Klotho regulates retinal pigment epithelial functions and protects against oxidative stress

Regulatory factors of Nrf2 in age-related macular degeneration pathogenesis

Age-related macular degeneration (AMD) is a complicated disease that causes irreversible visual impairment. Increasing evidences pointed retinal pigment epithelia (RPE) cells as the decisive cell involved in the progress of AMD, and the function of anti-oxidant capacity of PRE plays a fundamental physiological role. Nuclear factor erythroid 2 related factor 2 (Nrf2) is a significant transcription factor in the cellular anti-oxidant system as it regulates the expression of multiple anti-oxidative genes. Its functions of protecting RPE cells against oxidative stress (OS) and ensuing physiological changes, including inflammation, mitochondrial damage and autophagy dysregulation, have already been elucidated. Understanding the roles of upstream regulators of Nrf2 could provide further insight to the OS-mediated AMD pathogenesis. For the first time, this review summarized the reported upstream regulators of Nrf2 in AMD pathogenesis, including proteins and miRNAs, and their underlying molecular mechanisms, which may help to find potential targets via regulating the Nrf2 pathway in the future research and further discuss the existing Nrf2 regulators proved to be beneficial in preventing AMD.

Differential Performance of Xanthophylls in Combination with Phenol Classes against H2O2-Induced Oxidative Stress: An In Vitro Analysis Using Retinal Pigment Epithelial Cells

SCOPE

Xanthophylls, vital for ocular defense against blue light and reactive oxygen species, are prone to oxidative degradation; however, they may be regenerated antioxidant-rich plant phenols. Despite certain in vitro evidence, clinical studies show inconsistent findings and this may be due to varying phenolic reduction potentials. Therefore, the current study aims to investigate the ocular protective effect of various plant phenols combined with xanthophyll.

METHODS AND RESULTS

Human retinal pigment epithelial cells (ARPE-19) are subjected to oxidative stress induced by hydrogen peroxide (H2O2) after xanthophyll and phenol pretreatment. Assessments include xanthophyll uptake, total antioxidant capacity, cell viability, intracellular reactive oxygen species levels, apoptosis, phagocytosis, and vascular endothelial growth factor formation. The study finds that while the combination of lutein with phenols does not show significant protective effects compared to lutein-only, zeaxanthin combined with phenols exhibits enhanced protection compared to both the zeaxanthin-only and control groups.

CONCLUSION

The research reveals the complex relationship between xanthophylls and phenols, suggesting that the advantageous effects of their combination might vary among different xanthophylls. Caution is necessary when applying molecular theories to ocular health, and this necessitates further research, serving as a basis for proposing clinical trials to evaluate the efficacy of specific xanthophyll and phenol combinations.

Inhibition of ADORA3 promotes microglial phagocytosis and alleviates chronic ischemic white matter injury

BACKGROUND

Adenosine A3 receptor (ADORA3) belongs to the adenosine receptor families and the role of ADORA3 in vascular dementia (VaD) is largely unexplored. The present study sought to determine the therapeutic role of ADORA3 antagonist in a mouse model of VaD.

METHODS

The GSE122063 dataset was selected to screen the differential expression genes and pathways between VaD patients and controls. A mouse model of bilateral carotid artery stenosis (BCAS) was established. The cognitive functions were examined by the novel object recognition test, Y maze test, and fear of conditioning test. The white matter injury (WMI) was examined by 9.4 T MRI, western blot, and immunofluorescence staining. The mechanisms of ADORA3-regulated phagocytosis by microglia were examined using qPCR, western blot, dual immunofluorescence staining, and flow cytometry.

RESULTS

The expression of ADORA3 was elevated in brain tissues of VaD patients and ADORA3 was indicated as a key gene for VaD in the GSE122063. In BCAS mice, the expression of ADORA3 was predominantly elevated in microglia in the corpus callosum. ADORA3 antagonist promotes microglial phagocytosis to myelin debris by facilitating cAMP/PKA/p-CREB pathway and thereby ameliorates WMI and cognitive impairment in BCAS mice. The therapeutic effect of ADORA3 antagonist was partially reversed by the inhibition of the cAMP/PKA pathway.

CONCLUSIONS

ADORA3 antagonist alleviates chronic ischemic WMI by modulating myelin clearance of microglia, which may be a potential therapeutic target for the treatment of VaD.

Serum α-Klotho and fibroblast growth factor 23 levels are not associated with non-proliferative diabetic retinopathy in type 1 diabetes mellitus

Diabetic retinopathy is a commonly observed cause of blindness and is a common problem in individuals with diabetes. Recent investigations have showed the capability of serum α-Klotho and FGF 23 in mitigating the effects of diabetic retinopathy. This study aimed to discover the correlation between FGF 23, α-Klotho, and diabetic retinopathy in type 1 diabetics. This case-control study included 63 diabetic patients and 66 healthy controls. Following an overnight duration of fasting, morning blood samples were taken from both the patient and the control groups. The serum concentrations of α-Klotho and FGF 23 were quantified. An experienced ophthalmologist inspected the retinopathy. All participants in this study have moderate non-proliferative retinopathy. A p value under 0.05 was considered statistically significant. The mean α-Klotho level for retinopathic diabetic patients was 501.7 ± 172.2 pg/mL and 579.6 ± 312.1 pg/mL for non-retinopathic diabetic patients. In comparison, α-Klotho level of the control group was 523.2 ± 265.4 pg/mL (p = 0.531). The mean of FGF 23 level did not demonstrate a significant difference (p = 0.259). The mean FGF 23 level were 75.7 ± 14.0 pg/mL, 74.0 ± 14.8 pg/mL and 79.3 ± 14.4 pg/mL in groups, respectively. In conclusion, there was no significant difference in FGF 23 and α-Klotho levels between type 1 diabetics with and without retinopathy when compared to the control group.

