Airspace enlargement with airway cell apoptosis in klotho mice: a model of aging lung

Analysis of the correlation between serum Klotho and FeNO: a cross-sectional study from NHANES (2007-2012)

BACKGROUND

Klotho is an anti-aging protein that has multiple functions and may play a key role in the pathogenesis and progression of chronic respiratory diseases such as chronic obstructive pulmonary disease (COPD). Fractional Exhaled Nitric Oxide (FeNO) is a non-invasive and novel biomarker that has the advantages of being simple, fast and reproducible. It can effectively assess the degree of airway inflammation in diseases such as asthma and COPD. Despite these insights, the relationship between serum Klotho levels and FeNO has not been explored yet.

METHODS

Leveraging data from the National Health and Nutrition Examination Survey (NHANES) spanning 2007 to 2012, we investigated the correlation between FeNO and serum Klotho levels. This association was scrutinized both as continuous variables and within quartile distributions, utilizing the Kruskal-Wallis H test. The correlation between the two variables was assessed through Spearman rank analysis. Employing survey weight-adjusted linear regression models, we gauged the strength of these associations.

RESULTS

This study included 6,527 participants with a median FeNO level of 14.5 parts per billion (ppb). We found that FeNO levels varied significantly across different quartiles of Klotho protein (H = 7.985, P = 0.046). We also found a significant positive correlation between serum Klotho levels and FeNO levels in the whole population (Spearman's rho = 0.029, P = 0.019). This correlation remained significant after adjusting for covariates such as age, gender, lung function, smoking status, alcohol use, BMI, cardiovascular disease (including hypertension, heart failure, coronary heart disease, and myocardial infarction), diabetes, inflammatory markers, serum vitamin D level and BUN (P < 0.05 for all). Furthermore, this correlation was stronger at the high (K3) and super high (K4) levels of Klotho than at the low (K1) and medium (K2) levels (β = 1.979 ppb and β = 1.993 ppb for K3 and K4 vs. K1, respectively; 95% CI: 0.497 ~ 2.953 and 95% CI: 0.129 ~ 2.827, respectively; P = 0.007 and P = 0.032, respectively). The β coefficient for serum Klotho was 0.002 ppb/pg/ml.

CONCLUSIONS

Our study illuminates a positive correlation between serum Klotho levels and FeNO. Further study is needed to verify the causality of this association and elucidate the underlying mechanisms.

Back to the Basics: Usefulness of Naturally Aged Mouse Models and Immunohistochemical and Quantitative Morphologic Methods in Studying Mechanisms of Lung Aging and Associated Diseases

Aging-related molecular and cellular alterations in the lung contribute to an increased susceptibility of the elderly to devastating diseases. Although the study of the aging process in the lung may benefit from the use of genetically modified mouse models and omics techniques, these approaches are still not available to most researchers and produce complex results. In this article, we review works that used naturally aged mouse models, together with immunohistochemistry (IHC) and quantitative morphologic (QM) methods in the study of the mechanisms of the aging process in the lung and its most commonly associated disorders: cancer, chronic obstructive pulmonary disease (COPD), and infectious diseases. The advantage of using naturally aged mice is that they present characteristics similar to those observed in human aging. The advantage of using IHC and QM methods lies in their simplicity, economic accessibility, and easy interpretation, in addition to the fact that they provide extremely important information. The study of the aging process in the lung and its associated diseases could allow the design of appropriate therapeutic strategies, which is extremely important considering that life expectancy and the number of elderly people continue to increase considerably worldwide.

Aging and aging-related diseases: from molecular mechanisms to interventions and treatments

Aging is a gradual and irreversible pathophysiological process. It presents with declines in tissue and cell functions and significant increases in the risks of various aging-related diseases, including neurodegenerative diseases, cardiovascular diseases, metabolic diseases, musculoskeletal diseases, and immune system diseases. Although the development of modern medicine has promoted human health and greatly extended life expectancy, with the aging of society, a variety of chronic diseases have gradually become the most important causes of disability and death in elderly individuals. Current research on aging focuses on elucidating how various endogenous and exogenous stresses (such as genomic instability, telomere dysfunction, epigenetic alterations, loss of proteostasis, compromise of autophagy, mitochondrial dysfunction, cellular senescence, stem cell exhaustion, altered intercellular communication, deregulated nutrient sensing) participate in the regulation of aging. Furthermore, thorough research on the pathogenesis of aging to identify interventions that promote health and longevity (such as caloric restriction, microbiota transplantation, and nutritional intervention) and clinical treatment methods for aging-related diseases (depletion of senescent cells, stem cell therapy, antioxidative and anti-inflammatory treatments, and hormone replacement therapy) could decrease the incidence and development of aging-related diseases and in turn promote healthy aging and longevity.

