Hironobu Tsubouchi

Epithelial Pten Controls Acute Lung Injury and Fibrosis by Regulating Alveolar Epithelial Cell Integrity

RATIONALE Injury to alveolar epithelial cells (AECs) and to their repair process is integral to the pathogenesis of acute lung injury (ALI) and idiopathic pulmonary fibrosis (IPF). The mechanisms regulating the integrity of AECs and their intrinsic regulators remain unclear. Pten is a tumor suppressor, and its function in epithelial cells during organ fibrosis is unknown. OBJECTIVES To determine the role of epithelial Pten in ALI and lung fibrosis. METHODS Bronchioalveolar epithelium-specific Pten-deleted SP-C-rtTA/(tetO)(7)-Cre/Pten(Δ/Δ) (SOPten(Δ/Δ)) mice were studied by structural, biochemical, and physiologic analyses and compared with wild-type mice. Further mechanistic studies were performed in vivo, in vitro, and on samples from patients with IPF. MEASUREMENTS AND MAIN RESULTS SOPten(Δ/Δ) mice demonstrated exacerbated alveolar flooding and subsequent augmented lung scarring with enhanced disassembly of tight junctions (TJs) of AECs and degradation of basement membranes. The induction of dominant negative PTEN gene in lung epithelial cells led to augmented transforming growth factor-1-induced disruptions of TJs. Epithelial-derived myofibroblasts were increased in the epithelium-specific Pten-deficient mice. The lungs of bleomycin-treated SOPten(Δ/Δ) mice showed increased pAkt, pS6K, Snail, and matrix metalloproteinase expressions and decreased claudin-4, E-cadherin, and laminin-β1 expressions. Akt inactivation definitively saved SOPten(Δ/Δ) mice through amelioration of ALI and retention of AEC integrity. We detected a reduction of PTEN expression and AKT hyperactivation in the AECs of human IPF lungs. CONCLUSIONS Our results highlight epithelial Pten as a crucial gatekeeper controlling ALI and lung fibrosis by modulating AEC integrity, and the Pten/PI3K/Akt pathway as a potential therapeutic target in these intractable diseases.

Canagliflozin, a sodium glucose cotransporter 2 inhibitor, attenuates obesity-induced inflammation in the nodose ganglion, hypothalamus, and skeletal muscle of mice

&NA; Chronic inflammation in systemic organs, such as adipose tissue, nodose ganglion, hypothalamus, and skeletal muscles, is closely associated with obesity and diabetes mellitus. Because sodium glucose cotransporter 2 (SGLT2) inhibitors exert both anti‐diabetic and anti‐obesity effects by promoting urinary excretion of glucose and subsequent caloric loss, we investigated the effect of canagliflozin, an SGLT2 inhibitor, on obesity‐induced inflammation in neural tissues and skeletal muscles of mice. High‐fat diet (HFD)‐fed male C57BL/6J mice were treated with canagliflozin for 8 weeks. Canagliflozin attenuated the HFD‐mediated increases in body weight, liver weight, and visceral and subcutaneous fat weight. Additionally, canagliflozin decreased blood glucose as well as the fat, triglyceride, and glycogen contents of the liver. Along with these metabolic corrections, canagliflozin attenuated the increases in the mRNA levels of the proinflammatory biomarkers Iba1 and Il6 and the number of macrophages/microglia in the nodose ganglion and hypothalamus. In the skeletal muscle of HFD‐fed obese mice, canagliflozin decreased inflammatory cytokine levels, macrophage accumulation, and the mRNA level of the specific atrophic factor atrogin‐1. Canagliflozin also increased the mRNA level of insulin‐like growth factor 1, protected against muscle mass loss, and restored the contractile force of muscle. These findings suggested that SGLT2 inhibition disrupts the vicious cycle of obesity and inflammation, not only by promoting caloric loss, but also by suppression of obesity‐related inflammation in both the nervous system and skeletal muscle.

