Biomedical subjects

Albert C M Ong

Publications and source records attributed to Albert C M Ong.

14 recordsLinked to original sources

PubMed2007

Polycystic kidney disease is a risk factor for new-onset diabetes after transplantation.

BACKGROUND: Data from matched historical cohort studies suggest that autosomal-dominant polycystic kidney disease (ADPKD) may be a risk factor for new-onset diabetes after transplantation (NODAT). METHOD: A retrospective study of 429 renal allografts transplanted from 1990 through 2004 in nondiabetic patients was performed. A multivariate analysis of risk factors for NODAT was performed with focus on ADPKD. RESULTS: A total of 6.5% of all patients developed NODAT and a further 11% developed impaired glucose tolerance. NODAT developed in 13.4% of patients with ADPKD compared with 5.2% of non-ADPKD patients (P=0.01). There were significant univariate associations between NODAT and recipient age (P=0.001) and weight (P<0.0001). There was no association between NODAT and recipient gender, human leukocyte antigen mismatch, acute rejection, or cumulative methylprednisolone dose. In a multivariate analysis, ADPKD was a strong risk factor for the development of NODAT (odds ratio [OR]=2.41, P=0.035) after correction for recipient age, weight, gender, ethnicity, and tacrolimus use. Age (OR=1.06), weight (OR=1.04), and nonwhite race (OR=5.04) were the other significant variables. CONCLUSION: We conclude that ADPKD is a significant risk factor for the development of NODAT. This may influence the follow up and management choices of these patients in the future.

Adult↗

PubMed2007

Functional characterization of GATA3 mutations causing the hypoparathyroidism-deafness-renal (HDR) dysplasia syndrome: insight into mechanisms of DNA binding by the GATA3 transcription factor.

The hypoparathyroidism-deafness-renal (HDR) dysplasia syndrome is an autosomal dominant disorder caused by mutations of the dual zinc finger transcription factor, GATA3. We investigated 21 HDR probands and 14 patients with isolated hypoparathyroidism for GATA3 abnormalities. Thirteen different heterozygous germline mutations were identified in patients with HDR. These consisted of three nonsense mutations, six frameshifting deletions, two frameshifting insertions, one missense (Leu348Arg) mutation and one acceptor splice site mutation. The splice site mutation was demonstrated to cause a pre-mRNA processing abnormality leading to the use of an alternative acceptor site 8 bp downstream of the normal site, resulting in a frameshift and prematurely terminated protein. Electrophoretic mobility shift assays (EMSAs) revealed three classes of GATA3 mutations: those that lead to a loss of DNA binding which represent over 90% of all mutations, and involved a loss of the carboxy-terminal zinc finger; those that resulted in a reduced DNA-binding affinity; and those (e.g. Leu348Arg) that did not alter DNA binding or the affinity but likely altered the conformational change that occurs during binding in the DNA major groove as predicted by a three-dimensional modeling. These results elucidate further the molecular mechanisms underlying the altered functions of mutants of this zinc finger transcription factor and their role in causing this developmental anomaly. No mutations were identified in patients with isolated hypoparathyroidism, thereby indicating that GATA3 abnormalities are more likely to result in two or more of the phenotypic features of the HDR syndrome and not in one, such as isolated hypoparathyroidism.

Abnormalities, Multiple↗

PubMed2007

Endothelin B receptor blockade accelerates disease progression in a murine model of autosomal dominant polycystic kidney disease.

Autosomal dominant polycystic kidney disease (ADPKD) is the most common genetic disease that causes kidney failure and accounts for 10% of all patients who are on renal replacement therapy. However, the marked phenotypic variation between patients who carry the same PKD1 or PKD2 mutation suggests that nonallelic factors may have a greater influence on the cystic phenotype. Endothelin-1 (ET-1) transgenic mice have been reported to develop profound renal cystic disease and interstitial fibrosis without hypertension. The hypothesis that ET-1 acts as a modifying factor for cystic disease progression was tested in an orthologous mouse model of ADPKD (Pkd2(WS25/-)). Four experimental groups (n = 8 to 11) were treated from 5 to 16 wk of age with the highly selective orally active receptor antagonists ABT-627 (ETA) and A-192621 (ETB) singly or in combination. Unexpected, ETB blockade led to accelerated cystic kidney disease. Of significance, this was associated with a reduction in urine volume and sodium excretion and increases in urine osmolarity and renal cAMP and ET-1 concentrations. The deleterious effect of chronic ETB blockade was neutralized by simultaneous ETA blockade. ETA blockade alone resulted in a significant increase in tubular cell proliferation but did not alter the cystic phenotype. It is concluded that the balance between ETA and ETB signaling is critical for maintaining tubular structure and function in the cystic kidney. These results implicate ET, acting via vasopressin-dependent and independent pathways, as a major modifying factor for cystic disease progression in human ADPKD.

