Early activation of ubiquitin-proteasome system at the diaphragm tissue occurs independently of left ventricular dysfunction in SHR rats

Abstract

Hypertensive status induces modifications in the respiratory profile. Previous studies have indicated that hypertensive rats show increased respiratory-sympathetic coupling compared to normotensive rats. However, these effects and especially the mechanisms underlying such effects are not well known. Thus, we evaluated the influence of high blood pressure and autonomic dysfunction on a ventilatory pattern associated with lung injury and on the ubiquitin-proteasome system of the diaphragm muscle. Autonomic cardiovascular modulation (systolic BP variance and low-frequency band and pulse interval variance) and arterial blood gases patterns (pH, pO₂, HCO₃, SpO₂), can be changed by hypertension, as well exacerbated chemoreflex pressor response. We observed that the diaphragm muscle of SHR showed increase in type I cross-sectional fiber (16%) and reduction in type II cross-sectional fiber area (41%), increased activity of the ubiquitin-proteasome system and lipid peroxidation, with no differences between groups in the analysis of ubiquitinated proteins and misfolded proteins. Our results showed that hypertension induced functional compensatory/adverse alterations associated with diaphragm fiber type changes and protein degradation as well as changed autonomic control of circulation. In conclusion, we believe there is an adaptation in ventilatory pattern in regarding to prevent the development of fatigue and muscle weakness and improve ventilatory endurance.

Impact statement: It was well known that hypertension can be driven by increased sympathetic activity and has been documented as a central link between autonomic dysfunction and alterations in the respiratory pattern. Our study demonstrated the impact of hypertension in ventilatory mechanics and their relationship with diaphragm muscle protein degradation. These findings may assist us in future alternative treatments to prevent diaphragm fatigue and weakness in hypertensive patients.

Keywords: Hypertension; diaphragm; fibrosis; pulmonary vessel; ubiquitin-proteasome.

Figure 1.

Baseline characteristics of respiratory frequency in normotensive and hypertensive group. Data are reported as mean ± SEM. N: normotensive group; H: hypertensive group.***P < 0.001 vs. N. Student t test.

Figure 2.

(a) Body Weight and (b) Lung Weight among the animals. (c) Wall-to-lumen ratio of the pulmonary artery and (d) percentage of collagen in the pulmonary artery of the intra-acinar groups normotensive and hypertensive. Data are reported as mean ± SEM. White column: normotensive group; Black column: hypertensive group. *P < 0.05 vs. N. Student t test. (A color version of this figure is available in the online journal.)

Figure 3.

(a) Dynamic (Edyn) and (b) Static (Est) elastances in White column: normotensive group; Black column: hypertensive group determined by the end-inspiratory airway occlusion method. ***P < 0.05 when comparing NT and H.

Figure 4.

Representative ATPase staining at pH 10.3 in diaphragm muscle (20×) from normotensive (top left) and hypertensive group (top right). Type I (white), IIa (Black), and IIb (gray) fibers are indicated. Cross-sectional areas (CSA) of different types of diaphragm muscle fibers of groups of normotensive and hypertensive groups. Data are reported as mean ± SEM. Number by groups 5–6. N: normotensive group; H: hypertensive group.*P < 0.05 vs. N. Student t test.

Figure 5.

26S Proteasome activity (a), lipid hydroperoxidation (b), ubiquitinated proteins (c), misfolded proteins (d) and correlation between lipid hidroperoxidation vs. proteasome activity in normotensive and hypertensive groups. Data are reported as mean ± SEM. Number by groups 7–8. N: normotensive group; H: hypertensive group.*P < 0.05 vs. N. Student t test.