Retinoic acid induces hyaluronic acid production through the klotho-mediated EGFR signaling pathway in human epidermal keratinocytes

All-trans retinoic acid (RA) is an effective anti-aging chemical substance widely used in skin-care products. RA compromises epidermal differentiation and induces keratinocyte proliferation, causing hyaluronic acid production through mechanisms that are not completely understood. Klotho protein causes the differentiation of human epidermal keratinocytes. Klotho gene expression is mediated by epidermal growth factor (EGF), which inhibits cell apoptosis in aging-related diseases. The klotho gene causes human aging syndrome, including short lifespan, skin atrophy, and osteoporosis. We investigated the relationship between RA and klotho in epidermal keratinocytes for the first time. In human epidermal keratinocytes, RA induced klotho gene expression. Treatment with both RA and recombinant klotho induced hyaluronic acid production in human epidermal keratinocytes. However, in klotho small interfering RNA (siRNA)-transfected keratinocytes, RA produced less hyaluronic acid than in the control group, indicating that RA may partially regulate hyaluronic acid production through a klotho-dependent pathway. Knockdown of klotho gene expression inactivated the EGFR-extracellular signal-regulated kinase (ERK) signaling pathway, which is involved in hyaluronic acid production. We concluded that the effect of RA on hyaluronic acid production is partly regulated through the klothomediated EGFR signaling pathway in human epidermal keratinocytes.

Serum β-klotho is a potential biomarker in the prediction of clinical outcomes among patients with NSCLC

Background

We aimed to investigate the β-klotho (KLB) expression in non-small cell lung cancer (NSCLC) and to determine its value as a novel molecular target for survival prognosis in patients with NSCLC.

Methods

The serum KLB concentrations in 50 patients with NSCLC and the 20 healthy persons were measured by enzyme-linked immunosorbent assay (ELISA) methods. The relationship between serum KLB level, including the level change after therapy, and the progression-free survival (PFS) and overall survival (OS) were analyzed. The KLB expression in A549 cells was measured by real-time polymerase chain reaction (RT-PCR) and western blotting. The function of cells was revealed by in vitro studies.

Results

The concentrations of serum KLB in patients with NSCLC were obviously lower than those in healthy subjects. KLB expression was significantly increased in patients after chemotherapy and epidermal growth factor receptor tyrosine kinase inhibitor (EGFR-TKI) targeted therapy. In addition, expression of KLB was positively related with PFS and OS. Compared with 16-human bronchial epithelial (HBE) cells, the expression level of KLB was significantly decreased in A549 cells. Overexpression of KLB suppressed the proliferation of A549 cells, along with G1-to-S phase arrest and apoptosis induction.

Conclusions

KLB plays an anti-tumorigenic role in NSCLC. KLB may be a candidate target for the diagnosis and treatment of NSCLC and may serve a potentially significant role in future clinical applications.

The aging lung: Physiology, disease, and immunity

The population is aging at a rate never seen before in human history. As the number of elderly adults grows, it is imperative we expand our understanding of the underpinnings of aging biology. Human lungs are composed of a unique panoply of cell types that face ongoing chemical, mechanical, biological, immunological, and xenobiotic stress over a lifetime. Yet, we do not fully appreciate the mechanistic drivers of lung aging and why age increases the risk of parenchymal lung disease, fatal respiratory infection, and primary lung cancer. Here, we review the molecular and cellular aspects of lung aging, local stress response pathways, and how the aging process predisposes to the pathogenesis of pulmonary disease. We place these insights into context of the COVID-19 pandemic and discuss how innate and adaptive immunity within the lung is altered with age.

Decreased ADAM17 expression in the lungs of α-Klotho reduced mouse

The deficiency of α-Klotho in mice causes phenotypes resembling human age-associated disorders at 3-4 weeks after birth and shows short lifespans of ∼2 months. One of the crucial symptoms is pulmonary emphysema, although α-Klotho is not expressed in the lungs. α-Klotho secreted from the kidneys is probably involved in the pathology of emphysema because kidney-specific knockout mice exhibit emphysematous structural changes. We examined whether any glycan changes in α-Klotho mouse lungs were observed, because α-Klotho is reported to have glycosidase activity. Here, we found the accumulation of heparan sulphate in the microsomal fraction of α-Klotho mouse lungs. Meanwhile, a disintegrin and metalloproteinase 17 (ADAM17) expression was decreased in α-Klotho mice. From these results, it is thought that the increase in heparan sulphate is due to insufficient cleavage of the core protein by ADAM17. Additionally, a reduction in α-Klotho and a decline of ADAM17 were also observed both in normal aged mice and in senescence marker protein-30 (SMP30) knockout mice, a mouse model of premature ageing. Thus, the decrease in ADAM17 is caused by the reduction in α-Klotho. These may be involved in the deterioration of lung function during ageing and may be associated with the pathology of pulmonary emphysema.

