Active behavior of triple-negative breast cancer with adipose tissue invasion: a single center and retrospective review.

BACKGROUND: Interactions between adipocyte and breast cancer (BC) cells have yet to be fully elucidated. Here we investigated the prognostic impact of marginal adipose tissue invasion in both luminal breast cancer (HR+/HER2-) and triple-negative breast cancer (TNBC) (HR-/HER2-). METHODS: A total of 735 patients with early-stage invasive BC (1999-2014) were retrospectively registered. Median length of patient follow-up was 8.9 years. Survival curves were calculated using a Kaplan-Meier cumulative survival plot. The prognostic difference between two groups were assessed by the univariate Cox-proportional hazard regression model. RESULTS: Patients with adipose tissue invasion (n = 614) had a significantly poorer prognosis than those without adipose tissue invasion (n = 121) in overall survival (OS) (hazard ratio, 2.1; 95% Confidence interval [CI], 1.1 to 4.0; P = 0.025). While a poorer prognosis was observed in TNBC (n = 137) than in luminal BC patients (n = 496) (hazard ratio, 0.45; 95% CI, 0.30 to 0.68, P < 0.001), this aggressive nature of TNBC was noted in node-positive disease (hazard ratio, 0.3; 95% CI, 0.18 to 0.5, P < 0.001) but not in node-negative disease (hazard ratio, 0.78; 95% CI, 0.39 to 1.55, P = 0.472), and also noted in adipose tissue invasion-positive patients (hazard ratio, 0.4; 95% CI, 0.26 to 0.6, P < 0.001) but not in adipose tissue invasion-negative patients (hazard ratio, 0.73; 95% CI, 0.16 to 3.24, P = 0.675). In addition, although patients suffering from TNBC with adipose tissue invasion had a poorer outcome than those without adipose tissue invasion (hazard ratio, 3.63; 95% CI, 1.11 to 11.84; P = 0.033), the difference was not observed in luminal BC (hazard ratio, 1.75; 95% CI, 0.64 to 4.82; P = 0.277). CONCLUSIONS: Adipose tissue invasion was correlated with poor survival in TNBC. Cancer cell invasion into local fat may be a first step on cancer progression and systemic disease in TNBC.

Low-Dose Phosphodiesterase III Inhibitor Reduces the Vascular Amyloid Burden in Amyloid-ß Protein Precursor Transgenic Mice.

A previous study reported that relatively high-dose cilostazol (0.3%) promoted the drainage of cerebrovascular amyloid-ß (Aß) protein in Aß Precursor Protein (APP) transgenic mice overexpressing vasculotropic Aß. We investigated whether lower-dose cilostazol can decrease micro-hemorrhages and Aß deposition in the brain using APP transgenic mice. At baseline, 14-month-old female Tg2576 mice were randomly assigned to a control group (vehicle), aspirin group (0.01% aspirin), or cilostazol group (0.01% cilostazol). The severity of cerebral micro-hemorrhages (i.e., number), area of senile plaque, and severity of vascular amyloid burden (quantified with cerebral amyloid angiopathy (CAA) score (=number of Aß-positive vessels × severity of amyloid burden of Aß-positive vessels) were evaluated in the brain of mice aged 15 and 21-23 months. At 15 months, no differences were shown in each pathological change among the three groups. At 21-23 months, there were no differences in the severity of cerebral micro-hemorrhages or area of senile plaque among the three groups. However, the CAA score was significantly lower in the cilostazol compared to the control group (p = 0.046, Mann-Whitney U test), although no difference was seen between the control and aspirin group. Our study showed that lower-dose cilostazol could reduce the vascular amyloid burden without increasing cerebral micro-hemorrhages in APP transgenic mice.

MUC4 expression in meningiomas: under-recognized immunophenotype particularly in meningothelial and angiomatous subtypes.

