Biology subjects

Danner, R. L.

Publications and source records attributed to Danner, R. L..

5 recordsLinked to original sources

bioRxiv2025

Myocyte Damage and Mass Loss Drives Increasing Water Content, Compliance, and Survival in Septic Cardiomyopathy

Introduction/PurposeDuring the septic cardiomyopathy, the mechanism and relationship to outcome of changes in left ventricular (LV) end diastolic volume (EDV) and ejection fraction (EF) remains obscure. We compared serial changes in LVEF and LVEDV to successive alterations in LV wall ultrastructure, water content, and total mass to investigate whether these measures can explain their basis. MethodsWe performed cardiac magnetic resonance imaging at 0,6,18,30,42,54, and 92h post-bacterial challenge in a large-animal model (n=57) that mimics human septic cardiomyopathy. LV tissue was obtained for electron microscopy (EM) upon death and 66h in sacrificed survivors. ResultsBetween 0-6h post-challenge, LV compliance and EDV reached its greatest decline. Non-survivors (n=18) exhibited significantly greater reductions in LVEDV, along with more myocyte edema, mitochondrial swelling and myofilament fragmentation on EM. This increased tissue damage may explain why non-survivors developed worse LV compliance and a greater decline in LVEDV, which persisted until death. From 6-30h, LVEDV significantly improved to baseline in non-survivors, while survivors experienced [~]20% increases (n=39). Concurrently, there was significant LV mass loss and increases in percent water content that were significantly associated with increases in LVEDV. This is consistent with a passive mechanism for rapidly improving LV compliance and EDV. Full recovery of EF required additional days. We hypothesize the prolonged significant mass loss over 5d reflects an active process for remodeling fragmented myofilaments, eliminating myocyte edema, and mitochondrial swelling, ultimately restoring contractile function. ConclusionThe septic cardiomyopathy constitutes a diffuse ultrastructural injury to myocytes with three phases. Initially, there is a decrease in LVEDV, and EF due to myocyte damage within 6h of bacterial challenge; next, the patient sees a passive LVEDV recovery from 6-30h, where LV mass loss increases relative wall percent water content, which facilitates wall compliance and LVEDV; and lastly, the patient sees mass loss beyond 30h consistent with an active repair mechanism of myocytes, returning systolic function to normal. Therefore, EDV changes are a pathophysiological biomarker for sepsis outcomes. A lower LVEDV indicates persistent unrepairable ultrastructure damage with worsening wall compliance and poorer outcomes. LVEDV dilation is a sign of near-full recovery of ultrastructure injury, augmenting wall compliance and improving outcomes. Clinical ImplicationsWe explain herein why septic cardiomyopathy findings dont have clinical implications like heart failure. Septic patients who exhibit signs of heart failure, low LVEF with high EDVs, are doing well - reflecting mild myocyte injury, effective damaged tissues clearance, increased relative LV wall water content, and compliance. This augments the LVEDV, lowering the LVEF. Septic patients who deteriorate rapidly, contrary to heart failure patients, show high/normal LVEF and low/normal LVEDV. Here, the myocyte damage is severe, leading to insufficient wall repair, and this decreased wall compliance persists, preventing the LV from dilating and making LVEDV low which ultimately raises the LVEF.

physiology↗

bioRxiv2024

In a Canine Model of Septic Shock, Cardiomyopathy Occurs Independent of Catecholamine Surges and Cardiac Microvascular Ischemia