Rikkunshito ameliorates bleomycin-induced acute lung injury in a ghrelin-independent manner

Acute lung injury (ALI) is a critical syndrome consisting of acute respiratory failure associated with extensive pulmonary infiltrates. The pathological characterization of ALI includes injuries of alveolar epithelial cells (AECs), alveolar neutrophilic infiltration, and increases in proinflammatory cytokines, which cause destruction of the alveolar capillary barrier and subsequent devastating lung fibrosis. Rikkunshito (RKT), a traditional Japanese herbal medicine, is widely used for the treatment of patients with gastrointestinal symptoms and is known to stimulate ghrelin secretion. The therapeutic effects of RKT on organ inflammation and fibrosis remain unknown. We investigated the pharmacological potential of RKT in the treatment of ALI by using a bleomycin-induced ALI model in mice. RKT or distilled water (DW) was given to mice daily starting 12 h after bleomycin administration. The RKT-treated mice showed a definitively higher survival rate than the DW-treated mice after injury. They also had smaller reductions in body weight and food intake. The amelioration of neutrophil alveolar infiltration, pulmonary vascular permeability, induction of proinflammatory cytokines, activation of the NF-κB pathway, apoptosis of AECs, and subsequent lung fibrosis were notable in the RKT-treated mice. RKT administration increased the plasma ghrelin levels in wild-type mice, and it also mitigated the ALI response in both ghrelin-deficient mice and growth hormone secretagogue receptor-deficient mice after lung injury. Our results indicate that RKT administration exerts protective effects against ALI by protecting the AECs and regulating lung inflammation independently of the ghrelin system, and they highlight RKT as a promising therapeutic agent for the management of this intractable disease.

Breakdown of Epithelial Barrier Integrity and Overdrive Activation of Alveolar Epithelial Cells in the Pathogenesis of Acute Respiratory Distress Syndrome and Lung Fibrosis.

Individual alveolar epithelial cells (AECs) collaboratively form a tight barrier between atmosphere and fluid-filled tissue to enable normal gas exchange. The tight junctions of AECs provide intercellular sealing and are integral to the maintenance of the AEC barrier integrity. Disruption and failure of reconstitution of AEC barrier result in catastrophic consequences, leading to alveolar flooding and subsequent devastating fibrotic scarring. Recent evidences reveal that many of the fibrotic lung diseases involve AECs both as a frequent target of injury and as a driver of ongoing pathological processes. Aberrantly activated AECs express most of the growth factors and chemokines responsible for the proliferation, migration, and activation of fibroblasts. Current evidences suggest that AECs may acquire overdrive activation in the initial step of fibrosis by several mechanisms, including abnormal recapitulation of the developmental pathway, defects of the molecules essential for epithelial integrity, and acceleration of aging-related properties. Among these initial triggering events, epithelial Pten, a multiple phosphatase that negatively regulates the PI3K/Akt pathway and is crucial for lung development, is essential for the prevention of alveolar flooding and lung fibrosis through the regulation of AEC barrier integrity after injury. Reestablishment of AEC barrier integrity also involves the deployment of specialized stem/progenitor cells.

Ghrelin relieves cancer cachexia associated with the development of lung adenocarcinoma in mice

Cancer cachexia is a multifactorial, critical illness syndrome characterized by an ongoing loss of skeletal muscle and adipose tissue. The reductions in body weight and skeletal muscle mass are important prognostic indicators for cancer patients that are refractory to current therapies. Ghrelin, an endogenous ligand for the growth hormone secretagogue receptor, is produced in the stomach, stimulates food intake and growth hormone secretion, suppresses inflammation, and prevents muscle catabolism. We investigated the pharmacological potential of ghrelin in the treatment of cancer cachexia by using urethane-treated, bronchioalveolar epithelium-specific Pten-deficient mice that developed lung adenocarcinomas. Ghrelin or phosphate-buffered saline was given to mice daily for four weeks beginning at five months after urethane injection, which corresponded to the time point of lung adenocarcinoma formation. Ghrelin inhibited the inductions of C-reactive protein, tumor necrosis factor-α, interleukin-1β, and interleukin-6, mitigated the reduction of food intake and fat mass, and consequently ameliorated body weight loss in the mouse model of lung adenocarcinoma. We also demonstrated that skeletal muscle mass and muscle contraction force in both fast-twitch muscle and slow-twitch muscle were retained in ghrelin-treated mice in conjunction with an upregulation of local insulin-like growth factor 1/Akt signaling. In addition, ghrelin administration reduced the expressions of phosphorylated-p38 mitogen-activated protein kinase, phosphorylated-nuclear factor-kappa B, Forkhead box protein O1, muscle RING-finger protein-1, and F-Box protein 32 in the lysates of skeletal muscle in the tumor-bearing state. Our results indicate that ghrelin administration exerts a protective effect against cancer cachexia by ameliorating skeletal muscle wasting and regulating systemic inflammation.

