Dose-dependent regulation of kidney mitochondrial function by angiotensin II

Abstract

Background: Intrarenal hypoxia has been suggested a unifying pathway to chronic kidney disease (CKD) and increased mitochondria leak respiration, which increases mitochondrial oxygen usage and is one important mechanism contributing to the development of the hypoxia. Previous studies indicate that angiotensin II (Ang II) effects on mitochondria function could be dose dependent. We investigated how moderate and high levels of Ang II affect kidney mitochondria function and pathways of leak respiration.

Methods: C57 black 6 mice were treated with either vehicle or Ang II in low dose (400 ng/kg/min) or high dose (1,000 ng/kg/min) for 4 weeks. The function of kidney cortex mitochondria was measured by high-resolution respirometry. Ang II effects on gene expression in kidney tissue were measured by quantitative real-time PCR. Thiobarbituric acids reactive substances were determined as a marker of oxidative stress, and urinary protein excretion was measured as a maker of kidney injury.

Results: Low-dose Ang II induced overall mitochondria respiration, without compromising capacity of ATP production. Mitochondrial leak respiration was increased, and levels of oxidative stress were unchanged. However, high-dose Ang II decreased overall mitochondria respiration and reduced mitochondrial capacity for ATP production. Mitochondrial leak respiration was decreased, and oxidative stress increased in kidney tissue. Furthermore, gene expression of mediators that stimulate vasoconstriction and ROS production was increased, while components of counteracting pathways were decreased.

Conclusions: In conclusion, Ang II dose-dependently affects mitochondrial function and leak respiration. Thus, Ang II has the potential to directly affect cellular metabolism during conditions of altered Ang II signaling.

Keywords: Angiotensin II; kidney; mitochondria function; mitochondria leak respiration; oxidative stress; renin-angiotensin II-aldosterone system; uncoupling.

Figure 1

Estimation of unregulated leak respiration of isolated kidney cortex mitochondria of C57 black 6 mice receiving vehicle, low-dose (400 ng/kg/min) angiotensin II (Ang II), or high-dose (1,000 ng/kg/min) Ang II for 4 weeks. Panels show absolute oxygen consumption (QO₂) after the addition of oligomycin to inhibit the ATP synthase and QO₂ related to ATP production. Data presented as means ± SEM. * denotes P < 0.05 compared to vehicle-treated group, and # denotes P < 0.05 compared to low-dose treatment.

Figure 2

Pathways of regulated leak respiration of isolated kidney cortex mitochondria of C57 black 6 mice receiving vehicle, low-dose (400 ng/kg/min) angiotensin II (Ang II), or high-dose (1,000 ng/kg/min) Ang II for 4 weeks. Panels show delta change in oxygen consumption (QO₂) after the addition of (A) GDP to inhibit UCP-mediated leak respiration; and (B) CAT to inhibit ANT-mediated leak respiration. Data presented as means ± SEM. * denotes P < 0.05 compared to vehicle-treated group, and # denotes P < 0.05 compared to low-dose treatment.

Figure 3

Estimation of unregulated leak respiration of isolated kidney cortex mitochondria of C57 black 6 mice receiving vehicle, low-dose (400 ng/kg/min) angiotensin II (Ang II), or high-dose (1,000 ng/kg/min) Ang II for 4 weeks. Panels show absolute oxygen consumption (QO₂) after the addition of oligomycin, GDP, and CAT to inhibit regulated pathways of QO₂. Data presented as means ± SEM. Statistical comparisons between all groups were made using a one-way ANOVA followed by Tukey’s post hoc test. * denotes P < 0.05 compared to vehicle-treated group, and # denotes P < 0.05 compared to low-dose treatment.

Figure 4

Respiratory control ratio of isolated kidney cortex mitochondria of C57 black 6 mice receiving vehicle, low-dose (400 ng/kg/min) angiotensin II (Ang II), or high-dose (1,000 ng/kg/min) Ang II for 4 weeks. Data presented as means ± SEM. * denotes P < 0.05 compared to vehicle-treated group, and # denotes P < 0.05 compared to low-dose treatment.

Figure 5

Thiobarbituric acids reactive substances (TBARS) in kidney cortex tissue from C57 black 6 mice receiving vehicle, low-dose (400 ng/kg/min) angiotensin II (Ang II), or high-dose (1,000 ng/kg/min) Ang II for 4 weeks. Values are presented as means ± SEM. * denotes P < 0.05 compared to vehicle-treated group, and # denotes P < 0.05 compared to low-dose treatment.