BackgroundHigh levels of catecholamines are cardiotoxic and associated with stress-induced cardiomyopathies. Septic patients are routinely exposed to endogenously released and exogenously administered catecholamines, which may alter cardiac function and perfusion causing ischemia. Early during human septic shock, left ventricular ejection fraction (LVEF) decreases but normalizes in survivors over 7-10 days. Employing a septic shock model that reproduces these human septic cardiac findings, we investigated the effects of catecholamines on microcirculatory perfusion and cardiac function. MethodsPurpose-bred beagles received intrabronchial Staphylococcus aureus (n=30) or saline (n=6) challenges and septic animals recieved either epinephrine (1mcg/kg/min, n=15) or saline (n=15) infusions from 4 to 44 hours. Serial cardiac magnetic resonance imaging (CMR), invasive hemodynamics and laboratory data including catecholamine levels and troponins were collected over 92 hours. Adenosine-stress perfusion CMR was performed on eight of the fifteen septic epinephrine, and eight of the fifteen septic saline animals. High-dose sedation was titrated for comfort and suppress endogenous catecholamine release. ResultsCatecholamine levels were largely within the normal range throughout the study in animals receiving an intrabronchial bacteria or saline challenge. However, septic versus non-septic animals developed significant worsening of LV; EF, strain, and -aortic coupling that was not explained by differences in afterload, preload, or heart rate. In septic animals that received epinephrine versus saline infusions, plasma epinephrine levels increased 800-fold, pulmonary and systemic pressures significantly increased, and cardiac edema decreased. Despite this, septic animals receiving epinephrine versus saline during and after infusions, had no significant further worsening of LV; EF, strain, or -aortic coupling. Animals receiving saline had a sepsis-induced increase in microcirculatory reserve without troponin elevations. In contrast, septic animals receiving epinephrine had blunted microcirculatory perfusion and elevated troponin levels that persisted for hours after the infusion stopped. During infusion, septic animals that received epinephrine versus saline had significantly greater lactate, creatinine, and alanine aminotransferase levels. ConclusionsCardiac dysfunction during sepsis is not primarily due to elevated endogenous or exogenous catecholamines nor is it principally due to decreased microvascular perfusion-induced ischemia. However, epinephrine itself has potentially harmful long lasting ischemic effects during sepsis including impaired microvascular perfusion that persists after stopping the infusion. Clinical PerspectiveO_ST_ABSWhat is new?C_ST_ABSO_LIMyocardial depression of sepsis occurs without high levels of circulating catecholamines. C_LIO_LIWhereas large vessel coronary perfusion is known to be well maintained during sepsis, we show that during the myocardial depression of sepsis, in a model without exogenous catecholamine infusion, no perfusion abnormalities in the coronary microcirculation nor troponin elevations develop, indicating that the cardiac dysfunction of sepsis is not an ischemic injury. C_LIO_LIEpinephrine use during sepsis produces a form of injury tangential to the myocardial depression of sepsis. C_LIO_LIEpinephrine infusions depressed microcirculatory perfusion reserve and increased troponin I levels indicating a secondary prolonged mild ischemic effect on the myocardium. C_LI What are the clinical implications?O_LIProlonged high doses of epinephrine can secondarily contribute to perfusion abnormalities. C_LIO_LIDecoupling the septic heart from microvascular perfusion abnormalities and ischemia may lead to better strategies for managing shock associated with severe infections. In clinical practice in septic patients particularly potentially with coronary artery disease, commonly used vasopressors that are less associated with increased lactate production than epinephrine, alongside adjunct cardiac microcirculatory vasodilators, could help better maintain or improve cardiac performance during septic shock. C_LI

physiology↗

bioRxiv2024

Cardiac Magnetic Resonance Studies in a Large Animal Model that Simulates the Cardiac Abnormalities of Human Septic Shock

