Influence of the familial Alzheimer's disease-associated T43I mutation on the transmembrane structure and γ-secretase processing of the C99 peptide

Extracellular deposition of β-amyloid (Aβ) peptides in the brain is a hallmark of Alzheimer's disease (AD). Upon β-secretase-mediated cleavage of the β C-terminal fragment (β-CTF) from the Aβ precursor protein, the γ-secretase complex produces the Aβ peptides associated with AD. The familial T43I mutation within the transmembrane domain of the β-CTF (also referred to as C99) increases the ratio between the Aβ42 and Aβ40 peptides largely due to a decrease in Aβ40 formation. Aβ42 is the principal component of amyloid deposits within the brain parenchyma, and an increase in the Aβ42/Aβ40 ratio is correlated with early-onset AD. Using NMR and FTIR spectroscopy, here we addressed how the T43I substitution influences the structure of C55, the minimal sequence containing the entire extracellular and transmembrane (TM) domains of C99 needed for γ-secretase processing. 13C NMR chemical shifts indicated that the T43I substitution increases helical structure within the TM domain of C55. These structural changes were associated with a shift of the C55 dimer to the monomer and an increase in the tilt of the TM helix relative to the membrane normal in the T43I mutant compared with that of WT C55. The A21G (Flemish) mutation was previously found to increase secreted Aβ40 levels; here, we combined this mutation in the extracellular domain of C99 with T43I and observed that the T43I/A21G double mutant decreases Aβ40 formation. We discuss how the observed structural changes in the T43I mutant may decrease Aβ40 formation and increase the Aβ42/Aβ40 ratio.

Contribution of the Endosomal-Lysosomal and Proteasomal Systems in Amyloid-β Precursor Protein Derived Fragments Processing

Aβ peptides, the major components of Alzheimer's disease (AD) amyloid deposits, are released following sequential cleavages by secretases of its precursor named the amyloid precursor protein (APP). In addition to secretases, degradation pathways, in particular the endosomal/lysosomal and proteasomal systems have been reported to contribute to APP processing. However, the respective role of each of these pathways toward APP metabolism remains to be established. To address this, we used HEK 293 cells and primary neurons expressing full-length wild type APP or the β-secretase-derived C99 fragment (β-CTF) in which degradation pathways were selectively blocked using pharmacological drugs. APP metabolites, including carboxy-terminal fragments (CTFs), soluble APP (sAPP) and Aβ peptides were studied. In this report, we show that APP-CTFs produced from endogenous or overexpressed full-length APP are mainly processed by γ-secretase and the endosomal/lysosomal pathway, while in sharp contrast, overexpressed C99 is mainly degraded by the proteasome and to a lesser extent by γ-secretase.

β-Sheet Structure within the Extracellular Domain of C99 Regulates Amyloidogenic Processing

Familial mutations in C99 can increase the total level of the soluble Aβ peptides produced by proteolysis, as well as the Aβ42/Aβ40 ratio, both of which are linked to the progression of Alzheimer’s disease. We show that the extracellular sequence of C99 forms β-sheet structure upon interaction with membrane bilayers. Mutations that disrupt this structure result in a significant increase in Aβ production and, in specific cases, result in an increase in the amount of Aβ42 relative to Aβ40. Fourier transform infrared and solid-state NMR spectroscopic studies reveal a central β-hairpin within the extracellular sequence comprising Y10-E11-V12 and L17-V18-F19 connected by a loop involving H13-H14-Q15. These results suggest how familial mutations in the extracellular sequence influence C99 processing and provide a structural basis for the development of small molecule modulators that would reduce Aβ production.

Presenilin 2-Dependent Maintenance of Mitochondrial Oxidative Capacity and Morphology