Alpha-Klotho, a critical protein for lung health, is not expressed in normal lung

Alpha-Klotho (αKlotho), produced by the kidney and selected organs, is essential for tissue maintenance and protection. Homozygous αKlotho-deficiency leads to premature multi-organ degeneration and death; heterozygous insufficiency leads to apoptosis, oxidative stress, and increased injury susceptibility. There is inconsistent data in the literature regarding whether αKlotho is produced locally in the lung or derived from circulation. We probed murine and human lung by immunohistochemistry (IHC) and immunoblot (IB) using two monoclonal (anti-αKlotho Kl1 and Kl2 domains) and three other common commercial antibodies. Monoclonal anti-Kl1 and anti-Kl2 yielded no labeling in lung on IHC or IB; specific labeling was observed in kidney (positive control) and also murine lungs following tracheal delivery of αKlotho cDNA, demonstrating specificity and ability to detect artificial pulmonary expression. Other commercial antibodies labeled numerous lung structures (IHC) and multiple bands (IB) incompatible with known αKlotho mobility; labeling was not abolished by blocking with purified αKlotho or using lungs from hypomorphic αKlotho-deficient mice, indicating nonspecificity. Results highlight the need for rigorous validation of reagents. The lung lacks native αKlotho expression and derives full-length αKlotho from circulation; findings could explain susceptibility to lung injury in extrapulmonary pathology associated with reduced circulating αKlotho levels, for example, renal failure. Conversely, αKlotho may be artificially expressed in the lung, suggesting therapeutic opportunities.

Reduced expression of the Ion channel CFTR contributes to airspace enlargement as a consequence of aging and in response to cigarette smoke in mice

Chronic Obstructive Pulmonary Disease (COPD) is a complex disease resulting in respiratory failure and represents the third leading cause of global death. The two classical phenotypes of COPD are chronic bronchitis and emphysema. Owing to similarities between chronic bronchitis and the autosomal-recessive disease Cystic Fibrosis (CF), a significant body of research addresses the hypothesis that dysfunctional CF Transmembrane Conductance Regulator (CFTR) is implicated in the pathogenesis of COPD. Much less attention has been given to emphysema in this context, despite similarities between the two diseases. These include early-onset cellular senescence, similar comorbidities, and the finding that CF patients develop emphysema as they age. To determine a potential role for CFTR dysfunction in the development of emphysema, Cftr^+/+ (Wild-type; WT), Cftr^+/− (heterozygous), and Cftr^−/− (knock-out; KO) mice were aged or exposed to cigarette smoke and analyzed for airspace enlargement. Aged knockout mice demonstrated increased alveolar size compared to age-matched wild-type and heterozygous mice. Furthermore, both heterozygous and knockout mice developed enlarged alveoli compared to their wild-type counterparts following chronic smoke exposure. Taken into consideration with previous findings that cigarette smoke leads to reduced CFTR function, our findings suggest that decreased CFTR expression sensitizes the lung to the effects of cigarette smoke. These findings may caution normally asymptomatic CF carriers against exposure to cigarette smoke; as well as highlight emphysema as a future challenge for CF patients as they continue to live longer. More broadly, our data, along with clinical findings, may implicate CFTR dysfunction in a pathology resembling accelerated aging.

