ABSTRACTaKlotho is a multifunctional protein highly expressed in the kidney. Soluble aKlotho is released through cleavage of the extracellular domain from membrane aKlotho by secretases to function as an endocrine/paracrine substance. The role of the kidney in circulating aKlotho production and handling is incompletely understood, however. Here, we found higher aKlotho concentration in suprarenal compared with infrarenal inferior vena cava in both rats and humans. In rats, serum aKlotho concentration dropped precipitously after bilateral nephrectomy or upon treatment with inhibitors of aKlotho extracellular domain shedding. Furthermore, the serum half-life of exogenous aKlotho in anephric rats was four-to five-fold longer than that in normal rats, and exogenously injected labeled recombinant aKlotho was detected in the kidney and in urine of rats. Both in vivo (micropuncture) and in vitro (proximal tubule cell line) studies showed that aKlotho traffics from the basal to the apical side of the proximal tubule via transcytosis. Thus, we conclude that the kidney has dual roles in aKlotho homeostasis, producing and releasing aKlotho into the circulation and clearing aKlotho from the blood into the urinary lumen.

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.

Polymeric nanoparticles (NPs) are promising carriers of biological agents to lung due to advantages including biocompatibility, ease of surface modification, localized action and reduced systemic toxicity. However, there have been no studies extensively characterizing and comparing the behavior of polymeric NPs for pulmonary protein/DNA delivery both in vitro and in vivo. We screened six polymeric NPs: gelatin, chitosan, alginate, poly lactic-co-glycolic acid (PLGA), PLGA-chitosan, and PLGA-polyethylene glycol (PEG), for inhalational protein/ DNA delivery. All NPs except PLGA-PEG and alginate were <300 nm in size with bi-phasic core compound release profile. Gelatin, PLGA NPs and PLGA-PEG NPs remained stable in deionized water, serum, saline and simulated lung fluid (Gamble’s solution) over 5 days. PLGA-based NPs and natural polymer NPs exhibited highest cytocompatibility and dose-dependent in vitro uptake respectively by human alveolar type-1 epithelial cells. Based on these profiles, gelatin and PLGA NPs were used to encapsulate a) plasmid DNA encoding yellow fluorescent protein (YFP) or b) rhodamine-conjugated erythropoietin (EPO) for inhalational delivery to rats. Following a single inhalation, widespread pulmonary EPO distribution persisted for up to 10 days while increasing YFP expression was observed for at least 7 days for both NPs. The overall results support both PLGA and gelatin NPs as promising carriers for pulmonary protein/DNA delivery.

nary dysfunction develops in type 2 diabetes mellitus (T2DM) in direct correlation with glycemia and is exacerbated by obesity; however, the associated structural derangement has not been quantified. We studied lungs from obese diabetic (fa/fa) male Zucker diabetic fatty (ZDF) rats at 4, 12, and 36 wk of age, before and after onset of T2DM, compared with lean nondiabetic (ϩ/ϩ) rats. Surfactant proteins A and C (SP-A and SP-C) immunoexpression in lung tissue was quantified at ages 14 and 18 wk, after the onset of T2DM. In fa/fa animals, lung volume was normal despite obesity. Numerous lipid droplets were visible within alveolar interstitium, lipofibroblasts, and macrophages, particularly in subpleural regions. Total triglyceride content was 136% higher. By 12 wk, septum volume was 21% higher, and alveolar duct volume was 36% lower. Capillary basement membrane was 29% thicker. Volume of lamellar bodies was 45% higher. By age 36 wk, volumes of interstitial collagen fibers, cells, and matrix were respectively 32, 25, and 80% higher, and capillary blood volume was 18% lower. ZDF rats exhibited a strain-specific increase in resistance of the air-blood diffusion barrier with age, which was exaggerated in fa/fa lungs compared with ϩ/ϩ lungs. In fa/fa lungs, SP-A and SP-C expression were elevated at age 14 -18 wk; the normal age-related increase in SP-A expression was accelerated, whereas SP-C expression declined with age. Thus lungs from obese T2DM animals develop many qualitatively similar changes as in type 1 diabetes mellitus but with extensive lipid deposition, altered alveolar type 2 cell ultrastructure, and surfactant protein expression patterns that suggest additive effects of hyperglycemia and lipotoxicity. diabetes mellitus; lung morphometry; lipid deposition; collagen; surfactant-associated proteins THE LUNG IS A RECOGNIZED TARGET of diabetic microangiopathy, manifested by modest restrictions of ventilatory capacity, lung volume, and diffusing capacity (12,24,41). Because alveolar microvascular reserves are extensive, pulmonary dysfunction is usually not the presenting complaint in diabetes mellitus, although modest pulmonary dysfunction may become overtly debilitating under physiological stress (e.g., high-altitude exposure or exercise) or following the loss of alveolar microvascular reserves brought on by aging or disease (23,24). In patients with type 1 diabetes mellitus (T1DM), we have found a significant restrictive defect associated with decreased lung diffusing capacity for carbon monoxide (DL CO ) at a given pulmonary blood flow, mainly due to a reduction of membrane conductance compared with age-matched nondiabetic healthy subjects (41, 52). Structural abnormalities observed at autopsy in diabetic human lungs include thickened epithelial and capillary basement membranes (72, 77), alveolar septal destruction, and enlarged air spaces (32). In streptozotocin-induced T1DM, volumes of basal laminae, extracellular matrix, and interstitial connective tissue are increased in diabetic lungs compared with contr...

αKlotho is a circulating protein that originates predominantly from the kidney and exerts cytoprotective effects in distant sites. We previously showed in rodents that the lung is particularly vulnerable to αKlotho deficiency. Because acute lung injury is a common and serious complication of acute kidney injury (AKI), we hypothesized that αKlotho deficiency in AKI contributes to lung injury. To test the hypothesis, we created AKI by renal artery ischemia-reperfusion in rats and observed the development of alveolar interstitial edema and increased pulmonary oxidative damage to DNA, protein, and lipids. Administration of αKlotho-containing conditioned media 6 h post-AKI did not alter plasma creatinine but improved recovery of endogenous αKlotho production 3 days post-AKI, reduced lung edema and oxidative damage, and increased endogenous antioxidative capacity in the lung. Intravenously injected αKlotho rapidly exits alveolar capillaries as a macromolecule, suggesting transcytosis and direct access to the epithelium. To explore the epithelial action of αKlotho, we simulated oxidative stress in vitro by adding hydrogen peroxide to cultured A549 lung epithelial cells. Purified recombinant αKlotho directly protected cells at 20 pM with half-maximal effects at 40-50 pM, which is compatible with circulating αKlotho levels. Addition of recombinant αKlotho activated an antioxidant response element reporter and increased the levels of target proteins of the nuclear factor erythroid-derived 2 related factor system. In summary, αKlotho deficiency in AKI contributes to acute lung injury by reducing endogenous antioxidative capacity and increasing oxidative damage in the lung. αKlotho replacement partially reversed these abnormalities and mitigated pulmonary complications in AKI.