The MICOS Complex Regulates Mitochondrial Structure and Oxidative Stress During Age-Dependent Structural Deficits in the Kidney.

The kidney filters nutrient waste and bodily fluids from the bloodstream, in addition to secondary functions of metabolism and hormone secretion, requiring an astonishing amount of energy to maintain its functions. In kidney cells, mitochondria produce adenosine triphosphate (ATP) and help maintain kidney function. Due to aging, the efficiency of kidney functions begins to decrease. Dysfunction in mitochondria and cristae, the inner folds of mitochondria, is a hallmark of aging. Therefore, age-related kidney function decline could be due to changes in mitochondrial ultrastructure, increased reactive oxygen species (ROS), and subsequent alterations in metabolism and lipid composition. We sought to understand if there is altered mitochondrial ultrastructure, as marked by 3D morphological changes, across time in tubular kidney cells. Serial block facing-scanning electron microscope (SBF-SEM) and manual segmentation using the Amira software were used to visualize murine kidney samples during the aging process at 3 months (young) and 2 years (old). We found that 2-year mitochondria are more fragmented, compared to the 3-month, with many uniquely shaped mitochondria observed across aging, concomitant with shifts in ROS, metabolomics, and lipid homeostasis. Furthermore, we show that the mitochondrial contact site and cristae organizing system (MICOS) complex is impaired in the kidney due to aging. Disruption of the MICOS complex shows altered mitochondrial calcium uptake and calcium retention capacity, as well as generation of oxidative stress. We found significant, detrimental structural changes to aged kidney tubule mitochondria suggesting a potential mechanism underlying why kidney diseases occur more readily with age. We hypothesize that disruption in the MICOS complex further exacerbates mitochondrial dysfunction, creating a vicious cycle of mitochondrial degradation and oxidative stress, thus impacting kidney health.

Osteopontin stabilization and collagen containment slows amorphous calcium phosphate transformation during human aortic valve leaflet calcification.

Calcification of aortic valve leaflets is a growing mortality threat for the 18 million human lives claimed globally each year by heart disease. Extensive research has focused on the cellular and molecular pathophysiology associated with calcification, yet the detailed composition, structure, distribution and etiological history of mineral deposition remains unknown. Here transdisciplinary geology, biology and medicine (GeoBioMed) approaches prove that leaflet calcification is driven by amorphous calcium phosphate (ACP), ACP at the threshold of transformation toward hydroxyapatite (HAP) and cholesterol biomineralization. A paragenetic sequence of events is observed that includes: (1) original formation of unaltered leaflet tissues: (2) individual and coalescing 100's nm- to 1 µm-scale ACP spherules and cholesterol crystals biomineralizing collagen fibers and smooth muscle cell myofilaments; (3) osteopontin coatings that stabilize ACP and collagen containment of nodules preventing exposure to the solution chemistry and water content of pumping blood, which combine to slow transformation to HAP; (4) mm-scale nodule growth via ACP spherule coalescence, diagenetic incorporation of altered collagen and aggregation with other ACP nodules; and (5) leaflet diastole and systole flexure causing nodules to twist, fold their encasing collagen fibers and increase stiffness. These in vivo mechanisms combine to slow leaflet calcification and establish previously unexplored hypotheses for testing novel drug therapies and clinical interventions as viable alternatives to current reliance on surgical/percutaneous valve implants.

Is it time to reduce the length of postgraduate training for physician-scientists in internal medicine?

Physician-scientists play a crucial role in advancing medical knowledge and patient care, yet the long periods of time required to complete training may impede expansion of this workforce. We examined the relationship between postgraduate training and time to receipt of NIH or Veterans Affairs career development awards (CDAs) for physician-scientists in internal medicine. Data from NIH RePORTER were analyzed for internal medicine residency graduates who received specific CDAs (K08, K23, K99, or IK2) in 2022. Additionally, information on degrees and training duration was collected. Internal medicine residency graduates constituted 19% of K awardees and 28% of IK2 awardees. Of MD-PhD internal medicine-trained graduates who received a K award, 92% received a K08 award; of MD-only graduates who received a K award, a majority received a K23 award. The median time from medical school graduation to CDA was 9.6 years for K awardees and 10.2 years for IK2 awardees. The time from medical school graduation to K or IK2 award was shorter for US MD-PhD graduates than US MD-only graduates. We propose that the time from medical school graduation to receipt of CDAs must be shortened to accelerate training and retention of physician-scientists.