Klotho increases antioxidant defenses in astrocytes and ubiquitin-proteasome activity in neurons

Klotho is an antiaging protein, and its levels decline with age and chronic stress. The exogenous administration of Klotho can enhance cognitive performance in mice and negatively modulate the Insulin/IGF1/PI3K/AKT pathway in terms of metabolism. In humans, insulin sensitivity is a hallmark of healthy longevity. Therefore, this study aimed to determine if exogenous Klotho, when added to neuronal and astrocytic cell cultures, could reduce the phosphorylation levels of certain insulin signaling effectors and enhance antioxidant strategies in these cells. Primary cell cultures of cortical astrocytes and neurons from mice were exposed to 1 nM Klotho for 24 h, with or without glucose. Klotho decreased pAKT and mTOR levels. However, in astrocytes, Klotho increased FOXO-3a activity and catalase levels, shielding them from intermediate oxidative stress. In neurons, Klotho did not alter FOXO-3 phosphorylation levels but increased proteasome activity, maintaining lower levels of PFKFB3. This study offers new insights into the roles of Klotho in regulating energy metabolism and the redox state in the brain.

Klotho: A new therapeutic target in diabetic retinopathy?

Klotho (Kl) is considered an antiaging gene, mainly for the inhibition of the insulin-like growth factor-1 signaling. Kl exists as full-length transmembrane, which acts as co-receptor for fibroblast growth factor receptor, and in soluble forms (sKl). The sKl may exert pleiotropic effects on organs and tissues by regulating several pathways involved in the pathogenesis of diseases associated with oxidative and inflammatory state. In diabetic Patients, serum levels of Kl are significantly decreased compared to healthy subjects, and are related to duration of diabetes. In diabetic retinopathy (DR), one of the most common microvascular complications of type 2 diabetes, serum Kl levels are negatively correlated with progression of the disease. A lot of evidences showed that Kl regulates several mechanisms involved in maintaining homeostasis and functions of retinal cells, including phagocytosis, calcium signaling, secretion of vascular endothelial growth factor A (VEGF-A), maintenance of redox status, and melanin biosynthesis. Experimental data have been shown that Kl exerts positive effects on several mechanisms involved in onset and progression of DR. In particular, treatment with Kl: (1) Prevents apoptosis induced by oxidative stress in human retinal endothelial cells and in retinal pigment epithelium (RPE) cells; (2) reduces secretion of VEGF-A by RPE cells; and (3) decreases subretinal fibrosis and preserves autophagic activity. Therefore, Kl may become a novel biomarker and a good candidate for the treatment of DR.

Klotho prevents transforming growth factor-β2-induced senescent-like morphological changes in the retinal pigment epithelium

Degenerative changes of the retinal pigment epithelium (RPE) triggered by transforming growth factor-β2 (TGF-β2) and oxidative stress play a critical role in the progression of age-related macular degeneration (AMD). The expression of α-klotho, an antiaging protein, declines with age, increasing the risk factors for age-related diseases. Here, we investigated the protective effects of soluble α-klotho on TGF-β2-induced RPE degeneration. The morphological changes induced by TGF-β2, including epithelial-mesenchymal transition (EMT), were attenuated in the mouse RPE by the intravitreal injection (IVT) of α-klotho. In ARPE19 cells, EMT and morphological alterations by TGF-β2 were attenuated by co-incubation with α-klotho. TGF-β2 decreased miR-200a accompanied by zinc finger e-box binding homeobox1 (ZEB1) upregulation and EMT, all of which were prevented by α-klotho co-treatment. Inhibitor of miR-200a mimicked TGF-β2-induced morphological changes, which were recovered by ZEP1 silencing, but not by α-klotho, implying the upstream regulation of α-klotho on miR-200a-ZEP1-EMT axis. α-Klotho inhibited receptor binding of TGF-β2, Smad2/3 phosphorylation, extracellular signal-regulated protein kinase 1/2 (ERK1/2)-a mechanistic target of rapamycin (mTOR) activation and oxidative stress via NADPH oxidase 4 (NOX4) upregulation. Furthermore, α-klotho recovered the TGF-β2-induced mitochondrial activation and superoxide generation. Interestingly, TGF-β2 upregulated α-klotho expression in the RPE cells, and genetic suppression of endogenous α-klotho aggravated TGF-β2-induced oxidative stress and EMT. Lastly, α-klotho abrogated senescence-associated signaling molecules and phenotypes induced by long-term incubation with TGF-β2. Hence, our findings indicate that the antiaging α-klotho plays a protective role against EMT and degeneration of the RPE, demonstrating the therapeutic potential for age-related retinal diseases, including the dry type of AMD.

