Low-density lipoprotein stimulates mesangial cell proteoglycan and hyaluronan synthesis

The impact of body weight management in chronic kidney disease patients with obesity

OBJECTIVE

Chronic kidney disease (CKD) and obesity are important public health concerns. Because obesity may initiate and/or accelerate kidney damage, weight control may benefit CKD patients.

DESIGN AND METHODS

We examined the influence of dietary management and physical exercise in 38 obese CKD patients with or without target reduction of body weight 3% or more from baseline.

RESULTS

After a 2-month lifestyle intervention program, those with target body weight control had significant improvement of blood pressure control, as well as reduced lipid profiles, serum creatinine level (1.1 ± 0.3 vs. 0.8 ± 0.3; P < .001), estimated glomerular filtration rate (75.9 ± 21.2 vs. 104.9 ± 38.1; P < .001), and proteinuria (76.3% vs. 50.0%; P = .02). They had greater improvement in cardiorespiratory endurance in an 800-m running test (375.1 ± 64.7 vs. 327.1 ± 84.0 seconds; P = .001), better abdominal muscle strength and endurance in a timed sit-up test (13.6 ± 9.1 vs. 19.9 ± 9.2 number/minute; P = .005), and greater flexibility in a sit-and-reach test (18.8 ± 10.9 vs. 27.8 ± 10.9 cm; P < .001) comparing baseline and postintervention values.

CONCLUSIONS

A combination of dietary management and exercise were associated with improvements in health-related physical fitness, cardiovascular risk factors (blood pressure and lipid control), and renal profiles in obese CKD patients. Supportive individualized programs for lifestyle change could exert beneficial effects, but long-term research with a larger patient population is needed to elucidate the optimal effective combination of dietary management and exercise.

Reversibility of renal injury with cholesterol lowering in hyperlipidemic diabetic mice

Hyperlipidemia is a risk factor for development and progression of diabetic nephropathy. However, it is not known if reduction of hyperlipidemia is protective against progression of disease. The goal of this study was to determine if reduction of hypercholesterolemia could limit progression of diabetic nephropathy. Diabetic and nondiabetic LDL receptor deficient (LDLR(-/-)) mice were fed diets containing either no cholesterol (0%) or high cholesterol (0.12%) for 36 weeks. One group each of diabetic and nondiabetic mice were fed the high-cholesterol diet for 26 weeks then changed to the 0% cholesterol diet for the last 10 weeks. Consumption of the high-cholesterol diet exacerbated the development of diabetic nephropathy with elevations in urine albumin excretion, glomerular and renal hypertrophy, and mesangial matrix expansion. Increased glomerular lipid and apolipoprotein B accumulation was found in diabetic mice that consumed the 0.12% cholesterol diet compared with other groups. However, diabetic mice that changed from the high-cholesterol diet to the 0% cholesterol diet for the last 10 weeks had lower urine albumin excretion and mesangial matrix expansion compared with mice that consumed the 0.12% cholesterol diet throughout. This suggests that hyperlipidemia causes continuous renal injury, and that lowering cholesterol levels by dietary means can improve renal function in diabetic LDLR(-/-) mice.

Hyaluronan induces the selective accumulation of matrix- and cell-associated proteoglycans by mesangial cells

Mesangial cells (MCs) are essential for normal renal function through the synthesis of their own extracellular matrix, which forms the structural support of the renal glomerulus. In many renal diseases this matrix is reorganized in response to a variety of cytokines and growth factors. This study examines proteoglycan and hyaluronan (HA) synthesis by MCs triggered by proinflammatory agents and investigates the effect of an exogenous HA matrix on matrix synthesis by MCs. Metabolic labeling, ion exchange and size exclusion chromatography, Western blotting, and immunocytochemistry were used to identify changes in matrix accumulation. When incubated with interleukin-1, platelet-derived growth factor, or fetal calf serum, MCs initiated rapid HA synthesis associated with the up-regulation of HA synthase-2 and increased the synthesis of versican, perlecan, and decorin/biglycan. HA was both released into the medium and incorporated into extensive pericellular coats. Adding exogenous HA to unstimulated cells that had undetectable pericellular coats of HA selectively reduced perlecan and versican turnover, whereas other proteoglycans were unaffected. These results suggest that high levels of HA in the mesangium in disease is a mechanism controlling the accumulation of specific mesangial matrix components. HA may thus be an attractive target for therapeutic intervention.

The human hyaluronan synthase genes: genomic structures, proximal promoters and polymorphic microsatellite markers

The glycosaminoglycan (GAG) hyaluronan (HA) is a key component of the vertebrate extracellular matrix (ECM) and is synthesised by the HA synthase (HAS) enzymes HAS1, HAS2 and HAS3 at the plasma membrane. Accumulating evidence emphasises the relevance of HA metabolism in an increasing number of processes of clinical interest including renal fibrosis and peritoneal mesothelial wound healing. In the present study, the genomic sequences and organisation of the genes encoding the human HAS isoforms were deduced, in silico, from reference cDNA and genomic sequence data. These data were confirmed in vitro by sequencing of PCR-amplified HAS exons and flanking genomic sequences, comparison with sequence data for the corresponding murine Has orthologues, rapid amplification of 5' cDNA ends analysis and luciferase reporter assays on putative proximal promoter sequences. The HAS1 gene comprised five exons, with the translation start site situated 9bp from the 3' end of exon 1. In contrast, the genomic structures for HAS2 and both HAS3 variants spanned four exons, exon 1 forming a discrete 5'-untranslated region (5'-UTR) and the translation start site lying at nucleotide 1 of exon 2. Dinucleotide microsatellite loci were identified in intron 1 of HAS1 and HAS2, and immediately upstream of the HAS3 gene and their utility as linkage markers demonstrated in genomic DNA (gDNA) studies. We thus present a comprehensive resource for mutation detection screening of all HAS exons and/or linkage analysis of each HAS gene in a variety of disorders for which they are attractive candidates.

