Gremlin gene expression in bovine retinal pericytes exposed to elevated glucose

Role of gremlin-1 in the pathophysiology of the adipose tissues

Gremlin-1 is a secreted bone morphogenetic protein (BMP) antagonist playing a pivotal role in the regulation of tissue formation and embryonic development. Since its first identification in 1997, gremlin-1 has been shown to be a multifunctional factor involved in wound healing, inflammation, cancer and tissue fibrosis. Among others, the activity of gremlin-1 is mediated by its interaction with BMPs or with membrane receptors such as the vascular endothelial growth factor receptor 2 (VEGFR2) or heparan sulfate proteoglycans (HSPGs). Growing evidence has highlighted a central role of gremlin-1 in the homeostasis of the adipose tissue (AT). Of note, gremlin-1 is involved in AT dysfunction during type 2 diabetes, obesity and non-alcoholic fatty liver disease (NAFLD) metabolic disorders. In this review we discuss recent findings on gremlin-1 involvement in AT biology, with particular attention to its role in metabolic diseases, to highlight its potential as a prognostic marker and therapeutic target.

TGF-β Superfamily Signaling in the Eye: Implications for Ocular Pathologies

The TGF-β signaling pathway plays a crucial role in several key aspects of development and tissue homeostasis. TGF-β ligands and their mediators have been shown to be important regulators of ocular physiology and their dysregulation has been described in several eye pathologies. TGF-β signaling participates in regulating several key developmental processes in the eye, including angiogenesis and neurogenesis. Inadequate TGF-β signaling has been associated with defective angiogenesis, vascular barrier function, unfavorable inflammatory responses, and tissue fibrosis. In addition, experimental models of corneal neovascularization, diabetic retinopathy, proliferative vitreoretinopathy, glaucoma, or corneal injury suggest that aberrant TGF-β signaling may contribute to the pathological features of these conditions, showing the potential of modulating TGF-β signaling to treat eye diseases. This review highlights the key roles of TGF-β family members in ocular physiology and in eye diseases, and reviews approaches targeting the TGF-β signaling as potential treatment options.

Epigenetic Modulation of Gremlin-1/NOTCH Pathway in Experimental Crescentic Immune-Mediated Glomerulonephritis

Crescentic glomerulonephritis is a devastating autoimmune disease that without early and properly treatment may rapidly progress to end-stage renal disease and death. Current immunosuppressive treatment provides limited efficacy and an important burden of adverse events. Epigenetic drugs are a source of novel therapeutic tools. Among them, bromodomain and extraterminal domain (BET) inhibitors (iBETs) block the interaction between bromodomains and acetylated proteins, including histones and transcription factors. iBETs have demonstrated protective effects on malignancy, inflammatory disorders and experimental kidney disease. Recently, Gremlin-1 was proposed as a urinary biomarker of disease progression in human anti-neutrophil cytoplasmic antibody (ANCA)-associated crescentic glomerulonephritis. We have now evaluated whether iBETs could regulate Gremlin-1 in experimental anti-glomerular basement membrane nephritis induced by nephrotoxic serum (NTS) in mice, a model resembling human crescentic glomerulonephritis. In NTS-injected mice, the iBET JQ1 inhibited renal Gremlin-1 overexpression and diminished glomerular damage, restoring podocyte numbers. Chromatin immunoprecipitation assay demonstrated BRD4 enrichment of the Grem-1 gene promoter in injured kidneys, consistent with Gremlin-1 epigenetic regulation. Moreover, JQ1 blocked BRD4 binding and inhibited Grem-1 gene transcription. The beneficial effect of iBETs was also mediated by modulation of NOTCH pathway. JQ1 inhibited the gene expression of the NOTCH effectors Hes-1 and Hey-1 in NTS-injured kidneys. Our results further support the role for epigenetic drugs, such as iBETs, in the treatment of rapidly progressive crescentic glomerulonephritis.

