally, S1PR2 inhibition protected mice from CCl4-induced liver fibrosis. Therefore, EC-derived SK1-containing exosomes regulate HSC signaling and migration through FN-integrin-dependent exosome adherence and dynamin-dependent exosome internalization. These findings advance our understanding of EC/HSC cross-talk and identify exosomes as a potential target to attenuate pathobiology signals.

Activation of ERK pathway is required for 15-HETE-induced angiogenesis in human umbilical vascular endothelial cells

Angiogenesis plays a critical role in the progression of cardiovascular disease, retinal ischemia, or tumorigenesis. The imbalance of endothelial cell proliferation and apoptosis disturbs the establishment of the vasculogenesis, which is affected by several arachidonic acid metabolites. 15-Hydroxyeicosatetraenoic acid (15-HETE) is one of the metabolites. However, the underlying mechanisms of angiogenesis induced by 15-HETE in human umbilical vascular endothelial cells (HUVECs) are still poorly understood. Since extracellular signal-regulated kinase (ERK) is a critical regulator of cell proliferation, there may be a crosstalk between 15-HETE-regulating angiogenic process and ERK-proliferative effect in HUVECs. To test this hypothesis, we study the effect of 15-HETE on cell proliferation, angiogenesis, and apoptosis using cell viability measurement, cell cycle analysis, western blot, scratch-wound, tube formation assay, and nuclear morphology determination. We found that 15-HETE promoted HUVEC angiogenesis, which were mediated by ERK. Moreover, 15-HETE-induced proliferation and cell cycle transition from the G(0)/G(1) phase to the G(2)/M + S phase. All these effects were reversed after blocking ERK with PD98059 (an ERK inhibitor). In addition, HUVEC apoptosis was relieved by 15-HETE through the ERK pathway. Thus, ERK is necessary for the effects of 15-HETE in the regulation of HUVEC angiogenesis, which may be a novel potential target for the treatment of angiogenesis-related diseases.

Fibroblast growth factors in cardiovascular disease: The emerging role of FGF21

Early detection of risk factors for enhanced primary prevention and novel therapies for treating the chronic consequences of cardiovascular disease are of the utmost importance for reducing morbidity. Recently, fibroblast growth factors (FGFs) have been intensively studied as potential new molecules in the prevention and treatment of cardiovascular disease mainly attributable to metabolic effects and angiogenic actions. Members of the endocrine FGF family have been shown to increase metabolic rate, decrease adiposity, and restore glucose homeostasis, suggesting a multiple metabolic role. Serum levels of FGFs have been associated with established cardiovascular risk factors as well as with the severity and extent of coronary artery disease and could be useful for prediction of cardiovascular death. Furthermore, preclinical investigations and clinical trials have tested FGF administration for therapeutic angiogenesis in ischemic vascular disease, demonstrating a potential role in improving angina and limb function. FGF21 has lately emerged as a potent metabolic regulator with multiple effects that ultimately improve the lipoprotein profile. Early studies show that FGF21 is associated with the presence of atherosclerosis and may play a protective role against plaque formation by improving endothelial function. The present review highlights recent investigations suggesting that FGFs, in particular FGF21, may be useful as markers of cardiovascular risk and may also serve as protective/therapeutic agents in cardiovascular disease.