Retinoic acid affects the cell cycle and increases total protein content in epithelial cells

State-of-the-art nanoplatform-integrated MALDI-MS impacting resolutions in urinary proteomics

Urine proteomics has become a subject of interest, since it has led to a number of breakthroughs in disease diagnostics. Urine contains information not only from the kidney and the urinary tract but also from other organs, thus urinary proteome analysis allows for identification of biomarkers for both urogenital and systemic diseases. The following review gives a brief overview of the analytical techniques that have been in practice for urinary proteomics. MALDI-MS technique and its current application status in this area of clinical research have been discussed. The review comments on the challenges facing the conventional MALDI-MS technique and the upgradation of this technique with the introduction of nanotechnology. This review projects nano-based techniques such as nano-MALDI-MS, surface-assisted laser desorption/ionization, and nanostructure-initiator MS as the platforms that have the potential in trafficking MALDI-MS from the lab to the bedside.

Advances in urinary proteome analysis and biomarker discovery

Noninvasive diagnosis of kidney diseases and assessment of the prognosis are still challenges in clinical nephrology. Definition of biomarkers on the basis of proteome analysis, especially of the urine, has advanced recently and may provide new tools to solve those challenges. This article highlights the most promising technological approaches toward deciphering the human proteome and applications of the knowledge in clinical nephrology, with emphasis on the urinary proteome. The data in the current literature indicate that although a thorough investigation of the entire urinary proteome is still a distant goal, clinical applications are already available. Progress in the analysis of human proteome in health and disease will depend more on the standardization of data and availability of suitable bioinformatics and software solutions than on new technological advances. It is predicted that proteomics will play an important role in clinical nephrology in the very near future and that this progress will require interactive dialogue and collaboration between clinicians and analytical specialists.

Retinoids in nephrology: Promises and pitfalls

BACKGROUND

Retinoids, a family of vitamin A metabolites or analogs, play an important role in regulating cell proliferation, differentiation, and apoptosis.

METHODS

The biological importance of retinoids in the kidney and the potential of retinoids in the treatment of renal diseases are reviewed.

RESULTS

Vitamin A deficiency and mutations of retinoid nuclear receptors cause abnormalities in fetal kidneys, which might predispose to adult diseases such as hypertension. Further, the therapeutic value of retinoids in animal models of kidney diseases, such as lupus nephritis, puromycin aminonucleoside nephrosis, anti-glomerular basement membrane nephritis, mesangioproliferative nephritis, and acute renal allograft rejection has been unveiled recently. Retinoids target mesangial cells, podocytes, tubular epithelial cells, interstitial fibroblasts, as well as lymphocytes and macrophages. The anti-inflammation, anti-coagulation effects, and the proliferation- and immunity-modulating actions of retinoids, have been widely appreciated. Our recent in vitro data revealed a direct antifibrotic effect and a cytoprotective effect of retinoids in various renal cell types. In animal studies, the adverse effects of retinoids are generally minimal; however, the clinical use of retinoids in other diseases points to some major side effects. In addition, in vitro, retinoids can induce lipid accumulation in smooth muscle cells and macrophages and increase expression of some proinflammatory molecules, indicating that their clinical toxicity profile in the setting of renal diseases needs to be better understood.

CONCLUSION

Retinoids not only are important in renal development, but also show promise as a new generation of renal medication and deserve to be tested in clinical trials to clarify their full potential.

Retinoic acid exacerbates experimental radiation nephropathy

Studies have shown that angiotensin-converting enzyme inhibitors and an angiotensin II receptor blocker can delay, but cannot reverse, the progression of experimentally induced radiation nephropathy. In an effort to find a method for reversing injury, three agents were tested in a rat model of radiation nephropathy. Pirfenidone (a phenyl-pyridone antifibrotic) and thiaproline (an inhibitor of collagen deposition) were not capable of retarding the development of radiation nephropathy. However, all-trans retinoic acid (an anti-inflammatory agent) exacerbated radiation nephropathy. We speculated that the detrimental effects of retinoic acid might be the result of stimulation of renal cell proliferation. However, retinoic acid had no effect on tubular or glomerular cell proliferation in normal animals and did not enhance radiation-induced proliferation. A recent report that retinoic acids inhibit nitric oxide production suggested an alternative mechanism, since inhibition of production of nitric oxide is known to exacerbate radiation nephropathy. Experiments demonstrated that retinoic acid exacerbated the radiation-induced drop in renal production of nitric oxide, suggesting that the detrimental effect of all-trans retinoic acid might be explained by inhibition of renal nitric oxide activity. Particularly in view of the recent clinical report of enhancement of radiation nephropathy by retinoic acid in patients receiving bone marrow transplantation, the combination of retinoic acid and renal irradiation should be carried out with great caution.

