Stimulated phosphorylation of ERK in mouse kidney mesangial cells is dependent upon expression of Cav3.1

Background

T-type calcium channels (TTCC) are low voltage activated channels that are widely expressed in the heart, smooth muscle and neurons. They are known to impact on cell cycle progression in cancer and smooth muscle cells and more recently, have been implicated in rat and human mesangial cell proliferation. The aim of this study was to investigate the roles of the different isoforms of TTCC in mouse mesangial cells to establish which may be the best therapeutic target for treating mesangioproliferative kidney diseases. 

Methods

In this study, we generated single and double knockout (SKO and DKO) clones of the TTCC isoforms Ca_V3.1 and Ca_V3.2 in mouse mesangial cells using CRISPR-cas9 gene editing. The downstream signals linked to this channel activity were studied by ERK1/2 phosphorylation assays in serum, PDGF and TGF-β1 stimulated cells. We also examined their proliferative responses in the presence of the TTCC inhibitors mibefradil and TH1177.

Results

We demonstrate a complete loss of ERK1/2 phosphorylation in response to multiple stimuli (serum, PDGF, TGF-β1) in Ca_V3.1 SKO clone, whereas the Ca_V3.2 SKO clone retained these phospho-ERK1/2 responses. Stimulated cell proliferation was not profoundly impacted in either SKO clone and both clones remained sensitive to non-selective TTCC blockers, suggesting a role for more than one TTCC isoform in cell cycle progression. Deletion of both the isoforms resulted in cell death.

Conclusion

This study confirms that TTCC are expressed in mouse mesangial cells and that they play a role in cell proliferation. Whereas the Ca_V3.1 isoform is required for stimulated phosphorylation of ERK1/2, the Ca _V3.2 isoform is not. Our data also suggest that neither isoform is necessary for cell proliferation and that the anti-proliferative effects of mibefradil and TH1177 are not isoform-specific. These findings are consistent with data from in vivo rat mesangial proliferation Thy1 models and support the future use of genetic mouse models to test the therapeutic actions of TTCC inhibitors.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12882-022-02844-1.

Evaluation of Urinary Biomarkers of Proximal Tubular Injury, Inflammation, and Fibrosis in Patients With Albuminuric and Nonalbuminuric Diabetic Kidney Disease

Introduction

Albuminuric and nonalbuminuric pathways contribute to diabetic kidney disease. Proximal tubule and inflammation play important roles in these processes. Urinary biomarker(s) to detect early kidney damage and predict progression are needed.

Methods

Nine urinary biomarkers were measured at baseline in 400 patients with diabetes. Correlation and multivariate logistic and linear regression analyses were performed to assess the association of biomarkers with chronic kidney disease and progression.

Results

In the albumin/creatinine ratio (ACR) <3 cohort, the only biomarker significantly associated with estimated glomerular filtration rate < 60 ml/min was N-acetyl-β-d-glucosaminidase. A combination of ACR and monocyte chemoattractant protein 1 (MCP1) were significantly associated with stage 2 chronic kidney disease in this cohort. Logistic models showed that in patients with all levels of albuminuria, ACR, retinol binding protein (RBP), and MCP1 were associated with progression. A model including MCP1, interleukin 6, and neutrophil gelatinase-associated lipocalin showed significant association with progression to chronic kidney disease 3/4 in the ACR <3 cohort. Linear mixed-model regression analyses demonstrated MCP1, RBP, and ACR as significant proteins associated with progression to stage 3 or worse, whereas MCP1 was the only significant biomarker in the ACR <3 cohort. Time-to-event and Cox proportional hazard models confirmed significant hazard ratios for progression for ACR, RBP, and MCP1, with significant differences noted between quantiles of biomarkers for ACR, RBP, and MCP1.

Conclusion

In this study of diabetic patients with single baseline measurements of urinary biomarkers, albumin, RBP, and MCP1 were significantly associated with chronic kidney disease progression at all levels of albuminuria. Inflammatory cytokines, neutrophil gelatinase-associated lipocalin, and MCP1 were associated with progression in patients without albuminuria. N-acetyl-β-d-glucosaminidase demonstrated a significant association with an estimated glomerular filtration rate < 60 ml/min in the ACR <3 cohort.

Acute kidney injury leading to CKD is associated with a persistence of metabolic dysfunction and hypertriglyceridemia

Fibrosis is the pathophysiological hallmark of progressive chronic kidney disease (CKD). The kidney is a highly metabolically active organ, and it has been suggested that disruption in its metabolism leads to renal fibrosis. We developed a longitudinal mouse model of acute kidney injury leading to CKD and an in vitro model of epithelial to mesenchymal transition to study changes in metabolism, inflammation, and fibrosis. Using transcriptomics, metabolic modeling, and serum metabolomics, we observed sustained fatty acid metabolic dysfunction in the mouse model from early to late stages of CKD. Increased fatty acid biosynthesis and downregulation of catabolic pathways for triglycerides and diacylglycerides were associated with a marked increase in these lipids in the serum. We therefore suggest that the kidney may be the source of the abnormal lipid profile seen in patients with CKD, which may provide insights into the association between CKD and cardiovascular disease.

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Following AKI, markers of fibrosis and inflammation go up simultaneously

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AKI is associated with reduced fatty acid oxidation and oxidative phosphorylation

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Changes in metabolism persist as chronic kidney disease develops

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Changes in metabolism are associated with increased serum levels of triglycerides

Collecting duct cells show differential retinoic acid responses to acute versus chronic kidney injury stimuli

Retinoic acid (RA) activates RA receptors (RAR), resulting in RA response element (RARE)-dependent gene expression in renal collecting duct (CD). Emerging evidence supports a protective role for this activity in acute kidney injury (AKI) and chronic kidney disease (CKD). Herein, we examined this activity in RARE-LacZ transgenic mice and by RARE-Luciferase reporter assays in CD cells, and investigated how this activity responds to neurotransmitters and mediators of kidney injury. In RARE-LacZ mice, Adriamycin-induced heavy albuminuria was associated with reduced RA/RAR activity in CD cells. In cultured CD cells, RA/RAR activity was repressed by acetylcholine, albumin, aldosterone, angiotensin II, high glucose, cisplatin and lipopolysaccharide, but was induced by aristolochic acid I, calcitonin gene-related peptide, endothelin-1, gentamicin, norepinephrine and vasopressin. Compared with age-matched normal human CD cells, CD-derived renal cystic epithelial cells from patients with autosomal recessive polycystic kidney disease (ARPKD) had significantly lower RA/RAR activity. Synthetic RAR agonist RA-568 was more potent than RA in rescuing RA/RAR activity repressed by albumin, high glucose, angiotensin II, aldosterone, cisplatin and lipopolysaccharide. Hence, RA/RAR  in CD cells is a convergence point of regulation by neurotransmitters and mediators of kidney injury, and may be a novel therapeutic target.

Hypothesis: Pentoxifylline is a potential cytokine modulator therapeutic in COVID-19 patients

We propose a new hypothesis that the established drug pentoxifylline deserves attention as a potential repurposed therapeutic for COVID-19. Pentoxifylline is an immunomodulator with anti-inflammatory properties. It is a nonselective phosphodiesterase inhibitor and through Adenosine A2A Receptor-mediated pathways reduces tumor necrosis factor alpha, interleukin 1, interleukin 6, and interferon gamma and may act to reduce tissue damage during the cytokine storm host response to SARS-CoV-2 infection. This agent has been used clinically for many years and has a favorable profile of safety and tolerability. Pre-clinical data support pentoxifylline as effective in cytokine-driven lung damage. Clinical studies of pentoxifylline in radiation and cytokine-induced lung damage in humans are positive and consistent with anti-inflammatory efficacy. Pentoxifylline is a readily available, off-patent and inexpensive drug, suitable for large-scale use including in resource-limited countries. Current trials of therapeutics are largely focused on the inhibition of viral processes. We advocate urgent randomized trials of pentoxifylline for COVID-19 as a complementary approach to target the host responses.

Ion-Channel modulator TH1177 reduces glomerular injury and serum creatinine in chronic mesangial proliferative disease in rats

Background

T-type calcium channels (TTCC) are involved in mesangial cell proliferation. In acute thy-1 nephritis in the rat TTCC inhibition reduces glomerular damage and cell proliferation. This work is extended here by a study of the non-selective TTCC inhibitor TH1177 in a chronic model of proliferative glomerulonephritis (GN) including late treatment starting after the initial inflammation has resolved. The objective was to determine the effects of TH1177 in a model of chronic mesangioproliferative renal disease.

Methods

Chronic GN was induced in WKY rats by unilateral nephrectomy (day − 7) followed by day 0 injection of Ox7 thy-1 mAb. Treatment with TH1177 (10–20 mg/Kg daily IP) was started on day 2 (early treatment) or on day 14 (late treatment) and compared to vehicle-treated controls until sacrifice at day 42. Glomerular disease was assessed with a damage score, fibrosis assay, cellular counts and renal function measured by serum creatinine.