Smoking is associated with renal impairment and proteinuria in the normal population: the AusDiab kidney study. Australian Diabetes, Obesity and Lifestyle Study

BACKGROUND

Smoking has been associated with the prevalence, development, and progression of kidney disease. The effect of smoking on kidney function in the healthy population is unclear. We examined the relationship between smoking and indicators of kidney damage in a healthy population without impaired fasting glucose levels, impaired glucose tolerance, diabetes mellitus, or hypertension.

METHODS

This is a randomly selected, population-based, cross-sectional study of 11,247 Australian adults. Smoking status was determined by questionnaire. Subjects were tested for indicators of kidney damage: renal impairment by Cockcroft-Gault-estimated glomerular filtration rate less than 60 mL/min/1.73 m2 and proteinuria by urine protein-creatinine ratio of 0.20 mg/mg or greater.

RESULTS

After adjusting for potential confounding factors, smoking was significantly associated with renal impairment in men with an odds ratio of 3.59, but not in women. Smoking was significantly associated with proteinuria in subjects with high-normal systolic blood pressure, with odds ratios ranging from 3.64 at 131.5 mm Hg to 5.76 at 139.5 mm Hg, and in subjects with high-normal 2-hour glucose levels, with odds ratios ranging from 1.76 at 7.0 mmol/L to 10.84 at 7.7 mmol/L. Lifetime exposure, but not current level of smoking, correlated with lower estimated glomerular filtration rate and greater urine protein-creatinine ratio.

CONCLUSION

Smoking is associated with renal impairment and proteinuria in a population without hypertension or abnormal glucose metabolism. A dose-response relationship was found between cumulative amount of smoking and indicators of kidney damage. In conjunction with other studies and plausible biological mechanisms, this study suggests that smoking may cause kidney damage, even in a healthy population.

Cellular glycosaminoglycans and low density lipoprotein receptor are involved in hepatitis C virus adsorption

The initial binding of Hepatitis C virus (HCV) to the cell membrane is a critical determinant of pathogenesis. Two putative HCV receptors have been identified, CD81 and low-density lipoprotein receptor (LDLr). CD81 interacts in vitro with the HCV E2 envelope glycoprotein, and LDLr interacts with HCV present in human plasma. In order to characterize these potential receptors for HCV, virus from plasma, able to replicate in cell culture, was inoculated on Vero cells or human hepatocarcinoma cells. HCV adsorption was assessed by quantitating cell-associated viral RNA by a real-time RT-PCR method. Anti-LDLr antibody, low and very low density lipoproteins inhibited significantly HCV adsorption, confirming the role of LDLr as HCV receptor. Only one out of the two anti-CD81 antibodies used in this study led to a partial inhibition of HCV binding. This study also highlights a role for glycosaminoglycans (GAGs) in HCV adsorption: treatment of virus with heparin led to 70% inhibition of attachment, as did desulfation of cellular GAGs. Treatment of Vero cells with heparin-lyase significantly inhibited virus attachment but by only 30%. These results demonstrate the complexity of the HCV binding step in which LDLr interacts strongly with HCV, whereas the interaction of HCV with GAGs and particularly with CD81 seem to be more moderate.

Hyperphagia as a mediator of renal disease initiation in obese Zucker rats

OBJECTIVE

We sought to determine whether prevention of overeating would block the very earliest manifestations of renal injury in young obese Zucker rats (OZRs).

RESEARCH METHODS AND PROCEDURES

Three groups of rats were studied, obese (fa/fa) Zucker rats and lean (Fa/Fa). Zucker controls were allowed to feed ad libitum, whereas a group of obese (fa/fa) Zucker rats was pair-fed to the lean group. Urine albumin and serum lipids were studied weekly from 6 to 10 weeks of age. Renal pathology and renal glomerular gene expression were examined when the rats were killed at 10 weeks of age.

RESULTS

Obese rats fed ad libitum developed significant albuminuria by 6 weeks of age, increasing at each subsequent time-point. This increase was completely blocked by pair-feeding. Serum triglycerides were significantly increased in obese rats fed ad libitum vs. the other groups. Urine albumin correlated significantly with both body weight and serum triglyceride level. Renal histopathology was normal in all groups. Analysis of gene expression of glomerular proteins by reverse transcriptase-polymerase chain reaction revealed that pair-feeding attenuated the increased expression of glomerular desmin, fibronectin, and the 92-kDa collagenase that was seen in obese animals fed ad libitum.

DISCUSSION

Prevention of overeating in young OZR normalizes albuminuria and attenuates the pathogenic alterations in glomerular gene expression seen at the initiation of renal disease in obese animals allowed to feed ad libitum. This model may be relevant for studying the early end-organ effects of obesity.

Interaction of native and modified low-density lipoproteins with extracellular matrix

Lipoprotein-matrix interactions play an important role in arterial disease. Extracellular matrix proteoglycans bind and retain specific positively charged domains on apolipoproteins B- and E-containing lipoproteins during atherogenesis. Retained lipoproteins can undergo several modifications, which may alter their interaction with extracellular matrix molecules. Growth factors, cytokines and oxidized low density lipoproteins influence proteoglycan structure, rendering them more likely to bind and retain lipoproteins during atherogenesis. Lipoproteins, native and modified, also can modulate the expression of several of the matrix degrading enzymes present in vascular tissue, thereby influencing plaque stability. Thus, the interaction of atherogenic lipoproteins with arterial wall matrix molecules can influence the genesis and progression of atherosclerosis and its complications.