Club cell protein 16 (Cc16) deficiency increases inflamm-aging in the lungs of mice

Low serum CC16 levels are associated with accelerated lung function decline in human population studies, but it is not known whether low serum CC16 levels contribute to lung function decline, or are an epiphenomenon. We tested the hypothesis that unchallenged Cc16-/- mice develop accelerated rates of pulmonary function test abnormalities and pulmonary pathologies over time compared with unchallenged WT mice. Respiratory mechanics, airspace enlargement, and small airway fibrosis were measured in unchallenged wild-type (WT) versus Cc16-/- mice over 6-18 months of age. Lung leukocyte counts and lung levels of metalloproteinases (Mmps), cytokines, oxidative stress, cellular senescence markers (p19 and p21), and lung cell apoptosis, and serum C-reactive protein (CRP) levels were measured in age-matched WT versus Cc16-/- mice. Unchallenged Cc16-/- mice developed greater increases in lung compliance, airspace enlargement, and small airway fibrosis than age-matched WT mice over 6-18 months of age. Cc16-/- mice had greater: (1) lung leukocyte counts; (2) lung levels of Ccl2, Ccl-5, interleukin-10, Mmp-2, and Mmp-9; (3) pulmonary oxidative stress levels, (4) alveolar septal cell apoptosis and staining for p16 and p21; and (5) serum CRP levels. Unchallenged Cc16-/- mice had greater nuclear factor-κB (NF-κB) activation in their lungs than age-matched WT mice, but similar lung levels of secretory phospholipase-A2 activity. Cc16 deficiency in mice leads spontaneously to an accelerated lung aging phenotype with exaggerated pulmonary inflammation and COPD-like lung pathologies associated with increased activation of NF- κB in the lung. CC16 augmentation strategies may reduce lung aging in CC16-deficient individuals.

Transgenic Mice Overexpressing Vitamin D Receptor (VDR) Show Anti-Inflammatory Effects in Lung Tissues

Vitamin D insufficiency is increasingly recognized as a prevalent problem worldwide, especially in patients with a chronic lung disease. Chronic obstructive pulmonary disease (COPD) is a type of chronic inflammatory lung disease. Previous clinical studies have shown that COPD leads to low vitamin D levels, which further increase the severity of COPD. Vitamin D homeostasis represents one of the most important factors that potentially determine the severity of COPD. Nonetheless, the mechanisms underlying the anti-inflammatory effects of vitamin D receptor (VDR) in lung tissues are still unclear. To investigate the anti-inflammatory effects of VDR, we generated transgenic mice that show lung-specific VDR overexpression under the control of the surfactant protein C promoter (TG mice). The TG mice were used to study the expression patterns of proinflammatory cytokines using real-time polymerase chain reaction and immunohistochemistry. The TG mice had lower levels of T helper 1 (Th1)-related cytokines than wild-type (WT) mice did. No significant differences in the expression of Th2 cytokines were observed between TG and WT mice. This study is the first to achieve lung-specific overexpression of VDR in TG mice: an interesting animal model useful for studying the relation between airway cell inflammation and vitamin D signaling. VDR expression is an important factor that influences anti-inflammatory responses in lung tissues. Our results show the crucial role of VDR in anti-inflammatory effects in lungs; these data are potentially useful for the treatment or prevention of COPD.

Alpha-1 Antitrypsin Investigations Using Animal Models of Emphysema

Animal models of disease help accelerate the translation of basic science discoveries to the bedside, because they permit experimental interrogation of mechanisms at relatively high throughput, while accounting for the complexity of an intact organism. From the groundbreaking observation of emphysema-like alveolar destruction after direct instillation of elastase in the lungs to the more clinically relevant model of airspace enlargement induced by chronic exposure to cigarette smoke, animal models have advanced our understanding of alpha-1 antitrypsin (AAT) function. Experimental in vivo models that, at least in part, replicate clinical human phenotypes facilitate the translation of mechanistic findings into individuals with chronic obstructive pulmonary disease and with AAT deficiency. In addition, unexpected findings of alveolar enlargement in various transgenic mice have led to novel hypotheses of emphysema development. Previous challenges in manipulating the AAT genes in mice can now be overcome with new transgenic approaches that will likely advance our understanding of functions of this essential, lung-protective serine protease inhibitor (serpin).

Effects of Klotho on fibrosis and cancer: A renal focus on mechanisms and therapeutic strategies

Klotho is a membrane-bound protein predominantly expressed in the kidney, where it acts as a permissive co-receptor for Fibroblast Growth Factor 23. In its shed form, Klotho exerts anti-fibrotic effects in several tissues. Klotho-deficient mice spontaneously develop fibrosis and Klotho deficiency exacerbates the disease progression in fibrotic animal models. Furthermore, Klotho overexpression or supplementation protects against fibrosis in various models of renal and cardiac fibrotic disease. These effects are mediated at least partially by the direct inhibitory effects of soluble Klotho on TGFβ1 signaling, Wnt signaling, and FGF2 signaling. Soluble Klotho, as present in the circulation, appears to be the primary mediator of anti-fibrotic effects. Similarly, through inhibition of the TGFβ1, Wnt, FGF2, and IGF1 signaling pathways, Klotho also inhibits tumorigenesis. The Klotho promoter gene is generally hypermethylated in cancer, and overexpression or supplementation of Klotho has been found to inhibit tumor growth in various animal models. This review focuses on the protective effects of soluble Klotho in inhibiting renal fibrosis and fibrosis in distant organs secondary to renal Klotho deficiency. We also discuss the structure-function relationships of Klotho domains and biological effects in the context of potential targeted treatment strategies.