Results

Treatment with TH11777 was associated with reduced serum creatinine, less glomerular damage, reduced fibrosis and reduced glomerular cellularity. The results for early and late TH1177 treatments were essentially the same and differed significantly from vehicle.

Conclusions

The ion-channel modulator TH1177 is capable of improving glomerular outcome in chronic rat GN even when treatment starts 14 days after initiation of the disease. These data are discussed in the context of the possible targets of TH1177 including TTCC, TRP family, Stim/Orai group and other cation channels. The work supports the use of genetic models to examine the roles of individual cation channels in progressive glomerulonephritis to further define the targets of TH1177.

Inhibition of Kirsten-Ras reduces fibrosis and protects against renal dysfunction in a mouse model of chronic folic acid nephropathy

Chronic Kidney Disease is a growing problem across the world and can lead to end-stage kidney disease and cardiovascular disease. Fibrosis is the underlying mechanism that leads to organ dysfunction, but as yet we have no therapeutics that can influence this process. Ras monomeric GTPases are master regulators that direct many of the cytokines known to drive fibrosis to downstream effector cascades. We have previously shown that K-Ras is a key isoform that drives fibrosis in the kidney. Here we demonstrate that K-Ras expression and activation are increased in rodent models of CKD. By knocking down expression of K-Ras using antisense oligonucleotides in a mouse model of chronic folic acid nephropathy we can reduce fibrosis by 50% and prevent the loss of renal function over 3 months. In addition, we have demonstrated in vitro and in vivo that reduction of K-Ras expression is associated with a reduction in Jag1 expression; we hypothesise this is the mechanism by which targeting K-Ras has therapeutic benefit. In conclusion, targeting K-Ras expression with antisense oligonucleotides in a mouse model of CKD prevents fibrosis and protects against renal dysfunction.

Treatment-limiting renal tubulopathy in patients treated with tenofovir disoproxil fumarate

OBJECTIVES

Tenofovir disoproxil fumarate (TDF) is widely used in the treatment or prevention of HIV and hepatitis B infection. TDF may cause renal tubulopathy in a small proportion of recipients. We aimed to study the risk factors for developing severe renal tubulopathy.

METHODS

We conducted an observational cohort study with retrospective identification of cases of treatment-limiting tubulopathy during TDF exposure. We used multivariate Poisson regression analysis to identify risk factors for tubulopathy, and mixed effects models to analyse adjusted estimated glomerular filtration rate (eGFR) slopes.

RESULTS

Between October 2002 and June 2013, 60 (0.4%) of 15,983 patients who had received TDF developed tubulopathy after a median exposure of 44.1 (IQR 20.4, 64.4) months. Tubulopathy cases were predominantly male (92%), of white ethnicity (93%), and exposed to antiretroviral regimens that contained boosted protease inhibitors (PI, 90%). In multivariate analysis, age, ethnicity, CD4 cell count and use of didanosine or PI were significantly associated with tubulopathy. Tubulopathy cases experienced significantly greater eGFR decline while receiving TDF than the comparator group (-6.60 [-7.70, -5.50] vs. -0.34 [-0.43, -0.26] mL/min/1.73 m²/year, p < 0.0001).

CONCLUSIONS

Older age, white ethnicity, immunodeficiency and co-administration of ddI and PI were risk factors for tubulopathy in patients who received TDF-containing antiretroviral therapy. The presence of rapid eGFR decline identified TDF recipients at increased risk of tubulopathy.

The role of tenofovir alafenamide in future HIV management

HIV infection has become a chronic condition rather than an acute life-threatening disease in developed countries, thanks to consistent innovation and evolution of effective interventions. This has altered HIV management and created new challenges. People living with HIV (PLWHIV) are living longer and so encounter comorbidities linked not only with their disease, but also with ageing, lifestyle and chronic exposure to antiretroviral therapy (ART). Although longevity, viral suppression and the prevention of viral transmission remain key goals, more needs to be achieved to encompass the vision of attaining an optimum level of overall health. Treatment choices and management practices should ensure patients' long-term health with minimal comorbidity. Treatments that balance optimal efficacy with the potential for improved long-term safety are needed for all patients. In this review, we consider the evolution and development of tenofovir alafenamide (TAF), a novel prodrug of tenofovir which offers high antiviral efficacy at doses over ten times lower than that of tenofovir disoproxil fumarate (TDF). Emerging clinical data suggest that elvitegravir, cobicistat, emtricitabine and TAF (E/C/F/TAF) as a single-tablet regimen offers highly effective viral suppression in treatment-naïve and treatment-experienced patients with an improved renal and bone safety profile compared with TDF, this having been demonstrated in diverse groups including patients with existing renal impairment and adolescents. The profile of TAF identifies it as an agent with a promising role within future ART regimens that aim to deliver the vision of undetectable viral load, while requiring less monitoring and having a safety profile designed to minimize comorbid risks while supporting good long-term health.

Clinical characteristics and outcomes of HIV-associated immune complex kidney disease

BACKGROUND

The pathogenesis and natural history of HIV-associated immune complex kidney disease (HIVICK) is not well understood. Key questions remain unanswered, including the role of HIV infection and replication in disease development and the efficacy of antiretroviral therapy (ART) in the prevention and treatment of disease.

METHODS

In this multicentre study, we describe the renal pathology of HIVICK and compare the clinical characteristics of patients with HIVICK with those with IgA nephropathy and HIV-associated nephropathy (HIVAN). Poisson regression models were used to identify risk factors for each of these pathologies.

RESULTS

Between 1998 and 2012, 65 patients were diagnosed with HIVICK, 27 with IgA nephropathy and 70 with HIVAN. Black ethnicity and HIV RNA were associated with HIVICK, receipt of ART with IgA nephropathy and black ethnicity and CD4 cell count with HIVAN. HIVICK was associated with lower rates of progression to end-stage kidney disease compared with HIVAN and IgA nephropathy (P < 0.0001). Patients with HIVICK who initiated ART and achieved suppression of HIV RNA experienced improvements in estimated glomerular filtration rate and proteinuria.

CONCLUSIONS

These findings suggest a pathogenic role for HIV replication in the development of HIVICK and that ART may improve kidney function in patients who have detectable HIV RNA at the time of HIVICK diagnosis. Our data also suggest that IgA nephropathy should be viewed as a separate entity and not included in the HIVICK spectrum.

An in vitro model for the pro-fibrotic effects of retinoids: mechanisms of action

BACKGROUND AND PURPOSE

Retinoids, including all-trans retinoic acid (tRA), have dose-dependent pro-fibrotic effects in experimental kidney diseases. To understand and eventually prevent such adverse effects, it is important to establish relevant in vitro models and unravel their mechanisms.

EXPERIMENTAL APPROACH

Fibrogenic effects of retinoids were assessed in NRK-49F renal fibroblasts using picro-Sirius red staining for collagens and quantified by spectrophotometric analysis of the eluted stain. Other methods included RT-qPCR, immunoassays and matrix metalloproteinase (MMP) activity assays.

KEY RESULTS

With or without TGF-β1, tRA was dose-dependently pro-fibrotic, notably increasing collagen accumulation. tRA and TGF-β1 additively suppressed expression of mRNA for MMP2, 3 and 13 and suppressed MMP activity. tRA, in the presence of TGF-β1, induced plasminogen activator inhibitor-1 (PAI-1) mRNA and they additively induced PAI-1 protein expression. A PAI-1 inhibitor, a pan-retinoic acid receptor (RAR) antagonist and a pan-retinoid X receptor (RXR) antagonist each partially prevented the pro-fibrotic effect of tRA. The dose-dependent pro-fibrotic effects of a pan-RXR agonist were similar to those of tRA. A pan-RAR agonist showed weaker, less dose-dependent pro-fibrotic effects and the pro-fibrotic effects of RARα and RARβ-selective agonists were even smaller. An RARγ-selective agonist did not affect fibrogenesis.

CONCLUSIONS AND IMPLICATIONS

An in vitro model for the pro-fibrotic effects of retinoids was established in NRK-49F cells. It was associated with reduced MMP activity and increased PAI-1 expression, and was probably mediated by RXR and RAR. To avoid or antagonize the pro-fibrotic activity of tRA, further studies on RAR isotype-selective agonists and PAI-1 inhibitors might be of value.

Effect of exercise training on estimated GFR, vascular health, and cardiorespiratory fitness in patients with CKD: a pilot randomized controlled trial

BACKGROUND

Exercise capacity, which is predictive of all-cause mortality and cardiovascular disease risk, is reduced significantly in patients with non-dialysis-dependent chronic kidney disease. This pilot study examined the effect of moderate-intensity exercise training on kidney function and indexes of cardiovascular risk in patients with progressive chronic kidney disease stages 3 to 4.

STUDY DESIGN

Single-blind, randomized, controlled, parallel trial.