Comparative specialization of intrinsic cardiac neurons in humans, mice, and pigs.

Intrinsic cardiac neurons (ICNs) play a crucial role in the proper functioning of the heart; yet a paucity of data pertaining to human ICNs exists. We took a multidisciplinary approach to complete a detailed cellular comparison of the structure and function of ICNs from mice, pigs, and humans. Immunohistochemistry of whole and sectioned ganglia, transmission electron microscopy, intracellular microelectrode recording and dye filling for quantitative morphometry were used to define the neurophysiology, histochemistry, and ultrastructure of these cells across species. The densely packed, smaller ICNs of mouse lacked dendrites, formed axosomatic connections, and had high synaptic efficacy constituting an obligatory synapse. At Pig ICNs, a convergence of subthreshold cholinergic inputs onto extensive dendritic arbors supported greater summation and integration of synaptic input. Human ICNs were tonically firing, with synaptic stimulation evoking large suprathreshold excitatory postsynaptic potentials like mouse, and subthreshold potentials like pig. Ultrastructural examination of synaptic terminals revealed conserved architecture, yet small clear vesicles (SCVs) were larger in pigs and humans. The presence and localization of ganglionic neuropeptides was distinct, with abundant VIP observed in human but not pig or mouse ganglia, and little SP or CGRP in pig ganglia. Action potential waveforms were similar, but human ICNs had larger after-hyperpolarizations. Intrinsic excitability differed; 93% of human cells were tonic, all pig neurons were phasic, and both phasic and tonic phenotypes were observed in mouse. In combination, this publicly accessible, multimodal atlas of ICNs from mice, pigs, and humans identifies similarities and differences in the evolution of ICNs.

Mechanism of Ventricular Tachycardia Occurring in Chronic Myocardial Infarction Scar.

Cardiac arrest is the leading cause of death in the more economically developed countries. Ventricular tachycardia associated with myocardial infarct is a prominent cause of cardiac arrest. Ventricular arrhythmias occur in 3 phases of infarction: during the ischemic event, during the healing phase, and after the scar matures. Mechanisms of arrhythmias in these phases are distinct. This review focuses on arrhythmia mechanisms for ventricular tachycardia in mature myocardial scar. Available data have shown that postinfarct ventricular tachycardia is a reentrant arrhythmia occurring in circuits found in the surviving myocardial strands that traverse the scar. Electrical conduction follows a zigzag course through that area. Conduction velocity is impaired by decreased gap junction density and impaired myocyte excitability. Enhanced sympathetic tone decreases action potential duration and increases sarcoplasmic reticular calcium leak and triggered activity. These elements of the ventricular tachycardia mechanism are found diffusely throughout scar. A distinct myocyte repolarization pattern is unique to the ventricular tachycardia circuit, setting up conditions for classical reentry. Our understanding of ventricular tachycardia mechanisms continues to evolve as new data become available. The ultimate use of this information would be the development of novel diagnostics and therapeutics to reliably identify at-risk patients and prevent their ventricular arrhythmias.

Anatomical and functional organization of cardiac fibers in the porcine cervical vagus nerve allows spatially selective efferent neuromodulation.