Fat mass and obesity-associated protein alleviates Aβ1-40 induced retinal pigment epithelial cells degeneration via PKA/CREB signaling pathway

Amyloid-β (Aβ) is thought to be a critical pathologic factor of retinal pigment epithelium (RPE) degeneration in age-related macular degeneration (AMD). Aβ induces inflammatory responses in RPE cells and recent studies demonstrate the N6-methyladenosine (m6A) regulatory role in RPE cell inflammation. m6A is a reversible epigenetic posttranslational modification, but its relationship with Aβ-induced RPE degeneration is yet to be thoroughly investigated. The present study explored the role and mechanism of m6A in Aβ-induced RPE degeneration model. This model was induced via intravitreally injecting oligomeric Aβ and the morphology of its retina was analyzed. One of m6A demethylases, the fat mass and obesity-associated (FTO) gene expression, was assessed. An m6A-messenger RNA (mRNA) epitranscriptomic microarray was employed for further bioinformatic analyses. It was confirmed that Aβ induced FTO upregulation within the RPE. Hypopigmentation alterations and structural disorganization were observed in Aβ-treated eyes, and inhibition of FTO exacerbated retinal degeneration and RPE impairment. Moreover, the m6A-mRNA epitranscriptomic microarray suggested that protein kinase A (PKA) was a target of FTO, and the PKA/cyclic AMP-responsive element binding (CREB) signaling pathway was involved in Aβ-induced RPE degeneration. m6A-RNA binding protein immunoprecipitation confirmed that FTO demethylated PKA within the RPE cells of Aβ-treated eyes. Altered expression of PKA and its downstream targets (CREB and brain-derived neurotrophic factor) was confirmed by quantitative reverse-transcription polymerase chain reaction and Western blot analyses. Hence, this study's findings shed light on FTO-mediated m6A modification in Aβ-induced RPE degeneration and indicate potential therapeutic targets for AMD.

The Anti-Aging Hormone Klotho Promotes Retinal Pigment Epithelium Cell Viability and Metabolism by Activating the AMPK/PGC-1α Pathway

Initially discovered by Makuto Kuro-o in 1997, Klotho is a putative aging-suppressor gene when overexpressed and accelerates aging when deleted in mice. Previously, we showed that α-Klotho regulates retinal pigment epithelium (RPE) functions and protects against oxidative stress. However, the mechanisms by which Klotho influences RPE and retinal homeostasis remain elusive. Here, by performing a series of in vitro and in vivo experiments, we demonstrate that Klotho regulates cell viability under oxidative stress, mitochondrial gene expression and activity by inducing the phosphorylation of AMPK and p38MAPK, which in turn phosphorylate and activate CREB and ATF2, respectively, triggering PGC-1α transcription. The inhibition of Klotho in human RPE cells using CRISPR-Cas9 gene editing confirmed that a lack of Klotho negatively affects RPE functions, including mitochondrial activity and cell viability. Proteomic analyses showed that myelin sheath and mitochondrial-related proteins are downregulated in the RPE/retina of Kl^-/- compared to WT mice, further supporting our biochemical observations. We conclude that Klotho acts upstream of the AMPK/PGC-1α pathway and regulates RPE/retinal resistance to oxidative stress, mitochondrial function, and gene and protein expressions. Thus, KL decline during aging could negatively impact retinal health, inducing age-related retinal degeneration.

Effect of Formaldehyde and Curcumin on Histomorphological Indices, Gene Expression Associated with Ovarian Follicular Development, and Total Antioxidant to Oxidant Levels in Wistar Rats

The present experimental study was undertaken to investigate the effect of formaldehyde (FA) and curcumin (CUR) on histomorphological features, antioxidant potential, and messenger ribonucleic acid (mRNA) levels of genes related to follicular development in FA-exposed rats. 24 Wistar female rats were divided into four study groups and given intraperitoneal injections of FA (10 mg/kg) (N = 6), FA (10 mg/kg) + CUR (100 mg/kg) (N = 6), sham (N = 6), and control (N = 6) for 14 days. Ovarian follicular histology, the related gene expression, blood factors, and anti/oxidation potentials were assessed using ovarian tissue and serum, respectively. The klotho was significantly overexpressed in the FA group compared with controls and shams. Contradictory, the factor in germ line alpha was significantly down-regulated in FA and FA + CUR groups compared to shams and controls. A significant decline was seen in the number of ovarian follicles in the FA group, independent of the developmental stage. Regarding the comparison of the FA + CUR group to other groups, a significant change was seen in the number of secondary, graafian, and atretic follicles. The FA group demonstrated significantly lower hemoglobin, red blood cell count, hematocrit, and mean corpuscular hemoglobin concentration than controls. The activity of glutathione peroxidase increased significantly in the FA group than in the controls. Despite the deleterious effects of FA on histological and molecular aspects of rat ovarian follicles, CUR does not appear to have a protective effect against the hazardous effects of this chemical. However, CUR in some cases has positive effects such as reducing follicular destruction and interstitial edema.

