Thyroid hormone (TH) is critical for the maintenance of cellular homeostasis during stress responses, but its role in lung fibrosis is unknown. Here, we found that the activity and expression of iodothyronine deiodinase 2 (DIO2), an enzyme that activates TH, was higher in lungs of patients with idiopathic pulmonary fibrosis compared to control individuals and correlated with disease severity. We also found that Dio2 knockout mice exhibited enhanced bleomycin-induced lung fibrosis. Aerosolized TH delivery increased survival and resolved fibrosis in two models of pulmonary fibrosis in mice (intratracheal bleomycin and inducible TGF-β1). Sobetirome, a TH mimetic, also blunted bleomycin-induced lung fibrosis. Given after bleomycin-induced injury, TH promoted mitochondrial biogenesis, improved mitochondrial bioenergetics and attenuated mitochondria-regulated apoptosis in alveolar epithelial cells both in vivo and in vitro. TH did not blunt fibrosis in Ppargc1a or Pink1 knockout mice suggesting dependence on these pathways. We conclude that the TH anti-fibrotic properties are associated with protection of alveolar epithelial cells and restoration of mitochondrial function and thus may represent an effective therapy for pulmonary fibrosis.

The generation of reactive oxygen species (ROS) plays an important role for the maintenance of cellular processes and functions in the body. However, the excessive generation of oxygen radicals under pathological conditions such as acute lung injury (ALI) and its most severe form acute respiratory distress syndrome (ARDS) leads to increased endothelial permeability. Within this hallmark of ALI and ARDS, vascular microvessels lose their junctional integrity and show increased myosin contractions that promote the migration of polymorphonuclear leukocytes (PMNs) and the transition of solutes and fluids in the alveolar lumen. These processes all have a redox component, and this chapter focuses on the role played by ROS during the development of ALI/ARDS. We discuss the origins of ROS within the cell, cellular defense mechanisms against oxidative damage, the role of ROS in the development of endothelial permeability, and potential therapies targeted at oxidative stress.

Diabetes mellitus (DM) is a growing international concern. Considerable mortality and morbidity associated with diabetes mellitus arise predominantly from thrombotic cardiovascular events. Oxidative stress‐mediated mitochondrial damage contributes significantly to enhanced thrombosis in DM. A basal autophagy process has recently been described as playing an important role in normal platelet activation. We now report a substantial mitophagy induction (above basal autophagy levels) in diabetic platelets, suggesting alternative roles for autophagy in platelet pathology. Using a combination of molecular, biochemical, and imaging studies on human DM platelets, we report that platelet mitophagy induction serves as a platelet protective mechanism that responds to oxidative stress through JNK activation. By removing damaged mitochondria (mitophagy), phosphorylated p53 is reduced, preventing progression to apoptosis, and preserving platelet function. The absence of mitophagy in DM platelets results in failure to protect against oxidative stress, leading to increased thrombosis. Surprisingly, this removal of damaged mitochondria does not require contributions from transcription, as platelets lack a nucleus. The considerable energy and resources expended in “prepackaging” the complex mitophagy machinery in a short‐lived normal platelet support a critical role, in anticipation of exposure to oxidative stress.

-Sepsis is a systemic inflammatory response to infection and a major cause of death worldwide. Because specific therapies to treat sepsis are limited, and underlying pathogenesis is unclear, current medical care remains purely supportive. Therefore targeted therapies to treat sepsis need to be developed. Although an important mediator of sepsis is thought to be mitochondrial dysfunction, the underlying molecular mechanism is unclear. Modulation of mitochondrial processes may be an effective therapeutic strategy in sepsis. Here, we investigated the role of the kinase MKK3 in regulation of mitochondrial function in sepsis. Using clinically relevant animal models, we examined mitochondrial function in primary mouse lung endothelial cells exposed to LPS. MKK3 deficiency reduces lethality of sepsis in mice and by lowering levels of lung and mitochondrial injury as well as reactive oxygen species. Furthermore, MKK3 deficiency appeared to simultaneously increase mitochondrial biogenesis and mitophagy through the actions of Sirt1, Pink1, and Parkin. This led to a more robust mitochondrial network, which we propose provides protection against sepsis. We also detected higher MKK3 activation in isolated peripheral blood mononuclear cells from septic patients compared with nonseptic controls. Our findings demonstrate a critical role for mitochondria in the pathogenesis of sepsis that involves a previously unrecognized function of MKK3 in mitochondrial quality control. This mitochondrial pathway may help reveal new diagnostic markers and therapeutic targets against sepsis. sepsis; lung injury; mitogen-activated protein kinases; mitochondria; mitophagy; biogenesis SEPSIS, A SYSTEMIC INFLAMMATORY reaction to infection, is the leading cause of death globally. The incidence of sepsis worldwide is 18 million every year with 30% mortality. The economic impact of sepsis is substantial with costs of up to $50,000/patient and $17 billion annually in United States alone (30, 43). Death from sepsis occurs due to multiorgan failure, and biological therapies do not exist. Prevailing theories attribute multiple organ failure in sepsis to an uncontrolled inflammatory response, apoptosis, or disorders in the coagulation (38). Unfortunately, therapies against these responses, such as anti-inflammatory agents and activated protein C, have been unsuccessful. Since current medical care remains purely supportive, there is an urgent need to develop targeted therapies.Mitochondria are mediators of inflammatory responses (19, 54) and become dysfunctional in sepsis and lung injury (4, 6), suggesting they are involved in the observed pathology. Mitochondria are essential hubs of innate immune signaling and inflammation in sepsis (48, 49) and are also major sites of reactive oxygen species (ROS) production in the cells. Mitochondria are constantly exposed to ROS, and hence ongoing biogenesis and turnover are needed to maintain a functional network. Dysfunctional mitochondria are removed through selective degradation via autophagy by the lysosomal mach...

Although hemolytic anemia-associated pulmonary hypertension (PH) and pulmonary arterial hypertension (PAH) are more common than the prevalence of idiopathic PAH alone, the role of hemolysis in the development of PAH is poorly characterized. We hypothesized that hemolysis independently contributes to PAH pathogenesis via endothelial barrier dysfunction with resulting perivascular edema and inflammation. Plasma samples from patients with and without PAH (both confirmed by right heart catheterization) were used to measure free hemoglobin (Hb) and its correlation with PAH severity. A sugen (50 mg/kg)/hypoxia (3 wk)/normoxia (2 wk) rat model was used to elucidate the role of free Hb/heme pathways in PAH. Human lung microvascular endothelial cells were used to study heme-mediated endothelial barrier effects. Our data indicate that patients with PAH have increased levels of free Hb in plasma that correlate with PAH severity. There is also a significant accumulation of free Hb and depletion of haptoglobin in the rat model. In rats, perivascular edema was observed at early time points concomitant with increased infiltration of inflammatory cells. Heme-induced endothelial permeability in human lung microvascular endothelial cells involved activation of the p38/HSP27 pathway. Indeed, the rat model also exhibited increased activation of p38/HSP27 during the initial phase of PH. Surprisingly, despite the increased levels of hemolysis and heme-mediated signaling, there was no heme oxygenase-1 activation. This can be explained by observed destabilization of HIF-1a during the first 2 weeks of PH regardless of hypoxic conditions. Our data suggest that hemolysis may play a significant role in PAH pathobiology.