MAP kinases: Differential activation following in vivo and ex vivo irradiation

TRPM4 Participates in Irradiation-Induced Aortic Valve Remodeling in Mice

Simple Summary

Despite its benefit in cancer treatment, thoracic irradiation can induce aortic valve stenosis with fibrosis and calcification. The TRPM4 cation channel is known to participate in cellular remodeling including the transition of cardiac fibroblasts to myofibroblasts, similar to that observed during aortic valve stenosis. This study evaluates if TRPM4 is involved in irradiation-induced aortic valve damage. The aortic valve of mice was targeted by irradiation. Cardiac echography 5 months after treatment revealed an increase in aortic jet velocity, indicating stenosis. This was not observed in non-treated animals. Histological analysis revealed an increase in valvular cusp surface associated with fibrosis which was not observed in non-treated animals. The experiments were reproduced on mice after Trpm4 gene disruption. In these animals, irradiation did not induce valvular remodeling. It indicates that TRPM4 influences irradiation-induced aortic valve damage and thus could be a target to prevent such side effects of irradiation.

Abstract

Thoracic radiotherapy can lead to cardiac remodeling including valvular stenosis due to fibrosis and calcification. The monovalent non-selective cation channel TRPM4 is known to be involved in calcium handling and to participate in fibroblast transition to myofibroblasts, a phenomenon observed during aortic valve stenosis. The goal of this study was to evaluate if TRPM4 is involved in irradiation-induced aortic valve damage. Four-month-old Trpm4^+/+ and Trpm4^−/− mice received 10 Gy irradiation at the aortic valve. Cardiac parameters were evaluated by echography until 5 months post-irradiation, then hearts were collected for morphological and histological assessments. At the onset of the protocol, Trpm4^+/+ and Trpm4^−/− mice exhibited similar maximal aortic valve jet velocity and mean pressure gradient. Five months after irradiation, Trpm4^+/+ mice exhibited a significant increase in those parameters, compared to the untreated animals while no variation was detected in Trpm4^−/− mice. Morphological analysis revealed that irradiated Trpm4^+/+ mice exhibited a 53% significant increase in the aortic valve cusp surface while no significant variation was observed in Trpm4^−/− animals. Collagen staining revealed aortic valve fibrosis in irradiated Trpm4^+/+ mice but not in irradiated Trpm4^−/− animals. It indicates that TRPM4 influences irradiation-induced valvular remodeling.

Abrogation of the p38 MAPK α signaling pathway does not promote radioresistance but its activity is required for 5-Fluorouracil-associated radiosensitivity

The p38 Mitogen Activated Protein Kinase (MAPK) signaling pathway has become a major player in the response to DNA-damage. A growing body of evidences has been relating this signaling pathway to the cellular response to ionizing radiation (IR), suggesting a role in radioresistance. Here, we study the implication of this signaling pathway in the response to IR in terms of radioresistance. To this end we used 10 different cell lines derived from several types of tumors (colorectal, non-small cell lung cancer -NSCLC-, renal and glioblastoma). Although p38 MAPK is transiently activated by IR, our data, obtained by genetic and chemical approaches, showed that this signaling pathway is not implicated in cellular viability after IR exposure. Indeed, down-modulation of this signaling pathway promotes a mild radiosensitivity depending on the cell line. However, it is remarkable that lack of p38 MAPK α abrogates the radiosensitizing effect of 5-Fluorouracil (5-FU) in HCT116 cell line, supporting the role of this MAPK in the radiosensitizing action of 5-FU.

Radiation induces osteogenesis in human aortic valve interstitial cells

OBJECTIVE

Irradiation of the chest or chest wall has been shown to cause calcific aortic stenosis. However, the mechanisms are unknown. Aortic valve interstitial cells have been implicated in the pathogenesis of aortic stenosis; they have been shown to change from the phenotype of a myofibroblast to an osteoblastlike cell. We therefore hypothesized that irradiation of human aortic valve interstitial cells induces an osteogenic phenotype. In isolated human aortic valve interstitial cells, our purpose was to determine the effect of irradiation on the production of osteogenic factors: (1) bone morphogenetic protein 2, (2) osteopontin, (3) alkaline phosphatase, and (4) the transcription factor Runx2.