Rikkunshito ameliorates cachexia associated with bleomycin-induced lung fibrosis in mice by stimulating ghrelin secretion

Cachexia is a frequent complication in patients with respiratory failure, such as lung fibrosis, and it is a determining factor for functional capacity, health status, and mortality. Reductions in body weight and skeletal muscle mass are key features of cachexia that are resistant to current therapies. Rikkunshito (RKT), a traditional Japanese herbal medicine, is widely used for the treatment for patients with gastrointestinal symptoms and known to stimulate ghrelin secretion. By using bleomycin (BLM)-induced lung fibrosis mice in this study, we tested our hypothesis that RKT administration could ameliorate pulmonary cachexia. After BLM administration, mice were provided with either RKT or distilled water on a daily basis. Compared with the BLM-injected mice, the RKT-treated mice had smaller reductions of food intake and body weight. Skeletal muscle weights were retained in the RKT-treated mice, in conjunction with reduced expressions of MuRF-1 and atrogin-1 in the lysates of skeletal muscle found in lung fibrosis. Rikkunshito administration restored the plasma concentrations of ghrelin in BLM-injected mice. The anticachectic efficacies of RKT administration in BLM-injected mice were canceled by the concurrent treatment of a ghrelin receptor antagonist. Rikkunshito administration did not decrease the degree of loss of body weight or food intake reduction in either ghrelin-deficient mice or growth hormone secretagogue receptor-deficient mice. Our results indicate that RKT administration exerts protective effects on pulmonary cachexia by ameliorating skeletal muscle wasting and food intake reduction as mediated by the ghrelin system and, thus, highlight RKT as a potential therapeutic agent for the management of lung fibrosis.

The Impacts of Cellular Senescence in Elderly Pneumonia and in Age-Related Lung Diseases That Increase the Risk of Respiratory Infections

Pneumonia generates considerable negative impacts on the elderly. Despite the widespread uses of vaccines and appropriate antibiotics, the morbidity and mortality of elderly pneumonia are significantly higher compared to the counterparts of young populations. The definitive mechanisms of high vulnerability in the elderly against pathogen threats are unclear. Age-associated, chronic low-grade inflammation augments the susceptibility and severity of pneumonia in the elderly. Cellular senescence, one of the hallmarks of aging, has its own characteristics, cell growth arrest and senescence-associated secretory phenotype (SASP). These properties are beneficial if the sequence of senescence–clearance–regeneration is transient in manner. However, persisting senescent cell accumulation and excessive SASP might induce sustained low-grade inflammation and disruption of normal tissue microenvironments in aged tissue. Emerging evidence indicates that cellular senescence is a key component in the pathogenesis of chronic obstructive pulmonary disease (COPD) and idiopathic pulmonary fibrosis (IPF), which are known to be age-related and increase the risk of pneumonia. In addition to their structural collapses, COPD and IPF might increase the vulnerability to pathogen insults through SASP. Here, we discuss the current advances in understanding of the impacts of cellular senescence in elderly pneumonia and in these chronic lung disorders that heighten the risk of respiratory infections.