SETTING & PARTICIPANTS

20 patients (aged 18-80 years; 17 men) randomly assigned to rehabilitation (n=10) or usual care (n=10). Participants were included if they were 18 years or older and had evidence of rate of decline in creatinine-based estimated glomerular filtration rate (eGFRcr)≥2.9mL/min/1.73m(2) per year for 12 months preintervention. Patients were excluded if they had unstable medical conditions or had recently started regular exercise.

INTERVENTION

The rehabilitation group received resistance and aerobic training (3 days per week) for a 12-month period. The usual care group received standard care.

OUTCOMES

Kidney function assessed by comparing mean rate of change in eGFRcr (mL/min/1.73m(2) per year) from a 12-month preintervention period against the 12-month intervention period. Pulse wave velocity (PWV), peak oxygen uptake (Vo2peak), and waist circumference assessed at 0, 6, and 12 months.

MEASUREMENTS

eGFR assessed using creatinine, cystatin C (eGFRcys), and a combination of both values (eGFRcr-cys).

RESULTS

18 participants (rehabilitation, 8; usual care, 10) completed the study. A significant mean difference in rate of change in eGFRcr (+7.8±3.0 [95% CI, 1.1-13.5] mL/min/1.73m(2) per year; P=0.02) was observed between the rehabilitation and usual care groups, with the rehabilitation group demonstrating a slower decline. No significant between-group mean differences existed in absolute eGFRcr, eGFRcr-cys, or eGFRcys at 12 months of study intervention. Significant between-group mean differences existed in PWV (-2.30 [95% CI, -3.02 to -1.59] m/s), waist circumference (-7.1±12.8 [95% CI, -12.4 to -3.2] cm), and Vo2peak (5.7 [95% CI, 1.34-10.10] mL/kg/min). Change in eGFRcr was correlated inversely with PWV (r=-0.5; P=0.04) at 12 months.

LIMITATIONS

Small sample size, inconsistency between primary and secondary measures of kidney function.

CONCLUSIONS

The effect of a 1-year exercise intervention on progression of kidney disease is inconclusive. A larger study with longer follow-up may be necessary.

The quest for modernisation of traditional Chinese medicine

Traditional Chinese medicine (TCM) is an integral part of mainstream medicine in China. Due to its worldwide use, potential impact on healthcare and opportunities for new drug development, TCM is also of great international interest. Recently, a new era for modernisation of TCM was launched with the successful completion of the Good Practice in Traditional Chinese Medicine Research in the Post-genomic Era (GP-TCM) project, the European Union's Seventh Framework Programme (FP7) coordination action on TCM research. This 3.5-year project that involved inputs from over 200 scientists resulted in the production of 20 editorials and in-depth reviews on different aspects of TCM that were published in a special issue of Journal of Ethnopharmacology (2012; volume 140, issue 3). In this narrative review, we aim to summarise the findings of the FP7 GP-TCM project and highlight the relevance of TCM to modern medicine within a historical and international context. Advances in TCM research since the 1950s can be characterised into three phases: Phase I (1950s-1970s) was fundamental for developing TCM higher education, research and hospital networks in China; Phase II (1980s-2000s) was critical for developing legal, economic and scientific foundations and international networks for TCM; and Phase III (2011 onwards) is concentrating on consolidating the scientific basis and clinical practice of TCM through interdisciplinary, interregional and intersectoral collaborations. Taking into account the quality and safety requirements newly imposed by a globalised market, we especially highlight the scientific evidence behind TCM, update the most important milestones and pitfalls, and propose integrity, integration and innovation as key principles for further modernisation of TCM. These principles will serve as foundations for further research and development of TCM, and for its future integration into tomorrow's medicine.

Anti-proliferative actions of T-type calcium channel inhibition in Thy1 nephritis

Aberrant proliferation of mesangial cells (MCs) is a key finding in progressive glomerular disease. TH1177 is a small molecule that has been shown to inhibit low-voltage activated T-type Ca(2+) channels (TCCs). The current study investigates the effect of TH1177 on MC proliferation in vitro and in vivo. The effect of Ca(2+) channel inhibition on primary rat MC proliferation in vitro was studied using the microculture tetrazolium assay and by measuring bromodeoxyuridine incorporation. In vivo, rats with Thy1 nephritis were treated with TH1177 or vehicle. Glomerular injury and average glomerular cell number were determined in a blinded fashion. Immunostaining for Ki-67 and phosphorylated ERK were also performed. The expression of TCC isoforms in healthy and diseased tissue was investigated using quantitative real-time PCR. TCC blockade caused a significant reduction in rat MC proliferation in vitro, whereas L-type inhibition had no effect. Treatment of Thy1 nephritis with TH1177 significantly reduced glomerular injury (P < 0.005) and caused a 49% reduction in glomerular cell number (P < 0.005) compared to the placebo. TH1177 also reduced Ki-67-positive and pERK-positive cells per glomerulus by 52% (P < 0.01 and P < 0.005, respectively). These results demonstrate that TH1177 inhibits MC proliferation in vitro and in vivo, supporting the hypothesis that TCC inhibition may be a useful strategy for studying and modifying MC proliferative responses to injury.

Retinoic acid receptor-dependent, cell-autonomous, endogenous retinoic acid signaling and its target genes in mouse collecting duct cells

BACKGROUND

Vitamin A is necessary for kidney development and has also been linked to regulation of solute and water homeostasis and to protection against kidney stone disease, infection, inflammation, and scarring. Most functions of vitamin A are mediated by its main active form, all-trans retinoic acid (tRA), which binds retinoic acid receptors (RARs) to modulate gene expression. We and others have recently reported that renal tRA/RAR activity is confined to the ureteric bud (UB) and collecting duct (CD) cell lineage, suggesting that endogenous tRA/RARs primarily act through regulating gene expression in these cells in embryonic and adult kidney, respectively.

METHODOLOGY/PRINCIPAL FINDINGS

To explore target genes of endogenous tRA/RARs, we employed the mIMCD-3 mouse inner medullary CD cell line, which is a model of CD principal cells and exhibits constitutive tRA/RAR activity as CD principal cells do in vivo. Combining antagonism of RARs, inhibition of tRA synthesis, exposure to exogenous tRA, and gene expression profiling techniques, we have identified 125 genes as candidate targets and validated 20 genes that were highly regulated (Dhrs3, Sprr1a, and Ppbp were the top three). Endogenous tRA/RARs were more important in maintaining, rather than suppressing, constitutive gene expression. Although many identified genes were expressed in UBs and/or CDs, their exact functions in this cell lineage are still poorly defined. Nevertheless, gene ontology analysis suggests that these genes are involved in kidney development, renal functioning, and regulation of tRA signaling.

CONCLUSIONS/SIGNIFICANCE

A rigorous approach to defining target genes for endogenous tRA/RARs has been established. At the pan-genomic level, genes regulated by endogenous tRA/RARs in a CD cell line have been catalogued for the first time. Such a catalogue will guide further studies on molecular mediators of endogenous tRA/RARs during kidney development and in relation to renal defects associated with vitamin A deficiency.

Total protein, albumin and low-molecular-weight protein excretion in HIV-positive patients

BACKGROUND

Chronic kidney disease is common in HIV positive patients and renal tubular dysfunction has been reported in those receiving combination antiretroviral therapy (cART). Tenofovir (TFV) in particular has been linked to severe renal tubular disease as well as proximal tubular dysfunction. Markedly elevated urinary concentrations of retinal-binding protein (RBP) have been reported in patients with severe renal tubular disease, and low-molecular-weight proteins (LMWP) such as RBP may be useful in clinical practice to assess renal tubular function in patients receiving TFV. We analysed 3 LMWP as well as protein and albumin in the urine of a sample of HIV positive patients.

METHODS

In a cross-sectional fashion, total protein, albumin, RBP, cystatin C, and neutrophil gelatinase-associated lipocalin (NGAL) were quantified in random urine samples of 317 HIV positive outpatients and expressed as the ratio-to-creatinine (RBPCR, CCR and NGALCR). Exposure to cART was categorised as none, cART without TFV, and cART containing TFV and a non-nucleoside reverse-transcriptase-inhibitor (TFV/NNRTI) or TFV and a protease-inhibitor (TFV/PI).

RESULTS

Proteinuria was present in 10.4 % and microalbuminuria in 16.7 % of patients. Albumin accounted for approximately 10 % of total urinary protein. RBPCR was within the reference range in 95 % of patients while NGALCR was elevated in 67 % of patients. No overall differences in urine protein, albumin, and LMWP levels were observed among patients stratified by cART exposure, although a greater proportion of patients exposed to TFV/PI had RBPCR >38.8 μg/mmol (343 μg/g) (p = 0.003). In multivariate analyses, black ethnicity (OR 0.43, 95 % CI 0.24, 0.77) and eGFR <75 mL/min/1.73 m2 (OR 3.54, 95 % CI 1.61, 7.80) were independently associated with upper quartile (UQ) RBPCR. RBPCR correlated well to CCR (r2 = 0.71), but not to NGALCR, PCR or ACR.