Klotho's impact on diabetic nephropathy and its emerging connection to diabetic retinopathy

Diabetic nephropathy (DN) is the leading cause of end-stage renal disease worldwide and is a significant burden on healthcare systems. α-klotho (klotho) is a protein known for its anti-aging properties and has been shown to delay the onset of age-related diseases. Soluble klotho is produced by cleavage of the full-length transmembrane protein by a disintegrin and metalloproteases, and it exerts various physiological effects by circulating throughout the body. In type 2 diabetes and its complications DN, a significant decrease in klotho expression has been observed. This reduction in klotho levels may indicate the progression of DN and suggest that klotho may be involved in multiple pathological mechanisms that contribute to the onset and development of DN. This article examines the potential of soluble klotho as a therapeutic agent for DN, with a focus on its ability to impact multiple pathways. These pathways include anti-inflammatory and oxidative stress, anti-fibrotic, endothelial protection, prevention of vascular calcification, regulation of metabolism, maintenance of calcium and phosphate homeostasis, and regulation of cell fate through modulation of autophagy, apoptosis, and pyroptosis pathways. Diabetic retinopathy shares similar pathological mechanisms with DN, and targeting klotho may offer new insights into the prevention and treatment of both conditions. Finally, this review assesses the potential of various drugs used in clinical practice to modulate klotho levels through different mechanisms and their potential to improve DN by impacting klotho levels.

Recombinant human klotho protects against hydrogen peroxide-mediated injury in human retinal pigment epithelial cells via the PI3K/Akt-Nrf2/HO-1 signaling pathway

Globally, age-related macular degeneration (AMD) is a common irreversible ophthalmopathy. Oxidative stress of retinal pigment epithelial cells is involved in AMD occurrence and development. Klotho is an anti-aging protein with antioxidant properties. We investigated the protective properties of Klotho on hydrogen peroxide (H₂O₂)-induced injury of retinal pigment epithelial cells (ARPE-19 cells) and its associated pathomechanisms. We found that Klotho pretreatment for 24 h could up-regulate Bcl-2 levels, decrease the cleaved-caspase-3 and Bax levels, inhibit H₂O₂-induced ARPE-19 cell apoptosis, and promote cell proliferation. Klotho pretreatment inhibited the H₂O₂-mediated elevations of reactive oxygen species (ROS) in ARPE-19 cells. It enhanced antioxidant activities of the cells and restored the glutathione peroxidase (GPX), superoxide dismutase (SOD2), catalase (CAT), as well as malondialdehyde (MDA) levels to close to the normal level. N-acetylcysteine (NAC), a reactive oxygen scavenger, could reverse the harmful effects of H₂O₂ on proliferation, apoptosis, and oxidative stress of ARPE-19 cells. Further, Klotho pretreatment enhanced Akt phosphorylation and expression as well as nuclear translocation of Nrf2 in H₂O₂-treated ARPE-19 cells. This indicates that Klotho protects cells from oxidative stress by activating phosphatidylinositol 3 kinase (PI3K)/protein kinase B (Akt)-nuclear factor E2-related factor 2 (Nrf2)/heme oxygenase 1 (HO-1) signaling pathway. Klotho is, therefore, a potential preventive or treatment option for AMD.

[Neuroprotective properties of latanoprost]

Glaucoma is the main cause of irreversible blindness in the world. Latanoprost - an ester prodrug of prostaglandin F_2α (PGF_2α) - was the first prostaglandin analogue used to treat glaucoma. The review shows that latanoprost possesses direct neuroprotective properties such as blocking the entry of calcium ions into neurons and inhibiting the action of caspase-3, inhibiting the activity of cyclooxygenase and activation of polypeptide 2B1 (OATP2B1) and Klotho protein. It is emphasized that when the drug is instilled into the eye, the concentration of the drug inside the vitreous body is twice as high as what is required to ensure the survival of retinal ganglion cells.

Tacrolimus Decreases Cognitive Function by Impairing Hippocampal Synaptic Balance: a Possible Role of Klotho

The influence of long-term tacrolimus treatment on cognitive function remains to be elucidated. Using a murine model of chronic tacrolimus neurotoxicity, we evaluated the effects of tacrolimus on cognitive function, synaptic balance, its regulating protein (Klotho), and oxidative stress in the hippocampus. Compared to vehicle-treated mice, tacrolimus-treated mice showed significantly decreased hippocampal-dependent spatial learning and memory function. Furthermore, tacrolimus caused synaptic imbalance, as demonstrated by decreased excitatory synapses and increased inhibitory synapses, and downregulated Klotho in a dose-dependent manner; the downregulation of Klotho was localized to excitatory hippocampal synapses. Moreover, tacrolimus increased oxidative stress and was associated with activation of the PI3K/AKT pathway in the hippocampus. These results indicate that tacrolimus impairs cognitive function via synaptic imbalance, and that these processes are associated with Klotho downregulation at synapses through tacrolimus-induced oxidative stress in the hippocampus.

Klotho inhibits neuronal senescence in human brain organoids

Aging is a major risk factor for many neurodegenerative diseases. Klotho (KL) is a glycosylated transmembrane protein that is expressed in the choroid plexus and neurons of the brain. KL exerts potent anti-aging effects on multiple cell types in the body but its role in human brain cells remains largely unclear. Here we show that human cortical neurons, derived from human pluripotent stem cells in 2D cultures or in cortical organoids, develop the typical hallmarks of senescent cells when maintained in vitro for prolonged periods of time, and that moderate upregulation or repression of endogenous KL expression in cortical organoids inhibits and accelerates senescence, respectively. We further demonstrate that KL expression alters the expression of senescence-associated genes including, extracellular matrix genes, and proteoglycans, and can act in a paracrine fashion to inhibit neuronal senescence. In summary, our results establish an important role for KL in the regulation of human neuronal senescence and offer new mechanistic insight into its role in human brain aging.