Mitochondrial dysfunction plays a pivotal role in the progression of Alzheimer's disease (AD), and yet the mechanisms underlying the impairment of mitochondrial function in AD remain elusive. Recent evidence suggested a role for Presenilins (PS1 or PS2) in mitochondrial function. Mutations of PSs, the catalytic subunits of the γ-secretase complex, are responsible for the majority of inherited AD cases (FAD). PSs were shown to be present in mitochondria and particularly enriched in mitochondria-associated membranes (MAM), where PS2 is involved in the calcium shuttling between mitochondria and the endoplasmic reticulum (ER). We investigated the precise contribution of PS1 and PS2 to the bioenergetics of the cell and to mitochondrial morphology in cell lines derived from wild type (PS+/+), PS1/2 double knock-out (PSdKO), PS2KO and PS1KO embryos. Our results showed a significant impairment in the respiratory capacity of PSdKO and PS2KO cells with reduction of basal oxygen consumption, oxygen utilization dedicated to ATP production and spare respiratory capacity. In line with these functional defects, we found a decrease in the expression of subunits responsible for mitochondrial oxidative phosphorylation (OXPHOS) associated with an altered morphology of the mitochondrial cristae. This OXPHOS disruption was accompanied by a reduction of the NAD⁺/NADH ratio. Still, neither ADP/ATP ratio nor mitochondrial membrane potential (ΔΨ) were affected, suggesting the existence of a compensatory mechanism for energetic balance. We observed indeed an increase in glycolytic flux in PSdKO and PS2KO cells. All these effects were truly dependent on PS2 since its stable re-expression in a PS2KO background led to a complete restoration of the parameters impaired in the absence of PS2. Our data clearly demonstrate here the crucial role of PS2 in mitochondrial function and cellular bioenergetics, pointing toward its peculiar role in the formation and integrity of the electron transport chain.

Presenilin transmembrane domain 8 conserved AXXXAXXXG motifs are required for the activity of the γ-secretase complex

Understanding the molecular mechanisms controlling the physiological and pathological activity of γ-secretase represents a challenging task in Alzheimer disease research. The assembly and proteolytic activity of this enzyme require the correct interaction of the 19 transmembrane domains (TMDs) present in its four subunits, including presenilin (PS1 or PS2), the γ-secretase catalytic core. GXXXG and GXXXG-like motifs are critical for TMDs interactions as well as for protein folding and assembly. The GXXXG motifs on γ-secretase subunits (e.g. APH-1) or on γ-secretase substrates (e.g. APP) are known to be involved in γ-secretase assembly and in Aβ peptide production, respectively. We identified on PS1 and PS2 TMD8 two highly conserved AXXXAXXXG motifs. The presence of a mutation causing an inherited form of Alzheimer disease (familial Alzheimer disease) in the PS1 motif suggested their involvement in the physiopathological configuration of the γ-secretase complex. In this study, we targeted the role of these motifs on TMD8 of PSs, focusing on their role in PS assembly and catalytic activity. Each motif was mutated, and the impact on complex assembly, activity, and substrate docking was monitored. Different amino acid substitutions on the same motif resulted in opposite effects on γ-secretase activity, without affecting the assembly or significantly impairing the maturation of the complex. Our data suggest that AXXXAXXXG motifs in PS TMD8 are key determinants for the conformation of the mature γ-secretase complex, participating in the switch between the physiological and pathological functional conformations of the γ-secretase.

Does site-specific labelling and individual processing of sextant biopsies improve the accuracy of prostate biopsy in predicting pathological stage in patients with T1c prostate cancer?

OBJECTIVE

To evaluate whether individual labelling and processing of the sextant of origin improves the accuracy of prostate biopsy in predicting the final pathological stage after radical prostatectomy in patients with T1c prostate cancer.

PATIENTS AND METHODS

The charts of 386 patients treated for prostate cancer by radical prostatectomy between January 1996 and June 1999 were reviewed. In all, 124 patients fulfilled the following inclusion criteria: no abnormality on digital rectal examination (DRE) or transrectal ultrasonography, a prostate specific antigen (PSA) level before biopsy of < or = 20 ng/mL, and prostate cancer diagnosed after one set of random sextant biopsies, with the cores being submitted in six separate containers individually labelled for the sextant of origin.

RESULTS

Within this series of patients with a low tumour burden, the preoperative PSA, biopsy Gleason score and unilateral vs bilateral involvement were not significant predictors of disease extension. The percentage of positive cores and the number and topography of positive sextants were both statistically significant predictors of organ-confined disease. Although these two variables appeared to be statistically equivalent on a first analysis in the overall series, a subgroup of patients was identified who benefited from the complete topographical information, i.e. those 52 (42%) patients with a Gleason score of < 7, 25-75% positive biopsies and < or =3 positive sextants.

CONCLUSION

These results support the individual labelling of biopsy cores in selected patients with a normal DRE and a moderately elevated PSA, as it helps to better predict the final pathological stage. This substantial benefit outweighs the additional effort by the pathologist.

Assessing the risk of unsuspected prostate cancer in patients with benign prostatic hypertrophy: a 13-year retrospective study of the incidence and natural history of T1a-T1b prostate cancers

OBJECTIVE

To determine the incidence and natural history of stage T1a-T1b prostate cancer in patients undergoing surgery for benign prostatic hypertrophy (BPH), and thus evaluate the effect that recent medical and 'minimally invasive' treatments (which provide no prostate sample for pathological examination) might have on the percentage of patients with unsuspected prostate cancer.