Gremlin mediates the TGF-β-induced induction of profibrogenic genes in human retinal pigment epithelial cells

Proliferative vitreoretinopathy (PVR) is characterised by the contraction and growth of fibrotic membranes on the retina and within the vitreous body. Retinal pigment epithelial (RPE) cells, a major cellular component of the fibrotic membrane, is one of the cell types that have been previously reported to associate with PVR pathogenesis. During PVR, RPE cells undergo increased cell proliferation, migration and the secretion of extracellular matrix molecules, such as fibronectin and type I collagen. A variety of cytokines and growth factors are involved in the formation of the fibrotic membrane. Although gremlin has been reported to serve an important role in the regulation of epithelial-to-mesenchymal transition in PVR, the relationship between gremlin and the expression of profibrogenic factors in human RPE cells remains unclear. In the present study, gremlin promoted RPE cell proliferation and the expression of type I collagen and fibronectin. In addition, knocking down gremlin expression by siRNA significantly suppressed the transforming growth factor (TGF)-β1- and TGF-β2-induced expression of type I collagen and fibronectin in RPE cells. These findings suggest that gremlin may serve an important role in the development of PVR.

Gremlin in the Vitreous of Patients with Proliferative Diabetic Retinopathy and the Downregulation of Gremlin in Retinal Pigment Epithelial Cells

Diabetic retinopathy (DR) is one of the most common causes of blindness globally. Proliferative DR (PDR), an advanced stage of DR, is characterized by the formation of fibrotic membranes at the vitreoretinal interface. The proliferation, migration, and secretion of extracellular matrix molecules in retinal pigment epithelial (RPE) cells contribute to the formation of fibrotic membranes in PDR. Gremlin has been reported to be upregulated in response to elevated glucose levels in the retina of diabetic rat and bovine pericytes. However, the role of gremlin in PDR remains unclear. In the present study, the vitreous concentrations of gremlin were significantly higher in the PDR (67.79 ± 33.96) group than in the control (45.31 ± 12.31) group, and high glucose levels induced the expression of gremlin in RPE cells. The elevated expression of extracellular matrix molecules, such as fibronectin and collagen IV, was significantly reduced by gremlin siRNA in human RPE cells under high-glucose conditions. Thus, gremlin may play a vital role in the development of PDR.

The Role of Bone Morphogenetic Proteins in Diabetic Complications

The prevalence of diabetes has reached epidemic proportions and is placing a significant burden on healthcare systems globally. Diabetes has a detrimental impact on many organs in the human body, including accelerating the development of micro- and macrovascular complications. Current therapeutic options to treat diabetic complications have their limitations. Importantly, many slow but fail to reverse the progression of diabetic complications. Bone morphogenetic proteins (BMPs) are a highly conserved subgroup of the transforming growth factor β (TGFβ) superfamily, signaling via serine/threonine kinase receptors, that have recently been implicated in glucose homeostasis and insulin resistance in the setting of diabetes. Downstream of the receptors, the signal can be transduced via the canonical Smad-dependent pathway or the noncanonical Smad-independent pathways. BMPs are essential in organ development, tissue homeostasis, and, as expected, disease pathogenesis. In fact, deletion of BMPs can be embryonically lethal or result in severe organ abnormalities. This review outlines the BMP signaling pathway and its relevance to diabetic complications, namely, diabetic nephropathy, diabetes-associated cardiovascular diseases, and diabetic retinopathy. Understanding the complexities of BMP signaling and particularly its tissue-, cellular-, and time-dependent actions will help delineate the underlying pathogenesis of the disease and may ultimately be harnessed in the treatment of diabetes-induced complications. This would replicate progress made in numerous other diseases, including cancer and atherosclerosis.

Interplay between BMPs and Reactive Oxygen Species in Cell Signaling and Pathology

The integration of cell extrinsic and intrinsic signals is required to maintain appropriate cell physiology and homeostasis. Bone morphogenetic proteins (BMPs) are cytokines that belong to the transforming growth factor-β (TGF-β) superfamily, which play a key role in embryogenesis, organogenesis and regulation of whole-body homeostasis. BMPs interact with membrane receptors that transduce information to the nucleus through SMAD-dependent and independent pathways, including PI3K-AKT and MAPKs. Reactive oxygen species (ROS) are intracellular molecules derived from the partial reduction of oxygen. ROS are highly reactive and govern cellular processes by their capacity to regulate signaling pathways (e.g., NF-κB, MAPKs, KEAP1-NRF2 and PI3K-AKT). Emerging evidence indicates that BMPs and ROS interplay in a number of ways. BMPs stimulate ROS production by inducing NOX expression, while ROS regulate the expression of several BMPs. Moreover, BMPs and ROS influence common signaling pathways, including PI3K/AKT and MAPK. Additionally, dysregulation of BMPs and ROS occurs in several pathologies, including vascular and musculoskeletal diseases, obesity, diabetes and kidney injury. Here, we review the current knowledge on the integration between BMP and ROS signals and its potential applications in the development of new therapeutic strategies.

