Expression and regulation of αB-crystallin in the kidney in vivo and in vitro

Structure and function of the thin limbs of the loop of Henle

The thin limbs of the loop of Henle, which comprise the intermediate segment, connect the proximal tubule to the distal tubule and lie entirely within the renal medulla. The descending thin limb consists of at least two or three morphologically and functionally distinct subsegments and participates in transepithelial transport of NaCl, urea, and water. Only one functionally distinct segment is recognized for the ascending thin limb, which carries out transepithelial transport of NaCl and urea in the reabsorptive and/or secretory directions. Membrane transporters involved with passive transcellular Cl, urea, and water fluxes have been characterized for thin limbs; however, these pathways do not account for all transepithelial fluid and solute fluxes that have been measured in vivo. The paracellular pathway has been proposed to play an important role in transepithelial Na and urea fluxes in defined thin-limb subsegments. As the transport pathways become clearer, the overall function of the thin limbs is becoming better understood. Primary and secondary signaling pathways and protein-protein interactions are increasingly recognized as important modulators of thin-limb cell function and cell metabolism. These functions must be investigated under diverse extracellular conditions, particularly for those cells of the deep inner medulla that function in an environment of wide variation in hyperosmolality. Transgenic mouse models of several key water and solute transport proteins have provided significant insights into thin-limb function. An understanding of the overall architecture of the medulla, including juxtapositions of thin limbs with collecting ducts, thick ascending limbs, and vasa recta, is essential for understanding the role of the kidney in maintaining Na and water homeostasis, and for understanding the urine concentrating mechanism.

Developmental cigarette smoke exposure: kidney proteome profile alterations in low birth weight pups

The Brenner hypothesis states that a congenital reduction in nephron number predisposes to adult-onset hypertension and renal failure. The reduction in nephron number induced by proportionally smaller kidney mass may predispose offspring to glomerular hyperfiltration with maturity onset obesity. Developmental cigarette smoke exposure (CSE) results in intrauterine growth retardation with a predisposition to obesity and cardiovascular disease at maturity. Utilizing a mouse model of 'active' developmental CSE (gestational day [GD] 1-postnatal day [PD] 21; cotinine>50 ng/mL) characterized by persistently smaller offspring with proportionally decreased kidney mass, the present study examined the impact of developmental CSE on the abundance of proteins associated with cellular metabolism in the kidney. Following cessation of CSE on PD21, kidney tissue was collected from CSE and Sham exposed pups for 2D-SDS-PAGE based proteome profiling with statistical analysis by partial least squares-discriminant analysis (PLS-DA) with affected molecular pathways identified by ingenuity pathway analysis. Proteins whose expression in the kidney were affected by developmental CSE belonged to the inflammatory disease, cell to cell signaling/interaction, lipid metabolism, small molecule biochemistry, cell cycle, respiratory disease, nucleic acid and carbohydrate metabolism networks. The present findings indicate that developmental CSE alters the kidney proteome. The companion paper details the liver proteome alterations in the same offspring.

Kidney-specific cadherin correlates with the ontogenetic origin of renal cell carcinoma subtypes: an indicator of a malignant potential?

INTRODUCTION AND OBJECTIVES

To evaluate retrospectively kidney-specific cadherin (Ksp-cad) expression in renal cell carcinoma (RCC) subtypes and oncocytoma in correlation with its ontogenetic origin of distal and proximal tubules and to correlate Ksp-cad expression with tumour characteristics.

MATERIALS AND METHODS

Membranous and cytoplasmic expression of Ksp-cad was determined in 40 clear cell (ccRCC), 25 papillary (pRCC), 19 chromophobe carcinomas (chRCC), 27 oncocytomas (oncocytomas) (n = 111) and 32 benign kidney parenchyma specimens separated in distal tubules (DT) and proximal tubules (PT) by immunohistochemistry using tissue microarray technique. Staining intensity was quantified as a score ranging from 0 to 12. Comparison of data and correlation with tumour characteristics were done by Wilcoxon/Kruskal-Wallis tests (post hoc Tukey-Kramer analysis).

RESULTS

In benign renal tissue, membranous and cytoplasmic expression of Ksp-cad in the DT was significantly higher than that in the PT (12.0 ± 0 vs. 5.2 ± 0.3 and 6.3 ± 0.5 vs. 0.0 ± 0.0, respectively; (P < 0.05)). Membranous KSP-cad expression was significantly higher in chRCC (5.2 ± 0.8) and oncocytomas (3.7 ± 0.4) than that in ccRCC (0.8 ± 0.2) and pRCC (1.4 ± 0.4; P < 0.05), while expression between oncocytomas and chRCC did not differ significantly. In RCC, Ksp-cad expression was significantly associated with higher T stage and the occurrence of synchronous metastasis (P < 0.05). Higher N stages and grading tended to correlate with a lower Ksp-cad expression.