Identification of RPE65 in transformed kidney cells

The protein RPE65 has an important role in retinoid processing and/or retinoid transport in the eye. Retinoids are involved in cell differentiation, embryogenesis and carcinogenesis. Since the kidney is known as an important site for retinoid metabolism, the expression of RPE65 in normal kidney and transformed kidney cells has been examined. The RPE65 mRNA was detected in transformed kidney cell lines including the human embryonic kidney cell line HEK293 and the African green monkey kidney cell lines COS-1 and COS-7 by reverse transcription PCR. In contrast, it was not detected in human primary kidney cells or monkey kidney tissues under the same PCR conditions. The RPE65 protein was also identified in COS-7 and HEK293 cells by Western blot analysis using a monoclonal antibody to RPE65, but not in the primary kidney cells or kidney tissues. The RPE65 cDNA containing the full-length encoding region was amplified from HEK293 and COS-7 cells. DNA sequencing showed that the RPE65 cDNA from HEK293 cells is identical to the RPE65 cDNA from the human retinal pigment epithelium. The RPE65 from COS-7 cells shares 98 and 99% sequence identity with human RPE65 at the nucleotide and amino acid levels, respectively. Moreover, the RPE65 mRNA was detected in three out of four renal tumor cultures analyzed including congenital mesoblastic nephroma and clear cell sarcoma of the kidney. These results demonstrated that transformed kidney cells express this retinoid processing protein, suggesting that these transformed cells may have an alternative retinoid metabolism not present in normal kidney cells.

Reversal of the temperature-shift-induced growth restriction of a temperature-sensitive simian virus 40 T-antigen-transformed human fibroblast cell line by treatment with retinoic acid

We previously established a human fibroblast cell line, HFL 6-2, that contains a temperature sensitive simian virus 40 (SV40) T antigen, permitting cell growth at 35 degrees C but restricting growth at 39 degrees C. p21 (Waf1/Cip1) was significantly induced by temperature shifts in HFL 6-2 cells. Here we show that all-trans-retinoic acid (RA) treatment prevented the growth restriction of HFL 6-2 cells at 39 degrees C. In the presence of RA, HFL 6-2 cells proliferated into sizeable colonies even at 39 degrees C. [3H]Thymidine incorporation and flow cytometry analysis revealed that cells exposed to RA maintained DNA synthesis at 39 degrees C. Prevention of growth restriction by RA was correlated with a lack of induction of p21 at the transcription level. These observations suggest that RA may prevent the senescence process by repressing p21 gene expression, and perturb the growth regulation of somatic cells.

Determination of retinoids by reversed-phase capillary liquid chromatography with amperometric electrochemical detection

A method for separating and detecting retinoids by reversed-phase capillary liquid chromatography with amperometric electrochemical detection is described. Packed columns with an inner diameter of 180 microns were employed for the separation using C18 stationary phase and a mobile phase containing acetonitrile-water methanol (65:32.5:2.5, v/v/v) with 1% tetrabutylammonium perchlorate and 0.174 M acetate buffered at pH 5. The detection cell consisted of a carbon fiber barrel electrode held at 0.9 V versus an Ag/AgCl reference. Injection volumes of 2 microliters produced detection limits of 2.73, 0.472, 0.428, and 0.267 fmol (or 410, 64.1, 60.9, and 38.2 pg ml-1) for 13-cis-retinoic acid, all-trans-retinoic acid, retinaldehyde, and retinol, respectively. This represents an improvement in detection limits of at least three orders of magnitude for similar analyses using liquid chromatography and UV absorbance detection. The detector signal was linear over two orders of magnitude of analyte concentration. Retinoid concentrations in bovine serum were determined and found to be in good agreement with previously reported values.