PATIENTS AND METHODS

A series of 1648 patients undergoing surgery for BPH over a 13-year period were reviewed retrospectively; the period overlapped the introduction of serum prostate specific antigen (PSA) as a detection method.

RESULTS

Stage T1 prostate cancer was found in 182 patients (11%), comprising 126 (11%) of 1199 transurethral resections and 56 (12%) of 449 open enucleations. The introduction of systematic PSA assays gradually reduced the mean incidence of T1 cancer from 23% to 7%, with a greater effect on T1b (from 15% to 2%), while the incidence of T1a remained nearly constant (+/-5%). The pathological features of surgical specimens from 43 radical prostatectomies undertaken for T1 tumours were reviewed. Locally advanced disease (stage >/=pT3) was apparent in 13% of T1a and 28% of T1b tumours. Amongst the patients electing for surveillance, only 8% of those with T1a progressed within 30-97 months of follow-up (mean progression time 73 months), whereas 29% of those with stage T1b progressed within 36 months of follow-up (mean progression time 17 months).

CONCLUSION

These results show that the use of the PSA assay has decreased but not suppressed the incidence of pT1 prostate cancer, with a greater effect on those tumours at higher risk of progression (T1b). This suggests that the detection of prostate cancer based on PSA and transrectal ultrasonography is appropriate for screening patients and is sufficiently accurate that treatments for BPH that provide no pathological materials can be applied safely.

[Complete radical prostatectomy and positive lymph nodes (stages pT1 to 4, N1 to 3, M0, D1)]

Lymph node metastases are rarely detected during radical prostatectomy (55/647 patients in our series or 8.5%) and several authors consider that lymphadenectomy is unnecessary in most cases. Criteria based on clinical stage, PSA and tumor grade have been elaborated in order to avoid pelvic lymph node dissection in a low risk population. It is commonly admitted that patients with clinically localized prostate cancer, a PSA level < 10 ng/ml, and a Gleason score < 7 could be spared a pelvic lymphadenectomy. In our series, these patients account for 12% of positive nodes. The best treatment for prostate cancer patients with a nodal disease is controversial. We compare the evolution of two groups of patients: radical prostatectomy alone or combined with an immediate adjuvant hormonal treatment. We observe a difference between the two groups for biological progression (PSA failure) but not yet for clinical progression nor for survival as our mean follow-up in only 6 years.

Adjuvant radiation therapy does not cause urinary incontinence after radical prostatectomy: results of a prospective randomized study

PURPOSE

We analyzed the potential influence of adjuvant radiotherapy on urinary continence after radical prostatectomy.

MATERIALS AND METHODS

A total of 100 patients with N0M0 prostate cancer randomized in a prospective study on postoperative radiotherapy for locally advanced disease (positive surgical margin, capsular perforation and/or seminal vesicle infiltration) were studied. Objective pad weighing tests corroborated by direct personal interviews were used to evaluate urinary continence at regular postoperative intervals.

RESULTS

Of the patients 48 received 60 Gy. external radiotherapy with 18 MV photon beams between 12 and 16 weeks postoperatively, and 52 were followed expectantly. Risk factors were similar in both groups. With a mean followup of 24 months, no difference in complete urinary continence was observed. Of the irradiated group 77% and of the surveillance group 83% were totally dry. The fate of the bladder neck had no significant influence on final continence status, although there was a trend for faster recovery when the bladder neck was preserved.

CONCLUSIONS

In this prospective randomized study 60 Gy. external radiation therapy administered between 3 and 4 months after radical prostatectomy for pathologically locally advanced prostate cancer had no significant influence on urinary continence.

[Severe and unexpected occurrence of water-electrolyte disorders in the postoperative period]

Unexpected severe electrolyte imbalance in the postoperative period. Report two cases. Two cases of inappropriate secretion of antidiuretic hormone are reported. In each patient, the physiopathology is reviewed. Differential diagnosis and treatment of hyponatremia is discussed.

Obstructive urinary retention in a young female: case report

The authors report a case of acute urinary retention in a young female patient with a large uterine leiomyoma. Urinary symptoms resolved completely after surgery.

Free to total prostate-specific antigen (PSA) ratio improves the discrimination between prostate cancer and benign prostatic hyperplasia (BPH) in the diagnostic gray zone of 1.8 to 10 ng/mL total PSA

OBJECTIVES

Improved discrimination between prostate cancer (PC) and benign prostatic hyperplasia (BPH) is clearly needed. Our aim in this study was to evaluate whether the free to total prostate-specific antigen (PSA) ratio would be useful in the gray zone of 1.8-10 ng/mL total PSA range.