A comprehensive overview on osteoporosis and its risk factors

Osteoporosis is a bone disorder with remarkable changes in bone biologic material and consequent bone structural distraction, affecting millions of people around the world from different ethnic groups. Bone fragility is the worse outcome of the disease, which needs long term therapy and medical management, especially in the elderly. Many involved genes including environmental factors have been introduced as the disease risk factors so far, of which genes should be considered as effective early diagnosis biomarkers, especially for the individuals from high-risk families. In this review, a number of important criteria involved in osteoporosis are addressed and discussed.

Suppression of hepatic stellate cell activation through downregulation of gremlin1 expression by the miR-23b/27b cluster

The imbalance between transforming growth factor β and bone morphogenetic protein 7 signaling pathways is a critical step in promoting hepatic stellate cell activation during hepatic fibrogenesis. Gremlin1 may impair the balance. Something remains unclear about the regulatory mechanisms of gremlin1 action on hepatic stellate cell activation and hepatic fibrosis. In the current study, gremlin1 overexpression promotes activation of hepatic stellate cells. Knockdown of gremlin1 with siRNAs suppresses hepatic stellate cell activation and attenuates hepatic fibrosis in rat model. Our results also show that miR-23b/27b cluster members bind to 3'-untranslated region of gremlin1 resulting in reduction of transforming growth factor β, α-smooth muscle actin and collagenI α1/2 gene expression. Our findings suggest that gremlin1 promotes hepatic stellate cell activation and hepatic fibrogenesis through impairment of the balance between transforming growth factor β and bone morphogenetic protein 7 signaling pathways. The miR-23b/27b cluster suppresses activation of hepatic stellate cells through binding gremlin1 to rectify the imbalance.

Gremlin1 Accelerates Hepatic Stellate Cell Activation Through Upregulation of TGF-Beta Expression

Gremlin1, the antagonist of bone morphogenetic protein-7 and one of the target genes of transforming growth factor (TGF)-β signal pathway, plays an important role in embryonic development and its expression decreases along with aging. To explore the expression of gremlin1 in liver fibrosis and the causal link between gremlin1 and hepatic stellate cell (HSC) activation, we detected the expression of gremlin1 in mice with hepatic fibrosis induced by porcine serum using real time quantitative PCR (RT-qPCR) and immunohistochemical staining. The hepatic fibrosis mice were evaluated by the external feature of the liver, histology, hepatic function, collagen deposition, and the expression of fibrosis-related genes (genes COLIα2 and COLIVα2) in the liver. In the HSC-T6, western blotting was used to analyze the expression of α-smooth muscle actin (α-SMA), COL1α, and TGF-β1 in conditions of overexpression of gremlin1 or gremlin1 being knocked down by specific siRNA, respectively. The results showed that the mRNA expression of the gremlin1 gene was significantly increased consistent with increased expression of COLIα2 and COLIVα2 in the liver tissue of the hepatic fibrosis mice. Increased expression of gremlin1 coincided with the same area of the collagen deposition. Furthermore, the results also showed that the expression of α-SMA, COLIα1, and TGF-β1 was consistent with the expression of gremlin1 not only in the HSC-T6 overexpressing gremlin1 but also in the HSC-T6 that gremlin1 is knocked down by specific siRNA. The findings suggest that gremlin1 might play an important role in the progression of hepatic fibrosis and that it modulates HSC activation.

Bone Morphogenetic Proteins and Their Receptors in the Eye

The human genome encodes at least 42 different members of the transforming growth factor-β superfamily of growth factors. Bone morphogenetic proteins (BMPs) are the largest subfamily of proteins within the transforming growth factor-β superfamily and are involved in numerous cellular functions including development, morphogenesis, cell proliferation, apoptosis, and extracellular matrix synthesis. This article first reviews BMPs and BMP receptors, BMP signaling pathways, and mechanisms controlling BMP signaling. Second, we review BMP and BMP receptor expression during embryonic ocular development/ differentiation and in adult ocular tissues. Lastly, future research directions with respect to BMP, BMP receptors, and ocular tissues are suggested.