Klotho Protein and Cardio-Vascular System

Klotho protein affects a number of metabolic pathways essential for pathogenesis of cardio-vascular diseases and their prevention. It inhibits lipid peroxidation and inflammation, as well as prevents endothelial injury and calcification of blood vessels. Klotho decreases rigidity of blood vessels and suppresses development of the heart fibrosis. Low level of its expression is associated with a number of diseases. Cardioprotective effect of klotho is based on its ability to interact with multiple receptors and ion channels. Being a pleiotropic protein, klotho could be a useful target for therapeutic intervention in the treatment of cardio-vascular diseases. In this review we present data on pharmaceuticals that stimulate klotho expression and suggest some promising research directions.

MERTK-Mediated LC3-Associated Phagocytosis (LAP) of Apoptotic Substrates in Blood-Separated Tissues: Retina, Testis, Ovarian Follicles

Timely and efficient elimination of apoptotic substrates, continuously produced during one’s lifespan, is a vital need for all tissues of the body. This task is achieved by cells endowed with phagocytic activity. In blood-separated tissues such as the retina, the testis and the ovaries, the resident cells of epithelial origin as retinal pigmented epithelial cells (RPE), testis Sertoli cells and ovarian granulosa cells (GC) provide phagocytic cleaning of apoptotic cells and cell membranes. Disruption of this process leads to functional ablation as blindness in the retina and compromised fertility in males and females. To ensure the efficient elimination of apoptotic substrates, RPE, Sertoli cells and GC combine various mechanisms allowing maintenance of tissue homeostasis and avoiding acute inflammation, tissue disorganization and functional ablation. In tight cooperation with other phagocytosis receptors, MERTK—a member of the TAM family of receptor tyrosine kinases (RTK)—plays a pivotal role in apoptotic substrate cleaning from the retina, the testis and the ovaries through unconventional autophagy-assisted phagocytosis process LAP (LC3-associated phagocytosis). In this review, we focus on the interplay between TAM RTKs, autophagy-related proteins, LAP, and Toll-like receptors (TLR), as well as the regulatory mechanisms allowing these components to sustain tissue homeostasis and prevent functional ablation of the retina, the testis and the ovaries.

The HIF-1α/p53/miRNA-34a/Klotho axis in retinal pigment epithelial cells promotes subretinal fibrosis and exacerbates choroidal neovascularization

Wet age‐related macular degeneration (wAMD), characterized by choroidal neovascularization (CNV), is a leading cause of irreversible vision loss among elderly people in developed nations. Subretinal fibrosis, mediated by epithelial‐mesenchymal transition (EMT) of retinal pigment epithelium (RPE) cells, leads to unsuccessful anti‐vascular endothelial growth factor (VEGF) agent treatments in CNV patients. Under hypoxic conditions, hypoxia‐inducible factor‐1α (HIF‐1α) increases the stability and activation of p53, which activates microRNA‐34a (miRNA‐34a) transcription to promote fibrosis. Additionally, Klotho is a target gene of miRNA‐34a that inhibits fibrosis. This study aimed to explore the role of the HIF‐1α/p53/miRNA‐34a/Klotho axis in subretinal fibrosis and CNV. Hypoxia‐induced HIF‐1α promoted p53 stability, phosphorylation and nuclear translocation in ARPE‐19 cells (a human RPE cell line). HIF‐1α‐dependent p53 activation up‐regulated miRNA‐34a expression in ARPE‐19 cells following hypoxia. Moreover, hypoxia‐induced p53‐dependent miRNA‐34a inhibited the expression of Klotho in ARPE‐19 cells. Additionally, the HIF‐1α/p53/miRNA‐34a/Klotho axis facilitated hypoxia‐induced EMT in ARPE‐19 cells. In vivo, blockade of the HIF‐1α/p53/miRNA‐34a/Klotho axis alleviated the formation of mouse laser‐induced CNV and subretinal fibrosis. In short, the HIF‐1α/p53/miRNA‐34a/Klotho axis in RPE cells promoted subretinal fibrosis, thus aggravating the formation of CNV.

Klotho Levels are Decreased and Associated with Enhanced Oxidative Stress and Inflammation in the Aqueous Humor in Patients with Exudative Age-related Macular Degeneration

PURPOSE

To evaluate anti-aging protein klotho levels in the aqueous humor and its association with oxidative stress and inflammation in patients with age-related macular degeneration (AMD).

METHODS

Levels of klotho, oxidative, and antioxidative stress markers, and proinflammatory and anti-inflammatory markers in the aqueous humor from 28 patients with exudative AMD and 35 age-matched controls were measured.

RESULTS

Patients with AMD had lower levels of klotho, which were negatively correlated with macular lesion size. Patients with AMD also exhibited increased levels of 8-hydroxy-2'-deoxyguanosine (8-OHdG) and interleukin (IL)-6 but not tumor necrosis factor‑α, and decreased levels of total antioxidant status (TAS) and IL-10. Moreover, levels of klotho were negatively correlated with levels of 8-OHdG and IL-6, but positively correlated with levels of TSA and IL-10.

CONCLUSION

Klotho levels in the aqueous humor are decreased and associated with oxidative stress and inflammation in patients with exudative AMD.

