Trauma-induced proliferation of astrocytes in the brains of young and aged rats

The time-course and magnitude of astrocyte proliferation following neural trauma was evaluated in young adult (3 months) and mid-aged (16-19 months) male Fischer 344 rats. One to 4 days after a needle wound was made through the cortex and the hippocampus, rats received three intraperitoneal injections of 3H-thymidine at 8 hour intervals and were sacrificed 1 hour after the last injection. For astrocyte quantification, 3H-thymidine autoradiography was combined with immunohistochemical staining for glial fibrillary acidic protein followed by semithin sectioning. In areas of the cortex and hippocampus adjacent to the wound, astrocytes were categorized as unlabeled or labeled with silver grains over the nuclei. Labeling index and numerical density of astrocytes were determined using stereological methods. The results showed that in both young and older rats, astrocyte proliferation is an early glial response to neural trauma, occurring during the first 4 postlesion days and contributing to an increase in astrocyte population. Regional differences in labeling index and numerical density suggest heterogeneity in the proliferative capacity of astrocyte subpopulations in the rat brain. Compared with young animals, older rats demonstrated greater labeling in the cortex but not in the hippocampus. Thus, aging is associated with region-specific increase in astrocyte reactivity to trauma possibly due to increased availability of mitogens or enhanced sensitivity of astrocytes to mitogenic signals.     

Origin of nuclear and chromosomal alterations derived from the action of an aneugenic agent—Trifluralin herbicide

Trifluralin is a herbicide capable of interfering in mitotic cell division due to either microtubule depolymerization or alteration in the concentration of calcium ions within the cell. The aim of this study was to investigate the effects of trifluralin in Allium cepa meristematic cells, evaluating the induction mechanisms of the chromosomal and nuclear aberrations. In this study, A. cepa root tips were submitted for 24 h treatment to several concentrations of this herbicide and 48 h recovery post-treatment. The results showed that some concentrations of trifluralin can lead to a mitotic index inhibition, besides inducing chromosomal and nuclear alterations throughout the mitotic cycle. Some of the alterations found seem to be resulting from the herbicide action in different phases and in more than one consecutive cell cycle.     

Acrylamide effects on kinesin-related proteins of the mitotic/meiotic spindle

The microtubule (MT) motor protein kinesin is a vital component of cells and organs expressing acrylamide (ACR) toxicity. As a mechanism of its potential carcinogenicity, we determined whether kinesins involved in cell division are inhibited by ACR similar to neuronal kinesin [Sickles, D.W., Brady, S.T., Testino, A.R., Friedman, M.A., and Wrenn, R.A. (1996). Direct effect of the neurotoxicant acrylamide on kinesin-based microtubule motility. Journal of Neuroscience Research 46, 7-17.] Kinesin-related genes were isolated from rat testes [Navolanic, P.M., and Sperry, A.O. (2000). Identification of isoforms of a mitotic motor in mammalian spermatogenesis. Biology of Reproduction 62, 1360-1369.], their kinesin-like proteins expressed in bacteria using recombinant DNA techniques and the effects of ACR, glycidamide (GLY) and propionamide (a non-neurotoxic metabolite) on the function of two of the identified kinesin motors were tested. KIFC5A MT bundling activity, required for mitotic spindle formation, was measured in an MT-binding assay. Both ACR and GLY caused a similar concentration-dependent reduction in the binding of MT; concentrations of 100 microM ACR or GLY reduced its activity by 60%. KRP2 MT disassembling activity was assayed using the quantity of tubulin disassembled from taxol-stabilized MT. Both ACR and GLY inhibited KRP2-induced MT disassembly. GLY was substantially more potent; significant reductions of 60% were achieved by 500 microM, a comparable inhibition by ACR required a 5 mM concentration. Propionamide had no significant effect on either kinesin, except KRP2 at 10 mM. This is the first report of ACR inhibition of a mitotic/meiotic motor protein. ACR (or GLY) inhibition of kinesin may be an alternative mechanism to DNA adduction in the production of cell division defects and potential carcinogenicity. We conclude that ACR may act on multiple kinesin family members and produce toxicities in organs highly dependent on microtubule-based functions.     

Can the cardiomyocyte cell cycle be reprogrammed?

Cardiac repair following myocardial injury is restricted due to the limited proliferative potential of adult cardiomyocytes. The ability of mammalian cardiomyocytes to proliferate is lost shortly after birth as cardiomyocytes withdraw from the cell cycle and differentiate. We do not fully understand the molecular and cellular mechanisms that regulate this cell cycle withdrawal, although if we could it might lead to the discovery of novel therapeutic targets for improving cardiac repair following myocardial injury. For the last decade, researchers have investigated cardiomyocyte cell cycle control, commonly using transgenic mouse models or recombinant adenoviruses to manipulate cell cycle regulators in vivo or in vitro. This review discusses cardiomyocyte cell cycle regulation and summarises recent data from studies manipulating the expressions and activities of cell cycle regulators in cardiomyocytes. The validity of therapeutic strategies that aim to reinstate the proliferative potential of cardiomyocytes to improve myocardial repair following injury will be discussed.     