Gremlin regulates renal inflammation via the vascular endothelial growth factor receptor 2 pathway

Inflammation is a main feature of progressive kidney disease. Gremlin binds to bone morphogenetic proteins (BMPs), acting as an antagonist and regulating nephrogenesis and fibrosis among other processes. Gremlin also binds to vascular endothelial growth factor receptor-2 (VEGFR2) in endothelial cells to induce angiogenesis. In renal cells, gremlin regulates proliferation and fibrosis, but there are no data about inflammatory-related events. We have investigated the direct effects of gremlin in the kidney, evaluating whether VEGFR2 is a functional gremlin receptor. Administration of recombinant gremlin to murine kidneys induced rapid and sustained activation of VEGFR2 signalling, located in proximal tubular epithelial cells. Gremlin bound to VEGFR2 in these cells in vitro, activating this signalling pathway independently of its action as an antagonist of BMPs. In vivo, gremlin caused early renal damage, characterized by activation of the nuclear factor (NF)-κB pathway linked to up-regulation of pro-inflammatory factors and infiltration of immune inflammatory cells. VEGFR2 blockade diminished gremlin-induced renal inflammatory responses. The link between gremlin/VEGFR2 and NF-κB/inflammation was confirmed in vitro. Gremlin overexpression was associated with VEGFR2 activation in human renal disease and in the unilateral ureteral obstruction experimental model, where VEGFR2 kinase inhibition diminished renal inflammation. Our data show that a gremlin/VEGFR2 axis participates in renal inflammation and could be a novel target for kidney disease.

Low glucose microenvironment of normal kidney cells stabilizes a subset of messengers involved in angiogenesis

As glucose is a mandatory nutrient for cell proliferation and renewal, it is suspected that glucose microenvironment is sensed by all cell types to regulate angiogenesis. Several glucose-sensing components have been partially described to respond to high glucose levels. However, little is known about the response to low glucose. Here, we used well-differentiated isolated normal rat renal tubules under normal oxygenation conditions to assess the angiogenic response to low glucose. In apparent paradox, but confirming observations made separately in other models, high glucose but also low glucose increased mRNA level of vascular endothelial growth factor A (VEGFA). A subset of mRNAs including hypoxia-inducible factor 1A (HIF1A), angiopoietin receptor (TIE-2), and VEGF receptor 2 (FLK1) were similarly glucose-sensitive and responded to low glucose by increased stability independently of HIF1A and HIF2A proteins. These results contribute to gain some insights as to how normal cells response to low glucose may play a role in the tumor microenvironment.

Gremlin, a bone morphogenetic protein antagonist, is a crucial angiogenic factor in pituitary adenoma

Gremlin is an antagonist of bone morphogenetic protein (BMP) and a major driving force in skeletal modeling in the fetal stage. Several recent reports have shown that Gremlin is also involved in angiogenesis of lung cancer and diabetic retinopathy. The purpose of this study was to investigate the role of Gremlin in tumor angiogenesis in pituitary adenoma. Double fluorescence immunohistochemistry of Gremlin and CD34 was performed in pituitary adenoma tissues obtained during transsphenoidal surgery in 45 cases (7 PRLoma, 17 GHoma, 2 ACTHoma, and 2 TSHoma). Gremlin and microvascular density (MVD) were detected by double-immunofluorescence microscopy in CD34-positive vessels from tissue microarray analysis of 60 cases of pituitary adenomas (6 PRLoma, 23 GHoma, 22 NFoma, 5 ACTHoma, and 4 TSHoma). In tissue microarray analysis, MVD was significantly correlated with an increased Gremlin level (linear regression: P < 0.005,  r (2) = 0.4958). In contrast, Gremlin expression showed no correlation with tumor subtype or Knosp score. The high level of expression of Gremlin in pituitary adenoma tissue with many CD34-positive vessels and the strong coherence of these regions indicate that Gremlin is associated with angiogenesis in pituitary adenoma cells.