AIMS: MUC4 is a transmembrane glycoprotein that plays a role in cell growth signalling and is expressed in various epithelial tissues. Gene expression profiling and immunohistochemical analyses revealed that MUC4 is also constantly and specifically expressed in low-grade fibromyxoid sarcomas and sclerosing epithelioid fibrosarcomas among the mesenchymal tumours, and immunohistochemical detection of MUC4 is extremely useful for their diagnoses. In our routine pathological practice, we noticed that meningiomas are also often positive for MUC4, which has not yet been reported previously, despite the extensive scrutiny of its expression in soft tissue tumours. METHODS AND RESULTS: We examined immunohistochemically the expression of MUC4, progesterone receptor (PgR) and somatostatin receptor 2A (SSTR2A) in 140 meningiomas of various histological subtypes and 123 other mesenchymal tumours, including intracranial or sinonasal tumours and peripheral nerve sheath tumours. MUC4 was expressed in 130 meningiomas (92.9%). MUC4 expression was constant and almost diffuse in meningothelial and angiomatous subtypes, whereas it was limited in 5% or fewer tumour cells or absent in 26 of 28 fibrous meningiomas. All other mesenchymal tumours examined were negative for MUC4. PgR and SSTR2A were expressed in 94 (67.1%) and 134 (95.7%) meningiomas, respectively. Five of six SSTR2A-negative meningiomas focally expressed MUC4. CONCLUSIONS: MUC4 is expressed variably but almost consistently in meningiomas, particularly in meningothelial or angiomatous subtypes. Its immunohistochemical detection is useful to distinguish meningiomas from other intracranial or head and neck mesenchymal tumours, particularly those with epithelioid features. Our study could expand a variety of MUC4-positive mesenchymal tumours.

Inhibition of WNT/ß-catenin signaling under serum starvation and hypoxia induces adipocytic transdifferentiation in human leiomyoma cells.

Fatty metamorphosis is an uncommon alteration in uterine leiomyoma (i.e., lipoleiomyoma), and the pathogenetic mechanisms underlying this phenomenon remain poorly understood. Because a conditional deletion of ß-catenin, a major transducer of the canonical Wingless/integrated (WNT) pathway, in the developing mouse uterus can induce adipogenesis in the myometrium, it is hypothesized that inhibition of the WNT/ß-catenin signaling may be also involved in the development of fat cells within uterine leiomyoma. In the current study, which was performed to address this point, intracytoplasmic lipid droplets were detectable in cultured human leiomyoma cells by treatment with a potent tankyrase inhibitor, XAV939, which antagonizes ß-catenin, in a serum-starved culture medium without additional adipogenesis-inducing agents or supplements, and showed increasing accumulation in a time-dependent manner. In addition, the induction of fat cells was greatly enhanced under hypoxic conditions (i.e., 2.5% O2)-recapitulating the local in vivo situation of uterine leiomyoma-in comparison to that under normoxic conditions (i.e., 21% O2). The marker genes of differentiated fat cells such as ADIPOQ and PLIN were highly expressed in leiomyoma cells that were treated with XAV939 under hypoxia and serum starvation, whereas the immunohistochemical expression of desmin-a cytoskeletal protein representing smooth muscle differentiation-was downregulated, which appears in line with the switch in differentiation. The results of our study suggest that the inhibition of canonical WNT/ß-catenin signaling under the stress due to hypoxia and serum starvation can initiate adipocytic transdifferentiation or metaplasia in human uterine leiomyoma cells, which is potentially related to the development of lipoleiomyoma.

Retained medullary cord extending to a sacral subcutaneous meningocele.

BACKGROUND: A retained medullary cord (RMC) is a rare closed spinal dysraphism with a robust elongated neural structure continuous from the conus and extending to the dural cul-de-sac. One case extending down to the base of a subcutaneous meningocele at the sacral level has been reported. CLINICAL PRESENTATION: We report on three cases of closed spinal dysraphism, in which a spinal cord-like tethering structure extended out from the dural cul-de-sac and terminated at a skin-covered meningocele sac in the sacrococcygeal region, which was well delineated in curvilinear coronal reconstructed images of 3D-heavily T2-weighted images (3D-hT2WI). Intraoperative neurophysiology revealed the spinal cord-like tethering structure was nonfunctional, and histopathology showed that it consisted of central nervous system tissue, consistent with RMC. The tethering structure histologically contained a glioneuronal core with an ependymal-like lumen and smooth muscle, which may indicate developmental failure during secondary neurulation. CONCLUSIONS: When the RMC extending to a meningocele is demonstrated with the detailed magnet resonance imaging including 3D-hT2WI, decision to cut the cord-like structure for untethering of the nervous tissue should be made under careful intraoperative neurophysiological monitoring.

Interaction between Esophageal Squamous Cell Carcinoma and Adipose Tissue in Vitro.