Klotho regulates postnatal neurogenesis and protects against age-related spatial memory loss

Although the absence of the age-regulating klotho protein causes klotho-deficient mice to rapidly develop cognitive impairment and increasing klotho enhances hippocampal-dependent memory, the cellular effects of klotho that mediate hippocampal-dependent memory function are unknown. Here, we show premature aging of the klotho-deficient hippocampal neurogenic niche as evidenced by reduced numbers of neural stem cells, decreased proliferation, and impaired maturation of immature neurons. Klotho-deficient neurospheres show reduced proliferation and size that is rescued by supplementation with shed klotho protein. Conversely, 6-month-old klotho-overexpressing mice exhibit increased numbers of neural stem cells, increased proliferation, and more immature neurons with enhanced dendritic arborization. Protection from normal age-related loss of object location memory with klotho overexpression and loss of spatial memory when klotho is reduced by even half suggests direct, local effects of the protein. Together, these data show that klotho is a novel regulator of postnatal neurogenesis affecting neural stem cell proliferation and maturation sufficient to impact hippocampal-dependent spatial memory function.

Acute lung injury complicating acute kidney injury: A model of endogenous αKlotho deficiency and distant organ dysfunction

The lung interfaces with atmospheric oxygen via a large surface area and is perfused by the entire venous return bearing waste products collected from the whole body. It is logical that the lung is endowed with generous anti-oxidative capacity derived both locally and from the circulation. The single-pass pleiotropic alpha-Klotho (αKlotho) protein was discovered when its genetic disruption led to premature multi-organ degeneration and early death. The extracellular domain of αKlotho is cleaved by secretases and released into circulation as endocrine soluble αKlotho protein, exerting wide-ranging cytoprotective effects including anti-oxidation on distant organs including the lung, which exhibits high sensitivity to circulating αKlotho insufficiency. Because circulating αKlotho is derived mainly from the kidney, acute kidney injury (AKI) leads to systemic αKlotho deficiency that in turn increases the risks of pulmonary complications, i.e., edema and inflammation, culminating in the acute respiratory distress syndrome. Exogenous αKlotho increases endogenous anti-oxidative capacity partly via activation of the Nrf2 pathway to protect lungs against injury caused by direct hyperoxia exposure or AKI. This article reviews the current knowledge of αKlotho antioxidation in the lung in the setting of AKI as a model of circulating αKlotho deficiency, an under-recognized condition that weakens innate cytoprotective defenses and contributes to the dysfunction in distant organs.

Klotho, an antiaging molecule, attenuates oxidant-induced alveolar epithelial cell mtDNA damage and apoptosis

Alveolar epithelial cell (AEC) apoptosis and inadequate repair resulting from "exaggerated" lung aging and mitochondrial dysfunction are critical determinants promoting lung fibrosis. α-Klotho, which is an antiaging molecule that is expressed predominantly in the kidney and secreted in the blood, can protect lung epithelial cells against hyperoxia-induced apoptosis. We reasoned that Klotho protects AEC exposed to oxidative stress in part by maintaining mitochondrial DNA (mtDNA) integrity and mitigating apoptosis. We find that Klotho levels are decreased in both serum and alveolar type II (AT2) cells from asbestos-exposed mice. We show that oxidative stress reduces AEC Klotho mRNA and protein expression, whereas Klotho overexpression is protective while Klotho silencing augments AEC mtDNA damage. Compared with wild-type, Klotho heterozygous hypomorphic allele (kl/+) mice have increased asbestos-induced lung fibrosis due in part to increased AT2 cell mtDNA damage. Notably, we demonstrate that serum Klotho levels are reduced in wild-type but not mitochondrial catalase overexpressing (MCAT) mice 3 wk following exposure to asbestos and that EUK-134, a MnSOD/catalase mimetic, mitigates oxidant-induced reductions in AEC Klotho expression. Using pharmacologic and genetic silencing studies, we show that Klotho attenuates oxidant-induced AEC mtDNA damage and apoptosis via mechanisms dependent on AKT activation arising from upstream fibroblast growth factor receptor 1 activation. Our findings suggest that Klotho preserves AEC mtDNA integrity in the setting of oxidative stress necessary for preventing apoptosis and asbestos-induced lung fibrosis. We reason that strategies aimed at augmenting AEC Klotho levels may be an innovative approach for mitigating age-related lung diseases.

