Biology subjects

Redding, K.

Publications and source records attributed to Redding, K..

4 recordsLinked to original sources

bioRxiv2024

Transient protein structure guides surface diffusion pathways for electron transport in membrane supercomplexes

The biological significance of protein supercomplexes have remained contentious, particularly how they tune the shuttling of charge-carrier redox proteins across cell membranes during biological energy conversion. We employ multiscale modeling and single particle cryo-electron microscopy (cryo-EM) to determine the mechanisms of diffusive electron transfer in mitochondrial supercomplexes, composed of respiratory complexes III and IV (CIII and CIV). Using a combination of bioinformatic and entropy maximization tools, we model an ensemble of structures representing the conformational space of CIIIs disordered QCR6 hinge within the yeast CIII2CIV2 supercomplex. Molecular and Brownian Dynamics simulations of the entire supercomplex reveal a mechanism for electrostatic coupling between these negatively charged hinge conformations, and binding and directional diffusion of the redox proteins on the mitochondrial membrane, which is simulated over the millisecond timescale. Anionic lipids reinforce this conformationally-coupled recognition of the supercomplex by retaining a pool of the redox proteins in the vicinity of the membrane when the hinges are of a critical length. Cryo-EM models reveal a large-scale rearrangement of the {Delta}QCR6 supercomplex, which retains a surprisingly robust electrostatic environment for recognition of the redox protein, despite compromise in the supercomplexs negative charge, still enabling a surface-mediated electron transfer in this CIII2CIV2 variant. Altogether, the evolutionary need of confining electron carriers on the surface of bioenergetic membranes is found to give rise to a refolding-guided diffusion model of the redox proteins, which improves the energy conversion efficiency within the supercomplex by nearly 30%.

biophysics↗

bioRxiv2022

Liraglutide protects against diastolic dysfunction and improves ventricular protein translation

PurposeDiastolic dysfunction is an increasingly common cardiac pathology linked to heart failure with preserved ejection fraction. Previous studies have implicated glucagon-like peptide 1 (GLP-1) receptor agonists as potential therapies for improving diastolic dysfunction. In this study, we investigate the physiologic and metabolic changes in a mouse model of angiotensin II (AngII) mediated diastolic dysfunction with and without the GLP-1 receptor agonist liraglutide (Lira). MethodsMice were divided into sham, AngII, or AngII + Lira therapy for 4 weeks. Mice were monitored for cardiac function, weight change, and blood pressure at baseline and after 4 weeks of treatment. After 4 weeks of treatment, tissue was collected for histology, protein analysis, targeted metabolomics, and protein synthesis assays. ResultsAngII treatment causes diastolic dysfunction when compared to sham mice. Lira partially prevents this dysfunction. The improvement in function in Lira mice is associated with dramatic changes in amino acid accumulation in the heart. Lira mice also have improved markers of protein translation by Western blot and increased protein synthesis by puromycin assay, suggesting that increased protein turnover protects against fibrotic remodeling and diastolic dysfunction seen in the AngII cohort. Lira mice also lost lean muscle mass compared to the AngII cohort, raising concerns about peripheral muscle scavenging as a source of the increased amino acids in the heart. ConclusionsLira therapy protects against AngII-mediated diastolic dysfunction, at least in part by promoting amino acid uptake and protein turnover in the heart. Liraglutide therapy is associated with loss of mean muscle mass, and long-term studies are warranted to investigate sarcopenia and frailty with liraglutide therapy in the setting of diastolic disease.

physiology↗

bioRxiv2021

Metformin Confers Cardiac and Renal Protection in Sudden Cardiac Arrest via AMPK Activation

Cardiac arrest (CA) causes high mortality due to multi-system organ damage attributable to ischemia-reperfusion injury. Recent work in our group found that among diabetic patients who experienced cardiac arrest, those taking metformin had less evidence of cardiac and renal damage after cardiac arrest when compared to those not taking metformin. To investigate the potential for metformin to impact cardiac arrest outcomes, the current study investigates metformin interventions on cardiac and renal outcomes in a non-diabetic CA mouse model. We found that two weeks of metformin pretreatment protects against reduced ejection fraction and reduces kidney ischemia-reperfusion injury at 24 hours post-arrest. This cardiac and renal protection depends on AMPK signaling, as demonstrated by outcomes in mice pretreated with the AMPK activator AICAR or metformin plus the AMPK inhibitor compound C. At this 24-hour time point, gene expression analysis showed that metformin pretreatment caused changes supporting autophagy, antioxidant response, and protein translation. Further investigation found associated improvements in mitochondrial structure and markers of autophagy. We also found that markers of protein nitrosylation between sham and arrest were not significantly different and thus unlikely to be a driver of gene expression differences. Notably, Western analysis indicated that protein synthesis was preserved in arrest hearts of animals pretreated with metformin. The AMPK activation-mediated protection of protein synthesis was also demonstrated in a hypoxia/reoxygenation cell culture model. Despite the positive impacts of pretreatment in vivo and in vitro, metformin did not preserve ejection fraction when deployed at resuscitation. Taken together, we propose that metformins in vivo cardiac preservation occurs through AMPK activation, requires adaptation before arrest, and is associated with preserved protein translation. New and NoteworthyWe leveraged a mouse model of cardiac arrest to study whether metformin pretreatment could protect cardiac function after arrest. We find that AMPK activity is crucial to this protection and characterize several pathways associated with this response. Signaling nodes with strong association may be precise targets to promote cardiac function in ischemia/reperfusion injury or in cardiac stunning.

physiology↗

bioRxiv2020

A novel ultrasound-guided mouse model of sudden cardiac arrest

AimMouse models of sudden cardiac arrest are limited by challenges with surgical technique and reliable venous access. To overcome this limitation, we sought to develop a simplified method in the mouse that uses ultrasound-guided injection of potassium chloride directly into the heart. MethodsPotassium chloride was delivered directly into the left ventricular cavity under ultrasound guidance in intubated mice, resulting in immediate asystole. Mice were resuscitated with injection of epinephrine and manual chest compressions and evaluated for survival, body temperature, cardiac function, kidney damage, and diffuse tissue injury. ResultsThe direct injection sudden cardiac arrest model causes rapid asystole with high surgical survival rates and low surgical duration. Sudden cardiac arrest mice with 8-min of asystole have significant cardiac dysfunction at 24 hours and high lethality within the first seven days, where after cardiac function begins to improve. Sudden cardiac arrest mice have secondary organ damage, including significant kidney injury, but no clear evidence of neurologic dysfunction. ConclusionsUltrasound-guided direct injection of potassium chloride allows for rapid and reliable cardiac arrest in the mouse that mirrors human pathology. This technique lowers the barriers to entry for adoption of the mouse model of sudden cardiac arrest, which will improve investigators ability to study the mechanisms underlying post-arrest changes.

physiology↗