Esophageal squamous cell carcinoma (ESCC) develops within the squamous epithelial layer and invades the submucosa to the subadventitia that has adipose tissue (AT). AT seems critical to ESCC progression, but the underlying mechanism is unknown. We aimed to address the association between ESCC and AT in vitro. ESCC cells were cultured on rat or human subcutaneous AT-embedded or -non-embedded collagen gel. AT promoted the growth of ESCC cells and inhibited their apoptosis. AT promoted the expression of the squamous differentiation marker involucrin in ESCC cells. AT accelerated the expression of invasion-related factors in poorly differentiated ESCC cells only. AT promoted the expression of phosphorylated-insulin-like growth factor-1 receptor in ESCC cells, whereas it inhibited that of the human epidermal growth factor receptor 2. Insulin-like growth factor-1, but not leptin, adiponectin, or resistin, promoted and inhibited the growth and apoptosis of ESCC cells, respectively. In turn, ESCC cells decreased the production of these adipokines in AT and the number of preadipocytes and mesenchymal stem cell-like cells, which developed from AT. These results suggest that i) AT may influence the progression of ESCC with increased growth or invasion and decreased apoptosis through insulin-like growth factor-1/insulin-like growth factor-1 receptor signaling, ii) AT may affect human epidermal growth factor receptor 2-targeted therapy; and iii) the cancer cells may affect adipokine production in AT.

Retroperitoneal dedifferentiated liposarcoma with huge cystic degeneration: A case report.

Prominent cyst formation is an unusual feature of liposarcoma. We report here a case of dedifferentiated liposarcoma with huge cystic change without preoperative chemo- or radiation therapy. The lesion arose in the retroperitoneum juxtaposed to the right kidney of a 67-year-old woman. She underwent a surgical removal of the retroperitoneal cyst. The cystic tumor contained 1600 mL of old bloody fluid, and its wall was composed of edematous, inflamed or sclerosing fibrous tissue with fatty tissue containing abundant atypical stromal cells, which were immunohistochemically positive for MDM2 and CDK4, and demonstrated MDM2 gene amplification by fluorescence in situ hybridization. The wall was contiguous to an atypical lipomatous nodule located in the mesentery. The following surgical specimens of the right hemicolectomy and right nephrectomy revealed atypical cells infiltrating into the subserosa of the colon and the perirenal fat tissue or that in the renal sinus. This case indicates that well differentiated or dedifferentiated liposarcoma should be also considered as a differential diagnosis of perirenal cystic mass.

[A Case of Intracranial Localized Castleman's Disease Mimicking Convexity Meningioma].

A 68-year-old man presented with abnormal behavior and Todd's paralysis on the right side after having taken a bath. Computed tomography and magnetic resonance imaging revealed a tumor mimicking convexity meningioma that had a perifocal edema, although its mass was not very large. The patient underwent surgery, and full recovery was achieved following a total removal of the lesion. Pathohistological examination demonstrated an intermediate type of Castleman's disease. The final diagnosis was intracranial localized Castleman's disease because the results of the full physical examination and laboratory analyses were normal. Castleman's disease is a rare lymphoproliferative disorder of unknown etiology. Moreover, intracranial involvement is very rare. In cases of intracranial meningeal tumors with perifocal edema, we should take this disease into consideration in the differential diagnosis.

[A Very Rare Case of Diffuse Subependymal Metastases from Small Cell Lung Carcinoma].

While parenchymal metastases are common in solid systemic cancers, subependymal metastases are rare. Approximately half of the reported cases of intraventricular metastases originate from renal carcinoma. A 65-year-old man presented with general fatigue, appetite loss, nausea, and disorientation. Radiological examination revealed diffuse periventricular tumors. The patient underwent an open biopsy via right frontotemporal craniotomy. The patient was diagnosed with metastatic small cell lung carcinoma after histopathological examination. Although subependymal metastases from solid systemic cancer are very rare, this ventricular wall abnormality in the cancer patients must not be overlooked. Many small subependymal metastases might be missed on routine examination.

Interaction between thyrocytes and adipose tissue in vitro.

