Extracellular Histone-Induced Protein Kinase C Alpha Activation and Troponin Phosphorylation Is a Potential Mechanism of Cardiac Contractility Depression in Sepsis

Reduction in cardiac contractility is common in severe sepsis. However, the pathological mechanism is still not fully understood. Recently it has been found that circulating histones released after extensive immune cell death play important roles in multiple organ injury and disfunction, particularly in cardiomyocyte injury and contractility reduction. How extracellular histones cause cardiac contractility depression is still not fully clear. In this work, using cultured cardiomyocytes and a histone infusion mouse model, we demonstrate that clinically relevant histone concentrations cause significant increases in intracellular calcium concentrations with subsequent activation and enriched localization of calcium-dependent protein kinase C (PKC) α and βII into the myofilament fraction of cardiomyocytes in vitro and in vivo. Furthermore, histones induced dose-dependent phosphorylation of cardiac troponin I (cTnI) at the PKC-regulated phosphorylation residues (S43 and T144) in cultured cardiomyocytes, which was also confirmed in murine cardiomyocytes following intravenous histone injection. Specific inhibitors against PKCα and PKCβII revealed that histone-induced cTnI phosphorylation was mainly mediated by PKCα activation, but not PKCβII. Blocking PKCα also significantly abrogated histone-induced deterioration in peak shortening, duration and the velocity of shortening, and re-lengthening of cardiomyocyte contractility. These in vitro and in vivo findings collectively indicate a potential mechanism of histone-induced cardiomyocyte dysfunction driven by PKCα activation with subsequent enhanced phosphorylation of cTnI. These findings also indicate a potential mechanism of clinical cardiac dysfunction in sepsis and other critical illnesses with high levels of circulating histones, which holds the potential translational benefit to these patients by targeting circulating histones and downstream pathways

The Importance of Pore-Forming Toxins in Multiple Organ Injury and Dysfunction

BackgroundMultiple organ injury and dysfunction often occurs in acute critical illness and adversely affects survival. However, in patients who survive, organ function usually recovers without permanent damage. It is, therefore, likely that there are reversible mechanisms, but this is poorly understood in the pathogenesis of multiple organ dysfunction syndrome (MODS).AimsBased on our knowledge of extracellular histones and pneumolysin, as endogenous and exogenous pore-forming toxins, respectively, here we clarify if the extent of cell membrane disruption and recovery is important in MODS.MethodsThis is a combination of retrospective clinical studies of a cohort of 98 patients from an intensive care unit (ICU) in a tertiary hospital, with interventional animal models and laboratory investigation.ResultsIn patients without septic shock and/or disseminate intravascular coagulation (DIC), circulating histones also strongly correlated with sequential organ failure assessment (SOFA) scores, suggesting their pore-forming property might play an important role. In vivo, histones or pneumolysin infusion similarly caused significant elevation of cell damage markers and multiple organ injury. In trauma and sepsis models, circulating histones strongly correlated with these markers, and anti-histone reagents significantly reduced their release. Comparison of pneumolysin deletion and its parental strain-induced sepsis mouse model showed that pneumolysin was not essential for sepsis development, but enhanced multiple organ damage and reduced survival time. In vitro, histones and pneumolysin treatment disrupt cell membrane integrity, resulting in changes in whole-cell currents and elevated intracellular Ca2+ to lead to Ca2+ overload. Cell-specific damage markers, lactate dehydrogenase (LDH), alanine aminotransferase (ALT), and cardiac troponin I (cTnI), were released from damaged cells. Once toxins were removed, cell membrane damage could be rapidly repaired and cellular function recovered.ConclusionThis work has confirmed the importance of pore-forming toxins in the development of MODS and proposed a potential mechanism to explain the reversibility of MODS. This may form the foundation for the development of effective therapies

Molecular mechanisms of cell death: recommendations of the Nomenclature Committee on Cell Death 2018.

Over the past decade, the Nomenclature Committee on Cell Death (NCCD) has formulated guidelines for the definition and interpretation of cell death from morphological, biochemical, and functional perspectives. Since the field continues to expand and novel mechanisms that orchestrate multiple cell death pathways are unveiled, we propose an updated classification of cell death subroutines focusing on mechanistic and essential (as opposed to correlative and dispensable) aspects of the process. As we provide molecularly oriented definitions of terms including intrinsic apoptosis, extrinsic apoptosis, mitochondrial permeability transition (MPT)-driven necrosis, necroptosis, ferroptosis, pyroptosis, parthanatos, entotic cell death, NETotic cell death, lysosome-dependent cell death, autophagy-dependent cell death, immunogenic cell death, cellular senescence, and mitotic catastrophe, we discuss the utility of neologisms that refer to highly specialized instances of these processes. The mission of the NCCD is to provide a widely accepted nomenclature on cell death in support of the continued development of the field