Ghrelin alleviates paclitaxel-induced peripheral neuropathy by reducing oxidative stress and enhancing mitochondrial anti-oxidant functions in mice

ABSTRACT Paclitaxel is an effective chemotherapeutic agent, but has some treatment‐limiting adverse effects that markedly decrease patients’ quality of life. Peripheral neuropathy is one of these, and no treatment for it has been established yet. Ghrelin, an endogenous ligand for the growth hormone secretagogue receptor, is secreted from the stomach and has widespread effects on multiple systems. We investigated the pharmacological potential of ghrelin in preventing paclitaxel‐induced peripheral neuropathy using wild‐type mice, ghrelin‐null mice, and growth hormone secretagogue receptor‐null mice. In wild‐type mice, ghrelin administration alleviated mechanical and thermal hypersensitivity, and partially prevented neuronal loss of small unmyelinated intraepidermal nerve fibers but not large myelinated nerve fibers. Moreover, ghrelin administration decreased plasma oxidative and nitrosative stress and increased the expression of uncoupling protein 2 (UCP2) and superoxide dismutase 2 (SOD2) in the dorsal root ganglia, which are mitochondrial antioxidant proteins, and peroxisome proliferator‐activated receptor gamma coactivator 1‐alpha (PGC‐1&agr;), a regulator of mitochondrial number. Both ghrelin‐null mice and growth hormone secretagogue receptor‐null mice developed more severe nerve injuries than wild‐type mice. Our results suggest that ghrelin administration exerts a protective effect against paclitaxel‐induced neuropathy by reducing oxidative stress and enhancing mitochondrial anti‐oxidant functions, and that endogenous ghrelin has a neuroprotective effect that is mediated by ghrelin/growth hormone secretagogue receptor signaling. Ghrelin could be a promising therapeutic agent for the management of this intractable disease.

Clinical application of ghrelin for chronic respiratory failure

Chronic respiratory failure, which is often caused by chronic obstructive pulmonary disease, chronic lower respiratory tract infection, or interstitial pneumonia, often leads to cachexia with disease progression. Patients who have chronic respiratory failure with cachexia exhibit increased morbidity. Although cachectic status is an important clinical problem, there are no effective therapies for cachexia. Ghrelin has various effects, including increasing food intake, attenuating sympathetic nerve activity, inhibiting inflammation, increasing cardiac output, and controlling fat utilization. These effects of ghrelin are ideal targets for the treatment of severely wasting chronic respiratory disease. In a few clinical studies, including a small randomized controlled trial, ghrelin administration to cachectic patients with chronic respiratory failure improved exercise tolerance, dyspnea, and appetite. The patients in these studies gained muscle mass and weight. In another study of chronic lower respiratory tract infection with cachexia, ghrelin suppressed airway inflammation by decreasing neutrophil accumulation in the airway, resulting in improvements in oxygenation and exercise tolerance. Although further clinical investigations are needed to clarify its usefulness, ghrelin is expected to become a novel therapy for cachectic patients with chronic respiratory failure.

Desquamative interstitial pneumonia complicated by diffuse alveolar haemorrhage: DIP with diffuse alveolar haemorrhage

We report a rare case of desquamative interstitial pneumonia (DIP) with diffuse alveolar haemorrhage (DAH). A 56‐year‐old man diagnosed with DIP by surgical lung biopsy 2 years ago was admitted to our hospital because of severe acute respiratory failure. The DIP had progressed despite smoking cessation. On admission, the patient appeared extremely ill, and physical examination revealed respiratory distress. The patient required mechanical ventilation. High‐resolution computed tomography showed diffuse ground glass opacity in both lungs. The bronchoalveolar lavage fluid was bloody, and numerous haemosiderin‐laden alveolar macrophages were detected. Pulse steroid therapy followed by oral prednisolone immediately relieved the respiratory failure and improved the long‐term control of the DIP. Paired sera tests confirmed the diagnosis of influenza A/H3N2 virus infection, which was the cause of the DAH. Chronically progressive DIP with acute respiratory failure due to DAH was successfully treated by steroid therapy.