Heterogeneity of the intrahepatic biliary epithelium

The objectives of this review are to outline the recent findings related to the morphological heterogeneity of the biliary epithelium and the heterogeneous pathophysiological responses of different sized bile ducts to liver gastrointestinal hormones and peptides and liver injury/toxins with changes in apoptotic, proliferative and secretory activities. The knowledge of biliary function is rapidly increasing because of the recognition that biliary epithelial cells (cholangiocytes) are the targets of human cholangiopathies, which are characterized by proliferation/damage of bile ducts within a small range of sizes. The unique anatomy, morphology, innervation and vascularization of the biliary epithelium are consistent with function of cholangiocytes within different regions of the biliary tree. The in vivo models [e.g., bile duct ligation (BDL), partial hepatectomy, feeding of bile acids, carbon tetrachloride (CCl4) orα-naphthylisothiocyanate (ANIT)] and the in vivo experimental tools [e.g., freshly isolated small and large cholangiocytes or intrahepatic bile duct units (IBDU) and primary cultures of small and large murine cholangiocytes] have allowed us to demonstrate the morphological and functional heterogeneity of the intrahepatic biliary epithelium. These models demonstrated the differential secretory activities and the heterogeneous apoptotic and proliferative responses of different sized ducts. Similar to animal models of cholangiocyte proliferation/injury restricted to specific sized ducts, in human liver diseases bile duct damage predominates specific sized bile ducts. Future studies related to the functional heterogeneity of the intrahepatic biliary epithelium may disclose new pathophysiological treatments for patients with cholangiopathies.     

Inhibitory effect of Polo-like kinase 1 depletion on mitosis and apoptosis of gastric cancer cells

AIM:Polo-like kinase 1 (PLK1) serine/threonine kinaseplays a vital role in multiple phases of mitosis in gastriccancer cells.To investigate the effect of PLK1 depletionon mitosis and apoptosis of gastric cancer cells.METHODS:PLK1 expression was blocked by smallRNA interference(siRNA).The expression levels ofPLK1,cdc2,cyclin B and caspase 3 were detected byWestern blotting.Then,PLK1 depletion,cdc2 activity,cell proliferation,cell cycle phase distribution,mitoticspindle structure,and the rate of apoptosis of the PLK1knockdown cells were observed.RESULTS:PLK1 gene knockdown was associated withincreased cyclin B expression,increased cdc2 activity (butnot with the expression levels),accumulation of gastriccancer cells at G2/M,improper mitotic spindle formation,delayed chromosome separation and delayed or arrestedcytokinesis.Moreover,PLK1 depletion in gastric cancercells was associated with decreased proliferation,attenuated pro-caspase 3 levels and increased apoptosis.CONCLUSION:Blockage of PLK1 expression may leadto decreased mitosis or even apoptosis in gastric cancercells,indicating that PLK1 may be a valuable therapeutictarget for gastric cancer.     

Mitotic index and multipolar mitosis in routine histologic sections as prognostic markers of pancreatic cancers: A clinicopathological study

ObjectivesPancreatic cancer is characterized by genomic complexity and chromosomal instability, and atypical mitotic figures are morphological features of this phenotype. In the present study, we determined the frequency and the clinicopathological and prognostic significance of mitotic figures in pancreatic cancers.MethodsWe surveyed the mitotic figures of the normal ductal epithelium, acinar cells, pancreatic intraepithelial neoplasias, and pancreatic cancers on hematoxylin-and-eosin–stained tissue specimens (n = 121).ResultsPancreatic cancer cells showed significantly higher mitotic indices as compared with the ductal cells, acinar cells, and pancreatic intraepithelial neoplasias. Both normal and atypical mitosis were significantly elevated only in pancreatic cancers. In pancreatic cancers, approximately 30% of total mitosis was atypical including multipolar, lag-type, ring and asymmetrical mitosis, and anaphase bridges. The Kaplan–Meier curves in pancreatic cancers showed significant correlations between total mitosis and disease free survival. Furthermore, the cases with multipolar mitosis showed poorer prognosis than those without. Lymph node metastasis and multipolar mitosis were independent prognostic factors for overall survival of patients with pancreatic cancer. In addition, lymph node metastasis and total mitosis were independent factors for disease free survival.ConclusionThese findings suggest that routinely obtained pathological specimens, even small biopsy or cytological specimens, can provide valuable information concerning the prognosis of pancreatic cancers.     

Cytotoxic peptides hemiasterlin,hemiasterlin A and hemiasterlin B induce mitotic arrest and abnormal spindle formation

 Purpose: Hemiasterlin, hemiasterlin A and hemiasterlin B are newly isolated cytotoxic tripeptides with potential as antitumor drugs. We wished to determine their mechanism of cytotoxicity. Methods: We studied their effect on cell survival, cell cycle progression, and microtubule morphology in MCF-7 human mammary carcinoma cells. Results: At the nanomolar concentrations at which they were cytotoxic, the peptides induced arrest in mitotic metaphase. Hemiasterlin A produced abnormal mitotic spindles like those produced by the microtubule inhibitors taxol, nocodazole and vinblastine at low concentrations. At high concentrations hemiasterlin A did not cause microtubule bundling like taxol, but caused microtubule depolymerization like nocodazole and vinblastine. Conclusions: The hemiasterlins probably exert their cytotoxic effect by inhibiting spindle microtubule dynamics. Received: 21 September 1995 /  Accepted: 28 May 1996     

熟地黄抑制上皮细胞增生作用的实验研究

采用小白鼠动物实验模型探讨熟地黄治疗银屑病的作用机理。腹腔注射己烯雌酚，使小鼠阴道细胞增殖。熟地黄水提取物、乙亚胺、注射用水分别对三组小白鼠灌胃给药。实验结果表明，熟地黄具有抑制上皮细胞有丝分裂的作用。