Viability of primary cultured retinal neurons in a hyperglycemic condition

The retina of Wistar rats within 1-3 days of birth were dissociated into a retinal cell suspension using 0.05% trypsin digestion. The cell suspension was incubated in Dulbecco's modified Eagle's medium for 24 hours, followed by neurobasal medium for 5-7 days. Nissl staining showed that 79.86% of primary cultured retinal cells were positive and immunocytochemical staining showed that the purity of anti-neurofilament heavy chain antibody-positive cells was 71.53%, indicating that the primary culture system of rat retinal neurons was a reliable and stable cell system with neurons as the predominant cell type. The primary cultured retinal neurons were further treated with 0, 5.5, 15, 25, and 35 mM glucose for 24, 48, and 72 hours. The thiazolyl blue tetrazolium bromide test and flow cytometry showed that with increasing glucose concentration and treatment duration, the viability of retinal neurons was reduced, and apoptosis increased. In particular, 35 mM glucose exhibited the most significant effect at 72 hours. Thus, rat retinal neurons treated with 35 mM glucose for 72 hours can be used to simulate a neuronal model of diabetic retinopathy.

Gremlin-1 is an inhibitor of macrophage migration inhibitory factor and attenuates atherosclerotic plaque growth in ApoE-/- Mice

Monocyte infiltration and macrophage formation are pivotal steps in atherosclerosis and plaque vulnerability. Gremlin-1/Drm is crucial in embryo-/organogenesis and has been shown to be expressed in the adult organism at sites of arterial injury and to inhibit monocyte migration. The purpose of the present study was to evaluate and characterize the role of Gremlin-1 in atherosclerosis. Here we report that Gremlin-1 is highly expressed primarily by monocytes/macrophages in aortic atherosclerotic lesions of ApoE(-/-) mice and is secreted from activated monocytes and during macrophage development in vitro. Gremlin-1 reduces macrophage formation by inhibiting macrophage migration inhibitory factor (MIF), a cytokine critically involved in atherosclerotic plaque progression and vulnerability. Gremlin-1 binds with high affinity to MIF (KD = 54 nm), as evidenced by surface plasmon resonance analysis and co-immunoprecipitation, and reduces MIF-induced release of TNF-α from macrophages. Treatment of ApoE(-/-) mice with a dimeric recombinant fusion protein, mGremlin1-Fc, but not with equimolar control Fc or inactivated mGremlin1-Fc, reduced TNF-α expression, the content of monocytes/macrophages of atherosclerotic lesions, and attenuated atheroprogression. The present data disclose that Gremlin-1 is an endogenous antagonist of MIF and define a role for Gremlin-1/MIF interaction in atherosclerosis.

Biomolecular basis of the role of diabetes mellitus in osteoporosis and bone fractures

Osteoporosis has become a serious health problem throughout the world which is associated with an increased risk of bone fractures and mortality among the people of middle to old ages. Diabetes is also a major health problem among the people of all age ranges and the sufferers due to this abnormality increasing day by day. The aim of this review is to summarize the possible mechanisms through which diabetes may induce osteoporosis. Diabetes mellitus generally exerts its effect on different parts of the body including bone cells specially the osteoblast and osteoclast, muscles, retina of the eyes, adipose tissue, endocrine system specially parathyroid hormone (PTH) and estrogen, cytokines, nervous system and digestive system. Diabetes negatively regulates osteoblast differentiation and function while positively regulates osteoclast differentiation and function through the regulation of different intermediate factors and thereby decreases bone formation while increases bone resorption. Some factors such as diabetic neuropathy, reactive oxygen species, Vitamin D, PTH have their effects on muscle cells. Diabetes decreases the muscle strength through regulating these factors in various ways and ultimately increases the risk of fall that may cause bone fractures.

Gremlin induces cell proliferation and extra cellular matrix accumulation in mouse mesangial cells exposed to high glucose via the ERK1/2 pathway

Background

Gremlin, a bone morphogenetic protein antagonist, plays an important role in the pathogenesis of diabetic nephropathy (DN). However, the specific molecular mechanism underlying Gremlin’s involvement in DN has not been fully elucidated. In the present study, we investigated the role of Gremlin on cell proliferation and accumulation of extracellular matrix (ECM) in mouse mesangial cells (MMCs), and explored the relationship between Gremlin and the ERK1/2 pathway.

Methods

To determine expression of Gremlin in MMCs after high glucose (HG) exposure, Gremlin mRNA and protein expression were evaluated using real-time polymerase chain reaction and western blot analysis, respectively. To determine the role of Gremlin on cell proliferation and accumulation of ECM, western blot analysis was used to assess expression of pERK1/2, transforming growth factor-β1 (TGF-β1) and connective tissue growth factor (CTGF). Cell proliferation was examined by bromodeoxyuridine (BrdU) ELISA, and accumulation of collagen IV was measured using a radioimmunoassay. This enabled the relationship between Gremlin and ERK1/2 pathway activation to be investigated.