All-trans-retinoic acid stimulates synthesis of cyclic ADP-ribose in renal LLC-PK1 cells

Cyclic adenosine diphospho-ribose (cADPR) triggers Ca2+ release from intracellular stores and is therefore proposed to function as a second messenger in cellular signaling; however, an extracellular stimulus, i.e., first messenger (hormone or autacoid) that modulates cADPR metabolism has not been identified. We discovered that all-trans-retinoic acid (atRA) is a potent stimulus to increase cADPR synthesis by cultured LLC-PK1 cells. The stimulation of cADPR synthesis by atRA is dose dependent between 0.1 nM and 1 microM (maximum increase approximately delta + 600%), while atRA does not alter the rate of cADPR hydrolysis by LLC-PK1 cells. The activity of other intrinsic apical membrane enzymes was not significantly altered. The stimulation of cADPR synthesis by atRA occurs after a lag period of 6-8 h, and the stimulation is inhibited by actinomycin D and by cycloheximide. Our results therefore demonstrate that atRA in physiological concentrations is a potent extracellular stimulus, first messenger, that enhances cADPR synthesis, and the effect of atRA requires de novo protein synthesis. We suggest that some of the diverse biologic actions of atRA such as morphogenetic and cell differentiation may be mediated via cADPR.

Regulation of human renal adenocarcinoma cell growth by retinoic acid and its interactions with epidermal growth factor

Retinoic acid (RA) is a natural derivative of vitamin A which regulates the growth and differentiation of epithelia. We have previously proposed that RA participates in compensatory kidney growth and reported that RA inhibits rat mesangial cell growth. This paper describes the effects of RA on a human renal adenocarcinoma cell line (PAD) under different growth conditions, and its interactions with epidermal growth factor (EGF). PAD cells were shown to express RA receptors alpha and beta by Northern blot analysis. In serum free cultures, addition of RA (10(-7) M) markedly increased thymidine incorporation by PAD cells (155 +/- 7% mean +/- SE vs. control in 6 separate experiments; P < 0.0001). RA also caused a significant increase in thymidine incorporation by PAD cells under conditions of rapid growth in serum supplemented medium (115 +/- 2% vs. control; P < 0.001). RA by itself was unable to reverse contact inhibition of PAD cell growth (NS vs. control), but it synergistically enhanced the mitogenic effect of EGF on confluent monolayers (110 +/- 0.6% vs. EGF alone; P < 0.05). Northern blot analysis demonstrated that PAD cells express EGF receptor mRNA, and this was not significantly modified by the addition of RA. Growth arrested (serum starved) PAD cells expressed RAR-alpha mRNA which was upregulated eightfold at three hours following the addition of 10% FCS. Thus, our data show that RA is directly mitogenic for serum starved human renal adenocarcinoma cells and that it exerts complex modulation of cell growth in the presence of EGF and serum components.

Molecular mechanisms of tubulointerstitial hypertrophy and hyperplasia

Adult kidneys, which are principally composed of tubulointerstitium, do not normally regenerate or expand their working pool of functional cells at a very high rate. Loss of kidney tissue, however, can lead to some compensatory renal enlargement. The catalytic forces initiating such exchanges have not been fully articulated by current experimental endeavors. Increasing evidence, nevertheless, does suggest that factors other than simple changes in renal hemodynamics may be involved in this process. Different cellular elements in the tubulointerstitial microenvironment probably modulate changes in tubular enlargement or size through a complex cytokine network. Autocrine and paracrine stimulation of enlargement by different local growth factors also seem to play a pivotal role. After binding to cellular receptors, these factors activate signal transduction pathways resulting in expression of immediate early genes, which by themselves can synchronize the expression of subsequent genes through the medium of transacting factors. The renal enlargement response can also be modified by endocrine hormones that can activate such genes directly and/or stimulate other adjunctive processes, like receptor expression for the regional binding of growth factors. Furthermore, renal enlargement is under negative feedback of inhibitory factors like TGF beta. It is possible, for example, that special genes exist which are only expressed to arrest enlargement. It has been further suggested that activation of the Na+/H+ antiporter is a common denominator in renal enlargement. Recent findings, however, indicate that the activation of this antiporter is not always necessary, and might rather be a parallel event rather than a key phenomena in tubular enlargement. G0/G1 transition of tubular cells seems to involve similar factors in tubular hypertrophy and hyperplasia. The factors which are responsible for the final determination of the enlargement pattern (hypertrophy vs. proliferation) are unknown. The separation between hypertrophy and hyperplasia, although suggested by striking differences in cellular regulation, may be somewhat artificial, since responses leading to tubular enlargement also exist in circumstances where hyperplasia and hypertrophy are combined events. Recently it has been proposed that growth factors stimulate gluconeogenesis in proximal tubular cells producing hyperplasia, whereas factors inhibiting gluconeogenesis might induce hypertrophy. Whether the common pathway message of this intriguing hypothesis is correct still requires further validation.(ABSTRACT TRUNCATED AT 400 WORDS)