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Dissertation
The role of Prohibitin-1 in cardiac development, function and metabolism
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Summer 2024
DOI: 10.25820/etd.007694
Abstract
Prohibitins (PHB1/2) are highly conserved lipid-raft associated membrane proteins ubiquitously expressed in all cell types and localized to multiple compartments, particularly abundant in mitochondria. PHBs are associated with numerous signaling pathways responsible for cell differentiation, growth, and metabolism. In mitochondria, PHBs form a large, ring-shaped complex and play crucial roles in stabilizing mitochondrial cristae, maintaining mitochondrial dynamics, and supporting mitochondrial biogenesis. Given their diverse roles in mitochondrial function, PHBs have been found to be altered in various pathological conditions, such as liver injury, diabetes, cancer, and obesity, However, the role of PHBs in heart is understudied.
To determine the role that PHB1 plays in cardiac function, we first established a cardiac-specific PHB1-deficient mouse strain (PHBfl/fl, MHC-Cre+/-, cKO). Unexpectedly, the vast majority of cKO mice died in utero during pregnancy. The few that were born develop severe dilated cardiomyopathy, resulting in mortality by 8-9 weeks of age. Heart weight/body weight ratio is ~2-fold greater in the cKO mice vs. WT. Echocardiography reveals severely enlarged right atria and ventricles in cKO mice, corresponding to significantly decreased ejection faction (EF), increased end diastolic volume (EDV) and end systolic volume (ESV) compared to wild-type (WT) littermates (P < 0.05). Uterine sonography of the expired cKO embryos showed significantly decreased crown-rump length and increased placenta thickness with large amount of fluids, restricted uterine artery flow and detachment between amnion and chorion compared with normal embryos (P < 0.001). After embryonic day 14.5, the mortality rate among the cKO embryos increased and was associated with abnormal hemorrhage. Histological analyses confirmed that the absence of PHB1 in these embryos led to lethal cardiac defects, including significant cardiac malformations and myocardial thinning.
Due to high embryonic lethality, we generated a tamoxifen-inducible, cardiomyocyte-specific PHB1 knockout (PHB1fl/fl, MHC-MerCreMer+/-) mouse model. 6 weeks after tamoxifen injection, cardiomyocyte PHB1 expression was ~90% absent in adult cPHB1KO mice compared with WT, yet cardiac function remained normal. However, 12 weeks following tamoxifen, the cPHB1KO mice exhibited severe dilated cardiomyopathy, with female mice dying earlier than male mice. At 6 weeks post-tamoxifen, the cPHB1KO mice had normal cardiac function, mitochondrial respiration, and ATP production, along with observed changes in respiratory chain protein subunits and supercomplex formation. Additionally, both male and female cPHB1KO mice exhibited increased mitochondrial Ca2+ uptake, with females showing greater Ca2+ retention capacity. In situ confocal imaging indicated lower mitochondrial membrane potential and higher ROS production in female cPHB1KO mice compared to males. According to the transcriptomics and metabolomics data, 6-week post-tamoxifen cPHB1KO mice exhibited a considerable increase in the expression of genes associated with glutamine metabolism, coupled with a decline in fatty acid oxidation and glycolysis-related genes. This metabolic shift was mirrored by notably reduced glutamine levels within cardiac tissue, indicating glutamine metabolism serves as a bioenergetic adaptation to compensate energy defects and maintain the efficiency of the tricarboxylic acid (TCA) cycle. To validate these findings, cPHB1KO mice subjected to a high-glutamine diet over a 10-week period exhibited an extended lifespan and increased ejection fraction compared to mice without glutamine supplementation.
Taken together, our findings demonstrate that the critical role of PHB1 in both heart development and the regulation of mitochondrial homeostasis and cardiac metabolism in heart failure pathogenesis. We also provide a rationale for glutamine supplementation as a therapeutic strategy for managing cardiomyopathies induced by mitochondrial dysfunction.
Details
- Title: Subtitle
- The role of Prohibitin-1 in cardiac development, function and metabolism
- Creators
- Ran Huo
- Contributors
- Ethan J. Anderson (Advisor)Long-Sheng Song (Committee Member)David L. Roman (Committee Member)Marie E. Gaine (Committee Member)Nicole K. Brogden (Committee Member)
- Resource Type
- Dissertation
- Degree Awarded
- Doctor of Philosophy (PhD), University of Iowa
- Degree in
- Pharmacy (Clinical Pharmaceutical Sciences)
- Date degree season
- Summer 2024
- Publisher
- University of Iowa
- DOI
- 10.25820/etd.007694
- Number of pages
- xviii, 69 pages
- Copyright
- Copyright 2024 Ran Huo
- Language
- English
- Date submitted
- 07/23/2024
- Description illustrations
- Illustrations, tables, graphs, charts
- Description bibliographic
- Includes bibliographical references (pages 65-69).
- Public Abstract (ETD)
Prohibitins (PHB1/2) are important proteins found in all cell types, especially in the mitochondria, the cell's powerhouse. These proteins maintain the structure and function of mitochondria, support energy production, and play a role in various cell functions like growth and metabolism. Changes in prohibitins have been linked to several health conditions, but their role in heart health is not well understood.
To explore this, we created a group of mice that lacked the PHB1 protein specifically in their heart cells. Most of these mice died before birth, and those that survived developed a severe heart condition called dilated cardiomyopathy by the time they were 8-9 weeks old. This condition caused their hearts to enlarge and function poorly, leading to early death. Further studies showed that the absence of PHB1 caused major developmental issues in the heart and other organs, leading to high mortality rates in embryos. To overcome this, we developed another mouse model where they could control the deletion of PHB1 in adult mice. After removing PHB1 in adult mice, the heart initially functioned normally, but by 12 weeks, severe heart disease developed, especially in female mice. The research revealed that the absence of PHB1 affected the mitochondria's ability to produce energy efficiently. Female mice showed more severe mitochondrial damage and higher levels of harmful molecules compared to males. Additionally, changes in energy metabolism were observed, with a shift towards using glutamine, an amino acid, to compensate for the energy deficit. Interestingly, when the PHB1-deficient mice were given a high-glutamine diet, their heart function improved, and they lived longer. This suggests that glutamine supplementation could be a potential therapy for heart diseases related to mitochondrial dysfunction.
In summary, PHB1 is crucial for heart development and maintaining healthy heart function. Its absence leads to severe heart disease and changes in how the heart cells produce energy. This study highlights the potential of using glutamine supplements as a treatment strategy for heart conditions caused by mitochondrial issues.
- Academic Unit
- Pharmacy
- Record Identifier
- 9984697846102771
Metrics
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