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Cardiac-specific knockout and pharmacological inhibition of Endothelin receptor type B lead to cardiac resistance to extreme hypoxia

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Abstract

Oxygen plays a central role in cardiac energy metabolism. At high altitude where the ambient oxygen level is low, we found EDNRB is associated with human hypoxia adaptation. Our subsequent study in global heterozygous knockout mice (Ednrb−/+) revealed that cardiac function was conserved in these mice when exposed to extreme hypoxia. The major goal of this study was (i) to determine the functional role of cardiomyocyte EdnrB in maintaining cardiac function under hypoxic stress and (ii) to validate the phenotypes we detected in Ednrb−/+ mice using EDNRB blockers. Unlike the global knockouts, cardiac-specific heterozygote (EdnrBflox/+) and homozygote (EdnrBflox/flox) EdnrB knockout mice were phenotypically normal. When treated with graded low levels of oxygen (10% and 5% O2), both EdnrBflox/+ and EdnrBflox/flox were hypoxia tolerant. The cardiac indexes at 10% and 5% O2 for EdnrBflox/+ were significantly higher and lactate levels were significantly lower when compared to the cre-negative controls (P < 0.05). Simultaneously, mice treated with BQ-788 (EDNRB-specific blocker) had a significantly higher cardiac index (P < 0.005) and significantly lower lactate levels (P < 0.0001) than in control mice. A similar result was obtained with mice treated with Bosentan (non-specific). These data indicate that a lower level or complete lack of EdnrB in the cardiomyocytes significantly improves cardiac performance under extreme hypoxia, a novel role of cardiomyocyte EdnrB in the regulation of cardiac function. Furthermore, this rescue under extreme hypoxia can also be achieved using EDNRB-specific pharmacological agents, e.g., BQ-788. This systematically confirms, both genetically and pharmacologically, the protective role of a lower EDNRB under extreme hypoxia stress.

Key messages

  • Under normal condition, cardiomyocytes-specific EdnrB knockout mice, both heterozygote and homozygote, are phenotypically normal.

  • Under hypoxic condition, a lower level or complete deletion of cardiomyocyte EdnrB conserves cardiac function by maintaining high cardiac index.

  • Similarly, mice treated with both specific (BQ-788) and non-specific (Bosentan) EDNRB blockers are tolerant to hypoxia by maintaining better cardiac function.

  • The oxygen perfusion under extreme hypoxia is better in the mice with lower EDNRB, as depicted by lower lactate level at 5% oxygen.

  • Our current study systematically confirms, both genetically and pharmacologically, the protective role of a lower EDNRB under extreme hypoxia stress.

  • Overall, it supports our hypothesis that studies on human hypoxia adaptation provide new insight to common disease pathogenesis and treatments.

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Acknowledgements

We thank Dr. Donald Kohan (Univ. of Utah) and Dr. David Webb (Univ. Of Edinburgh) for providing the EdnrB-LoxP mice.

Sources of funding

This work was supported by National Institutes of Health (NIH) grant (R01 HL127403-02) to GGH. TS was supported by the Emerald Foundation Inc. This work was partially supported by NIH grants from the Heart Lung and Blood Institute (P01-HL110900, R01-HL126945, and T32-HL007444) PC.

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Authors and Affiliations

  1. Division of Respiratory Medicine, Department of Pediatrics, University of California, San Diego, 9500 Gilman Drive, MC 0735, La Jolla, CA, 92093, USA

    Tsering Stobdan, Dan Zhou & Gabriel G. Haddad

  2. Department of Bioengineering, University of California, San Diego, La Jolla, CA, 92093, USA

    Alexander T. Williams & Pedro Cabrales

  3. Department of Neurosciences, University of California, San Diego, La Jolla, CA, 92093, USA

    Gabriel G. Haddad

  4. Rady Children’s Hospital, San Diego, CA, 92123, USA

    Gabriel G. Haddad

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  1. Tsering Stobdan
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  4. Pedro Cabrales
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Correspondence to Gabriel G. Haddad.

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Electronic supplementary material

Supplementary Fig S1

Cardiac output comparison between cardiac-specific EdnrB homozygous (EdnrBflox/flox), heterozygous (EdnrBflox/+) and controls mice. EdnrBflox/+ mice maintains a higher CO under hypoxia. Error bar indicates ± standard error.(PNG 73 kb)

High resolution image (TIF 481 kb)

Supplementary Fig S2

Cardiac output comparison between BQ-788, Bosentan treated and control mice. Both BQ-788 and Bosentan treated mice maintains a relative higher CO under extreme hypoxia of 10% and 5% O2. However,CO in BQ-788 treated mice was significantly higher at 5% O2 when compared to both Bosentan and control mice. Error bar indicates ± standard error.(PNG 50 kb)

High resolution image(TIF 164 kb)

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Stobdan, T., Zhou, D., Williams, A.T. et al. Cardiac-specific knockout and pharmacological inhibition of Endothelin receptor type B lead to cardiac resistance to extreme hypoxia. J Mol Med 96, 975–982 (2018). https://doi.org/10.1007/s00109-018-1673-2

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  • DOI: https://doi.org/10.1007/s00109-018-1673-2

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