From "Kidneys Govern Bones" to Chronic Kidney Disease, Diabetes Mellitus, and Metabolic Bone Disorder: A Crosstalk between Traditional Chinese Medicine and Modern Science

Although traditional Chinese medicine (TCM) and Western medicine have evolved on distinct philosophical foundations and reasoning methods, an increasing body of scientific data has begun to reveal commonalities. Emerging scientific evidence has confirmed the validity and identified the molecular mechanisms of many ancient TCM theories. One example is the concept of "Kidneys Govern Bones." Here we discuss the molecular mechanisms supporting this theory and its potential significance in treating complications of chronic kidney disease (CKD) and diabetes mellitus. Two signaling pathways essential for calcium-phosphate metabolism can mediate the effect of kidneys in bone homeostasis, one requiring renal production of bioactive vitamin D and the other involving an endocrine axis based on kidney-expressed Klotho and bone-secreted fibroblast growth factor 23. Disruption of either pathway can lead to calcium-phosphate imbalance and vascular calcification, accelerating metabolic bone disorder. Chinese herbal medicine is an adjunct therapy widely used for treating CKD and diabetes. Our results demonstrate the therapeutic effects and underlying mechanisms of a Chinese herbal formulation, Shen-An extracts, in diabetic nephropathy and renal osteodystrophy. We believe that the smart combination of Eastern and Western concepts holds great promise for inspiring new ideas and therapies for preventing and treating complications of CKD and diabetes.

α-Klotho protects against oxidative damage in pulmonary epithelia

α-Klotho exerts pleiotropic biological actions. Heterozygous α-Klotho haplo-insufficient mice (kl/+) appear normal at baseline except for age-related changes in the lung, suggesting heightened pulmonary susceptibility to α-Klotho deficiency. We used in vivo and in vitro models to test whether α-Klotho protects lung epithelia against injury. Normally, α-Klotho is not expressed in the lung, but circulating α-Klotho levels are reduced -40% in kl/+ mice and undetectable in homozygous α-Klotho-deficient mice (kl/kl). kl/+ mice show distal air space enlargement at a given airway pressure, with elevated lung oxidative damage marker (8-hydroxydeoxyguanosine; 8-OHdG); these abnormalities are exacerbated in kl/kl mice. Studies were performed in A549 lung epithelial cells and/or primary culture of alveolar epithelial cells. Hyperoxia (95% O2) and high inorganic phosphate concentrations (Pi, 3-5 mM) additively caused cell injury (lactate dehydrogenase release), oxidative DNA damage (8-OHdG), lipid oxidation (8-isoprostane), protein oxidation (carbonyl), and apoptosis (caspase-8 activity and TUNEL stain). Transfection of transmembrane or soluble α-Klotho, or addition of soluble α-Klotho-containing conditioned media, increased cellular antioxidant capacity (Cu- and Fe-based assays) via increased nuclear factor erythroid-derived 2-related factors 1 and 2 (Nrf1/2) transcriptional activity and ameliorated hyperoxic and phosphotoxic injury. To validate the findings in vivo, we injected α-Klotho-containing conditioned media into rat peritoneum before and during hyperoxia exposure and found reduced alveolar interstitial edema and oxidative damage. We conclude that circulating α-Klotho protects the lung against oxidative damage and apoptosis partly via increasing endogenous antioxidative capacity in pulmonary epithelia. Cytoprotection by α-Klotho may play an important role in degenerative diseases of the lung.

17β-estradiol replacement reverses age-related lung disease in estrogen-deficient C57BL/6J mice

The role that estrogens play in the aging lung is poorly understood. Remodeling of the aging lung with thickening of the alveolar walls and reduction in the number of peripheral airways is well recognized. The present study was designed to address whether estrogen deficiency would affect age-associated changes in the lungs of female C57BL/6J mice. Lungs isolated from old mice (24 months old, estrogen-deficient) demonstrated decreased lung volume and decreased alveolar surface area. There was no difference in alveolar number in the lungs of old and young mice (6 months old, estrogen-replete). Estrogen replacement restored lung volume, alveolar surface area, and alveolar wall thickness to that of a young mouse. Estrogen receptor-α (ERα) protein expression increased without a change in ERβ protein expression in the lung tissue isolated from old mice. In the lungs of old mice, the number of apoptotic cells was increased as well as the activation of matrix metalloproteinase-2 and ERK. Young mice had the highest serum 17β-estradiol levels that decreased with age. Our data suggest that in the aging female mouse lung, estrogen deficiency and an increase of ERα expression lead to the development of an emphysematous phenotype. Estrogen replacement partially prevents these age-associated changes in the lung architecture by restoration of interalveolar septa. Understanding the role of estrogens in the remodeling of the lung during aging may facilitate interventions and therapies for aging-related lung disease in women.

