Regulation of Vascular Proteoglycan Synthesis by Metabolic Factors Associated with Diabetes

Biglycan and atherosclerosis: Lessons from high cardiovascular risk conditions

Atherosclerosis (ATH) is a chronic, dynamic, evolutive process involving morphological and structural subversion of artery walls, leading to the formation of atherosclerotic plaques. ATH generally initiates during the childhood, occurring as a result of a number of changes in the intima tunica and in the media of arteries. A key event occurring during the pathobiology of ATH is the accumulation of lipoproteins in the sub-intimal spaces mediated by extracellular matrix (ECM) molecules, especially by the chondroitin sulfate/dermatan sulfate (CS/DS) -containing proteoglycans (CS/DSPGs). Among them, the proteoglycan biglycan (BGN) is critically involved in the onset and progression of ATH and evidences show that BGN represents the missing link between the pro-atherogenic status induced by both traditional and non-traditional cardiovascular risk factors and the development and progression of vascular damage. In the light of these findings, the role of BGN in dyslipidemia, hypertension, cigarette smoking, diabetes, chronic kidney disease and inflammatory status is briefly analyzed and discussed in order to shed new light on the underlying mechanisms governing the association between BGN and ATH.

Micromanaging human placental function: differential microRNA expression in feto-placental endothelial cells of gestational diabetes pregnancies

Healthy development in utero relies on the appropriate exchange of nutrients and other signalling between the maternal and fetal circulations. Disruption to this fine balance is associated with several pregnancy and adverse birth outcomes, including gestational diabetes mellitus (GDM). This is a complex condition influenced by genetic, environment and potentially epigenetic factors in association with a range of altered developmental outcomes. A recent study, published in Clinical Science, explores miRNAs as a molecular mechanism underpinning the altered function of placental endothelial cells in GDM pregnancies.

Gestational diabetes alters microRNA signatures in human feto-placental endothelial cells depending on fetal sex

MicroRNAs (miRNAs), small non-coding RNAs, have emerged as important, epigenetic regulators of endothelial function. Metabolic disturbances such as diabetes alter miRNA expression. In adults, the miRNA transcriptome as well as endothelial function differ between the sexes. Here, we hypothesized that metabolic disturbances associated with gestational diabetes (GDM) alter miRNA signatures in feto-placental endothelial cells (fpEC), dependent on fetal sex. We isolated human primary fpEC after normal and GDM-complicated pregnancies with male and female neonates and screened for differential miRNA expression using next-generation miRNA sequencing. To test for miRNAs commonly regulated in fpEC of female and male progeny, data were stratified for fetal sex and maternal body mass index (BMI). Analyses were also performed separately for female and male fpEC, again accounting for maternal BMI as covariate. Potential biological pathways regulated by the altered set of miRNAs were determined using mirPath software. Maternal GDM altered 26 miRNA signatures when male and female fpEC were analyzed together. Separate analysis of male versus female fpEC revealed 22 GDM affected miRNAs in the females and only 4 in the males, without overlap. Biological functions potentially modulated by the affected miRNAs related to ‘Protein Processing in Endoplasmic Reticulum’ and ‘Proteoglycans in Cancer’. Maternal GDM alters miRNA signatures in fpEC, and biological functions affected by these miRNAs relate to well-known adverse functional consequences of diabetes on endothelium. GDM effects were highly dependent on fetal sex with miRNA signatures in female fpEC being more susceptible to metabolic derangements of GDM than miRNAs in male fpEC.

Prevention of renal apoB retention is protective against diabetic nephropathy: role of TGF-β inhibition

Animal studies demonstrate that hyperlipidemia and renal lipid accumulation contribute to the pathogenesis of diabetic nephropathy (DN). We previously demonstrated that renal lipoproteins colocalize with biglycan, a renal proteoglycan. The purpose of this study was to determine whether prevention of renal lipid (apoB) accumulation attenuates DN. Biglycan-deficient and biglycan wild-type Ldlr^-/- mice were made diabetic via streptozotocin and fed a high cholesterol diet. As biglycan deficiency is associated with elevated transforming growth factor-β (TGF-β), in some experiments mice were injected with either the TGF-β-neutralizing antibody, 1D11, or with 13C4, an irrelevant control antibody. Biglycan deficiency had no significant effect on renal apoB accumulation, but led to modest attenuation of DN with ∼30% reduction in albuminuria; however, biglycan deficiency caused a striking elevation in TGF-β. Use of 1D11 led to sustained suppression of TGF-β for approximately 8 weeks at a time. The 1D11 treatment caused decreased renal apoB accumulation, decreased albuminuria, decreased renal hypertrophy, and improved survival, compared with the 13C4 treatment. Thus, prevention of renal apoB accumulation is protective against development of DN. Furthermore, this study demonstrates that prevention of renal apoB accumulation is a mechanism by which TGF-β inhibition is nephroprotective.