Anti-aging Klotho Protects SH-SY5Y Cells Against Amyloid β1-42 Neurotoxicity: Involvement of Wnt1/pCREB/Nrf2/HO-1 Signaling

Alzheimer's disease (AD) is considered a prevalent neurological disorder with a neurodegenerative nature in elderly people. Oxidative stress and neuroinflammation due to amyloid β (Aβ) peptides are strongly involved in AD pathogenesis. Klotho is an anti-aging protein with multiple protective effects that its deficiency is involved in development of age-related disorders. In this study, we investigated the beneficial effect of Klotho pretreatment at different concentrations of 0.5, 1, and 2 nM against Aβ1-42 toxicity at a concentration of 20 μM in human SH-SY5Y neuroblastoma cells. Our findings showed that Klotho could significantly and partially restore cell viability and decrease reactive oxygen species (known as ROS) and improve superoxide dismutase activity (SOD) in addition to reduction of caspase 3 activity and DNA fragmentation following Aβ1-42 challenge. In addition, exogenous Klotho also reduced inflammatory biomarkers consisting of nuclear factor-kB (NF-kB), interleukin-1β (IL-1β), and tumor necrosis factor-α (TNF-α) in Aβ-exposed cells. Besides, Klotho caused downregulation of Wnt1 level, upregulation of phosphorylated cyclic AMP response element binding (pCREB), and mRNA levels of nuclear factor erythroid 2-related factor 2 (Nrf2) and heme oxygenase 1 (HO-1) with no significant alteration of epsilon isoform of protein kinase C (PKCε) after Aβ toxicity. In summary, Klotho could alleviate apoptosis, oxidative stress, and inflammation in human neuroblastoma cells after Aβ challenge and its beneficial effect is partially exerted through appropriate modulation of Wnt1/pCREB/Nrf2/HO-1 signaling.

Klotho-HIV and Oxidative Stress: The Role of Klotho in Cardiovascular Disease Under HIV Infection-A Review

Combined antiretroviral therapy has improved quality and life expectancy of people living with human immunodeficiency virus (HIV). However, this therapy increases oxidative stress (OS), which in turn causes alterations in lipid and carbon metabolism, kidney disease, liver cirrhosis, and increased risk of cardiovascular disease. The Klotho gene has been implicated in cardiovascular risk increase. Klotho protein expression at X level decreases the risk of heart disease. HIV-positive people usually present low plasma levels of Klotho; thus, contributing to some extent to an increase in cardiovascular risk for these types of patients, mostly by favoring atherosclerosis. Therefore, our aim is to provide an overview of the effect of OS on Klotho protein and its consequent cardiometabolic alterations in HIV-positive patients on antiretroviral therapy.

[Long-term use of latanoprost in the treatment of glaucoma]

Glaucoma is the main cause of irreversible blindness in the world. Latanoprost - an ester prodrug of prostaglandin F2α (PGF2α) - was the first prostaglandin analogue used in the treatment of glaucoma. The present review shows that latanoprost is the most balanced prostaglandin analogue in terms of efficacy-safety. Its use improves the quality of life of glaucoma patients, provides reliable IOP reduction, has high patient compliance, and helps with the long-term preservation of visual functions. The review also reveals the possibility of long-term (more than five years) use of the drug, as well as effective combined treatment using latanoprost and beta-blockers, considers the pediatric use of latanoprost, and discusses its neuroprotective properties.

Klotho Pathways, Myelination Disorders, Neurodegenerative Diseases, and Epigenetic Drugs

In this review we outline a rationale for identifying neuroprotectants aimed at inducing endogenous Klotho activity and expression, which is epigenetic action, by definition. Such an approach should promote remyelination and/or stimulate myelin repair by acting on mitochondrial function, thereby heralding a life-saving path forward for patients suffering from neuroinflammatory diseases. Disorders of myelin in the nervous system damage the transmission of signals, resulting in loss of vision, motion, sensation, and other functions depending on the affected nerves, currently with no effective treatment. Klotho genes and their single-pass transmembrane Klotho proteins are powerful governors of the threads of life and death, true to the origin of their name, Fates, in Greek mythology. Among its many important functions, Klotho is an obligatory co-receptor that binds, activates, and/or potentiates critical fibroblast growth factor activity. Since the discovery of Klotho a little over two decades ago, it has become ever more apparent that when Klotho pathways go awry, oxidative stress and mitochondrial dysfunction take over, and age-related chronic disorders are likely to follow. The physiological consequences can be wide ranging, potentially wreaking havoc on the brain, eye, kidney, muscle, and more. Central nervous system disorders, neurodegenerative in nature, and especially those affecting the myelin sheath, represent worthy targets for advancing therapies that act upon Klotho pathways. Current drugs for these diseases, even therapeutics that are disease modifying rather than treating only the symptoms, leave much room for improvement. It is thus no wonder that this topic has caught the attention of biomedical researchers around the world.

Role of Klotho in Chronic Calcineurin Inhibitor Nephropathy

Calcineurin inhibitors (CNIs) are the most popular immunosuppressants in organ transplantation, but nephrotoxicity is a major concern. The common mechanism underlying chronic CNI nephropathy is oxidative stress, and the process of chronic CNI nephropathy is similar to that of aging. Current studies provide evidence that antiaging Klotho protein plays an important role in protecting against oxidative stress, and its signaling is a target for preventing oxidative stress-induced aging process. In this review, we focus on the association between Klotho and oxidative stress and the protective mechanism of action of Klotho against oxidative stress in chronic CNI nephropathy. In addition, we discuss the delivery strategy for Klotho in CNI-induced nephropathy.