BackgroundSeptic shock, in humans and in our well-established animal model, is associated with increases in biventricular end diastolic volume (EDV) and decreases in ejection fraction (EF). These abnormalities occur over 2 days and reverse within 10 days. Septic non-survivors do not develop an increase in EDV. The mechanism for this cardiac dysfunction and EDV differences is unknown. MethodsPurpose-bred beagles randomized to receive intrabronchial Staphylococcus aureus (n=27) or saline (n=6) were provided standard ICU care including sedation, mechanical ventilation, and fluid resuscitation to a pulmonary arterial occlusion pressure of over 10mmHg. No catecholamines were administered. Over 96h, cardiac magnetic resonance imaging, echocardiograms, and invasive hemodynamics were serially performed, and laboratory data was collected. Tissue was obtained at 66h from six septic animals. ResultsFrom 0-96h after bacterial challenge, septic animals vs. controls had significantly increased left ventricular wall edema (6%) and wall thinning with loss of mass (15%) which was more pronounced at 48h in non-survivors than survivors. On histology, edema was located predominantly in myocytes, the interstitium, and endothelial cells. Edema was associated with significantly worse biventricular function (lower EFs), ventricular-arterial coupling, and circumferential strain. In septic animals, from 0-24h, the EDV decreased from baseline and, despite cardiac filling pressures being similar, decreased significantly more in non-survivors. From 24-48h, all septic animals had increases in biventricular chamber sizes. Survivors biventricular EDVs were significantly greater than baseline and in non-survivors, where biventricular EDVs were not different from baseline. Preload, afterload, or HR differences did not explain these differential serial changes in chamber size. ConclusionSystolic and diastolic cardiac dysfunction during sepsis is associated with ventricular wall edema. Rather than differences in preload, afterload, or heart rate, structural alterations to the ventricular wall best account for the volume changes associated with outcome during sepsis. In non-survivors, from 0-24h, sepsis induces a more severe diastolic dysfunction, further decreasing chamber size. The loss of left ventricular mass with wall thinning in septic survivors may, in part explain, the EDV increases from 24-48h. However, these changes continued and even accelerated into the recovery phase consistent with a reparative process rather than ongoing injury. Clinical PerspectiveO_ST_ABSWhat is new?C_ST_ABSO_LIUtilizing multimodal imaging and hemodynamics, we demonstrate the cardiac changes of sepsis have injury and reparative phases. C_LIO_LIThe injury phase (0-24h) has EDV decreases more profound in non-survivors and is associated with worse ventricular compliance, myocardial edema, and diastolic dysfunction. C_LIO_LIThe recovery phase has left ventricular mass loss with wall thinning in survivors that explains the EDV increases (24-96h). These progressed into the EF recovery phase consistent with a reparative process removing damaged tissue. C_LIO_LIThis is the first controlled CMR sepsis study supporting ventricular wall edema is a fundamental aspect of sepsis pathophysiology and dry mass loss a reparative mechanism. C_LI What are the clinical implications?O_LIDespite optimizing filling pressures, the cardiac changes in ventricular wall structure and function associated with survival and non-survival in sepsis still occurred, thereby discounting fluid resuscitation as the major factor of therapeutic importance for cardiac function and survival. C_LIO_LIThe changes reported here have potential implications for sepsis treatment especially in the field of fluid resuscitation. These findings yield new understanding into the pathophysiology of sepsis cardiac dysfunction and allow for novel phenotyping and prognosticating of the syndrome with ventricular compliance and EDVs. This also offers potentially high yielding targets for research for new therapeutic approaches for sepsis and heart failure. C_LI

physiology↗

bioRxiv2024

Endothelial PHD2 deficiency induces apoptosis resistance and inflammation via AKT activation and AIP1 loss independent of HIF2α