Results

HG exposure induced expression of Gremlin, which peaked 12 h after HG exposure. HG exposure alone or transfection of normal-glucose (NG) exposed MMCs with Gremlin plasmid (NG + P) increased cell proliferation. Transfection with Gremlin plasmid into MMCs previously exposed to HG (HG + P) significantly increased this HG-induced phenomenon. HG and NG + P conditions up-regulated protein levels of TGF-β1, CTGF and collagen IV accumulation, while HG + P significantly increased levels of these further. Inhibition of Gremlin with Gremlin siRNA plasmid reversed the HG-induced phenomena. These data indicate that Gremlin can induce cell proliferation and accumulation of ECM in MMCs. HG also induced the activation of the ERK1/2 pathway, which peaked 24 h after HG exposure. HG and NG + P conditions induced overexpression of pERK1/2, whilst HG + P significantly induced levels further. Inhibition of Gremlin by Gremlin siRNA plasmid reversed the HG-induced phenomena. This indicates Gremlin can induce activation of the ERK1/2 pathway in MMCs.

Conclusion

Culture of MMCs in the presence of HG up-regulates expression of Gremlin. Gremlin induces cell proliferation and accumulation of ECM in MMCs. and enhances activation of the ERK1/2 pathway.

Arthroscopically assisted use of injectable bone graft substitutes for management of scaphoid nonunions

PURPOSE

The purpose of this study was to analyze the clinical follow-up results (minimum, 2 years) in patients with nonunions of the scaphoid with minimal sclerosis treated with arthroscopically assisted percutaneous internal fixation augmented by injection of a bone graft substitute.

METHODS

From January 2006 through November 2007, a consecutive series of 15 patients with fibrous union or nonunion of a carpal scaphoid fracture with minimal sclerosis or resorption at the nonunion site were treated with arthroscopically assisted percutaneous internal fixation combined with the use of injectable bone graft substitute. Preoperative and postoperative evaluations included measurement of clinical (grip strength and range of motion), radiographic, and functional (Mayo Modified Wrist Score) parameters, as well as satisfaction. The sample included 13 men and 2 women with a mean age of 31 years (range, 20 to 45 years). We recorded union and return to activity and analyzed data with regular clinical follow-up at a mean of 33 months (range, 24 to 46 months).

RESULTS

We confirmed union in 14 of 15 patients (93%) at a mean of 15.4 weeks according to clinical examinations and standard radiography. For the Mayo Modified Wrist Score, there were 10 excellent and 4 good results. A total of 14 of 15 patients (93%) returned to work or sports activities at their preinjury level.

CONCLUSIONS

Arthroscopically assisted treatment with percutaneous internal fixation with injectable bone graft substitute is a reliable and minimally invasive method to achieve union and scaphoid healing.

LEVEL OF EVIDENCE

Level IV, therapeutic case series.

Identification of Diabetic Retinopathy Genes through a Genome-Wide Association Study among Mexican-Americans from Starr County, Texas

To identify genetic loci for severe diabetic retinopathy, 286 Mexican-Americans with type 2 diabetes from Starr County, Texas, completed physical examinations including fundus photography for diabetic retinopathy grading. Individuals with moderate-to-severe non-proliferative and proliferative diabetic retinopathy were defined as cases. Direct genotyping was performed using the Affymetrix GeneChip Human Mapping 100 K Set, and SNPs passing quality control criteria were used to impute markers available in HapMap Phase III Mexican population (MXL) in Los Angeles, California. Two directly genotyped markers were associated with severe diabetic retinopathy at a P-value less than .0001: SNP rs2300782 (P = 6.04 × 10(-5)) mapped to an intron region of CAMK4 (calcium/calmodulin-dependent protein kinase IV) on chromosome 5, and SNP rs10519765 (P = 6.21 × 10(-5)) on chromosomal 15q13 in the FMN1 (formin 1) gene. Using well-imputed markers based on the HapMap III Mexican population, we identified an additional 32 SNPs located in 11 chromosomal regions with nominal association with severe diabetic retinopathy at P-value less than .0001. None of these markers were located in traditional candidate genes for diabetic retinopathy or diabetes itself. However, these signals implicate genes involved in inflammation, oxidative stress and cell adhesion for the development and progression of diabetic retinopathy.