Animals↗

PubMed2006

Haploinsufficiency of Pkd2 is associated with increased tubular cell proliferation and interstitial fibrosis in two murine Pkd2 models.

BACKGROUND: Autosomal dominant polycystic kidney disease (ADPKD) is the most common inherited human kidney disease and is caused by germline mutations in PKD1 (85%) or PKD2 (15%). It has been estimated that around 1% of tubular cells give rise to cysts, and cell hyperproliferation has been noted to be a cardinal feature of cystic epithelium. Nevertheless, it is uncertain whether the increase in proliferative index observed is an early or late feature of the cystic ADPKD kidney. METHODS: Two Pkd2 mouse mutants (WS25 and WS183) have been recently generated as orthologous models of PKD2. To determine the effect of Pkd2 dosage on cell proliferation, cyst formation and renal fibrosis, we studied renal tissue from Pkd2(WS25/WS25) and Pkd2(+/-) mice by histological analysis. We also examined the proliferative index in archival nephrectomy tissue obtained from patients with ADPKD and normal controls. RESULTS: The proliferative index of non-cystic tubules in Pkd2 mutant mice as assessed by proliferating cell nuclear antigen and Ki67-positive nuclei was between 1-2%, values 5-10 times higher than control tissue. Similarly, the proliferative index of non-cystic tubules in human ADPKD kidneys was 40 times higher than corresponding controls. In Pkd2 mutant mice, significant correlations were found between the fibrosis score and the mean cyst area as well as with the proliferative index. Of significance, proliferating tubular cells were uniformly positive for polycystin-2 expression in Pkd2(+/-) kidney. CONCLUSION: These results suggest that an increase in cell proliferation is an early event preceding cyst formation and can result from haploinsufficiency at Pkd2. The possible pathogenic link between tubular cell proliferation, interstitial fibrosis and cyst formation is discussed.

Adult↗

PubMed2006

Identification of an N-terminal glycogen synthase kinase 3 phosphorylation site which regulates the functional localization of polycystin-2 in vivo and in vitro.

PKD2 is mutated in 15% of patients with autosomal dominant polycystic kidney disease. Polycystin-2 (PC2), the PKD2 protein, is a non-selective Ca(2+)-permeable cation channel which may function at the cell surface and ER. Nevertheless, the factors that regulate the dynamic translocation of PC2 between the ER and other compartments are not well understood. Constitutive phosphorylation of PC2 at a single C-terminal site (Ser(812)) has been previously reported. As we were unable to abolish phospholabelling of PC2 in HEK293 cells by site-directed mutagenesis of Ser(812) or all five predicted phosphorylation sites in the C-terminus, we hypothesized that PC2 could also be phosphorylated at the N-terminus. In this paper, we report the identification of a new phosphorylation site for PC2 within its N-terminal domain (Ser(76)) and demonstrate that this residue is phosphorylated by glycogen synthase kinase 3 (GSK3). The consensus recognition sequence for GSK3 (Ser(76)/Ser(80)) is evolutionarily conserved down to lower vertebrates. In the presence of specific GSK3 inhibitors, the lateral plasma membrane pool of endogenous PC2 redistributes into an intracellular compartment in MDCK cells without any change in primary cilia localization. Finally, co-injection of wild-type but not a S76A/S80A mutant PKD2 capped mRNA could rescue the cystic phenotype induced by an antisense morpholino oligonucleotide to pkd2 in zebrafish pronephric kidney. We conclude that surface localization of PC2 is regulated by phosphorylation at a unique GSK3 site in its N-terminal domain in vivo and in vitro. This site is functionally significant for the maintenance of normal glomerular and tubular morphology.