BACKGROUNDIn hypoxic and pseudohypoxic rodent models of pulmonary arterial hypertension (PAH), hypoxia-inducible factor (HIF) inhibition reduces disease severity. However, HIF activation alone, due to genetic alterations or use of inhibitors of prolyl hydroxylase domain (PHD) enzymes, has not been definitively shown to cause PAH in humans, indicating the involvement of other mechanisms. METHODSPseudohypoxia was investigated in primary human lung endothelial cells by silencing PHD2, and in Tie2-Cre/Phd2 knockout mice, a rodent model of PAH. Lung vascular endothelial cells from PAH patients, and lung tissue from both SU5416/hypoxia PAH rats and PAH patients, were examined for validation. RESULTSPHD2 silencing or inhibition, while activating HIF2, induces apoptosis-resistance, hypo-proliferation, and IFN/STAT activation in endothelial cells, independent of HIF signaling. Mechanistically, PHD2 deficiency activates AKT and ERK, inhibits JNK, and reduces AIP1 (ASK1-interacting protein 1), all independent of HIF2. Like PHD2, AIP1 silencing affects these same kinase pathways and produces a similar dysfunctional endothelial cell phenotype, which can be partially reversed by AKT inhibition. These findings are corroborated in lung tissues of rodent PAH models and pulmonary vascular endothelial cells and tissues from PAH patients. CONCLUSIONSPHD2 deficiency in lung vascular endothelial cells induces an apoptosis-resistant, inflammatory, and hypo-proliferative phenotype. AKT activation and AIP1 loss, but not HIF signaling, drive these aberrant phenotypic changes. Our study suggests that HIF blockade alone may not suffice for PAH therapy; targeting PHD2, AKT, and AIP1 has the potential for developing more effective treatment. GRAPHIC ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=110 SRC="FIGDIR/small/578286v1_ufig1.gif" ALT="Figure 1"> View larger version (38K): org.highwire.dtl.DTLVardef@1fd0a0borg.highwire.dtl.DTLVardef@19e6ba9org.highwire.dtl.DTLVardef@1ae2827org.highwire.dtl.DTLVardef@ce31ec_HPS_FORMAT_FIGEXP M_FIG C_FIG HighlightsO_LIPHD2 silencing in human lung vascular endothelial cells suppresses apoptosis, inhibits proliferation, and activates STAT signaling, effects that persist despite HIF2 inhibition or knockdown. C_LIO_LIPHD2 silencing activates AKT and ERK, inhibits JNK, and decreases AIP1, all independently of HIF2 C_LIO_LILike PHD2, AIP1 silencing led to similar alterations in kinase signaling and endothelial cell phenotypes, which are partially reversed by ATK inhibition. C_LIO_LIThese in vitro findings align with observations in lung vascular endothelial cells and tissues from rodent models of PAH as well as PAH patients. C_LI

cell biology↗

bioRxiv2024

Disruption of DLL4/NOTCH1 Causes Dysregulated PPARγ/AKT Signaling in Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a progressive cardiopulmonary disease characterized by vascular remodeling of small pulmonary arteries. Endothelial dysfunction in advanced PAH is associated with proliferation, apoptosis resistance, and endothelial to mesenchymal transition (EndoMT) due to aberrant signaling. DLL4, a cell membrane associated NOTCH ligand, activates NOTCH1 signaling and plays a pivotal role maintaining vascular integrity. Inhibition of DLL4 has been associated with the development of pulmonary hypertension, but the mechanism is incompletely understood. Here we report that BMPR2 silencing in PAECs activated AKT and decreased DLL4 expression. DLL4 loss was also seen in lungs of patients with IPAH and HPAH. Over-expression of DLL4 in PAECs induced BMPR2 promoter activity and exogenous DLL4 increased BMPR2 mRNA through NOTCH1 activation. Furthermore, DLL4/NOTCH1 signaling blocked AKT activation, decreased proliferation and reversed EndoMT in BMPR2- silenced PAECs and ECs from IPAH patients. PPAR{gamma}, suppressed by BMPR2 loss, was induced and activated by DLL4/NOTCH1 signaling in both BMPR2-silenced and IPAH PAECs, reversing aberrant phenotypic changes, in part through AKT inhibition. Finally, leniolisib, a well-tolerated oral PI3K8/AKT inhibitor, decreased cell proliferation, induced apoptosis and reversed markers of EndoMT in BMPR2-silenced PAECs. Restoring DLL4/NOTCH1/PPAR{gamma} signaling and/or suppressing AKT activation may be beneficial in preventing or reversing the pathologic vascular remodeling of PAH.

cell biology↗