Klotho Ameliorates Cellular Inflammation via Suppression of Cytokine Release and Upregulation of miR-29a in the PBMCs of Diagnosed Alzheimer's Disease Patients

Alzheimer's disease (AD) is the most common neurodegenerative disorder characterized by neural inflammation and oxidative stress. In the current study, the protective effects of klotho and linagliptin treatment on human peripheral blood mononuclear cells (PBMCs) of AD patients and healthy controls (HCs) are assessed through measurement of inflammatory cytokines, signaling proteins, and miRNA expression. Sixteen diagnosed AD patients and sixteen HCs were enrolled in the study. Blood samples were obtained and PBMCs were isolated. PBMCs were treated with klotho at different concentrations (0.5, 1, and 2 nM) and linagliptin (50 μM). The concentration of interleukin-1β (IL-1β), interleukin 6 (IL-6), tumor necrosis factor-alpha (TNF-α), epsilon isoform of protein kinase C (PKCε), phosphorylated cyclic AMP response element binding (pCREB), and Wnt1 were measured by ELISA. The expression of miR-29a and miR-195 was detected by real-time PCR. The results showed that klotho significantly reduced IL-1β, IL-6, and TNF-α levels in both groups of the experiment. Linagliptin also remarkably reduced TNF-α levels in the AD group. Moreover, klotho caused the downregulation of Wnt1 in the PBMCs of both groups and the upregulation of the pCREB in HCs. Meanwhile, klotho induced miR-29a expression in the PBMCs of HCs, while miR-29a expression was induced in the AD group by klotho and linagliptin. The current findings revealed that klotho alleviates inflammation in human PBMCs, probably through the suppression of inflammatory cytokines and the upregulation of miR-29a, and part of its beneficial effect is mediated through appropriate modulation of the Wnt1/pCREB signaling cascade. In addition, linagliptin exerts protective effects by reducing TNF-α and inducing miR-29a expression in PBMCs.

Organic dust, causing both oxidative stress and Nrf2 activation, is phagocytized by bronchial epithelial cells

Inhalation of organic dust (OD) from swine confinement facilities leads to pulmonary inflammation, airway hyperresponsiveness, and oxidative stress. In mice, pretreatment with a hydroxyl radical scavenger prevents airway inflammation and airway hyperresponsiveness (AHR) induced by OD exposure. We sought to determine a mechanism by which OD could induce oxidative stress in bronchial epithelial cells. Human bronchial epithelial cells (BEAS-2B or NHBE) were treated with various concentrations of OD, followed by evaluation of intracellular oxidative stress using 2',7'-dichlorofluorescein diacetate (DCFDA). After stimulation with OD, gene expression of antioxidant genes was assessed by real-time quantitative PCR followed by quantification of Nrf2 nuclear translocation using a luciferase reporter assay. Phagocytic markers (CD36 and CD68) were analyzed by FACS. Cells were treated with an actin inhibitor, cytochalasin D, before OD exposure and evaluated for Nrf2 nuclear translocation and DCFDA. Mice were pretreated with sulforaphane, the Nrf2 activator, before OD exposure and evaluated for pulmonary inflammation and airway reactivity. OD induced a time- and concentration-dependent increase in DCFDA. mRNA expression levels of Nrf2-dependent genes and Nrf2 nuclear translocation were increased after OD exposure. OD exposure increased the expression of CD68 and CD36. Cytochalasin D prevented oxidative stress and Nrf2 nuclear translocation after OD. Pretreatment with sulforaphane prevented OD-induced inflammation and AHR while increasing the uptake of OD in bronchial epithelial cells. Bronchial epithelial cells can phagocytose OD, resulting in an increase in endogenous oxidative stress. Nrf2-dependent mechanisms mediate the antioxidant response to OD.

Matrine attenuates high-fat diet-induced in vivo and ox-LDL-induced in vitro vascular injury by regulating the PKCα/eNOS and PI3K/Akt/eNOS pathways

Lipid metabolism disorders lead to vascular endothelial injury. Matrine is an alkaloid that has been used to improve obesity and diabetes and for the treatment of hepatitis B. However, its effect on lipid metabolism disorders and vascular injury is unclear. Here, we investigated the effect of matrine on high‐fat diet fed mice and oxidized low‐density lipoprotein (ox‐LDL)‐induced human umbilical vein endothelial cells (HUVECs). Computational virtual docking analyses, phosphoinositide 3‐kinase (PI3K) and protein kinase C‐α (PKCα) inhibitors were used to localize matrine in vascular injuries. The results showed that matrine‐treated mice were more resistant to abnormal lipid metabolism and inflammation than vehicle‐treated mice and exhibited significantly alleviated ox‐LDL‐stimulated dysfunction of HUVECs, restored diminished nitric oxide release, decreased reactive oxygen species generation and increased expression phosphorylation of AKT‐Ser473 and endothelial nitric oxide synthase (eNOS)‐Ser1177. Matrine not only up‐regulates eNOS‐Ser1177 but also down‐regulates eNOS‐Thr495, a PKCα‐controlled negative regulator of eNOS. Using computational virtual docking analyses and biochemical assays, matrine was also shown to influence eNOS/NO via PKCα inhibition. Moreover, the protective effects of matrine were significantly abolished by the simultaneous application of PKCα and the PI3K inhibitor. Matrine may thus be potentially employed as a novel therapeutic strategy against high‐fat diet‐induced vascular injury.