CONCLUSIONS

In HIV positive patients, proteinuria was predominantly of tubular origin and microalbuminuria was common. RBPCR in patients without overt renal tubular disease was generally within the reference range, including those receiving TFV. RBP therefore appears a promising biomarker for monitoring renal tubular function in patients receiving TFV and for distinguishing patients with normal tubular function or mild tubular dysfunction from those with severe renal tubular disease or Fanconi syndrome.

Traditional Chinese medicine research in the post-genomic era: good practice, priorities, challenges and opportunities

BACKGROUND AND AIMS

GP-TCM is the 1st EU-funded Coordination Action consortium dedicated to traditional Chinese medicine (TCM) research. This paper aims to summarise the objectives, structure and activities of the consortium and introduces the position of the consortium regarding good practice, priorities, challenges and opportunities in TCM research. Serving as the introductory paper for the GP-TCM Journal of Ethnopharmacology special issue, this paper describes the roadmap of this special issue and reports how the main outputs of the ten GP-TCM work packages are integrated, and have led to consortium-wide conclusions.

MATERIALS AND METHODS

Literature studies, opinion polls and discussions among consortium members and stakeholders.

RESULTS

By January 2012, through 3 years of team building, the GP-TCM consortium had grown into a large collaborative network involving ∼200 scientists from 24 countries and 107 institutions. Consortium members had worked closely to address good practice issues related to various aspects of Chinese herbal medicine (CHM) and acupuncture research, the focus of this Journal of Ethnopharmacology special issue, leading to state-of-the-art reports, guidelines and consensus on the application of omics technologies in TCM research. In addition, through an online survey open to GP-TCM members and non-members, we polled opinions on grand priorities, challenges and opportunities in TCM research. Based on the poll, although consortium members and non-members had diverse opinions on the major challenges in the field, both groups agreed that high-quality efficacy/effectiveness and mechanistic studies are grand priorities and that the TCM legacy in general and its management of chronic diseases in particular represent grand opportunities. Consortium members cast their votes of confidence in omics and systems biology approaches to TCM research and believed that quality and pharmacovigilance of TCM products are not only grand priorities, but also grand challenges. Non-members, however, gave priority to integrative medicine, concerned on the impact of regulation of TCM practitioners and emphasised intersectoral collaborations in funding TCM research, especially clinical trials.

CONCLUSIONS

The GP-TCM consortium made great efforts to address some fundamental issues in TCM research, including developing guidelines, as well as identifying priorities, challenges and opportunities. These consortium guidelines and consensus will need dissemination, validation and further development through continued interregional, interdisciplinary and intersectoral collaborations. To promote this, a new consortium, known as the GP-TCM Research Association, is being established to succeed the 3-year fixed term FP7 GP-TCM consortium and will be officially launched at the Final GP-TCM Congress in Leiden, the Netherlands, in April 2012.

Antisense knockdown of Kras inhibits fibrosis in a rat model of unilateral ureteric obstruction

Tubulointerstitial fibrosis is the hallmark of chronic kidney disease and is characterized by an increase in the number and activity of interstitial fibroblasts and by excessive matrix deposition. Ras is an intracellular signaling molecule involved in cell proliferation and differentiation. It has recently been implicated in the pathogenesis of renal fibrosis. Of the three different isoforms of Ras (Kirsten, Harvey, and Neural), we previously demonstrated that the Kirsten isoform is key in the control of renal fibroblast proliferation in vitro. In this study, we used gene therapy in the form of antisense oligonucleotides (ASOs) specifically to silence Kras (alias Ki-ras) expression in a rat model of renal fibrosis caused by unilateral ureteric obstruction. We demonstrate that renal Kras expression increases by 70% in this model compared with sham-operated animals and that treatment with ASOs can reduce total renal Kras by >90% to levels well below basal. This silencing is associated with a dramatic inhibition of interstitial fibrosis, a fivefold reduction in α-smooth muscle actin expression, and a 2.4-fold reduction in collagen I deposition. This inhibition was observed despite histologic evidence of marked interstitial inflammation. These findings demonstrate that silencing Kras expression can markedly inhibit renal fibrosis. This strategy should be considered as a new potential therapeutic avenue.

Acute kidney injury in patients admitted to a liver intensive therapy unit with paracetamol-induced hepatotoxicity

BACKGROUND

Paracetamol overdose can cause acute kidney injury (AKI) independent of its hepatotoxic effects. We aimed to determine the prevalence of AKI (AKI Network definition) in those with paracetamol-induced hepatotoxicity, identify factors associated with development, assess impact on the outcomes of patient survival and length of stay and determine the proportion of patients recovering renal function (estimated glomerular filtration rate > 60 mL/min) by the time of hospital discharge or transfer out.

METHODS

Between 2000 and 2007, patients admitted to a tertiary referral liver intensive therapy unit (LITU) with paracetamol-induced hepatotoxicity were identified from a prospectively maintained database and evaluated.

RESULTS

Those receiving a liver transplant were excluded (n = 54), leaving 302 patients. Renal function remained normal in 21%, the remainder developing AKI (Stages 1-8%, 2-6% and 3-65%). Vasopressor requirement, mechanical ventilation, higher admission phosphate and lower sodium levels along with a higher Day 3 lactate and lower haematocrit were associated with AKI. In survivors with AKI, 51% had recovery of renal function, while 7% remained dialysis dependant although none required it chronically. Overall, there was 25% mortality, all having Stage 3 AKI but AKI was only a univariate not multivariate predictor of reduced patient survival. AKI independently predicted longer length of stay.

CONCLUSIONS

AKI is very common in critically ill patients with paracetamol-induced hepatotoxicity requiring LITU admission. Although outcomes are poorer with AKI than with normal renal function, they are better than those found in other intensive therapy unit populations. Gradual recovery of renal function is seen in all patients.

Tenofovir-associated kidney toxicity in HIV-infected patients: a review of the evidence

Tenofovir (TDF) is an effective and widely used treatment for both human immunodeficiency virus (HIV) and hepatitis B virus infection. Although studies suggest that TDF has a low overall toxicity profile and only a modest effect on estimated glomerular filtration rate, numerous case reports have since appeared in the literature describing TDF-associated renal tubular dysfunction, and this is now a significant source of HIV-related referrals to nephrologists. The main target of toxicity appears to be the proximal tubule, and in severe cases, patients can develop renal Fanconi syndrome. We review findings from recent studies in this area performed by ourselves and others and discuss our direct experience as practicing nephrologists. In particular, we discuss: (1) the nature and extent of TDF-associated kidney toxicity in the HIV-infected population, (2) potential underlying mechanisms of toxicity in the proximal tubule, (3) risk factors for developing tubular dysfunction, and (4) suggested strategies to monitor patients on TDF therapy.

Endogenous retinoic acid activity in principal cells and intercalated cells of mouse collecting duct system

BACKGROUND

Retinoic acid is the bioactive derivative of vitamin A, which plays an indispensible role in kidney development by activating retinoic acid receptors. Although the location, concentration and roles of endogenous retinoic acid in post-natal kidneys are poorly defined, there is accumulating evidence linking post-natal vitamin A deficiency to impaired renal concentrating and acidifying capacity associated with increased susceptibility to urolithiasis, renal inflammation and scarring. The aim of this study is to examine the presence and the detailed localization of endogenous retinoic acid activity in neonatal, young and adult mouse kidneys, to establish a fundamental ground for further research into potential target genes, as well as physiological and pathophysiological roles of endogenous retinoic acid in the post-natal kidneys.

METHODOLOGY/PRINCIPAL FINDINGS

RARE-hsp68-lacZ transgenic mice were employed as a reporter for endogenous retinoic acid activity that was determined by X-gal assay and immunostaining of the reporter gene product, β-galactosidase. Double immunostaining was performed for β-galactosidase and markers of kidney tubules to localize retinoic acid activity. Distinct pattern of retinoic acid activity was observed in kidneys, which is higher in neonatal and 1- to 3-week-old mice than that in 5- and 8-week-old mice. The activity was present specifically in the principal cells and the intercalated cells of the collecting duct system in all age groups, but was absent from the glomeruli, proximal tubules, thin limbs of Henle's loop and distal tubules.

CONCLUSIONS/SIGNIFICANCE

Endogenous retinoic acid activity exists in principal cells and intercalated cells of the mouse collecting duct system after birth and persists into adulthood. This observation provides novel insights into potential roles for endogenous retinoic acid beyond nephrogenesis and warrants further studies to investigate target genes and functions of endogenous retinoic acid in the kidney after birth, particularly in the collecting duct system.