METHODS

In a consecutive series of 435 clinic patients referred for prostate evaluation, 308 had a total PSA < 10 ng/mL (92 had PC and 216 BPH). Free and total PSA were measured, and the free to total PSA ratio calculated.

RESULTS

Total PSA values were significantly different between the two groups. For the 200 patients with a total PSA < 6 ng/mL, no significant difference in total PSA values were seen (P = 0.411), whereas free to total PSA ratios remained statistically different (P < 0.001). Receiver operating characteristic (ROC) curve analysis comparing the performances of total PSA over the ratio of free to total PSA showed a clear advantage for the ratio at all sensitivity levels.

CONCLUSIONS

These data demonstrate that in a significant number (n = 308) of prostatic patients in the diagnostic gray zone of 1.8-10 ng/mL total PSA, the routine use of free to total PSA might be advantageous in discriminating between cancer and benign hyperplasia. This advantage remained for total PSA < 4 ng/mL. Further study is warranted to confirm these findings in an unselected population.

Vessels around the ureteropelvic junction: significance and imaging by conventional radiology

We studied the influence of vessels crossing the ureteropelvic junction and of the grade of hydronephrosis in 86 patients who underwent endoureteropyelotomy. With a follow-up ranging from 1 to 12 years, the presence of crossing vessels had a significant negative influence on the outcome and recurrence rate of the procedure. The success rate was 82% when no vessels were present but only 33% when crossing vessels were documented. In 13 of 15 failures (87%), a crossing vessel was found at open pyeloplasty. The degree of hydronephrosis was a less potent detrimental factor, with an 81% success rate in low-grade and 54% in high-grade hydronephrosis. The best results (90% success) were obtained in patients with no crossing vessels and low-grade hydronephrosis and the worst (30% success) in those with high-grade hydronephrosis in the presence of crossing vessels. Selection of patients according to those prognostic factors is recommended. Conventional intravenous urographic imaging techniques proved insufficient, and only angiography provided diagnostic accuracy; less-invasive methods are desirable.

[Epipadiac duplication of the urethra]

Urethral duplication is a less frequent malformation. The Williams classification, which is currently admit, classifies them in sagital, hypospadias or complex and collateral duplications. They can be complete, incomplete or reduced to an incomplete sinus. The most severe cases are often accompanied by multi-abnormality syndromes. Clinical manifestations are various: asymptomatic, urinary infection, incontinence, double urinary stream,... We will report two new cases of incomplete epispadias duplication. The first case presents a purulent flow from the fistula, the second a frank epispadiac status. In both cases, corrective surgical treatment was performed, after a complete balance-sheet. The embryological, diagnostical and therapeutical aspects of the different forms of urethral duplication will be studied based on data from literature.

Laparoscopic nephrolithotomy: the value of intracorporeal sonography and color Doppler

Laparoscopic nephrolithotomy was used as an alternative to open surgery in a patient who had failed extracorporeal shock-wave lithotripsy and whose anteriorly located stone-bearing calix precluded percutaneous extraction. Endocavitary ultrasonography and color Doppler render the procedure safe and effective; localization of the stone, selection of an optimal nephrotomy site away from large vessels and where cortical thickness is minimal, and control of fragment clearance are greatly facilitated.

[PSA and anatomopathological stage of prostatic cancer]

Accurate preoperative staging is important for adequate selection of patients for radical prostatectomy. We reviewed the preoperative PSA levels of 214 patients who underwent radical retropubic prostatectomy and analysed the results in relation to pathological stage. 32 (15%) patients had a PSA level below 4 ng/ml; nevertheless 8 of them had already a extracapsular disease and one present with positive lymph nodes. Thus, although a specificity of 90%, the sensitivity is only 18%. 98 (46%) patients had PSA levels beyond 10 ng/ml of which 47 (48%) had extracapsular tumor; this gives a specificity of 62% and a sensitivity of 59%. Finally 35 (16%) patients had a PSA over 20 ng/ml of which 18 (51%) present a extracapsular disease thus the specificity is 87% but the sensibility remains low at 23%. We concluded that although PSA levels are grossly related to the pathological stage, that relation is not reliable to distinguish patients with organ-confined from those who have extracapsular tumor extension and for either definition of a positive PSA level many patients would be denied a curative operation. Therefore, PSA value cannot be used to decide whether to recommend radical prostatectomy for potential cure.

Leydig cell tumor: estradiol level at different locations

The authors report on estradiol levels at different locations in a patient with a Leydig cell tumor. The highest value was found in the testicular vein. The estradiol level was, however, ten times higher in the peritesticular vaginal fluid than in the peripheral veins.