Cardiac disease progression reflects the dynamic interaction between adversely remodeled neurohumoral control systems and an abnormal cardiac substrate. Vagal nerve stimulation (VNS) is an attractive neuromodulatory option to dampen this dynamic interaction; however, it is limited by off-target effects. Spatially-selective VNS (sVNS) offers a promising solution to induce cardioprotection while mitigating off-target effects by specifically targeting pre-ganglionic parasympathetic efferent cardiac fibers. This approach also has the potential to enhance therapeutic outcomes by eliminating time-consuming titration required for optimal VNS. Recent studies have demonstrated the independent modulation of breathing rate, heart rate, and laryngeal contraction through sVNS. However, the spatial organization of afferent and efferent cardiac-related fibers within the vagus nerve remains unexplored. By using trial-and-error sVNS in vivo in combination with ex vivo micro-computed tomography fascicle tracing, we show the significant spatial separation of cardiac afferent and efferent fibers (179±55° SD microCT, p<0.05 and 200±137° SD, p<0.05 sVNS - degrees of separation across a cross-section of nerve) at the mid-cervical level. We also show that cardiac afferent fibers are located in proximity to pulmonary fibers consistent with recent findings of cardiopulmonary convergent neurons and circuits. We demonstrate the ability of sVNS to selectively elicit desired scalable heart rate decrease without stimulating afferent-related reflexes. By elucidating the spatial organization of cardiac-related fibers within the vagus nerve, our findings pave the way for more targeted neuromodulation, thereby reducing off-target effects and eliminating the need for titration. This, in turn, will enhance the precision and efficacy of VNS therapy in treating cardiac pathology, allowing for improved therapeutic efficacy.

Human Heart Failure Alters Mitochondria and Fiber 3D Structure Triggering Metabolic Shifts.

This study, utilizing SBF-SEM, reveals structural alterations in mitochondria and myofibrils in human heart failure (HF). Mitochondria in HF show changes in structure, while myofibrils exhibit increased cross-sectional area and branching. Metabolomic and lipidomic analyses indicate concomitant dysregulation in key pathways. The findings underscore the need for personalized treatments considering individualized structural changes in HF.

Structural insights into the career path between pre- and postgraduate physician-scientist training programs.

The growing complexities of clinical medicine and biomedical research have clouded the career path for physician-scientists. In this perspective piece, we address one of the most opaque career stage transitions along the physician-scientist career path, the transition from medical school to research-focused internal medicine residency programs, or physician-scientist training programs (PSTPs). We present the perspectives of medical scientist training program (MSTP) and PSTP directors on critical features of PSTPs that can help trainees proactively align their clinical and scientific training for successful career development. We aim to provide both trainees and MSTP directors with a conceptual framework to better understand and navigate PSTPs. We also offer interview-specific questions to help trainees gather data and make informed decisions in choosing a residency program that best supports their career.

Vagal Nerve Stimulation Reduces Ventricular Arrhythmias and Mitigates Adverse Neural Cardiac Remodeling Post-Myocardial Infarction.

This study sought to evaluate the impact of chronic vagal nerve stimulation (cVNS) on cardiac and extracardiac neural structure/function after myocardial infarction (MI). Groups were control, MI, and MI + cVNS; cVNS was started 2 days post-MI. Terminal experiments were performed 6 weeks post-MI. MI impaired left ventricular mechanical function, evoked anisotropic electrical conduction, increased susceptibility to ventricular tachycardia and fibrillation, and altered neuronal and glial phenotypes in the stellate and dorsal root ganglia, including glial activation. cVNS improved cardiac mechanical function and reduced ventricular tachycardia/ventricular fibrillation post-MI, partly by stabilizing activation/repolarization in the border zone. MI-associated extracardiac neural remodeling, particularly glial activation, was mitigated with cVNS.

Heterogeneous cardiac sympathetic innervation gradients promote arrhythmogenesis in murine dilated cardiomyopathy.