Kidneys of Alb/TGF-beta1 transgenic mice are deficient in retinoic acid and exogenous retinoic acid shows dose-dependent toxicity

BACKGROUND

Alb/TGF-beta(1) transgenic mice overexpress active transforming growth factor-beta(1) (TGF-beta(1)) in the liver, leading to increased circulating levels of the cytokine and progressive renal fibrosis. This study was designed to explore if exogenous all-trans retinoic acid (tRA) prevents renal fibrosis in this animal model.

METHODS

The retinoid profile in kidney and liver of wild-type and Alb/TGF-beta(1) transgenic mice was examined by high-performance liquid chromatography and slow-release pellets containing different amounts of tRA were implanted subcutaneously to treat the Alb/TGF-beta(1) transgenic mice, starting at 1 week of age; mice were sacrificed 2 weeks later.

RESULTS

Kidneys of 3-week-old wild-type mice had abundant tRA, which was completely absent in kidneys of the transgenic mice. Low doses of tRA (6-10.7 mg/kg/day) failed to affect renal fibrosis although it tended to suppress the mRNA expression of some molecular markers of fibrosis and retinal dehydrogenase 2 (RALDH2), a gene encoding a key tRA-synthesising enzyme. These tendencies disappeared, mortality tended to increase and RALDH2 and connective tissue growth factor (CTGF) mRNAs significantly increased in the medium-dose group (12.7-18.8 mg/kg/day). High doses (20.1-27.4 mg/kg/day) showed even higher toxicity with increased renal fibrosis and significant mortality.

CONCLUSIONS

Alb/TGF-beta(1) transgenic mice are characterised by depletion of endogenous renal tRA. Exogenous tRA dose-dependently increases mortality and kidney fibrosis, which is associated with dose-dependent regulation of renal RALDH2 and CTGF mRNA expression.

Inhibition of human mesangial cell proliferation by targeting T-type calcium channels

BACKGROUND

Aberrant glomerular mesangial cell (MC) proliferation is a common finding in renal diseases. T-type calcium channels (T-CaCN) play an important role in the proliferation of a number of cell types, including vascular smooth muscle cells. The hypothesis that T-CaCN may play a role in the proliferation of human MC was investigated.

METHODS

The presence of T-CaCN in primary cultures of human MC was examined using voltage clamping and by RT-PCR. The effect of calcium channel inhibitors, and of siRNA directed against the Cav3.2 T-CaCN isoform, on MC proliferation was assessed using the microculture tetrazolium assay and nuclear BrdU incorporation.

RESULTS

Human MC express only the Cav3.2 T-CaCN isoform. Co-incubation of MC with a T-CaCN inhibitor (mibefradil, TH1177 or Ni(2+)) results in a concentration-dependent attenuation of proliferation. This effect cannot be attributed to direct drug-induced cytotoxicity or apoptosis and is not seen with verapamil, an L-type channel blocker. Transfection of MC with siRNA results in knockdown of T-CaCN Cav3.2 mRNA and a clear attenuation of MC proliferation.

CONCLUSIONS

These results demonstrate for the first time an important role for T-CaCN in human MC proliferation. This could potentially lead to a novel therapy in the treatment of proliferative renal diseases.

Tgf-beta auto-induction and connective tissue growth factor expression in human renal tubule epithelial cells requires N-ras

BACKGROUND/AIMS

Transforming growth factor (TGF) beta is strongly implicated in the progression of renal fibrosis. TGFbeta1 is reported to cause epithelial-mesenchymal transition, inhibition of epithelial cell proliferation, increased apoptosis, auto-induction of TGFbeta production and induction of secondary mediators of tissue fibrosis such as connective tissue growth factor (CTGF, CCN2). The aims of this study were to investigate the role of the Ras/MAP kinase pathway in TGFbeta1 inhibition of proliferation, TGFbeta auto-induction and TGFbeta1-induced CTGF expression in HKC human renal tubule epithelial cells.

METHODS AND RESULTS

TGFbeta1 (0-25 ng/ml) inhibited proliferation of HKC cells and at 25 ng/ml also induced apoptosis. After 5-10 min of incubation, TGFbeta1 increased cellular levels of phospho-ERK1/2 and phospho-AKT with a bell-shaped dose-response curve with a maximally effective concentration of 2.5 ng/ml. TGFbeta3 caused an increase in extracellular TGFbeta1, which was significantly reduced in the presence of PD 98059. TGFbeta1 increased cellular and secreted CTGF protein in HKC cells in a MEK-dependent manner. To identify the Ras isoform involved, specific antisense oligonucleotides targeted to Ha-Ras, Ki-Ras and N-Ras were employed. Only inhibition of N-Ras resulted in a significant reduction of auto-induced TGFbeta1 secretion and TGFbeta1-induced cellular and secreted CTGF.

CONCLUSION

These results establish that the Ras/MAP kinase pathway, specifically through N-Ras, mediates TGFbeta1 auto-induction and TGFbeta1-induced CTGF expression in human renal tubule epithelial cells.

Rho isoforms have distinct and specific functions in the process of epithelial to mesenchymal transition in renal proximal tubular cells

Epithelial to mesenchymal transition (EMT) is involved in embryological development, cancerous metastatic spread and organ fibrosis, including the kidney. This process is largely driven by transforming growth factor-beta and recent evidence has implicated Rho as a key intracellular signalling molecule. In this study we have used RNA interference to silence the genetically distinct Rho (A, B and C) isoforms to define their individual functions in human kidney epithelial cells undergoing EMT. We demonstrate that the downregulation of the epithelial cell marker E-cadherin is dependent upon the Rho effector, Rho-kinase. However, silencing RhoA or RhoC expression also results in E-cadherin loss, though each by different mechanisms. Loss of RhoA leads to an upregulation of Snail1 and a reduction in the transcription of E-cadherin whereas loss of RhoC upregulates its breakdown via proteasomal degradation. During EMT, the upregulation of alpha-smooth muscle actin can be blocked by inhibiting the expression of RhoA, but not by that of RhoB or RhoC. This effect is independent of Rho-kinase activity. RhoC is the isoform solely responsible for stress fibre formation and inhibiting its expression reduces EMT-induced migration by 50%. RhoB appears to play a role in cell survival as inhibiting its expression leads to >300% increase in cell apoptosis and a relocalization of focal adhesion kinase. We conclude that Rho is a key signalling molecule in the process of EMT but that each isoform has a distinct and specific role.

In vitro anti-fibrotic activities of herbal compounds and herbs

BACKGROUND

We recently developed high-throughput assays of inflammation-independent anti-fibrotic activities based on TGF-beta1-induced total collagen accumulation and nodule formation in normal rat kidney fibroblasts.

METHODS

These assays were applied to examine the anti-fibrotic activities of 21 compounds isolated from plants used in Chinese medicine and methanol extracts of 12 Chinese herbs. Lactate dehydrogenase release assay and cell detachment index were used to monitor cytotoxicity. Changes in fibrogenic molecular markers were observed by reverse transcriptase quantitative polymerase chain reaction and high-content imaging analysis of immunofluorescence.

RESULTS

Three flavonoids (quercetin, baicalein and baicalin) and two non-flavonoids (salvianolic acid B and emodin) demonstrated anti-fibrotic activities in both total collagen accumulation and nodule formation assays. The remaining 16 compounds had little anti-fibrotic effect or were cytotoxic. The anti-fibrotic compounds suppressed collagen I expression at both mRNA and protein levels and also variably suppressed alpha-smooth muscle actin expression and bromodeoxyuridine incorporation. Methanol extracts of Scutellaria baicalensis Georgi, Salvia miltiorrhiza Bunge and Rheum palmatum L., which are rich sources of baicalein, baicalin, salvianolic acid B and emodin, respectively, also showed in vitro anti-fibrotic activities.

CONCLUSIONS

Five herbal compounds and three herbal extracts have in vitro anti-fibrotic activities. These data warrant further studies on these anti-fibrotic entities and suggest it a promising strategy to discover new anti-fibrotic drugs by screening more plant materials.

Renal biopsy in liver transplant recipients

BACKGROUND

Renal impairment post-liver transplant (LT) is often attributed to calcineurin inhibitors (CNIs). A renal biopsy can be a useful tool but may be complicated in LT recipients. We aimed to determine the clinical scenarios that prompted a decision to perform a renal biopsy in this patient population, to assess histological findings and evaluate patient management and survival and renal outcome.

METHODS

Information on clinical variables and renal histology was extracted from single-centre prospectively compiled databases from 1996 onwards.

RESULTS

Over 2100 adults received an LT in the time period studied, and 54 of these (35 males and 19 females) were referred for renal review. Of these, 43% underwent a renal biopsy. They had a higher creatinine (P = 0.02), a greater deterioration in creatinine over the year prior to review and were more likely to be nephrotic (both P < 0.01). Histological findings included hypertensive changes (44%), CNI nephrotoxicity (48%), IgA nephropathy (9%), membranoproliferative glomerulonephritis (17%), acute tubular necrosis (4%), crescentic glomerulonephritis (4%) and diabetic nephropathy (9%). Major bleeding complications occurred in 17%. Treatment changed in the majority but, it was not significantly different in the two groups. Although initial renal function was worse in the biopsied group, final patient and renal survival did not differ between the two groups.