Adipose tissue (AT)-thyrocyte interaction is largely unknown. Here we described the interaction in a co-culture system, in which thyrocytes were cultured on AT fragment (ATF)-embedded collagen gel, using electron microscopy, immunocytochemistry, real-time reverse transcription-polymerase chain reaction (RT-PCR) and enzyme-linked immunosorbent assay (ELISA). ATFs promoted the hypertrophy, polarization and lipid accumulation of thyrocytes. ATFs did not affect the growth of thyroyctes, and inhibited their apoptosis. ATFs increased the protein expression of thyroglobulin (Tg) and paired box gene 8 (PAX8) in thyrocytes. In turn, thyrocytes decreased the concentration of leptin and adiponectin, and increased the expression of these mRNAs in ATFs. Thyrotropin (TSH) enhanced the ATF-induced nuclear hypertrophy and Tg protein expression in thyrocytes, while TSH enhanced the thyrocyte-induced expression of leptin and adiponectin mRNAs in ATFs. Finally, leptin promoted the hypertrophy and Tg protein expression in thyrocytes. TSH enhanced these leptin-induced effects. The data indicate an active interaction between thyrocytes and AT, suggesting that (i) ATFs may serve to regulate the morphology, survival and differentiation of thyrocytes probably through lipid accumulation partly in a TSH-synergistic way; (ii) thyrocytes may affect adipokine production from ATFs in a TSH-independent manner; and (3) leptin may be related to the hypertrophy and differentiation of thyrocytes in a TSH-synergistic way.

Cytokeratin immunohistochemistry improves interobserver variability between unskilled pathologists in the evaluation of tumor budding in T1 colorectal cancer.

Tumor budding is a major risk factor for T1 colorectal cancer. Quality control of the pathological diagnosis of budding is crucial, irrespective of the pathologist's experience. This study examines the interobserver variability according to pathologists' experience and evaluates the influence of cytokeratin (CK) immunostaining in the assessment of budding. Hematoxylin-eosin (HE) and CK-immunostained slides of 40 cases with T1 primary colorectal cancer were examined. Budding grades were individually evaluated by 12 pathologists who we categorized into three groups by their experience (expert, with >10 years of experience (n = 4), senior, with 5-10 years (n = 4), and junior, < 5 years (n = 4)). The results revealed a tendency for the more experienced pathologists to assign higher budding grades compared to the less-experienced pathologists. In the junior group, the interobserver variability obtained with HE slides was poor, but it was markedly improved in the evaluation using CK-immunostained slides. The benefit of CK immunostaining was only slight in the expert group. CK immunostaining would be useful when a pathologist is not experienced enough or does not have enough confidence in the assessment of budding.

Fluid dwell impact induces peritoneal fibrosis in the peritoneal cavity reconstructed in vitro.

Peritoneal fluid dwell impacts the peritoneum by creating an abnormal physiological microenvironment. Little is known about the precise effects of fluid dwell on the peritoneum, and no adequate in vitro models to analyze the impact of fluid dwell have been established. In this study, we developed a peritoneal fluid dwell model combined with an artificial peritoneal cavity and fluid stirring generation system to clarify the effects of different dwelling solutions on the peritoneum over time. To replicate the peritoneal cavity, we devised a reconstructed peritoneal cavity utilizing a mesothelial layer, endothelial layer, and collagen membrane chamber. The reconstructed peritoneal cavity was infused with Dulbecco's modified Eagle's medium, saline, lactated Ringer's solution or peritoneal dialysis solution with repeated 4-h dwells for 10 or 20 consecutive days. The above-described solutions induced epithelial-mesenchymal transition (EMT) and hyperplasia of mesothelial cells. All solution types modulated nitric oxide synthase activities in mesothelial and endothelial cells and nitric oxide concentrations in dwelling solutions. Inhibition of nitric oxide synthase activity acted synergistically on mesothelial EMT and hyperplasia. The present findings suggest that solutions infused into the peritoneal cavity are likely to affect nitric oxide production in the peritoneum and promote peritoneal fibrosis. Our newly devised peritoneal cavity model should be a promising tool for understanding peritoneal cellular kinetics and homeostasis.

Differential effects of adipose tissue stromal cells on the apoptosis, growth and invasion of bladder urothelial carcinoma between the superficial and invasive types.