CONCLUSIONS

In this cohort, the origin of tumour subtypes-chRCC and oncocytomas develop from DT and ccRCC and pRCC from PT cells-is mirrored by the respective Ksp-cad expression. This raises the question whether DT-derived tumours have a less malignant potential than PT-derived tumours.

Osmoadaptation of Mammalian cells - an orchestrated network of protective genes

In mammals, the cells of the renal medulla are physiologically exposed to interstitial osmolalities several-fold higher that found in any other tissue. Nevertheless, these cells not only have the ability to survive in this harsh environment, but also to function normally, which is critical for maintenance of systemic electrolyte and fluid homeostasis. Over the last two decades, a substantial body of evidence has accumulated, indicating that sequential and well orchestrated genomic responses are required to provide tolerance to osmotic stress. This includes the enhanced expression and action of immediate-early genes, growth arrest and DNA damage inducible genes (GADDs), genes involved in cell cycle control and apoptosis, heat shock proteins, and ultimately that of genes involved in the intracellular accumulation of nonperturbing organic osmolytes. The present review summarizes the sequence of genomic responses conferring resistance against osmotic stress. In addition, the regulatory mechanisms mediating the coordinated genomic response to osmotic stress will be highlighted.

Cyclooxygenase-2-dependent phosphorylation of the pro-apoptotic protein Bad inhibits tonicity-induced apoptosis in renal medullary cells

During antidiuresis, cell survival in the renal medulla requires cyclooxygenase-2 (COX-2) activity. We have recently found that prostaglandin E2 (PGE2) promotes cell survival by phosphorylation and, hence, inactivation of the pro-apoptotic protein Bad during hypertonic stress in Madin-Darby canine kidney (MDCK) cells in vitro. Here we determine the role of COX-2-derived PGE(2) on phosphorylation of Bad and medullary apoptosis in vivo using COX-2-deficient mice. Both wild-type and COX-2-knockout mice constitutively expressed Bad in tubular epithelial cells of the renal medulla. Dehydration caused a robust increase in papillary COX-2 expression, PGE2 excretion, and Bad phosphorylation in wild-type, but not in the knockout mice. The abundance of cleaved caspase-3, a marker of apoptosis, was significantly higher in papillary homogenates, especially in tubular epithelial cells of the knockout mice. Knockdown of Bad in MDCK cells decreased tonicity-induced caspase-3 activation. Furthermore, the addition of PGE2 to cells with knockdown of Bad had no effect on caspase-3 activation; however, PGE2 caused phosphorylation of Bad and substantially improved cell survival in mock-transfected cells. Thus, tonicity-induced COX-2 expression and PGE2 synthesis in the renal medulla entails phosphorylation and inactivation of the pro-apoptotic protein Bad, thereby counteracting apoptosis in renal medullary epithelial cells.

Osmoprotective proteome adjustments in mouse kidney papilla

The papilla of the mammalian kidney must tolerate greatly varying degrees of hyperosmotic stress during urine concentration and depending on whole organism hydration state. To identify proteome adaptations supporting cell function and survival in such a harsh environment we compared the proteome of a) the hyperosmotic renal papilla with that of adjacent iso-osmotic cortex tissue and b) the renal papilla of diuretic versus that of anti-diuretic mice. Though functionally distinct the papilla is in close physical proximity to the renal cortex, an iso-osmotic region. Proteomic differences between the papilla and cortex of C57BL6 mice were identified using two-dimensional gel electrophoresis and MALDI-TOF/TOF mass spectrometry. We found 37 different proteins characteristic of the cortex and 16 proteins over-represented in the papilla. Regional specificity was confirmed by Western blot and further substantiated by immunohistochemistry for selected proteins. Proteins that are characteristic of the renal papilla include αB crystallin, Hsp beta-1, Hsp90, 14-3-3 protein, glutathione S-transferase, aldose reductase, actin and tropomyosin. Gene ontology analysis confirmed a significant increase in molecular functions associated with protein chaperoning and cell stabilization. Proteins over-represented in the cortex were largely related to routine metabolism. During antidiuresis 15 different proteins changed significantly while 18 different proteins changed significantly during diuresis relative to normally hydrated controls. Changes were confirmed by Western blot for selected proteins. Proteins that are significantly altered by diuretic state are associated with cell structure (actin, tubulin), signaling (Rho GDP dissociation inhibitor, abhydrolase domain-containing protein 14B), chaperone functioning (Hsp beta-1, αB crystallin, T complex protein-1) and anti-oxidant functions (α-enolase, GAPDH and LDH). Taken together our study reveals that specific proteins involved in protein folding, cytoskeletal stabilization, antioxidant responses, and stress signaling contribute greatly to the unique hyperosmotic stress resistant phenotype of the kidney papilla.