Ventricular arrhythmias (VAs) in heart failure are enhanced by sympathoexcitation. However, radiotracer studies of catecholamine uptake in failing human hearts demonstrate a proclivity for VAs in patients with reduced cardiac sympathetic innervation. We hypothesized that this counterintuitive finding is explained by heterogeneous loss of sympathetic nerves in the failing heart. In a murine model of dilated cardiomyopathy (DCM), delayed PET imaging of sympathetic nerve density using the catecholamine analog [11C]meta-Hydroxyephedrine demonstrated global hypoinnervation in ventricular myocardium. Although reduced, sympathetic innervation in 2 distinct DCM models invariably exhibited transmural (epicardial to endocardial) gradients, with the endocardium being devoid of sympathetic nerve fibers versus controls. Further, the severity of transmural innervation gradients was correlated with VAs. Transmural innervation gradients were also identified in human left ventricular free wall samples from DCM versus controls. We investigated mechanisms underlying this relationship by in silico studies in 1D, 2D, and 3D models of failing and normal human hearts, finding that arrhythmogenesis increased as heterogeneity in sympathetic innervation worsened. Specifically, both DCM-induced myocyte electrical remodeling and spatially inhomogeneous innervation gradients synergistically worsened arrhythmogenesis. Thus, heterogeneous innervation gradients in DCM promoted arrhythmogenesis. Restoration of homogeneous sympathetic innervation in the failing heart may reduce VAs.

Sympathetic innervation of the supraclavicular brown adipose tissue: A detailed anatomical study.

BACKGROUND: The supraclavicular fossa is the dominant location for human brown adipose tissue (BAT). Activation of BAT promotes non-shivering thermogenesis by utilization of glucose and free fatty acids and has been the focus of pharmacological and non-pharmacological approaches for modulation in order to improve body weight and glucose homeostasis. Sympathetic neural control of supraclavicular BAT has received much attention, but its innervation has not been extensively investigated in humans. METHODS: Dissection of the cervical region in human cadavers was performed to find the distribution of sympathetic nerve branches to supraclavicular fat pad. Furthermore, proximal segments of the 4th cervical nerve were evaluated histologically to assess its sympathetic components. RESULTS: Nerve branches terminating in supraclavicular fat pad were identified in all dissections, including those from the 3rd and 4th cervical nerves and from the cervical sympathetic plexus. Histology of the proximal segments of the 4th cervical nerves confirmed tyrosine hydroxylase positive thin nerve fibers in all fascicles with either a scattered or clustered distribution pattern. The scattered pattern was more predominant than the clustered pattern (80% vs. 20%) across cadavers. These sympathetic nerve fibers occupied only 2.48% of the nerve cross sectional area on average. CONCLUSIONS: Human sympathetic nerves use multiple pathways to innervate the supraclavicular fat pad. The present finding serves as a framework for future clinical approaches to activate human BAT in the supraclavicular region.

Cryothermal energy demonstrates shorter ablation time and lower complication rates compared with radiofrequency in surgical hybrid ablation for recurrent ventricular tachycardia.

BACKGROUND: Recurrent ventricular tachycardia (VT) after prior endocardial catheter ablation(s) presents challenges in the setting of prior cardiac surgery where percutaneous epicardial access may not be feasible. OBJECTIVE: The purpose of this study was to compare the outcomes of cryothermal vs radiofrequency ablation in direct surgical epicardial access procedures. METHODS: We performed a retrospective study of consecutive surgical epicardial VT ablation cases. Surgical cases using cryothermal vs radiofrequency ablation were analyzed and outcomes were compared. RESULTS: Between 2009 and 2022, 43 patients underwent either a cryothermal (n = 17) or a radiofrequency (n = 26) hybrid epicardial ablation procedure with direct surgical access. Both groups were similarly matched for age, sex, etiology of VT, and comorbidities with a high burden of refractory VT despite previous endocardial and/or percutaneous epicardial ablation procedures. The surgical access site was lateral thoracotomy (76.5%) in the cryothermal ablation group compared with lateral thoracotomy (42.3%) and subxiphoid approach (38.5%) in the radiofrequency group, with the remainder in both groups performed via median sternotomy. The ablation time was significantly shorter in those undergoing cryothermal ablation vs radiofrequency ablation (11.54 ± 15.5 minutes vs 48.48 ± 23.6 minutes; P < .001). There were no complications in the cryothermal ablation group compared with 6 patients with complications in the radiofrequency group. Recurrent VT episodes and all-cause mortality were similar in both groups. CONCLUSION: Hybrid surgical VT ablation with cryothermal or radiofrequency energy demonstrated similar efficacy outcomes. Cryothermal ablation was more efficient and safer than radiofrequency in a surgical setting and should be considered when surgical access is required.