CONCLUSION

A renal biopsy is a valuable tool in those with renal insufficiency and/or proteinuria and haematuria but the benefits must be weighed against the relatively high complication rate in LT recipients.

Spectrum of chronic kidney disease in HIV-infected patients

OBJECTIVES

The aim of the study was to investigate the prevalence and aetiology of chronic kidney disease (CKD) and trends in estimated glomerular filtration rate (eGFR) in HIV-infected patients.

METHODS

Ascertainment and review of CKD cases among patients attending King's College and Brighton Hospitals, UK were carried out. CKD was defined as eGFR <60 mL/min for > or =3 months. Longitudinal eGFR slopes were produced to examine trends in renal function before, during and after exposure to indinavir (IDV) or tenofovir (TFV).

RESULTS

CKD prevalence was 2.4%. While HIV-associated nephropathy accounted for 62% of CKD in black patients, 95% of CKD in white/other patients was associated with diabetes mellitus, hypertension, atherosclerosis and/or drug toxicity. Exposure to IDV or TFV was associated with an accelerated decline in renal function (4.6-fold and 3.7-fold, respectively) in patients with CKD. In patients initiating IDV, age > or =50 years increased the odds of CKD [odds ratio (OR) 4.9], while in patients initiating TFV, age > or =50 years (OR 5.4) and eGFR 60-75 mL/min (OR 17.2) were associated with developing CKD.

CONCLUSION

This study highlights the importance of metabolic and vascular disease to the burden of CKD in an ageing HIV-infected cohort. In patients who developed CKD, treatment with IDV or TFV was associated with an accelerated decline in renal function.

HIV care and the incidence of acute renal failure

BACKGROUND

The clinical epidemiology of acute renal failure (ARF) in human immunodeficiency virus (HIV)-infected patients remains poorly defined.

METHODS

We conducted a retrospective analysis of patients who developed ARF while attending King's College Hospital (London, United Kingdom) during January 1998-December 2005. Serum creatinine level and estimated glomerular filtration rate were used to identify ARF. ARF episodes were classified as early onset if they occurred <3 months after initiation of HIV care and as late onset if they occurred > or =3 months after initiation of HIV care.

RESULTS

During the study period, 130 (5.7%) of 2274 patients developed 144 episodes of ARF. The incidences of early-onset and late-onset ARF were 19.3 episodes per 100 person-years (95% confidence interval [CI], 15.4-24.1 episodes per 100 person-years) and 1.1 episodes per 100 person-years (95% CI, 0.83-1.49 episodes per 100 person-years), respectively (rate ratio, 17.4; P<0.001). In multivariate analysis, nadir CD4 T cell count <100 x 10(9) cells/L (odds ratio [OR], 6.7; 95% CI, 2.5-18.3) and acquired immunodeficiency syndrome (OR, 6.7; 95% CI, 3.4-13.3) were associated with early-onset ARF, whereas injection drug use (OR, 4.8; 95% CI, 1.3-17.7), hepatitis C virus coinfection (OR, 3.4; 95% CI, 1.3-8.6), and nadir CD4 T cell count <100 x 10(9) cells/L (OR, 5.8; 95% CI, 2.5-13.4) were associated with late-onset ARF.

CONCLUSIONS

ARF was common and was associated with advanced immunodeficiency. The incidence of ARF decreased >10-fold in patients who had received HIV care for > or =3 months.

Predictors of renal outcome in HIV-associated nephropathy

BACKGROUND

Human immunodeficiency virus (HIV)-associated nephropathy (HIVAN) is an important cause of end-stage renal disease among African American patients. This study was performed to study the epidemiology of HIVAN in a predominantly black African population and the impact of highly active antiretroviral therapy and other factors on the development of end-stage renal disease.

METHODS

We retrospectively identified all patients with HIVAN, defined by biopsy or strict clinical criteria, in 8 clinics in the United Kingdom. Baseline renal function, HIV parameters, renal pathological index of chronic damage, and responses to highly active antiretroviral therapy were analyzed, and factors associated with adverse renal outcome were identified.

RESULTS

From 1998 through 2004, we studied 16,834 patients, 61 of whom had HIVAN. HIVAN prevalence in black patients was 0.93%, and HIVAN incidence in those without renal disease at baseline was 0.61 per 1000 person-years. After a median of 4.2 years, 34 patients (56%) had developed end-stage renal disease. There were no significant differences in renal function and HIV parameters at baseline, time to initiation of highly active antiretroviral therapy, and rates of HIV RNA suppression between the 20 patients who developed end-stage renal disease >3 months after receiving the HIVAN diagnosis and the 23 patients who maintained stable renal function. However, the index of chronic damage score was significantly higher in those who developed end-stage renal disease (P < .001), and an index of chronic damage score >75 was associated with shorter renal survival (P < .001).

CONCLUSIONS

Whereas overall patient survival suggested an important benefit of highly active antiretroviral therapy, no additional renal benefit of early initiation of highly active antiretroviral therapy or viral suppression could be demonstrated in this large cohort of patients with established HIVAN. Severity of chronic kidney damage, as quantified by biopsy, was the strongest predictor of renal outcome.

HIV and the kidney

Kidney disease is an important complication of HIV infection. Antiretroviral therapy has dramatically improved the life expectancy of HIV-infected patients with end-stage renal disease. Renal replacement therapy, including kidney transplantation, should be offered to HIV-positive patients.

Platelet-derived growth factor reorganizes the actin cytoskeleton through 3-phosphoinositide-dependent and 3-phosphoinositide-independent mechanisms in human mesangial cells

BACKGROUND

Platelet-derived growth factor (PDGF) is a potent activator of mesangial cell proliferation and migration. Although phosphoinositide 3-kinase (PI3K) enzymes are important downstream targets of the PDGF receptor, the contribution made by their 3-phosphoinositide products in the reorganization of actin cytoskeleton and focal adhesions has been questioned.

METHODS AND RESULTS

Pharmacological inhibition of the PI3K activity blocks PDGF-induced migration of human primary mesangial cells using an in vitro scrape wound healing assay. Acute (<10 min) inhibition of the PI3K activity did not alter the effect of PDGF on either stress fibre dissolution or reorganization of focal adhesions. However, at later times (>30 min), PDGF-stimulated responses were inhibited. In contrast, PDGF-stimulated membrane ruffling remained insensitive to PI3K inhibitors throughout. Inhibition of protein kinase C and Erk also attenuated PDGF-stimulated mesangial cell migration; however, neither signaling pathway was responsible for the initial effects on filamentous actin and focal adhesions.

CONCLUSIONS

We propose that following PDGF stimulation of mesangial cells, reorganization of the actin cytoskeleton occurs in a biphasic manner. The mechanism responsible for mesangial cell migration that occurs immediately following PDGF stimulation may serve to 'prime' for the subsequent 3-phosphoinositide-, protein-kinase-C-, and Erk-dependent migration.

The role of geranylgeranylated proteins in human mesangial cell proliferation

The Rho family of guanine 5'-triphosphatases (GTPases) play a key role in regulating cell proliferation, tubulointerstitial fibrosis, and glomerular hemodynamics. The post-translational prenylation of RhoGTPases by the addition of a geranylgeranyl moiety is critical for cellular localization and signaling activity. This study investigates the effects of (i) inhibiting geranylgeranylation (GG) in human mesangial cell (HMC) proliferation and apoptosis, using GGTI 298, a specific inhibitor of GG and (ii) lovastatin, an HMG-coacetyl A-reductase inhibitor, which depletes the availability of prenylation substrates. HMC proliferation was assessed using an assay of viable cell number and measuring bromodeoxyuridine (BrdU) incorporation. Hoechst 33342 staining was used to determine apoptosis. Extracellular signal-regulated protein kinase (Erk)1/2 and Akt activation were analysed by Western blotting. Rho activation was determined using the Rhotekin pull-down assay. Immunocytochemistry was performed to study the effects on the actin cytoskeleton and RhoA localization. GGTI 298 (10-20 muM) and lovastatin (5-10 muM) potently inhibited platelet-derived growth factor and serum-stimulated HMC proliferation and induced apoptosis. These effects of lovastatin were attenuated by co-incubation with geranylgeranylpyrophosphate. C3 exoenzyme, a clostridial toxin that specifically targets Rho also inhibited BrdU incorporation and promoted apoptosis. GGTI 298 increased cytosolic expression of RhoA, prevented RhoA activation, and inhibited the activation of Erk1/2 and the survival protein Akt. GGTI 298, lovastatin, and C3 exoenzyme inhibit HMC proliferation and promote apoptosis. Inhibiting GG increases cytosolic RhoA expression, disrupts the actin cytoskeleton, and inhibits RhoA activation. These results suggest that targeting geranylgeranylated proteins with statins or GGTI 298 is a promising therapeutic strategy in human mesangioproliferative renal disease.