OBJECTIVES: To clarify the interaction between adipose tissue stromal cells and bladder cancer cells. METHODS: Superficial (RT4) and invasive (EJ) urothelial carcinoma cells were cultured on adipose tissue stromal cell-embedded or non-embedded collagen gel. Cells were analyzed by immunohistochemistry, western blot and real-time reverse transcription polymerase chain reaction. RESULTS: Adipose tissue stromal cells inhibited growth of RT4, while they promoted the apoptosis. In contrast, adipose tissue stromal cells promoted growth of EJ, but they did not affect the apoptosis. Adipose tissue stromal cells slightly promoted expression of mitogen-activated protein kinase cascade in RT4 and EJ. Adipose tissue stromal cells promoted display of the molecular-targeted agent human epidermal growth factor receptor-2 in only RT4. In turn, RT4 and EJ enhanced α-smooth muscle actin (myofibroblast marker) and S-100 protein (adipocyte marker) expression of adipose tissue stromal cells, respectively. CONCLUSIONS: These findings suggest that: (i) adipose tissue stromal cells might suppress the progression of superficial-type cancer, whereas they might promote that of invasive type; (ii) adipose tissue stromal cell-activated mitogen-activated protein kinase pathway might play differential roles in both types of bladder cancer; (iii) human epidermal growth factor receptor-2 could represent a critical therapeutic agent for the superficial type under adipose tissue stromal cells-cancer interaction; and (iv) superficial bladder cancer might promote myofibroblast differentiation of adipose tissue stromal cells as a cancer-associate phenotype, whereas invasive bladder cancer might promote their adipocyte differentiation.

Histopathology of tenosynovium in trigger fingers.

Stenosing flexor tenosynovitis, trigger finger, is a common clinical disorder causing painful locking or contracture of the involved digits, and most instances are idiopathic. This problem is generally caused by a size mismatch between the swollen flexor tendon and the thickened first annular pulley. Although hypertrophic pulleys have been histologically and ultrasonographically detected, little is known about the histopathology of the tenosynovium covering the tendons of trigger fingers. We identified chondrocytoid cells that produced hyaluronic acid in 23 (61%) fingers and hypocellular collagen matrix in 32 (84%) fingers around the tenosynovium among 38 specimens of tenosynovium from patients with trigger fingers. These chondrocytoid cells expressed the synovial B cell marker CD44, but not the chondrocyte marker S-100 protein. The incidence of these findings was much higher than that of conventional findings of synovitis, such as inflammatory infiltrate (37%), increased vascularity (37%), hyperplasia of synovial lining cells (21%), or fibrin exudation (5%). We discovered the following distinctive histopathological features of trigger finger: hyaluronic acid-producing chondrocytoid cells originated from fibroblastic synovial B cells, and a hypocellular collagen matrix surrounding the tenosynovium. Thus, an edematous extracellular matrix with active hyaluronic acid synthesis might increase pressure under the pulley and contribute to the progression of stenosis.

Three-dimensional culture model for analyzing crosstalk between adipose tissue and hepatocytes.

Systemic adipose tissue is involved in the pathophysiology of obesity-associated liver diseases. However, a method has not been established for analyzing the direct interaction between adipose tissue and hepatocytes. We describe a useful three-dimensional model comprising a collagen gel coculture system in which HepG2 hepatocytes are cultured on a gel layer with visceral adipose tissue fragments (VAT) or subcutaneous tissue samples (SAT). Male adipose tissues were obtained from 5-week-old Wistar rats and human autopsy cases. Cellular behavior was analyzed by electron microscopy, immunohistochemistry, Western blot, real-time reverse transcription plus the polymerase chain reaction and enzyme-linked immunosorbent assay. VAT significantly promoted lipid accumulation and apoptosis in HepG2 cells and suppressed their growth and differentiation compared with SAT. VAT produced higher concentrations of fatty acids (palmitate, oleate, linoleate) than SAT. HepG2 cells significantly decreased the production of these fatty acids in VAT. Only HepG2 cells treated with 250 µM palmitate replicated VAT-induced apoptosis. Neither VAT nor SAT affected lipotoxicity-associated signals of nuclear factor kappa B, c-Jun N-terminal kinase and inositol requiring enzyme-1α in HepG2 cells. HepG2 cells never affected adiponectin, leptin, or resistin production in VAT and SAT. The data indicate that our model actively creates adipose tissue and HepG2 hepatocyte interactions, suggesting that (1) VAT plays more critical roles in hepatocyte lipotoxicity than SAT; (2) palmitate but not adipokines, is partly involved in the mechanisms of VAT-induced lipotoxicity; (3) HepG2 cells might inhibit fatty acid production in VAT to protect themselves against lipotoxicity. Our model should serve in studies of interactions between adipose tissue and hepatocytes and of the mechanisms in obesity-related lipotoxicity and liver diseases.

Adipose tissue behavior is distinctly regulated by neighboring cells and fluid flow stress: a possible role of adipose tissue in peritoneal fibrosis.