Smokers with CT detected emphysema and no airway obstruction have decreased plasma levels of EGF, IL-15, IL-8 and IL-1ra

RATIONALE

Low-grade inflammation and emphysema have been shown to be associated with an increased risk of lung cancer. However, the systemic inflammatory response in patients with emphysema is still unknown.

OBJECTIVE

TO COMPARE THE PLASMA CYTOKINE PROFILES IN TWO GROUPS OF CURRENT OR FORMER SMOKERS WITHOUT AIRWAY OBSTRUCTION: a control group of individuals without computed tomography (CT) detected emphysema vs. a study group of individuals with CT detected emphysema.

METHODS

Subjects underwent a chest CT, spirometry, and determination of EGF, IL-15, IL-1ra, IL-8, MCP-1, MIP-1β, TGFα, TNFα, and VEGF levels in plasma. Cytokine levels in each group were compared adjusting for confounding factors.

RESULTS

160 current smokers and former smokers without airway obstruction participated in the study: 80 without emphysema and 80 subjects with emphysema. Adjusted group comparisons revealed significant reductions in EGF (-0.317, p = 0.01), IL-15 (-0.21, p = 0.01), IL-8 (-0.180, p = 0.02) and IL-1ra (-0.220, p = 0.03) in subjects with emphysema and normal spirometry.

CONCLUSIONS

Current or former smokers expressing a well-defined disease characteristic such as emphysema, has a specific plasma cytokine profile. This includes a decrease of cytokines mainly implicated in activation of apoptosis or decrease of immunosurveillance. This information should be taken into account when evaluated patients with tobacco respiratory diseases.

Regulation and function of the FGF23/klotho endocrine pathways

Calcium (Ca(2+)) and phosphate (PO(4)(3-)) homeostasis are coordinated by systemic and local factors that regulate intestinal absorption, influx and efflux from bone, and kidney excretion and reabsorption of these ions through a complex hormonal network. Traditionally, the parathyroid hormone (PTH)/vitamin D axis provided the conceptual framework to understand mineral metabolism. PTH secreted by the parathyroid gland in response to hypocalcemia functions to maintain serum Ca(2+) levels by increasing Ca(2+) reabsorption and 1,25-dihydroxyvitamin D [1,25(OH)(2)D] production by the kidney, enhancing Ca(2+) and PO(4)(3-) intestinal absorption and increasing Ca(2+) and PO(4)(3-) efflux from bone, while maintaining neutral phosphate balance through phosphaturic effects. FGF23 is a recently discovered hormone, predominately produced by osteoblasts/osteocytes, whose major functions are to inhibit renal tubular phosphate reabsorption and suppress circulating 1,25(OH)(2)D levels by decreasing Cyp27b1-mediated formation and stimulating Cyp24-mediated catabolism of 1,25(OH)(2)D. FGF23 participates in a new bone/kidney axis that protects the organism from excess vitamin D and coordinates renal PO(4)(3-) handling with bone mineralization/turnover. Abnormalities of FGF23 production underlie many inherited and acquired disorders of phosphate homeostasis. This review discusses the known and emerging functions of FGF23, its regulation in response to systemic and local signals, as well as the implications of FGF23 in different pathological and physiological contexts.

Klotho and βKlotho

Endocrine fibroblast growth factors (FGFs) have been recognized as hormones that regulate a variety of metabolic processes. FGF19 is secreted from intestine upon feeding and acts on liver to suppress bile acid synthesis. FGF21 is secreted from liver upon fasting and acts on adipose tissue to promote lipolysis and responses to fasting. FGF23 is secreted from bone and acts on kidney to inhibit phosphate reabsorption and vitamin D synthesis. One critical feature of endocrine FGFs is that they require the Klotho gene family of transmembrane proteins as coreceptors to bind their cognate FGF receptors and exert their biological activities. This chapter overviews function of Klotho family proteins as obligate coreceptors for endocrine FGFs and discusses potential link between Klothos and age-related diseases.

