This Month in Investigative Urology

Article Outline

• Optical Coherence Tomography Imaging of the Kidney
• Prostate Tumor Initiating Cells Express Pluripotent Stem Cell Reprogramming Factors
• Vesicoureteral Reflux and Deletion of Fgfr2 in Kidney Mesenchyma
• Clinical Implications of TMPRSS2-ERG Gene Fusion Expression After Radical Prostatectomy
• Copyright

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Optical Coherence Tomography Imaging of the Kidney 

For the diagnosis of renal diseases a significant advancement would be to determine the histopathological status of the living human kidney in real time and in a noninvasive manner. Optical coherence tomography (OCT) is similar to ultrasound imaging except that it uses infrared light waves rather than acoustic waves to perform in vivo, cross-sectional, subsurface tomographic imaging of the microstructure of biological systems by measuring backscattered or back reflected infrared light. It has been shown to possess the requisite high spatial resolution to noninvasively determine histopathological changes in rodent kidneys with micron scale resolution. Onozato et al (page 2090) investigated whether OCT could effectively penetrate the connective tissue capsule surrounding human kidneys, provide a global survey of the human kidney surface and determine histopathological changes in the microstructure of human kidneys. They used a high-speed OCT imaging system equipped with a frequency swept laser light source system to obtain cross-sectional images of 4 ex vivo human kidneys. The scanned sections underwent subsequent conventional light microscopic histological analysis, allowing direct comparisons.

OCT imaging enabled characterization of the tubules, glomeruli and cortical vessels with a penetration depth up to 2 mm and 10 μm spatial resolution. It was also possible to survey and image an entire human kidney within minutes in noninvasive fashion. The acquired OCT images documented histopathological changes in the tubules, glomeruli and interstitium that closely matched the conventional histological observations. The authors conclude that OCT is a novel, potentially noninvasive global imaging procedure that can provide clinicians with an additional technique to examine renal microanatomy, identify key histological structures and provide additional morphometric information. The resolution and low cost of OCT, and the versatility of the probes required for imaging acquisition make this optical technology a promising modality for the diagnosis of renal pathologies.

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Prostate Tumor Initiating Cells Express Pluripotent Stem Cell Reprogramming Factors 

The origin of prostate cancer remains unclear and recent identification of prostate cancer stem cells has led to the speculation that this minor fraction of tumor cells, which possess the capability of self-renewal and multipotency, may initiate malignant transformation. Studies have suggested that cancer cells possess common molecular signatures that are similar to pluripotent embryonic stem cells. The core transcription factors of this stemness signature have also been used to successfully reprogram differentiated somatic cells into pluripotent stem cells. Bae et al (page 2045) from Gainesville, Florida examined the hypothesis that reprogrammed pluripotent stem cell transcription factors may have pivotal roles in the maintenance of stem cell-like tumor initiating cells in prostate cancer. Human prostate cancer cell lines DU145 and PC3, tumor tissue from 55 prostate cancer patients and normal prostate tissue were evaluated for reprogramming factors OCT3/4, SOX2, Nanog, c-Myc and Klf4 by semi-quantitative reverse transcriptase polymerase chain reaction, histological and immunohistochemical analysis. Enrichment of stem cell-like tumor cells was achieved by flow cytometric cell sorting and soft agar, and spheroid and in vivo growth were used to assess tumorigenicity.

mRNA expression of transcription factors OCT3/4 and SOX2 highly correlated in primary prostate tumor tissue samples and the number of OCT3/4 or SOX2 expressing cells was significantly increased in prostate cancer tissue compared to normal prostate or benign prostatic hyperplasia tissue. When isolated from prostate cancer cell lines, stem cell-like tumor cells expressing high levels of OCT3/4 and SOX2 possessed high tumorigenicity in immunodeficient mice. Importantly the in vivo growth of prostate cancer cell lines could be inhibited by short hairpin RNA knockdown of OCT3/4 or SOX2. The data confirmed the existence of stem cell-like tumor cells in prostate cancer cell lines but also demonstrated the presence of such cells in primary tumor tissue from patients. The authors suggest that prostate tumor initiating cells may be reprogrammed with pluripotent stem cell transcription factors and that these factors have a pivotal role in maintaining stem cell-like prostate tumor initiating cells. The observation that a pluripotent stem cell transcriptional balance is important for the survival of these tumor initiating cells and the identification of such cells in tumors of prostate cancer patients could prove highly relevant to the future design of novel targeted therapy for prostate cancer treatment.

