Biology subjects

Backx, P. H.

Publications and source records attributed to Backx, P. H..

4 recordsLinked to original sources

bioRxiv2024

Adiponectin-receptor agonism prevents right ventricular tissue pathology in a mouse model of Duchenne muscular dystrophy

Cardiac fibrosis during Duchenne muscular dystrophy (DMD) arises from cellular damage and inflammation and is associated with myofibre hypertrophy and metabolic dysfunction. However, the extent to which these relationships develop across all 4 cardiac chambers, particularly during early-stage disease, remains unknown. Here, we discovered that very young D2.mdx mice exhibit fibrosis exclusively in the right ventricle (RV) and left atrium. Concurrent cardiomyocyte hypertrophy and disorganization in the RV were related to a highly specific inflammatory signature of increased infiltrating pro-inflammatory macrophages (CD11b+CD45+CD64+F4/80+CCR2+), myofibre mitochondrial-linked apoptosis, and reduced carbohydrate and fat oxidation. This relationship did not occur in the left ventricle. Short-term daily administration of a peptidomimetic adiponectin receptor agonist, ALY688, completely prevented RV fibrosis, myofibre hypertrophy, infiltrating macrophages and mitochondrial stress as well as left atrial fibrosis. Our discoveries demonstrate early-stage cardiac tissue pathology occurs in a chamber-specific manner and is prevented by adiponectin receptor agonism, thereby opening a new direction for developing therapies that prevent tissue remodeling during DMD. TeaserHeterogeneous distribution of fibrosis, inflammation and metabolic dysfunction across the heart is prevented by adiponectin receptor agonism in a mouse model of Duchenne muscular dystrophy.

physiology↗

bioRxiv2024

Disrupted cardiac bioenergetics linked to oxidized mitochondrial creatine kinase are rescued by the mitochondrial-targeting peptide SBT-20 in the D2.mdx model of Duchenne muscular dystrophy

Mitochondrial creatine kinase (mtCK) regulates the "fast" export of phosphocreatine to support cytoplasmic phosphorylation of ADP to ATP which is more rapid than direct ATP export. Such "creatine-dependent" phosphate shuttling is attenuated in several muscles, including the heart, of the D2.mdx mouse model of Duchenne muscular dystrophy at only 4 weeks of age. However, the degree to which creatine-dependent and -independent systems of phosphate shuttling progressively worsen or potentially adapt in a hormetic manner throughout disease progression remains unknown. Here, we performed a series of proof-of-principle investigations designed to determine how phosphate shuttling pathways worsen or adapt in later disease stages in D2.mdx (12 months of age). We also determined whether changes in creatine-dependent phosphate shuttling are linked to alterations in mtCK thiol redox state. In permeabilized muscle fibres prepared from cardiac left ventricles, we found that 12-month-old male D2.mdx mice have reduced creatine-dependent pyruvate oxidation and elevated complex I-supported H2O2 emission (mH2O2). Surprisingly, creatine-independent ADP-stimulated respiration was increased and mH2O2 was lowered suggesting that impairments in the faster mtCK-mediated phosphocreatine export system resulted in compensation of the alternative slower pathway of ATP export. The apparent impairments in mtCK-dependent bioenergetics occurred independent of mtCK protein content but were related to greater thiol oxidation of mtCK and a more oxidized cellular environment (lower GSH:GSSG). Next, we performed a proof-of-principle study to determine whether creatine-dependent bioenergetics could be enhanced through chronic administration of the mitochondrial-targeting, ROS-lowering tetrapeptide, SBT-20. We found that 12 weeks of daily treatment with SBT-20 (from day 4 to [~]12 weeks of age) increased respiration and lowered mH2O2 only in the presence of creatine in D2.mdx mice without affecting calcium-induced mitochondrial permeability transition activity. In summary, creatine-dependent mitochondrial bioenergetics are attenuated in older D2.mdx mice in relation to mtCK thiol oxidation that seem to be countered by increased creatine-independent phosphate shuttling as a unique form of mitohormesis. Separate results demonstrate that creatine-dependent bioenergetics can also be enhanced with a ROS-lowering mitochondrial-targeting peptide. These results demonstrate a specific relationship between redox stress and mitochondrial hormetic reprogramming during dystrophin deficiency with proof-of-principle evidence that creatine-dependent bioenergetics could be modified with mitochondrial-targeting small peptide therapeutics.

physiology↗

bioRxiv2022

Advanced physiological maturation of iPSC-derived human cardiomyocytes using an algorithm-directed optimization of defined media components

Induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) hold tremendous promise for in vitro modeling to assess native myocardial function and disease mechanisms as well as testing drug safety and efficacy. However, current iPSC- CMs are functionally immature, resembling in vivo CMs of fetal or neonatal developmental states. The use of targeted culture media and organoid formats have been identified as potential high-yield contributors to improve CM maturation. This study presents a novel iPSC-CM maturation medium formulation, designed using a differential evolutionary approach targeting metabolic functionality for iterative optimization. Relative to gold-standard reference formulations, our medium significantly matured morphology, Ca2+ handling, electrophysiology, and metabolism, which was further validated by multiomic screening, for cells in either pure or co-cultured microtissue formats. Together, these findings not only provide a reliable workflow for highly functional iPSC-CMs for downstream use, but also demonstrate the power of high-dimensional optimization processes in evoking advanced biological function in vitro.

bioengineering↗

bioRxiv2017

Cellular Interplay and Cytokine Hierarchy Cause Pathological Cardiac Hypertrophy in RAF1-Mutant Noonan Syndrome

Noonan syndrome (NS) is caused by mutations in RAS/ERK pathway genes, and is characterized by craniofacial, growth, cognitive and cardiac defects. NS patients with kinase-activating RAF1 alleles typically develop pathological left ventricular hypertrophy (LVH), which is reproduced in Raf1L613V/+ knock-in mice. Here, using inducible Raf1L613V expression, we show that LVH results from the interplay of cardiac cell types. Cardiomyocyte Raf1L613V enhances Ca2+ sensitivity and cardiac contractility without causing hypertrophy. Raf1L613V expression in cardiomyocytes or activated fibroblasts exacerbates pressure overload-evoked fibrosis. Endothelial/endocardial (EC) Raf1L613V causes cardiac hypertrophy without affecting contractility. Co-culture and neutralizing antibody experiments reveal a cytokine (TNF/IL6) hierarchy in Raf1L613V-expressing ECs that drives cardiomyocyte hypertrophy in vitro. Furthermore, post-natal TNF inhibition normalizes the increased wall thickness and cardiomyocyte hypertrophy in vivo. We conclude that NS cardiomyopathy involves cardiomyocytes, ECs, and fibroblasts, TNF/IL6 signaling components represent potential therapeutic targets, and abnormal EC signaling might contribute to other forms of LVH.

cell biology↗