Prenylation is not necessary for endogenous Ras activation in non-malignant cells

Ras monomeric GTPases are pivotal to many core cellular processes such as proliferation and differentiation. The post-translational prenylation of Ras with a farnesyl or a geranylgeranyl moiety is thought to be critical for its membrane binding and consequent signaling activity. Inhibitors of Ras prenylation have an anti-proliferative effect in some Ras-transformed cells. We present a study of the effects of prenylation inhibitors on endogenous, wild-type Ras in three renal cell types, namely primary adult human renal fibroblasts, primary adult human mesangial cells, and a primate renal fibroblast cell line (Vero cells). We have previously demonstrated that Ras is necessary for normal proliferation in these cells. Here we show that Ras is farnesylated and not geranylgeranylated in all three cell types. Furthermore, inhibiting Ras farnesylation has no effect on cell proliferation or Ras activation. Although inhibiting geranylgeranylation in these cells does inhibit proliferation, this is through an Ras-independent mechanism. Non-prenylated Ras is able to localize to the plasma membrane, bind Raf when cells are stimulated by epidermal growth factor or platelet-derived growth factor, and activate the Ras downstream effectors mitogen-activated protein kinase and phosphotidylinositol 3-kinase. We conclude that in wild-type cells, endogenous Ras does not need to be prenylated to be active.

The differential role of Smad2 and Smad3 in the regulation of pro-fibrotic TGFbeta1 responses in human proximal-tubule epithelial cells

In chronic renal diseases, progressive loss of renal function correlates with advancing tubulo-interstitial fibrosis. TGFbeta1-Smad (transforming growth factor-beta1-Sma and Mad protein) signalling plays an important role in the development of renal tubulo-interstitial fibrosis. Secretion of CTGF (connective-tissue growth factor; CCN2) by PTECs (proximal-tubule epithelial cells) and EMT (epithelial-mesenchymal transdifferentiation) of PTECs to myofibroblasts in response to TGFbeta are critical Smad-dependent events in the development of tubulo-interstitial fibrosis. In the present study we have investigated the distinct contributions of Smad2 and Smad3 to expression of CTGF, E-cadherin, alpha-SMA (alpha-smooth-muscle actin) and MMP-2 (matrix-metalloproteinase-2) in response to TGFbeta1 treatment in an in vitro culture model of HKC-8 (transformed human PTECs). RNA interference was used to achieve selective and specific knockdown of Smad2 and Smad3. Cellular E-cadherin, alpha-SMA as well as secreted CTGF and MMP-2 were assessed by Western immunoblotting. TGFbeta1 treatment induced a fibrotic phenotype with increased expression of CTGF, MMP-2 and alpha-SMA, and decreased expression of E-cadherin. TGFbeta1-induced increases in CTGF and decreases in E-cadherin expression were Smad3-dependent, whereas increases in MMP-2 expression were Smad2-dependent. Increases in alpha-SMA expression were dependent on both Smad2 and Smad3 and were abolished by combined knockdown of both Smad2 and Smad3. In conclusion, we have demonstrated distinct roles for Smad2 and Smad3 in TGFbeta1-induced CTGF expression and markers of EMT in human PTECs. This can be of therapeutic value in designing targeted anti-fibrotic therapies for tubulo-interstitial fibrosis.

Distinct functions for Ras GTPases in the control of proliferation and apoptosis in mouse and human mesangial cells

In previous work, we have demonstrated that Ras GTPases regulate proliferation in a range of human renal cells. The present work compares human and mouse mesangial cell (HMC and MMC) responses to specific knockdown of Ras genes with antisense oligonucleotides (AS-oligos), and examines the role of the p21 (cip1) and p27 (kip1) cyclin-dependent kinase inhibitors in these responses in mouse cells. HMC and MMC were lipofectin transfected with ras-targeted AS-oligo at 200-400 nM for 18 h followed by growth of cells in 20% serum for 18-72 h. Cell proliferation was assessed with an MTS assay and bromodeoxyuridine (BrdU) uptake. Apoptosis was quantified using nuclear stain with Hoechst 33342 dye. In MMC, Ha-ras AS-oligo caused an increase in apoptosis from <2% to 10-15% of cells after 18 h in serum (P<0.01). Control, Ki-ras and N-ras AS-oligos had minimal effects on apoptosis. BrdU uptake studies showed that BrdU+ve MMC were increased by 20-40% (P<0.05) after Ha-ras AS-oligo at 24 h; other ras AS-oligos were inactive. HMC number was reduced by 40-80% (P<0.01) at 48-72 h by both Ha-ras and Ki-ras AS-oligos. These actions were associated with reductions in BrdU+ve cells. In HMC, the ras AS-oligos did not induce apoptosis. p21(-,-) MMC showed exaggerated apoptotic responses to Ha-Ras AS-oligo. In mouse cells, Ha-Ras expression appears necessary to prevent apoptotic cell death; Ras expression does not appear necessary for cells to progress through the cell cycle. In human cells, Ras does not appear necessary to prevent apoptosis but Ha-Ras and Ki-Ras appear to be required for cell cycle progression.

The inhibition of human mesangial cell proliferation by S-trans, trans-farnesylthiosalicylic acid

BACKGROUND

Many of the proliferative cytokines implicated in human mesangial cell (HMC) proliferation signal through the superfamily of Ras GTPases. The Ras antagonist, S-trans, trans- farnesylthiosalicylic acid (FTS), was used to investigate the effects of the inhibition of Ras signaling on HMC proliferation.

METHODS

Ras expression and membrane localization, MAPK, and Akt activation were analyzed by Western blotting. Ras activation was determined with a pull-down assay using the Ras-binding domain of Raf. HMC growth curves were assessed using the MTS assay of viable cell number, while DNA synthesis was measured with BrdU incorporation. Hoechst 33342 staining was used to determine apoptosis.

RESULTS

FTS reduced the membrane localization of Ras in both serum and platelet-derived growth factor (PDGF). FTS (7.5-20 micromol/L) potently inhibited PDGF-induced HMC proliferation but had no effect on serum-induced proliferation. FTS (10-20 micromol/L) inhibited both Ras and phospho-MAPK activation by serum and PDGF. Furthermore, FTS (10-20 micromol/L) increased HMC apoptosis in the presence of PDGF but not in serum. Moreover, PDGF-stimulated activation of the survival protein Akt was inhibited by FTS. In contrast, serum-stimulated activation of Akt was unaffected by FTS.

CONCLUSION

FTS (5-20 micromol/L) inhibits PDGF-induced but not serum-induced HMC proliferation. FTS (10-20 micromol/L) also promotes HMC apoptosis in the presence of PDGF but not serum. These effects appear to be mediated by inhibitory effects on Ras-dependent signaling that occur as a result of the dislodgment of Ras from its membrane-anchorage sites by FTS. The selectivity of FTS toward PDGF-driven HMC proliferation suggests that FTS may be a valuable therapeutic in mesangioproliferative renal disease.

TGF-β1-Induced Connective Tissue Growth Factor (CCN2) Expression in Human Renal Proximal Tubule Epithelial Cells Requires Ras/MEK/ERK and Smad Signalling

BACKGROUND

Connective tissue growth factor (CTGF, CCN2) plays a fundamental role in the development of tissue fibrosis by stimulating matrix deposition and mediating many of the pro-fibrotic effects of transforming growth factor (TGF)-beta. CCN2 induction by TGF-beta in renal proximal tubule epithelial cells (PTECs) is likely to play an important role in the development of tubulointerstitial fibrosis. In this study, we investigated the induction of CCN2 by TGF-beta1 and the possible mechanisms of this induction in human PTECs.

METHODS

Experiments were performed on primary and transformed (human kidney cell (HKC)-clone 8) human PTECs. Induction of CCN2 in response to TGF-beta1 was studied at the gene promoter level by reporter gene assay, mRNA by semi-quantitative RT-PCR and protein by immunoblotting. While chemical inhibitors were used to assess the role of Ras/MEK/ERK1,2 signalling, an HKC cell line over-expressing Smad7 was used to assess the role of Smad signalling in induction of CCN2 by TGF-beta1.

RESULTS

TGF-beta1 induced CCN2 promoter activity, mRNA and protein in human PTECs. TGF-beta1-dependent CCN2 promoter activity was reduced by inhibiting Ras and MEK activation. MEK inhibition also resulted in inhibition of the TGF-beta1-induced secreted CCN2 protein. There was no significant increase in CCN2 gene promoter activity or protein by TGF-beta1 in Smad7 over-expressing HKCs.

CONCLUSIONS

TGF-beta1 induces the expression of CCN2 in human PTECs. This induction is dependent on Ras/MEK/ERK and Smad signalling. Inhibiting TGF-beta induced CCN2 by targeting Smad and/or Ras/MEK/ERK1,2 signalling pathways could be of therapeutic value in renal fibrosis.