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Vesicoureteral Reflux and Deletion of Fgfr2 in Kidney Mesenchyma 

Vesicoureteral reflux (VUR) affects 1% to 2% of children, and kidney damage associated with chronic reflux is the fourth leading cause of chronic kidney disease and the most common cause of severe hypertension in children. One compelling hypothesis about the cause of VUR relates to where the ureter inserts into the bladder. It has been postulated that if the ureteric bud were to evaginate too low/posterior from the Wolffian duct, the ureter would insert too high and lateral in the bladder. It is known that mice with conditional deletion of fibroblast growth factor receptor 2 (Fgfr2) in metanephric mesenchyma (Fgfr2^Mes−/−) have ureteric bud induction abnormalities. Hains et al (page 2077) determined if Fgfr2^Mes−/− mutants developed abnormally positioned ureters predisposing to VUR. They performed 3-dimensional reconstructions, real-time polymerase chain reaction and whole mount in situ hybridization for Fgfr2 in the urinary tracts of embryonic day 15.5 (E15.5) embryos. They also performed cystograms followed by 3-dimensional reconstructions in postnatal animals.

Compared with controls Fgfr2^Mes−/− embryos had increased common nephric duct lengths (with no differences in apoptosis) indicating cranially displaced ureteric buds. Three-dimensional reconstructions at E15.5 showed low insertion of the ureters into the bladder near the bladder neck in Fgfr2^Mes−/− mice. Postnatal Fgfr2^Mes−/− mutants had high VUR rates vs controls (47.4% vs 4.0%, p = 0.00006). In postnatal mutants with unilateral reflux the refluxing ureters inserted closer to the bladder neck than nonrefluxing ureters. The external ureteral insertional angles at the outer bladder wall formed by the ureteral insertion points and bladder neck were greater in mutant refluxing ureters than in contralateral nonrefluxing and control ureters. At E15.5 Fgfr2 levels were decreased in Fgfr2^Mes−/− kidneys compared with controls but were not statistically different in ureters or bladders. The authors conclude that Fgfr2^Mes−/− mice have ureteric induction abnormalities associated with abnormal ureteral insertion in the bladder and subsequent VUR, and that Fgfr2 mutations could increase the risk of human VUR.

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Clinical Implications of TMPRSS2-ERG Gene Fusion Expression After Radical Prostatectomy 

In the diagnosis and treatment of prostate cancer (PCa) it is desirable to identify potentially aggressive or lethal disease to better support clinical decisions. Molecular prognostic factors could constitute useful tools for PCa that complement the classical clinicopathological factors. TMPRSS2 is an androgen regulated gene encoding a transmembrane serine protease, highly expressed in normal and cancerous prostate cells. In PCa a series of genetic rearrangements between the 5′-untranslated region of TMPRSS2 (21q22) and some members of the ETS family of transcription factors such as ERG, have important roles in several oncogenic pathways. Genetic rearrangements between TMPRSS2 and the ETS family of transcription factors have been described in PCa but the clinical significance is still unclear. Rubio-Briones et al (page 2054) from Valencia, Spain investigated the association between the TMPRSS2-ERG fusion gene and PCa outcome in patients treated with radical prostatectomy. They analyzed PCa tumors from 226 patients treated with radical prostatectomy with a median followup of 84 months (range 9 to 153). TMPRSS2-ERG fusion gene expression was determined by reverse transcriptase polymerase chain reaction. Clinicopathological and molecular variables were related to biochemical and clinical progression-free survival by the Kaplan-Meier proportional risk test (log rank). Cox proportional hazards model using stepwise selection was used to identify the independent predictors of poor outcome.

The TMPRSS2-ERG fusion was detected in 114 cases (50.4%). No association was observed between the fusion gene status and the clinicopathological characteristics of PCa. However, when patients were grouped according to TMPRSS2-ERG fusion gene status, different clinicopathological prognostic factors defined each group for biochemical and progression-free survival. Thus, prostate specific antigen, Gleason score in the specimen and margin status constituted independent prognostic factors for patients with PCa expressing the fusion gene, whereas in the nonexpressing TMPRSS2-ERG group the prognostic factors were cT, Gleason score and margin status. The authors conclude that TMPRSS2-ERG fusion gene status can be used to classify patients with PCa treated with radical prostatectomy by different prognostic factors that could constitute the basis for the design of more refined treatment strategies.