Animals↗

PubMed2005

Detection of proximal tubular motile cilia in a patient with renal sarcoidosis associated with hypercalcemia.

In a normal human kidney, almost every cell type gives rise to a solitary primary cilium, an apical hair like nonmotile organelle that recently was linked to the pathogenesis of polycystic kidney disease. Motile cilia normally are not expressed by renal tubular cells in the mammalian kidney. Here, we report the unexpected detection of motile cilia arising from proximal tubular cells in a patient with sarcoidosis associated with hypercalcemia and renal impairment. The possible significance of this unusual finding is discussed.

Adult↗

PubMed2005

Molecular pathogenesis of ADPKD: the polycystin complex gets complex.

Autosomal-dominant polycystic kidney disease (ADPKD) is one of the most common human monogenic diseases with an incidence of 1:400 to 1:1000. It is characterized by the progressive development and enlargement of focal cysts in both kidneys, typically resulting in end-stage renal disease (ESRD) by the fifth decade. The cystogenic process is highly complex with a cellular phenotype consistent with "dedifferentiation" (i.e., a high proliferative rate, increased apoptosis, altered protein sorting, changed secretory characteristics, and disorganization of the extracellular matrix). Although cystic renal disease is the major cause of morbidity, the occurrence of nonrenal cysts, most notably in the liver (occasionally resulting in clinically significant polycystic liver disease) and the increased prevalence of other abnormalities including intracranial aneurysms, indicate that ADPKD is a systemic disorder. Following the identification of the first ADPKD gene, PKD1, 10 years ago and PKD2 2 years later, considerable progress has been made in defining the etiology and understanding the pathogenesis of this disorder, knowledge that is now leading to the development of several promising new therapies. The purpose of this review is to summarize our current state of knowledge as to the structure and function of the PKD1 and PKD2 proteins, polycystin-1 and -2, respectively, and explore how mutation at these loci results in the spectrum of changes seen in ADPKD.

Animals↗

PubMed2004

Aberrant polycystin-1 expression results in modification of activator protein-1 activity, whereas Wnt signaling remains unaffected.

Polycystin-1, the polycystic kidney disease 1 gene product, has been implicated in several signaling complexes that are known to regulate essential cellular functions. We investigated the role of polycystin-1 in Wnt signaling and activator protein-1 (AP-1) activation. To this aim, a membrane-targeted construct encoding the conserved C-terminal region of mouse polycystin-1 reported to mediate signal transduction activity was expressed in human embryonic and renal epithelial cells. To ensure specificity and minimal cotransfection effects, we focused our study on the endogenous proteins that actually transduce the signals, beta-catenin and T-cell factor/lymphoid-enhancing factor for Wnt signaling and (phosphorylated) c-Jun, ATF2, and c-Fos for AP-1. Our data indicate that the C-terminal region of polycystin-1 activates AP-1 by inducing phosphorylation and expression of at least c-Jun and ATF2, whereas c-Fos was not affected. Under our experimental conditions, polycystin-1 did not modulate Wnt signaling. AP-1 activity was aberrant in human autosomal dominant polycystic kidney disease (ADPKD) renal cystic epithelial cells and in renal epithelial cells expressing transgenic full-length polycystin-1, resulting in decreased Jun-ATF and increased Jun-Fos activity, whereas Wnt signaling remained unaffected. Since our data indicate that aberrant polycystin-1 expression results in altered AP-1 activity, polycystin-1 may be required for adequate AP-1 activity.

Activating Transcription Factor 2↗

PubMed2003

Association of mutation position in polycystic kidney disease 1 (PKD1) gene and development of a vascular phenotype.

