Over Expression of Plk1 Does Not Induce Cell Division in Rat Cardiac Myocytes In Vitro

Background

Mammalian cardiac myocytes withdraw from the cell cycle during post-natal development, resulting in a non-proliferating, fully differentiated adult phenotype that is unable to repair damage to the myocardium, such as occurs following a myocardial infarction. We and others previously have shown that forced expression of certain cell cycle molecules in adult cardiac myocytes can promote cell cycle progression and division in these cells. The mitotic serine/threonine kinase, Polo-like kinase-1 (Plk1), is known to phosphorylate and activate a number of mitotic targets, including Cdc2/Cyclin B1, and to promote cell division.

Principal Findings

The mammalian Plk family are all differentially regulated during the development of rat cardiac myocytes, with Plk1 showing the most dramatic decrease in both mRNA, protein and activity in the adult. We determined the potential of Plk1 to induce cell cycle progression and division in cultured rat cardiac myocytes. A persistent and progressive loss of Plk1 expression was observed during myocyte development that correlated with the withdrawal of adult rat cardiac myocytes from the cell cycle. Interestingly, when Plk1 was over-expressed in cardiac myocytes by adenovirus infection, it was not able to promote cell cycle progression, as determined by cell number and percent binucleation.

Conclusions

We conclude that, in contrast to Cdc2/Cyclin B1 over-expression, the forced expression of Plk1 in adult cardiac myocytes is not sufficient to induce cell division and myocardial repair.     

Cell Wall Solubilization in Pedicel Abscission of Begonia Flower Buds

Effects of metabolic inhibitors and growth regulators on the course of abscission and on the activities of cell wall solubilizing enzymes were studied in pedicel explants of Begonia flower buds. Actinomycin D, chloramphenicol and 2,4-dinitrophenol slightly retarded abscission, whereas cycloheximide exerted a strong inhibition if applied until 10.5 h after explant excision. Indoleacetic acid retarded and ethylene promoted abscission and cell wall solubilization. However, the activities of cell wall solubilizing enzymes did not correspond with the course of abscission. No polygalacturonase and pectic acid and pectin transeliminases could be detected in the abscission zone during abscission, whereas a low pectin methylesterase activity did not change. Endo- and exocellulase activities did not increase until about 10 h after the onset of abscission, indicating that they are the result rather than the cause of abscission.     

The role of resveratrol on skeletal muscle cell differentiation and myotube hypertrophy during glucose restriction

Considering the well-known antioxidant properties of statins, it seems important to assess their impact on major markers of oxidative stress (superoxide anion radical, nitric oxide, and index of lipid peroxidation) to compare the antioxidative potentials of atorvastatin and simvastatin during the different degrees of hyperhomocysteinemia (HHcy) in rats. This study was conducted on adult male Wistar albino rats (n = 90; 4 weeks old; 100 ± 15 g body mass) in which HHcy was achieved by dietary manipulation. For 4 weeks, the animals were fed with one of the following diets: standard rodent chow, diet enriched in methionine with no deficiency in B vitamins (folic acid, B6, and B12), or diet enriched in methionine and deficient in B vitamins (folic acid, B6, and B12). At the same time, animals were treated with atorvastatin at doses of 3 mg/kg/day i.p. or simvastatin at doses of 5 mg/kg/day i.p. Levels of superoxide anion radical and TBARS were significantly decreased by administration of simvastatin in normal and high-homocysteine (Hcy) groups (p < 0.05). At 4 weeks after feeding with purified diets, the concentrations of the GSH, CAT, and SOD antioxidants were significantly affected among all groups (p < 0.05). Our results indicated that statin therapy had variable effects on the redox status in hyperhomocysteinemic rats, and simvastatin demonstrated stronger antioxidant effects than did atorvastatin.     

Abnormal metabolites produced by Daucus carota roots stored under conditions of stress

The formation of dihydroisocoumarins (I and II), the chromones (III and IV) and scopoletin (V) is induced in carrot roots by storage in the presence of low concentrations of ethylene and by inoculation with various fungi. There has been concern over possible toxic effects of dihydroisocoumarins and some preliminary toxicological data on (I), (II) and (IV) are included.