Evaluation of gremlin 1 (GREM1) as a candidate susceptibility gene for albuminuria-related traits in Mexican Americans with type 2 diabetes mellitus

Several novel genes that are up-regulated in the kidney in diabetes have been identified including GREM1, which encodes gremlin 1. GREM1 maps to human chromosome 15q12, a region previously found to be linked to albumin to creatinine ratio (ACR) in Mexican Americans. The objective of this study is to investigate whether genetic variants in GREM1, a positional candidate gene, contribute to variation in ACR. By sequencing 32 individuals for both exons and 2-kilobase putative promoter region of GREM1, we identified 19 genetic variants including 5 in the promoter region and 13 in the 3' untranslated region. Of 19 polymorphisms identified, 13 polymorphisms were genotyped in the entire cohort (N = 670, 39 large families) either by restriction fragment length polymorphism or by TaqMan (Applied Biosystems, Foster City, CA) assays. Association analyses between the genotypes and ACR, type 2 diabetes mellitus, and related phenotypes were carried out using a measured genotype approach as implemented in the variance component analytical tools (SOLAR). Of the variants examined for association, none exhibited statistically significant association with ACR after accounting for the effects of covariates such as age, sex, diabetes, duration of diabetes, systolic blood pressure, and antihypertensive medications. However, 2 novel variants at the 3' untranslated region showed significant association with estimated glomerular filtration rate (P = .010 and P = .049) and body mass index (P = .013 and P = .019) after accounting for trait-specific covariate influences. Furthermore, a novel variant located in the promoter exhibited a significant association with systolic (P = .038) and diastolic blood pressure (P = .005) after adjusting for the effects of age, sex, diabetes, and antihypertensive medications. In conclusion, the variants examined at GREM1 are not significant contributors to variation in ACR in Mexican Americans, although they appear to minimally influence risk factors related to ACR.

Bone morphogenetic protein 4 inhibits TGF-beta2 stimulation of extracellular matrix proteins in optic nerve head cells: role of gremlin in ECM modulation

The characteristic cupping of the optic nerve head (ONH) in glaucoma is associated with elevated TGF-beta2 and increased synthesis and deposition of extracellular matrix (ECM) proteins. In addition to TGF-beta2, the human ONH also expresses bone morphogenetic proteins (BMPs) and BMP receptors, which are members of the TGF-beta superfamily. We examined the potential effects of BMP4 and the BMP antagonist gremlin on TGF-beta2 induction of ECM proteins in ONH cells. BMP-4 dose dependently inhibited TGF-beta2-induced fibronectin (FN) and PAI-1 expression in ONH astrocytes and lamina cribrosa (LC) cells and also reduced TGF-beta2 stimulation of collagen I, collagen VI, and elastin. Addition of gremlin blocked this BMP-4 response, increasing cellular and secreted FN as well as PAI-1 levels in both cell types. Gremlin was expressed in ONH tissues and ONH cells, and gremlin protein levels were significantly increased in the LC region of human glaucomatous ONH tissues. Interestingly, recombinant gremlin dose dependently increased ECM protein expression in cultured ONH astrocytes and LC cells. Gremlin stimulation of ECM required activation of TGF-beta receptor and R-Smad3. TGF-beta2 increased gremlin mRNA expression and protein levels in ONH cells. Inhibition of either the type I TGF-beta receptor or Smad3 phosphorylation blocked TGF-beta2-induced gremlin expression. In conclusion, BMP4 blocked the TGF-beta2 induction of ECM proteins in ONH cells. The BMP antagonist gremlin reversed this inhibition, allowing TGF-beta2 stimulation of ECM synthesis. Increased expression of gremlin in the glaucomatous ONH may further exacerbate TGF-beta2 effects on ONH ECM metabolism by inhibiting BMP-4 antagonism of TGF-beta2 signaling. Modulation of the ECM via gremlin provides a novel therapeutic target for glaucoma.

Diabetes mellitus and apoptosis: inflammatory cells

Since the early observation that similarities between thyroiditis and insulitis existed, the important role played by inflammation in the development of diabetes has been appreciated. More recently, experiments have shown that inflammation also plays a prominent role in the development of target organ damage arising as complications, with both elements of the innate and the adaptive immune system being involved, and that cytokines contributing to local tissue damage may arise from both infiltrating and resident cells. This review will discuss the experimental evidence that shows that inflammatory cell-mediated apoptosis contributes to target organ damage, from beta cell destruction to both micro- and macro-vascular disease complications, and also how alterations in leukocyte turnover affects immune function.