BACKGROUND: Patients with autosomal dominant polycystic kidney disease (ADPKD) are at risk of developing intracranial aneurysms, and subarachnoid haemorrhage is a major cause of death and disability. Familial clustering of intracranial aneurysms suggests that genetic factors are important in the aetiology. We tested whether the germline mutation predisposes to this vascular phenotype. METHODS: DNA samples from patients with ADPKD and vascular complications were screened for mutations throughout the PKD1 and PKD2 genes. Comparisons were made between the PKD1 and PKD2 populations and with a control PKD1 cohort (without the vascular phenotype). FINDINGS: Mutations were characterised in 58 ADPKD families with vascular complications; 51 were PKD1 (88%) and seven PKD2 (12%). The median position of the PKD1 mutation was significantly further 59 in the vascular population than in the 87 control pedigrees (aminoacid position 2163 vs 2773, p=0.0034). Subsets of the vascular population with aneurysmal rupture, early rupture, or families with more than one vascular case had median mutation locations further 59 (aminoacid position 1811, p=0.0018; 1671, p=0.0052; and 1587, p=0.0003). INTERPRETATION: Patients with PKD2, as well as those with PKD1, are at risk of intracranial aneurysm. The position of the mutation in PKD1 is predictive for development of intracranial aneurysms (59 mutations are more commonly associated with vascular disease) and is therefore of prognostic importance. Since the PKD1 phenotype is associated with mutation position, the disease is not simply due to loss of all disease allele products.

Adult↗

PubMed2003

Polycystic kidney disease--the ciliary connection.

CONTEXT: "Cystic degeneration" of the kidneys was first described pathologically in 1841 and "polycystic kidneys" as a clinical syndrome in 1888. The heritable nature in some families was noted in 1899, and autosomal dominant and recessive patterns of inheritance of polycystic kidney disease (PKD) were later recognised. Autosomal dominant PKD is one of the most common human genetic diseases and results from mutations in PKD1 or PKD2. These genes encode two proteins, polycystin-1 and polycystin-2. STARTING POINT: Primary cilia are cellular organelles previously thought by some to be vestigial. New findings from several species, including algae, nematodes, and mice, implicate defects in structure or function of primary cilia as a possible common mechanism central to the development of some forms of recessive PKD. Two recent reports propose a causal link between ciliary dysfunction and autosomal dominant PKD. B Yoder and colleagues (J Am Soc Nephrol 2002; 13:2508-16) show that polycystin-1 and polycystin-2 are localised to primary cilia in cultured renal epithelial cells. S Nauli and colleagues (Nat Genet 2003; 33:129-37) show that polycystin-1 and polycystin-2 function as flow-sensitive mechanosensors in the same signal-transduction pathway. WHERE NEXT? Cystic epithelial cells show many altered cellular properties, including changes in proliferation, apoptosis, adhesion, differentiation, polarity, extracellular matrix synthesis, and fluid transport. The next important steps in PKD research will be to define the physiological roles of primary renal cilia and how defects in ciliary structure and function lead to the development of a cystic phenotype in different forms of PKD.

Animals↗

PubMed2003

Functional analysis of PKD1 transgenic lines reveals a direct role for polycystin-1 in mediating cell-cell adhesion.

The PKD1 protein, polycystin-1, is a large transmembrane protein of uncertain function and topology. To study the putative functions of polycystin-1, conditionally immortalized kidney cells transgenic for PKD1 were generated and an interaction between transgenic polycystin-1 and endogenous polycystin-2 has been recently demonstrated in these cells. This study provides the first functional evidence that transgenic polycystin-1 directly mediates cell-cell adhesion. In non-permeabilized cells, polycystin-1 localized to the lateral cell borders with N-terminal antibodies but not with a C-terminal antibody; there was a clear difference in surface intensity between transgenic and non-transgenic cells. Compared with non-transgenic cells, transgenic cells showed a dramatic increase in resistance to the disruptive effect of a polycystin-1 antibody raised to the PKD domains of polycystin-1 (IgPKD) in both cell adhesion and cell aggregation assays. The differential effect on cell adhesion between transgenic and non-transgenic cells could be reproduced using recombinant fusion proteins encoding non-overlapping regions of the IgPKD domains. In contrast, antibodies raised to other extracellular domains of polycystin-1 had no effect on cell adhesion. Finally, the specificity of this finding was confirmed by the lack of effect of IgPKD antibody on cell adhesion in a PKD1 cystic cell line deficient in polycystin-1. These results demonstrate that one of the primary functions of polycystin-1 is to mediate cell-cell adhesion in renal epithelial cells, probably via homophilic or heterophilic interactions of the PKD domains. Disruption of cell-cell adhesion during tubular morphogenesis may be an early initiating event for cyst formation in ADPKD.