METHODS

Human aortic valve interstitial cells were isolated from normal aortic valves obtained from explanted hearts of patients undergoing cardiac transplantation (n = 4) and were grown in culture. The cells were grown to confluence, irradiated with 10 Gy using a cesium-137 irradiator, and then lysed 24 hours after irradiation. Cell lysates were analyzed via immunoblot and densitometry for bone morphogenetic protein 2, osteopontin, alkaline phosphatase, and Runx2. Statistical analysis was performed using analysis of variance, with P < .05 indicating significance.

RESULTS

Irradiation induced an osteogenic phenotype in human aortic valve interstitial cells. Irradiation induced a 2-fold increase in bone morphogenetic protein 2, a 7-fold increase in osteopontin, a 3-fold increase in alkaline phosphatase, and a 2-fold increase in Runx2.

CONCLUSIONS

Radiation induces an osteogenic phenotype in human aortic valve interstitial cells. The irradiated cells had a significantly increased expression of the osteogenic factors bone morphogenetic protein 2, osteopontin, alkaline phosphatase, and Runx2. These data offer mechanistic insight into the pathogenesis of radiation-induced valvular heart disease.

Activation of MAP kinases during progression of radiation-induced pneumonitis in rats

Radiation-induced pneumonitis is closely associated with the interplay of various stress-activated signals and immune responses related to the progression of lung injury. Mitogen-activated protein (MAP) kinase pathways play critical roles in the progression of inflammation via a cellular damage. Here, we examined the regional distribution of phosphorylated MAP kinases (p-JNK, p-ERK, and p-p38) in the progression of pneumonitis after exposure of a single dose irradiation with 10 Gy for 0, 4, and 8 weeks in rats. Also, we identified positive cells for these kinases using specific cell-type markers related to inflammation and type II pneumocyte. p-JNK was present abundantly in activated macrophages, CD8(+)T-cells, peribronchiolar smooth muscle cells, and weakly type II pneumocytes at 4 weeks or 8 weeks after irradiation. p-p38 and p-ERK was predominantly expressed in macrophages, CD4(+) T-cells, fibrotic cells as well as present in various lung parenchymal cells including alveolar epithelial cells and type II pneumocytes. In conclusion, it is considered that MAP kinase pathways play a pivotal role in early damage of residual cells as well as in the long-term regulation of distinct inflammatory cells during the progression of radiation-induced pneumonitis.

Alteration of Mitogen-Activated Protein Kinase Pathway After Soman Poisoning

The p38 mitogen-activated protein kinase (MAPK) and activated MAPK transcription factors c-jun, c-myc, and elk-1 were investigated in rat enterocytes after sublethal poisoning with soman to study the pathogenetic mechanism of nonspecific long-term effects of nerve agents. Wistar rats were poisoned by intramuscular administration of soman at a dose 60 microg x kg(-1) (70% LD(50)) and sacrificed by cervical dislocation 3 and 5 days after poisoning. Control groups were administered physiologic saline instead of soman. Protein expression in immunohistochemically stained samples from colon transversum of control and poisoned rats was measured using image analysis. In comparison with control groups, activated p38 MAPK from soman-poisoned rats was significantly depressed at both time intervals. c-myc and c-jun expression was significantly increased 3 days after soman poisoning. On the other hand, a decrease in c-myc and c-jun expression was observed 5 days after soman poisoning. No changes in elk-1 expression were found. Long-term depression of MAPK pathway members might allow cells to proliferate in poisoned rats. This mechanism can be linked with apoptosis and carcinogenesis.