PKC translocation and ERK1/2 activation in compensated right ventricular hypertrophy secondary to chronic emphysema

Abstract

Background: Right ventricular hypertrophy (RVH) is an important complication of chronic lung disease. However, the signal transduction pathways involved as well as the physiological changes to the right ventricle have not been investigated. Emphysema was produced in male, Syrian Golden hamsters by intra-tracheal instillation of 250 IU/kg elastase (Emp, n = 17). Saline treated animals served as controls (Con, n = 15).

Results: Nine months later, Emp hamsters had 75% greater lung volume, and evidence of RVH at the gross and myocyte level (RV:tibia length Emp 6.84 +/- 1.18 vs. Con 5.14 +/- 1.11 mg/mm; myocyte cross sectional area Emp 3737 vs. Con 2695 microm2), but not left ventricular hypertrophy. Serial echocardiographic analysis from baseline to nine months after induction of emphysema revealed increasing right ventricular internal dimension and decreased pulmonary artery acceleration time only in Emp hamsters. There was an increase in translocation of PKC betaI and PKC epsilon from cytosolic to membranous cell fractions in RV of Emp hamsters. Phosphorylation of PKC epsilon was unchanged. Translocation of PKC alpha and betaII were unchanged. Emp animals had a 22% increase in phospho-ERK 1/2, but no change in levels of total ERK 1/2 compared to Con.

Conclusion: These data suggest that PKC betaI, epsilon and ERK 1/2 may play a role in mediating compensated RVH secondary to emphysema and may have clinical relevance in the pathogenesis of RVH.

Figure 1

A. Gross cross sections of hearts from hamsters with emphysema and age matched controls. Hamsters with emphysema demonstrate a range of RV free wall thickness and chamber dilation, however all are larger than controls. Reference scale on bottom of picture is in mm. B. Histological sections of hearts were stained with Masson's Trichrome to visualize collagen content. No significant evidence of fibrosis were seen in Emp hamsters compared to Con. C. Right ventricle:tibia length is greater in Emp animals compared to Con. D. Myocytes cross sectional area was greater in right ventricles from Emp animals compared to Con. Data collected from individual myocytes (524 control, 555 Emp) collected from 7 Con and 5 Emp hamsters. Con, control; Emp, emphysema.

Figure 2

A. An example of the right ventricular internal diastolic dimension (RVID) as measured from the apical four-chamber view (RA, right atrium; RV, right ventricle; LA, left atrium; LV, left ventricle). B. RVID was measured at baseline, 3, 6, 8 and 9 months in the Emp group and at baseline and nine months in the Con group. Note the significant RV enlargement over time in the Emp group. RVID in the Emp group was significantly larger than the Con group after nine months (*p ≤ 0.05). C. There is a significant positive linear correlation between RVID and lung volume for both the Emp and Con groups after nine months. Con, control; Emp, emphysema.

Figure 3

A. Representative examples of right ventricular outflow tract Doppler flow patterns in Con and Emp hamsters nine months after elastase or vehicle treatment. A more symmetric contour of the Doppler spectrum is seen in the Con group as compared to the Emp animals which show an earlier peak flow velocity. The points used for measurement of RVOT acceleration time are indicated. B. Right ventricular outflow tract Doppler spectra were measured at baseline, 3, 6, 8 and 9 months in the Emp group and at baseline and nine months in the Con group. Note the significant decrease in pulmonary artery acceleration time (PAAT) over time in the Emp group. Right ventricular outflow tract acceleration time in the Emp group was significantly shorter that the Con group after nine months (*p ≤ 0.05 vs. Con). C. Right ventricular internal diastolic dimension (RVID) vs. PAAT for both the Emp and Con groups after nine months. Note the significant inverse linear correlation between RVID and PAAT in the Emp hamsters. Con, control; Emp, emphysema.

Figure 4

A. Representative examples of right ventricular pressure tracing in Con (n = 7) and Emp (n = 7) hamsters. Right ventricular systolic pressure (RVSP) was significantly higher in the Emp group. B. First derivative of RV pressure (dP/dt) obtained in Con (n = 7) and Emp (n = 7) hamsters. There was a higher +dP/dt in the Emp group vs. Con. C. There is a significant positive linear correlation between RVID and RVSP in Con and Emp groups suggesting that the increased RVSP, although mild, is enough to produce RV enlargement. Con, control; Emp, emphysema.

Figure 5

A. Protein kinase C (PKC) immunoreactivity during right ventricular hypertrophy in hamsters with emphysema. Membranous (Mem) and cytosolic (Cyt) fractions were prepared from hamster right ventricle. Representative immunoblots for PKC ε and PKC βI demonstrate increased translocation in Emp, while PKC α and βII were unchanged. Translocation was quantified by taking ratio of membrane to cytosolic levels (M:C) of each isoform. Average PKC ε translocation index (of three separate trials) was 1.14 ± 0.11 for Con (n = 5) and 2.22 ± 0.33 for Emp (n = 5) animals. B. Graph of M:C illustrates fold change normalized to controls. Fold changes are averages of three separate experiments for each PKC isoform. C. Levels of total phosphorylated PKC ε from whole right ventricular homogenates were unchanged among Con and Emp hamsters. *p ≤ 0.05. Con, control; Emp, emphysema.

Figure 6

Immunoblots of whole RV homogenates demonstrating a 34% increase in phERK1/2 to ERK1/2 ratio. Con, control; Emp, emphysema.