AMPK dysregulation promotes diabetes-related reduction of superoxide and mitochondrial function

Diabetic microvascular complications have been considered to be mediated by a glucose-driven increase in mitochondrial superoxide anion production. Here, we report that superoxide production was reduced in the kidneys of a steptozotocin-induced mouse model of type 1 diabetes, as assessed by in vivo real-time transcutaneous fluorescence, confocal microscopy, and electron paramagnetic resonance analysis. Reduction of mitochondrial biogenesis and phosphorylation of pyruvate dehydrogenase (PDH) were observed in kidneys from diabetic mice. These observations were consistent with an overall reduction of mitochondrial glucose oxidation. Activity of AMPK, the major energy-sensing enzyme, was reduced in kidneys from both diabetic mice and humans. Mitochondrial biogenesis, PDH activity, and mitochondrial complex activity were rescued by treatment with the AMPK activator 5-aminoimidazole-4-carboxamide-1-β-D-ribofuranoside (AICAR). AICAR treatment induced superoxide production and was linked with glomerular matrix and albuminuria reduction in the diabetic kidney. Furthermore, diabetic heterozygous superoxide dismutase 2 (Sod2(+/-)) mice had no evidence of increased renal disease, and Ampka2(-/-) mice had increased albuminuria that was not reduced with AICAR treatment. Reduction of mitochondrial superoxide production with rotenone was sufficient to reduce AMPK phosphorylation in mouse kidneys. Taken together, these results demonstrate that diabetic kidneys have reduced superoxide and mitochondrial biogenesis and activation of AMPK enhances superoxide production and mitochondrial function while reducing disease activity.

Hyperglycemia reduces proteoglycan levels in tendons

RATIONALE

Diabetic tendinopathy is characterized by increased stiffness, thickness, and excess calcification of affected tendons. We investigated the hypothesis that proteoglycans (PGs), as key regulators of tendon structure and calcification, are altered in diabetic tendons.

METHODS

Adult porcine patellar tendons were incubated in iso-osmolar media with high or normal glucose levels for 2 weeks. The PG fraction was isolated and analyzed. Protein and mRNA levels of five PGs were measured. PG production was assessed in primary tenocyte monolayers by (35)S-sulfate labeling in high and normal glucose conditions with and without exposure to advanced glycation end-products (AGEs). Levels of transforming growth factor β, which commonly mediates some effects of hyperglycemia, were also measured and the effects of free radical scavengers on (35)S-sulfate incorporation were determined.

RESULTS

PG levels were significantly decreased in tendons exposed to high glucose media compared with tendons in iso-osmolar control media. Relative quantities of individual PGs were unchanged by exposure to hyperglycemia and mRNAs for PGs were variably affected. High glucose media decreased PG production by tenocytes as measured by (35)S-sulfate labeling, whereas AGE-modified type I collagen and free radical scavengers had no effects. Hyperglycemic conditions increased levels of transforming growth factor β1 in an AGE-independent manner.

CONCLUSIONS

Hyperglycemia produces a reduction in PG levels related to decreased synthesis or sulfation of glycosaminoglycans, which may contribute to the tendon pathology observed clinically in diabetes.

RhoGDI2 suppresses lung metastasis in mice by reducing tumor versican expression and macrophage infiltration

Half of patients with muscle-invasive bladder cancer develop metastatic disease, and this is responsible for most of the deaths from this cancer. Low expression of RhoGTP dissociation inhibitor 2 (RhoGDI2; also known as ARHGDIB and Ly-GDI) is associated with metastatic disease in patients with muscle-invasive bladder cancer. Moreover, a reduction in metastasis is observed upon reexpression of RhoGDI2 in xenograft models of metastatic cancer. Here, we show that RhoGDI2 suppresses lung metastasis in mouse models by reducing the expression of isoforms V1 and V3 of the proteoglycan versican (VCAN; also known as chondroitin sulfate proteoglycan 2 [CSPG2]). In addition, we found that high versican levels portended poor prognosis in patients with bladder cancer. The functional importance of tumor expression of versican in promoting metastasis was established in in vitro and in vivo studies in mice that implicated a role for the chemokine CCL2 (also known as MCP1) and macrophages. Further analysis indicated that RhoGDI2 suppressed metastasis by altering inflammation in the tumor microenvironment. In summary, we demonstrate what we believe to be a new mechanism of metastasis suppression that works by reducing host responses that promote metastatic colonization of the lung. Therapeutic targeting of these interactions may provide a novel adjuvant strategy for delaying the appearance of clinical metastasis in patients.