Photogrammetry of Perfusion-Fixed Heart: Innovative Approach to Study 3-Dimensional Cardiac Anatomy.

Photogrammetry generates a 3-dimensional high-resolution model from multiple 2-dimensional photographs. Herein, we demonstrate a photogrammetry of a perfusion-fixed cardiac sample around the left ventricular summit. The single photogrammetric model can be observed from almost all directions and illustrates important anatomical features for the general cardiologist. (Level of Difficulty: Advanced.).

Ischemia-induced ventricular proarrhythmia and cardiovascular autonomic dysreflexia after cardioneuroablation.

BACKGROUND: Cardioneuroablation (CNA) is an attractive treatment of vasovagal syncope. Its long-term efficacy and safety remain unknown. OBJECTIVE: The purpose of this study was to develop a chronic porcine model of CNA to examine the susceptibility to ventricular tachyarrhythmia (ventricular tachycardia/ventricular fibrillation [VT/VF]) and cardiac autonomic function after CNA. METHODS: A percutaneous CNA model was developed by ablation of left- and right-sided ganglionated plexi (n = 5), confirmed by histology. Reproducible bilateral vagal denervation was confirmed after CNA by extracardiac vagal nerve stimulation (VNS) and histology. Chronic studies included 16 pigs randomized to CNA (n = 8) and sham ablation (n = 8, Control). After 6 weeks, animals underwent hemodynamic studies, assessment of cardiac sympathetic and parasympathetic function using sympathetic chain stimulation and direct VNS, respectively, and proarrhythmic potential after left anterior descending (LAD) coronary artery ligation. RESULTS: After CNA, extracardiac VNS responses remained abolished for 6 weeks despite ganglia remaining in ablated ganglionated plexi. In the CNA group, direct VNS resulted in paradoxical increases in blood pressure, but not in sham-ablated animals (CNA group vs sham group: 8.36% ± 7.0% vs -4.83% ± 8.7%, respectively; P = .009). Left sympathetic chain stimulation (8 Hz) induced significant corrected QT interval prolongation in the CNA group vs the sham group (11.23% ± 4.0% vs 1.49% ± 4.0%, respectively; P < .001). VT/VF after LAD ligation was more prevalent and occurred earlier in the CNA group than in the control group (61.44 ± 73.7 seconds vs 245.11 ± 104.0 seconds, respectively; P = .002). CONCLUSION: Cardiac vagal denervation is maintained long-term after CNA in a porcine model. However, chronic CNA was associated with cardiovascular dysreflexia, diminished cardioprotective effects of cardiac vagal tone, and increased susceptibility to VT/VF in ischemia. These potential long-term negative effects of CNA suggest the need for rigorous clinical studies on CNA.

Linear epicardial cryoablation effects in a porcine model: Lesion characteristics and vascular risk.

INTRODUCTION: Cryoablation in open-chest surgical interventions for ventricular arrhythmias has been reported with reasonable procedural outcomes. However, the characteristics of cryoablation lesions on the ventricular myocardium are not well defined. The purpose of the present study was to determine the tissue and vascular effects of a linear epicardial cryoablation probe in a porcine animal model. METHODS: Five adult Yorkshire swine underwent median sternotomy and application of linear cryoablation lesions using a malleable aluminum linear cryoablation probe of varying duration (2, 3, 4, and 5 min), including one lesion placed intentionally over the left anterior descending coronary (LAD) artery. Histological analysis was performed. RESULTS: Maximum lesion depth was approximately 1.0 cm with 3 min freezes, with no significant increase in depth achieved with longer lesions. No transmural lesions were achieved. No large vessel epicardial coronary artery injuries were seen to the LAD; however, surprisingly, remote isolated interventricular septal injury was seen in all animals, suggestive of possible compromise of smaller coronary arterial vessels. CONCLUSION: Single application freezes with an aluminum linear cryoablation probe can create homogeneous ablative lesions over the ventricular myocardium with a maximum depth of approximately 1.0 cm. No large vessel injury occurred with direct lesion application of the LAD; however, small coronary vessels may be at risk.