Ultra-short echo time (UTE) MR imaging of the lung: comparison between normal and emphysematous lungs in mutant mice

PURPOSE

To investigate the utility of ultra-short echo time (UTE) sequence as pulmonary MRI to detect non-uniform disruption of lung architecture that is typical of emphysema.

MATERIALS AND METHODS

MRI of the lungs was conducted with a three-dimensional UTE sequence in transgenic mice with severe emphysema and their wild-type littermates in a 3 Tesla clinical MR system. Measurements of the signal intensity (SI) and transverse relaxation time (T2*) of the lung parenchyma were performed with various echo times (TEs) ranging from 100 micros to 2 ms.

RESULTS

Much higher SI of the lung parenchyma was observed at an UTE of 100 micros compared with longer TEs. The emphysematous lungs had reduced SIs and T2* than the controls, in particular at end-expiratory phase. The results suggested that both SI and T2* in lung parenchyma measured with the method represent fractional volume of lung tissue.

CONCLUSION

The UTE imaging provided MR signal from the lung parenchyma. Moreover, the UTE sequence was sensitive to emphysematous changes and may provide a direct assessment of lung parenchyma. UTE imaging has the potential to assist detection of localized pathological destruction of lung tissue architecture in emphysema.

A potential link between phosphate and aging--lessons from Klotho-deficient mice

Phosphate homeostasis is maintained primarily by a bone-kidney endocrine axis. When phosphate is in excess, fibroblast growth factor-23 (FGF23) is secreted from bone and acts on kidney to promote phosphate excretion into urine. FGF23 also reduces serum vitamin D levels to suppress phosphate absorption from intestine. Thus, FGF23 functions as a hormone that induces negative phosphate balance. One critical feature of FGF23 is that it requires Klotho, a single-pass transmembrane protein expressed in renal tubules, as an obligate co-receptor to bind and activate cognate FGF receptors. Importantly, defects in either FGF23 or Klotho not only cause phosphate retention but also a premature-aging syndrome in mice, which can be rescued by resolving hyperphosphatemia. In addition, changes in extracellular and intracellular phosphate concentration affect glucose metabolism, insulin sensitivity, and oxidative stress in vivo and in vitro, which potentially affect aging processes. These findings suggest an unexpected link between inorganic phosphate and aging in mammals.

Overview of the FGF23-Klotho axis

Recent studies have identified a novel bone-kidney endocrine axis that maintains phosphate homeostasis. When phosphate is in excess, fibroblast growth factor-23 (FGF23) is secreted from bone and acts on the kidney to promote phosphate excretion into urine and suppress vitamin D synthesis, thereby inducing negative phosphate balance. One critical feature of FGF23 is that it requires Klotho, a single-pass transmembrane protein expressed in renal tubules, as an obligate coreceptor to bind and activate FGF receptors. Several hereditary disorders that exhibit inappropriately high serum FGF23 levels are associated with phosphate wasting and impaired bone mineralization. In contrast, defects in either FGF23 or Klotho are associated with phosphate retention and a premature-aging syndrome. The aging-like phenotypes in Klotho-deficient or FGF23-deficient mice can be rescued by resolving hyperphosphatemia with dietary or genetic manipulation, suggesting a novel concept that phosphate retention accelerates aging. Phosphate retention is universally observed in patients with chronic kidney disease (CKD) and identified as a potent risk of death in epidemiological studies. Thus, the bone-kidney endocrine axis mediated by FGF23 and Klotho has emerged as a novel target of therapeutic interventions in CKD.

Klotho

The klotho gene was identified as an "aging-suppressor" gene in mice that accelerates aging when disrupted and extends life span when overexpressed. It encodes a single-pass transmembrane protein and is expressed primarily in renal tubules. The extracellular domain of Klotho protein is secreted into blood and urine by ectodomain shedding. The two forms of Klotho protein, membrane Klotho and secreted Klotho, exert distinct functions. Membrane Klotho forms a complex with fibroblast growth factor (FGF) receptors and functions as an obligate co-receptor for FGF23, a bone-derived hormone that induces phosphate excretion into urine. Mice lacking Klotho or FGF23 not only exhibit phosphate retention but also display a premature-aging syndrome, revealing an unexpected link between phosphate metabolism and aging. Secreted Klotho functions as a humoral factor that regulates activity of multiple glycoproteins on the cell surface, including ion channels and growth factor receptors such as insulin/insulin-like growth factor-1 receptors. Potential contribution of these multiple activities of Klotho protein to aging processes is discussed.