TonEBP stimulates multiple cellular pathways for adaptation to hypertonic stress: organic osmolyte-dependent and -independent pathways

TonEBP (tonicity-responsive enhancer binding protein) is a transcription factor that promotes cellular accumulation of organic osmolytes in the hypertonic renal medulla by stimulating expression of its target genes. Genetically modified animals with deficient TonEBP activity in the kidney suffer from severe medullary atrophy in association with cell death, demonstrating that TonEBP is essential for the survival of the renal medullary cells. Using both TonEBP knockout cells and RNA interference of TonEBP, we found that TonEBP promoted cellular adaptation to hypertonic stress. Microarray analyses revealed that the genetic response to hypertonicity was dominated by TonEBP in that expression of totally different sets of genes was increased by hypertonicity in those cells with TonEBP vs. those without TonEBP activity. Of over 100 potentially new TonEBP-regulated genes, we selected seven for further analyses and found that their expressions were all dependent on TonEBP. RNA interference experiments showed that some of these genes, asporin, insulin-like growth factor-binding protein-5 and -7, and an extracellular lysophospholipase D, plus heat shock protein 70, a known TonEBP target gene, contributed to the adaptation to hypertonicity without promoting organic osmolyte accumulation. We conclude that TonEBP stimulates multiple cellular pathways for adaptation to hypertonic stress in addition to organic osmolyte accumulation.

Strategies for treatment in Alexander disease

Alexander disease is a rare and generally fatal disorder of the CNS, originally classified among the leukodystrophies because of the prominent myelin deficits found in young patients. The most common form of this disease affects infants, who often have profound mental retardation and a variety of developmental delays, but later onset forms also occur, sometimes with little or no white matter pathology at all. The pathological hallmark of Alexander disease is the inclusion body, known as Rosenthal fiber, within the cell bodies and processes of astrocytes. Recent genetic studies identified heterozygous missense mutations in glial fibrillary acidic protein (GFAP), the major intermediate filament protein in astrocytes, as the cause of nearly all cases of Alexander disease. These studies have transformed our view of this disorder and opened new directions for investigation and clinical practice, particularly with respect to diagnosis. Mechanisms by which expression of mutant forms of glial fibrillary acidic protein (GFAP) lead to the pleiotropic manifestations of disease (afflicting cell types beyond the ones expressing the mutant gene) are slowly coming into focus. Ideas are beginning to emerge that suggest several compelling therapeutic targets for interventions that might slow or arrest the evolution of the disease. This review will outline the rationale for pursuing these strategies, and highlight some of the critical issues that must be addressed in the planning of future clinical trials.

Differential response of C57BL/6J mouse and DBA/2J mouse to optic nerve crush

Background

Retinal ganglion cell (RGC) death is the final consequence of many blinding diseases, where there is considerable variation in the time course and severity of RGC loss. Indeed, this process appears to be influenced by a wide variety of genetic and environmental factors. In this study we explored the genetic basis for differences in ganglion cell death in two inbred strains of mice.

Results

We found that RGCs are more susceptible to death following optic nerve crush in C57BL/6J mice (54% survival) than in DBA/2J mice (62% survival). Using the Illumina Mouse-6 microarray, we identified 1,580 genes with significant change in expression following optic nerve crush in these two strains of mice. Our analysis of the changes occurring after optic nerve crush demonstrated that the greatest amount of change (44% of the variance) was due to the injury itself. This included changes associated with ganglion cell death, reactive gliosis, and abortive regeneration. The second pattern of gene changes (23% of the variance) was primarily related to differences in gene expressions observed between the C57BL/6J and DBA/2J mouse strains. The remaining changes in gene expression represent interactions between the effects of optic nerve crush and the genetic background of the mouse. We extracted one genetic network from this dataset that appears to be related to tissue remodeling. One of the most intriguing sets of changes included members of the crystallin family of genes, which may represent a signature of pathways modulating the susceptibility of cells to death.

Conclusion

Differential responses to optic nerve crush between two widely used strains of mice were used to define molecular networks associated with ganglion cell death and reactive gliosis. These results form the basis for our continuing interest in the modifiers of retinal injury.

Structural perturbation of alphaB-crystallin by zinc and temperature related to its chaperone-like activity

alphaB-crystallin is a small heat shock protein that shows chaperone-like activity, as it protects the aggregation of denatured proteins. In this work, the possible relationships between structural characteristics and the biological activity of alphaB-crystallin were investigated on the native protein and on the protein undergoing the separate effects of metal ligation and temperature. The chaperone-like activity of alphaB-crystallin increased in the presence of zinc and when temperature was increased. By using fluorescent probes to monitor hydrophobic surfaces on alphaB-crystallin, it was found that exposed hydrophobic patches on the protein surface increased significantly both in the presence of zinc and when the temperature was raised from 25 to 37 degrees C. The zinc-induced increased exposure of lipophilic residues is in agreement with theoretical calculations performed on 3D-models of monomeric alphaB-crystallin, and may be significant to its increased biological activity.