[Urethral stenosis in children. Apropos of 33 pediatric cases]

Urethral stenosis in children is rare. Between 1961 and 1993, only five specific retrospective studies were published. Between January 1987 and December 1992, thirty-three children, i.e. thirty boys and three girls, were observed in our institution for urethral stenosis. Their ages ranged from two and half months to seventeen years. Etiology was congenital in six, traumatic in two, inflammatory in two and iatrogenic in thirteen patients. In additions, ten stenoses were consecutive with hypospadias repair. Seventeen patients underwent first-line endoscopic internal urethrotomy. Success rate was ninety-one percent. Two patients underwent a successful second similar procedure. Repeating this procedure more than twice and second-line urethrotomy doesn't improve success rate. It appeared that internal urethrotomy proved to be more effective in short and recent stenosis. Fourteen patients underwent urethroplasty by using various techniques, of whom only five first-line urethroplasty. Its indication in case of multioperated or complicated stenoses may explain the poor global success rate of about fifty percent.

[Immediate allergy to latex in urological practice]

Five cases of acute allergic reaction to latex are reported. Four of those were diagnosed during surgery and presented anaphylactic shock. One was suspected before surgery by systematic screening and dramatic presentation was avoided. Increasing frequency of latex allergy is reported in the literature and is usually seen in patients with extensive neurosurgical or urological histories, or by peoples currently exposed to natural rubber products (medical staff). Systematic screening in history before surgery is important so that exposure to latex should be avoided in suspected cases.

[Cholesteatoma of the upper urinary tract: endoscopic treatment]

We report here on a case of cholesteatoma of the upper urinary tract. This rare, but recurrent disease was managed successfully by means of repeated endourological treatment. Diagnosis was confirmed by histological examination of samples obtained by percutaneous extraction.

Coecocystoplasty: an evaluation of operative results

Coecocystoplasty for substituting or augmenting the bladder is a relatively common operation in the United States, but not in Scandinavia. In order to focus the attention on this voiding-preserving operation we evaluated the late postoperative results of 8 patients. Median follow-up was 5 years. Seven of the patients had symptoms from a contracted bladder and 1 patient with epispadias was undiverted from a ureteroileocutaneostomy. There were some early postoperative complications. Two patients had a revision of the coecocystoplasty, 1 patient ended up with a ureteroileocutaneostomy and 1 patient needed a nephrectomy because of a perirenal abscess. The patient with epispadias later had an artificial urinary sphincter because of persisting incontinence. At follow-up time all patients found that they had a better life than prior to operation since the invalidating symptoms from the contracted bladder had disappeared. One patient with residual urine had chronic urinary tract infection. All patients were continent at daytime, 3 patients had nocturnal incontinence. Urodynamic studies showed no infravesical obstruction and bladder capacity between 75 and 380 ml H2O. Three patients had decreased renal function. Based on our limited material we conclude that coecocystoplasty is a reasonable, though not unproblematic, treatment in patients with severe symptoms from a small contracted bladder and a therapeutical alternative in patients with a previously defunctionalised bladder and that this method should always be taken into consideration before a urinary diversion.

[Radio-urodynamic study of the lower urinary tract]

Radio-urodynamic examination of the lower urinary tract is the best method to study the complex functional problems involving those structures. It will very often provide a correct diagnostic orientation in a single session. The main indications are (1) urinary incontinence when symptoms are unclear, or recurring after surgical correction, (2) neurogenic bladder dysfunction, (3) incipient obstructive uropathy and (4) when it is necessary to ascertain that micturition is normal. The necessary investment in personnel, time and material is considerable, and the indications are therefore to be limited to complex problems and to certain centers that have a special clinical and research interest in urodynamics. It is nevertheless highly justified by the improvement in therapeutic results engendered by a correct and precise diagnosis.

Serum prostatic acid phosphatase determination in prostatic diseases: a critical comparison of an enzymatic and a radioimmunologic assay

A prospective study comparing a new radioimmunologic and a classical enzymatic assay for prostatic acid phosphatase was done to evaluate their respective roles in patients with prostatic diseases. We studied 50 patients with cancer of the prostate, 101 with benign prostatic hypertrophy and 17 with prostatitis as well as patients with nonprostatic malignancy, and various hematological and bone diseases. The results showed a low incidence of elevated values in patients with early cancer of the prostate and a high incidence of false positive values with the radioimmunoassay in patients with benign prostatic diseases, especially prostatitis. These data suggest that tests for serum prostatic acid phosphatase levels remain disappointing in the assessment of prostatic disease regardless of the technique used.