Renal accumulation of biglycan and lipid retention accelerates diabetic nephropathy

Hyperlipidemia worsens diabetic nephropathy, although the mechanism by which renal lipids accumulate is unknown. We previously demonstrated that renal proteoglycans have high low-density lipoprotein (LDL) binding affinity, suggesting that proteoglycan-mediated LDL retention may contribute to renal lipid accumulation. The aim of this study was to determine the relative effect of diabetes and hyperlipidemia on renal proteoglycan content. Diabetic and non-diabetic LDL receptor-deficient mice were fed diets containing 0% or 0.12% cholesterol for 26 weeks, and then kidneys were analyzed for renal lipid and proteoglycan content. Diabetic mice on the high-cholesterol diet had accelerated development of diabetic nephropathy with elevations in urine albumin excretion, glomerular and renal hypertrophy, and mesangial matrix expansion. Renal lipid accumulation was significantly increased by consumption of the 0.12% cholesterol diet, diabetes, and especially by both. The renal proteoglycans biglycan and decorin were detectable in glomeruli, with a significant increase in renal biglycan content in diabetic mice on the high-cholesterol diet. Renal biglycan and renal apolipoprotein B were colocalized, and regression analyses showed a significant relation between renal biglycan and renal apolipoprotein B content. The increased renal biglycan content in diabetic nephropathy probably contributes to renal lipid accumulation and the development of diabetic nephropathy.

Transforming growth factor-β regulation of proteoglycan synthesis in vascular smooth muscle: contribution to lipid binding and accelerated atherosclerosis in diabetes

Atherosclerosis is accelerated in the setting of diabetes, but the factors driving this phenomenon remain elusive. Hyperglycemia leads to elevated levels of transforming growth factor (TGF)-β and TGF-β has been implicated as a factor in atherosclerosis. Given the established association between hyperglycemia and elevated TGF-β, it is plausible that elevated TGF-β levels in diabetes play a pathogenic role in the development of accelerated atherosclerosis. TGF-β is a potent regulator of extracellular matrix synthesis, including many actions on proteoglycan synthesis that lead to increased binding to low-density lipoprotein and therefore potentially increased lipid retention in the vessel wall and accelerated atherosclerosis. TGF-β signals through the canonical TGF-β receptor I-mediated phosphorylation of Smad transcription factors and TGF-β signaling is also known to involve, positively and negatively, interactions with the mitogen-activated protein kinase pathways. The focus of the present review is on the effects of TGF-β on proteoglycan synthesis in vascular smooth muscle and particularly the signaling pathways through which TGF-β exerts its effects, because those pathways may be therapeutic targets for the prevention of pathological modifications in the proteoglycan component of the vessel wall in the vascular diseases of diabetes.

Proteoglycan mediated lipoprotein retention: a mechanism of diabetic atherosclerosis

The response to retention hypothesis outlines the initial stages of atherosclerotic lesion formation. The central theme of the hypothesis is that proteoglycan mediated lipoprotein retention plays a critical step in the initiation of atherosclerosis development. Recent research using human arterial specimens, transgenic mouse models and molecular biology techniques have added to our understanding of atherosclerosis development, and provided experimental data in support of the response to retention hypothesis. In this review we summarize the recent data, in particular that which addresses mechanisms by which diabetes can accelerate atherosclerosis formation, with a focus on proteoglycan-mediated LDL retention.

Serum amyloid A, but not C-reactive protein, stimulates vascular proteoglycan synthesis in a pro-atherogenic manner

Inflammatory markers serum amyloid A (SAA) and C-reactive protein (CRP) are predictive of cardiac disease and are proposed to play causal roles in the development of atherosclerosis, in which the retention of lipoproteins by vascular wall proteoglycans is critical. The purpose of this study was to determine whether SAA and/or CRP alters vascular proteoglycan synthesis and lipoprotein retention in a pro-atherogenic manner. Vascular smooth muscle cells were stimulated with either SAA or CRP (1 to 100 mg/L) and proteoglycans were then isolated and characterized. SAA, but not CRP, increased proteoglycan sulfate incorporation by 50 to 100% in a dose-dependent manner (P < 0.0001), increased glycosaminoglycan chain length, and increased low-density lipoprotein (LDL) binding affinity (K(d), 29 microg/ml LDL versus 90 microg/ml LDL for SAA versus control proteoglycans; P < 0.005). Furthermore, SAA up-regulated biglycan via the induction of endogenous transforming growth factor (TGF)-beta. To determine whether SAA stimulated proteoglycan synthesis in vivo, ApoE(-/-) mice were injected with an adenovirus expressing human SAA-1, a null virus, or saline. Mice that received adenovirus expressing SAA had increased TGF-beta concentrations in plasma and increased aortic biglycan content compared with mice that received either null virus or saline. Thus, SAA alters vascular proteoglycans in a pro-atherogenic manner via the stimulation of TGF-beta and may play a causal role in the development of atherosclerosis.