Expression of Ras GTPase isoforms in normal and diseased pancreas

BACKGROUND

Ki-Ras is well studied in its oncogenic form in relation to pancreatic pathologies. However, the individual contribution of each of the wild-type Ras isoforms (Ha-, Ki-, and N-) in pancreatic cells in health and disease is unknown.

METHODS

Archival formalin-fixed, paraffin-embedded specimens of normal (n = 6) and malignant pancreas (n = 35) were used for immuno-histochemical detection of Ras isoforms using a modified polymer system. In addition, immunogold labelling for Ras isoforms was done for subcellular localisation under electron microscopy.

RESULTS

Pancreatic ductal cells expressed Ha-Ras in the cytoplasm, with Ki-Ras in the apical region and N-Ras (50% of cases) in a supranuclear distribution. Pancreatic acinar cells express all three isoforms with some nuclear expression of Ki-Ras and supranuclear expression of N-Ras. Islets show Ki- and Ha-Ras mainly with differential expression of Ha-Ras (beta cells showing less Ha-Ras and more Ki-Ras than alpha cells). Electron microscopy shows that Ha-Ras is mainly localised in the endoplasmic reticulum and Golgi apparatus of the acinar cells with some plasma membrane localisation of Ki-Ras in the ductal cells. There was no change in any of the Ras isoform expression in the ductal or acinar cells in various malignancies studied (Mann-Whitney U test, p > 0.1).

CONCLUSIONS

Ras isoforms have distinct and separate cellular and subcellular distribution that may persist even in the malignantly transformed state. Understanding this distinct functional distribution patterns in detail is an essential step if mutant Ki-Ras is to be targeted in the pancreas by genetic or molecular therapeutic tools.

Subcellular distribution of Ras GTPase isoforms in normal human kidney

BACKGROUND

Ras GTPase isoforms have been implicated in proliferative renal disease and are known to have differential cellular expression in kidney. However, their exact subcellular location in various cells is unknown.

METHODS

Immunogold labelling for Ras isoforms (Harvey, Kirsten and Neural) was performed for subcellular localization under electron microscopy in fresh normal kidney specimens, obtained from the opposite pole of kidneys removed for renal cell cancer.

RESULTS

There was prominent staining shown by Ha-Ras only on the glomerular foot processes as compared with basement membrane or the endothelial cells. Mesangial cells showed intense staining in the cytosol with Ha-Ras (absent in the nucleus), minimal staining with Ki-Ras and none with N-Ras. In both the proximal and distal convoluted tubules, there was a clear staining of the mitochondria with Ha-Ras, with mild cytosolic staining with all of the isoforms.

CONCLUSIONS

Ras isoforms have distinct and separate subcellular distributions in normal kidney cells. Understanding the functional aspects of this distribution pattern is essential if Ras is to be targeted by genetic or molecular therapeutic tools.

The Renal National Service Framework: a step in the right direction

Part one of the National Service Framework (NSF) for Renal Services was published early in 2004. The document covers the treatment of patients with end stage renal failure with dialysis and transplantation. Five standards to be achieved by 2014 are proposed. These cover access to information, timely preparation for dialysis, quality planned access surgery, patient choice for dialysis modality, and improvements in the quantity and success of renal transplants. These standards are underpinned by five early actions to be achieved by 2006. These include improved information flow about current practice and outcomes, increases in haemodialysis capacity and adherence to National Institute for Clinical Excellence guidelines on immunosuppression. The Renal NSF is welcome as a significant boost to the profile of renal services in England. Implementation will be difficult and will require the sustained pressure of the 'Kidney Alliance' representing patients, clinicians and supporting organisations.

Human serum IgA1 is substituted with up to six O-glycans as shown by matrix assisted laser desorption ionisation time-of-flight mass spectrometry

The micro-heterogeneity of human serum IgA1 results from variable O-glycan substitutions in the 'hinge region' of the molecule and this O-glycosylation may be altered in a number of medical conditions. This micro-heterogeneity has been monitored by analysis of IgA1-derived tryptic O-glycopeptides using matrix assisted laser desorption ionisation time-of-flight mass spectrometry (MALDI-ToF-MS) analysis. With ammonium citrate-trihydroxyacetophenone matrix, individual compositional glycoforms have been baseline resolved in more than 70 samples and these spectra revealed for the first time that, in addition to expected substitution with 3,4 and 5 GalNAcs, a sixth GalNAc substitution was also present in the hinge region of the molecule. The spectra obtained from subsequent exoglycosidase-treated samples confirmed hexa-O-substitution. Following endoprotease digestions of the exoglycosidase treated samples, possible locations for the sixth GalNAc were indicated from further MALDI-ToF-MS analysis. Hexa-substitution accounts for around 5-10% the glycoforms. This is, we believe, the first report of hexa-O-substitution with GalNAc of human serum IgA1.

Glycoform composition profiling of O-glycopeptides derived from human serum IgA1 by matrix-assisted laser desorption ionization-time of flight-mass spectrometry

Pools of O-glycopeptides prepared from trypsin-digested reduced and alkylated human serum IgA1 have been analyzed using matrix-assisted laser desorption ionization-time of flight-mass spectrometry (MALDI-ToF-MS) in the positive-ion mode, using 2,4,6-trihydroxy acetophenone-ammonium citrate matrix. Dozens of such pools prepared from normal serum IgA1 and from serum of patients with a number of different medical conditions have been routinely analyzed in this manner. The glycopeptides present in these pools possess identical amino acid sequences but are substituted with a variety of neutral and sialylated glycans and the spectra obtained were such that individual compositional glycoforms were baseline resolved. In addition, the spectra were reproducible, exhibiting a relative peak intensity and area variation of around 11-16%, enabling the technique to be used for the relative quantitation of the different compositional glycoforms present. This could be achieved manually or by applying a Java program especially developed for this purpose. The MS analysis described here is a major improvement over present MALDI methods used for profiling the O-glycosylation of IgA1. The MS methodology together with the Java data analysis are expected to be generally applicable for profiling O-linked glycopeptides derived from other glycoproteins and probably for N-linked glycopeptide pools.

Expression of Ras GTPases in normal kidney and in glomerulonephritis

BACKGROUND

Small monomeric Ras GTPases play critical and specific roles in the control of cellular proliferation and apoptosis but the expression of the three Ras isoforms (Ha-Ras, Ki-Ras and N-Ras) in human renal tissue is unknown. This work is an immunohistochemical study of Ras expression in normal renal tissue and in membranous glomerulonephritis (MGN), IgA nephropathy (IgAN) and IgA-negative mesangioproliferative glomerulonephritis (MPGN).

METHODS

Formalin-fixed, paraffin-embedded tissue was stained using pan-Ras monoclonal antibody (mAb) and Ras isoform-specific mAb. Detection employed a (DAKO Envision) modified polymer system.

RESULTS

The expression of Ras isoforms in normal human kidney was cell-specific. For example, N-Ras was detected in tubule epithelial cells but not in glomerular or interstitial cells. Ki-Ras was expressed in mesangial cells, interstitial cells and in proximal convoluted tubule cells (PCT) (particularly localized at brush borders) and in collecting duct cells (CD) (localized to cell membranes) but not in podocytes. Cytoplasmic Ha-Ras was detected in all the above cell types except podocytes. MGN was associated with podocyte expression of all three Ras isoforms and with reduced mesangial cell expression of Ha-Ras and Ki-Ras. IgAN was characterized by podocyte expression of Ha-Ras (but not Ki-Ras) and reduced mesangial cell expression of Ki-Ras without alterations in mesangial Ha-Ras expression. MPGN was associated with reduced mesangial cell Ha-Ras and Ki-Ras expression without significant podocyte Ras expression.

CONCLUSION

These disease-specific and isoform-specific alterations in Ras expression may be of significance in pathogenesis and warrant further functional investigation.

Targeting Ras genes in kidney disease

Certain changes in cellular function are characteristic of renal disease. Foremost among these is the excessive proliferation of cells, but other phenotypic changes include dysregulated apoptosis, migration, adhesion, contraction, secretion, and receptor expression. Recent advances in cell biology have revealed an extensive role for the small monomeric GTPases of the Ras superfamily in the control of these cellular events through intracellular signalling cascades. The specific Ras genes appear to play discrete and identifiable roles in a range of complex signalling networks. These insights lead to the possibility of targeting Ras genes in a specific manner in renal therapies. For example, the process of renal cell proliferation might be sensitive to downregulation of Harvey Ras and Kirsten Ras; targeting of Rho A and related species may modulate cell migration, fibrosis, and intrarenal vasoconstriction. Possible strategies for such modulation could include the use of RNA-interacting agents such as antisense DNA and si-RNA and the use of small molecules acting on Ras directly or on related signalling molecules such as Rho kinase and Raf kinase.