Adipose tissue, together with the mesothelial layer and microvessels, is a major component of the mesenteric peritoneum, and the mesenterium is a target site for peritoneal fibrosis. Adipose tissue has been speculated to play a role in peritoneal dialysis (PD)-related fibrosis, but the precise cellular kinetics of adipose tissue during this process remain to be determined. To clarify this critical issue, we analyzed the kinetics of adipose tissue using a novel peritoneal reconstruction model in which the effects of mesothelial cells or endothelial cells could be identified. Adipose tissue was co-cultured with mesothelial cells or endothelial cells in a combined organ culture and fluid flow stress culture system. Spindle mesenchymal cells and immature adipocytes derived from adipose tissue were characterized by immunohistochemistry. Adipose tissue fragments cultured in this system yielded many spindle mesenchymal cells in non-co-culture conditions. However, the number of spindle mesenchymal cells emerging from adipose tissue was reduced in co-culture conditions with a covering layer of mesothelial cells. Mesothelial cells co-cultured in the separated condition did not inhibit the emergence of spindle mesenchymal cells from adipose tissue. Interestingly, endothelial cells promoted the emergence of lipid-laden immature adipocytes from adipose tissue under fluid flow stress. We have demonstrated that adipose tissue behavior is not only regulated by mesothelial cells and endothelial cells under fluid flow stress, but is also involved in fibrosis and fat mass production in the peritoneum. Our findings suggest that adipose tissue is a potential source of cells for peritoneal fibrosis caused by PD therapy.

Short-Term Collagen Nerve Wrapping Facilitates Motor and Sensory Recovery from Nerve Degeneration in a Sciatic Nerve Injury Rat Model.

Purpose: This study used a sciatic nerve injury rat model to investigate the short-term effects of a polyglycolic acid (PGA)-collagen tube for nerve injury in continuity. Materials and Methods: Sixteen female Wistar rats (6-8 weeks) were used, and the left sciatic nerve was crushed with a Sugita aneurysm clip. Sciatic nerve model rats were randomly categorized into two groups (n = 8; control group, n = 8; nerve wrapping group). Then, we measured four sensory thresholds, magnetically stimulated the lumbar region to induce motor-evoked potentials (MEPs), and evaluated the sciatic nerve histopathologically. Results: In the sensory thresholds, there were significant differences for the main effect in 250 and 2000 Hz stimulation (p = 0.048 and 0.006, respectively). Further, a significant difference was observed with 2000 Hz stimulation at 1 week (p = 0.003). In the heat stimulation, there were significant differences for the main effect in both weeks and groups (p = 0.0002 and 0.0185, respectively). The post-hoc test showed a significant difference between groups only in 2W (p = 0.0283). Three weeks after the surgery, both 2nd and 3rd MEPs waves-related latencies in the nerve wrapping group were significantly shorter than those in the control group (p = 0.0207 and 0.0271, respectively). Histological evaluation of the sciatic nerve revealed considerable differences in the number of axons between the two groups (p = 0.0352). Conclusion: The short-term PGA-collagen tube nerve wrapping facilitated motor and sensory recovery from nerve degeneration in the sciatic nerve injury rat model.

Prolonged effect of fluid flow stress on the proliferative activity of mesothelial cells after abrupt discontinuation of fluid streaming.

Encapsulating peritoneal sclerosis (EPS) often develops after transfer to hemodialysis and transplantation. Both termination of peritoneal dialysis (PD) and transplantation-related factors are risks implicated in post-PD development of EPS, but the precise mechanism of this late-onset peritoneal fibrosis remains to be elucidated. We previously demonstrated that fluid flow stress induced mesothelial proliferation and epithelial-mesenchymal transition via mitogen-activated protein kinase (MAPK) signaling. Therefore, we speculated that the prolonged bioactive effect of fluid flow stress may affect mesothelial cell kinetics after cessation of fluid streaming. To investigate how long mesothelial cells stay under the bioactive effect brought on by fluid flow stress after removal of the stress, we initially cultured mesothelial cells under fluid flow stress and then cultured the cells under static conditions. Mesothelial cells exposed to fluid flow stress for a certain time showed significantly high proliferative activity compared with static conditions after stoppage of fluid streaming. The expression levels of protein phosphatase 2A, which dephosphorylates MAPK, in mesothelial cells changed with time and showed a biphasic pattern that was dependent on the duration of exposure to fluid flow stress. There were no differences in the fluid flow stress-related bioactive effects on mesothelial cells once a certain time had passed. The present findings show that fluid flow stress exerts a prolonged bioactive effect on mesothelial cells after termination of fluid streaming. These findings support the hypothesis that a history of PD for a certain period could serve as a trigger of EPS after stoppage of PD.