Animals↗

PubMed2003

Expression and cellular localisation of renal endothelin-1 and endothelin receptor subtypes in autosomal-dominant polycystic kidney disease.

The major factors influencing the rate of progression of chronic renal disease in autosomal-dominant polycystic kidney disease (ADPKD) are unknown and there are currently no effective treatments for slowing the progression of chronic renal failure in ADPKD patients. As a first step in investigating the potential role of endothelin-1 (ET1) and its receptors (ETA and ETB) in the pathophysiology of progression in ADPKD, we have studied their expression and cellular localisation in ADPKD kidney. Immunoreactive ET1 was detected in cyst epithelia, mesangial cells and vascular smooth muscle cells suggesting continuing ET1 synthesis in the cystic kidney. Compared to healthy controls, ETA mRNA was 5-10-fold higher in ADPKD cystic kidney. In cystic kidney, neo-expression of ETA receptors was found overlying glomeruli and cysts and markedly increased in medium-sized renal arteries by microautoradiography. This is the first study to demonstrate a specific upregulation of ETA receptors in human renal disease. Future studies should address whether ETA selective antagonists may be effective in slowing renal disease progression in ADPKD.

Aged↗

PubMed2002

Identification, characterization, and localization of a novel kidney polycystin-1-polycystin-2 complex.

The functions of the two proteins defective in autosomal dominant polycystic kidney disease, polycystin-1 and polycystin-2, have not been fully clarified, but it has been hypothesized that they may heterodimerize to form a "polycystin complex" involved in cell adhesion. In this paper, we demonstrate for the first time the existence of a native polycystin complex in mouse kidney tubular cells transgenic for PKD1, non-transgenic kidney cells, and normal adult human kidney. Polycystin-1 is heavily N-glycosylated, and several glycosylated forms of polycystin-1 differing in their sensitivity to endoglycosidase H (Endo H) were found; in contrast, native polycystin-2 was fully Endo H-sensitive. Using highly specific antibodies to both proteins, we show that polycystin-2 associates selectively with two species of full-length polycystin-1, one Endo H-sensitive and the other Endo H-resistant; importantly, the latter could be further enriched in plasma membrane fractions and co-immunoprecipitated with polycystin-2. Finally, a subpopulation of this complex co-localized to the lateral cell borders of PKD1 transgenic kidney cells. These results demonstrate that polycystin-1 and polycystin-2 interact in vivo to form a stable heterodimeric complex and suggest that disruption of this complex is likely to be of primary relevance to the pathogenesis of cyst formation in autosomal dominant polycystic kidney disease.

Animals↗

PubMed2002

Polycystin-2 expression is increased following experimental ischaemic renal injury.

BACKGROUND: Mutations in PKD2 account for 15% of patients with autosomal dominant polycystic kidney disease. Expression of the PKD2 protein, polycystin-2, is developmentally regulated, suggesting a major role for this protein during nephrogenesis. However, the regulation of polycystin-2 expression in the adult kidney has not been previously explored. METHODS: We have utilized an established model of renal ischaemic injury to study polycystin-2 expression in adult rat kidney for up to 120 h following ischaemia. RESULTS: Our results indicate that polycystin-2 expression is increased in the post-ischaemic kidney by up to 5-fold, with a peak in expression at 48 h reperfusion. This time course mirrored the increase in cell proliferation observed. In the non-ischaemic kidney, polycystin-2 expression was highest in distal nephron segments but faint proximal tubular staining was also observed. No expression was seen in glomeruli. In the ischaemic kidney, polycystin-2 expression was greatly increased but the increase in expression was not restricted to segments with the highest number of proliferating cells. Moreover, polycystin-2 was detectable mainly intracellularly following ischaemia. Consistent with this, polycystin-2 was completely sensitive to endoglycosidase H during renal recovery, suggesting that it remains largely retained within the endoplasmic reticulum under these conditions. CONCLUSIONS: Our results provide the first evidence that polycystin-2 is increased following renal ischaemia, but show that this increase is not restricted to actively proliferating cells. The increase in polycystin-2 may relate instead to the process of cellular repair or differentiation following injury.

Animals↗