The osteogenic potential of pseudoarthrosis tissue and bone from human scaphoid non-unions

Scaphoid fractures have the highest prevalence of non-union in the human body, but little is known about the osteogenic potential of cells at the pseudoarthrosis. It was our goal to determine whether cells isolated from non-unions could be stimulated to differentiate into osteoblasts and produce bone in vitro. Fifteen human scaphoid non-unions were excised during surgery and bone from either side of the non-union and the fibrocartilagenous central regions were harvested. Osteoblastic populations were subcultured from these. The number of bone nodules (colonies of osteoblast cells that produced bone) from all three regions was similar to the number of nodules derived from iliac bone cultures from the same patients. Treatment of cells with rhBMP-2 resulted in a 3- to 10-fold increase in bone nodule formation in vitro from cells derived from the non-unions. These data demonstrate that cells at the pseudoarthrosis have osteogenic capability and can be stimulated by rhBMP-2, possibly increasing the ability to heal.

Chordin-like 1, a bone morphogenetic protein-4 antagonist, is upregulated by hypoxia in human retinal pericytes and plays a role in regulating angiogenesis

PURPOSE

Pericytes play a specialized role in regulating angiogenesis and vascular function by providing vascular stability and controlling endothelial cell proliferation. Disorders in pericyte function and pericyte-endothelial interaction have been observed in several disease states including tumor angiogenesis and diabetic microangiopathy. In ischemic retinal disease, hypoxia is a potent driver of retinal angiogenesis. This study investigated the effects of hypoxia on retinal pericyte gene expression, and demonstrates a role in angiogenesis regulation for the hypoxia driven gene, chordin-like 1 (CHL-1).

METHODS

In the current studies, we investigated hypoxia-induced gene expression in human retinal pericytes and found that expression of CHL-1, a member of the bone morphogenetic protein (BMP) superfamily, is upregulated by hypoxia. We investigated regulation of CHL-1 expression and the ability of CHL-1 to antagonize the antiangiogenic properties of BMP-4 using a human cell-based angiogenesis assay.

RESULTS

We report that hypoxia induced hypoxia inducible factor-1alpha-driven expression of CHL-1. Both CHL-1 and BMP-4 were secreted from human retinal pericytes. We found that CHL-1 complexes with BMP-4 to antagonize the antiangiogenic effects of BMP-4, and that BMP-4 and vascular endothelial growth factor (VEGF) co-regulate angiogenesis.

CONCLUSIONS

We propose that hypoxia-induced upregulation of CHL-1 alters the homeostatic balance between BMP-4 and VEGF to synergize with VEGF in driving retinal angiogenesis.

Oxidative stress and glaucoma: injury in the anterior segment of the eye

The perturbation of the pro-oxidant/antioxidant balance can lead to increased oxidative damage, especially when the first line of antioxidant defense weakens with age. Chronic changes in the composition of factors present in aqueous or vitreous humor may induce alterations both in trabecular cells and in cells of the optic nerve head. Free radicals and reactive oxygen species are able to affect the cellularity of the human trabecular meshwork (HTM). These findings suggest that intraocular pressure increase, which characterizes most glaucomas, is related to oxidative and degenerative processes affecting the HTM and, more specifically, its endothelial cells. This supports the theory that glaucomatous damage is the pathophysiological consequence of oxidative stress. Glaucomatous subjects might have a genetic predisposition, rendering them more susceptible to reactive oxygen species-induced damage. It is likely that specific genetic factors contribute to both the elevation of IOP and susceptibility of the optic nerve/retinal ganglion cells (RGCs) to degeneration. Thus, oxidative stress plays a fundamental role during the arising of glaucoma-associated lesions, first in the HTM and then, when the balance between nitric oxide and endothelins is broken, in neuronal cell. Vascular damage and hypoxia, often associated with glaucoma, lead to apoptosis of RGCs and may also contribute to the induction of oxidative damage to the HTM. On the whole, these findings support the hypothesis that oxidative damage is an important step in the pathogenesis of primary open-angle glaucoma and might be a relevant target for both prevention and therapy.