Stem Cell Derived Retinal Pigment Epithelium: The Role of Pigmentation as Maturation Marker and Gene Expression Profile Comparison with Human Endogenous Retinal Pigment Epithelium

In age-related macular degeneration (AMD) the retinal pigment epithelium (RPE) deteriorates, leading to photoreceptor decay and severe vision loss. New therapeutic strategies aim at RPE replacement by transplantation of pluripotent stem cell (PSC)-derived RPE. Several protocols to generate RPE have been developed where appearance of pigmentation is commonly used as indicator of RPE differentiation and maturation. It is, however, unclear how different pigmentation stages reflect developmental stages and functionality of PSC-derived RPE cells. We generated human embryonic stem cell-derived RPE (hESC-RPE) cells and investigated their gene expression profiles at early pigmentation (EP) and late pigmentation (LP) stages. In addition, we compared the hESC-RPE samples with human endogenous RPE. We used a common reference design microarray (44 K). Our analysis showed that maturing hESC-RPE, upon acquiring pigmentation, expresses markers specific for human RPE. Interestingly, our analysis revealed that EP and LP hESC-RPE do not differ much in gene expression. Our data further showed that pigmented hESC-RPE has a significant lower expression than human endogenous RPE in the visual cycle and oxidative stress pathways. In contrast, we observed a significantly higher expression of pathways related to the process adhesion-to-polarity model that is typical of developing epithelial cells. We conclude that, in vitro, the first appearance of pigmentation hallmarks differentiated RPE. However, further increase in pigmentation does not result in much significant gene expression changes and does not add important RPE functionalities. Consequently, our results suggest that the time span for obtaining differentiated hESC-RPE cells, that are suitable for transplantation, may be greatly reduced.

Antioxidant effects of compound walnut oil capsule in mice aging model induced by D-galactose

Background

Many plant original foods have been shown beneficial effects in humans. In the previous work, we have developed a compound capsule which contains major constituents of walnut oil and grape seed extract.

Objective

To investigate the antioxidant effects of the Compound Walnut Oil Capsule (WOC) in aging model induced by D-gal.

Design

70 C57BL/6J mice were randomly divided into seven groups. Mice in normal group received daily subcutaneous injection of saline while the control group, WOC groups, Vitamin C (VC) group and pure walnut oil group received daily subcutaneous injection of D-galactose (D-gal) for 8 weeks. Total antioxidant capacity (T-AOC), super dismutase (SOD), glutathione peroxidase (GSH-Px) and malondialdehyde (MDA) in serum, liver and brain were determined. The expression of Heme Oxygenase (HO-1), iNOS and Klotho in liver and brain were obtained.

Results

WOC could improve the pathologic lesions caused by oxidative stress and significantly enhance the T-AOC, increase the activities of SOD, GSH-Px and decrease the contents of MDA in serum, liver and brain. Also, the WOC could obviously up-regulate the expression of HO-1 and Klotho and down-regulate the expression of iNOS.

Conclusion

WOC can be used as an anti-aging food for its effectively eliminating free radicals, enhancing the antioxidant capacity and alleviating the damages of oxidative stress.

Changes in expression of klotho affect physiological processes, diseases, and cancer

Klotho (KL) encodes a single-pass transmembrane protein and is predominantly expressed in the kidney, parathyroid glands, and choroid plexus. Genetic studies on the KL gene have revealed that DNA hypermethylation is one of the major risk factors for aging, diseases, and cancer. Besides, KL exerts anti-inflammatory and anti-tumor effects by regulating signaling pathways and the expression of target genes. KL participates in modulation of the insulin/insulin-like growth factor-1 (IGF-1) signaling, which induces the growth hormone (GH) secretion. Accordingly, KL mutant mice display multiple aging-like phenotypes, which are ameliorated by overexpression of KL. Therefore, KL is an important contributor to lifespan. KL is further identified as a regulator of calcium (Ca²⁺) channel-dependent cell physiological processes. KL has been also shown to induce cancer cell apoptosis, thus, it is considered as a potential tumor suppressor. Our recent studies have indicated that KL modulates an influx of Ca²⁺ from the extracellular space, leading to a change in CCL21-dependent migration in dendritic cells (DCs). Interestingly, the regulation of the expression of KL was mediated through a phosphoinositide 3-kinase (PI3K) pathway in DCs. Moreover, downregulating of KL expression by using siRNA knockdown technique, we observed that the expression of Ca²⁺ channels including Orai3, but not Orai1, Orai2, TRPV5 and TRPV6 was significantly reduced in KL-silenced as compared to control BMDCs. Clearly, additional research is required to define the role of KL in the regulation of organismic and cellular functions through the PI3K signaling and the expression of the Ca²⁺ channels.

Klotho and Endothelin-1 in Pseudoexfoliation Syndrome and Glaucoma

PURPOSE

Klotho is a newly discovered protein that presumably has an important role in the aging process. The goal of this research is to compare the levels of Klotho and Endothelin-1 (ET-1) in the serum and aqueous humor of patients with pseudoexfoliation syndrome (PES) and pseudoexfoliative glaucoma (PEG).

PATIENTS AND METHODS

Aqueous humor and serum samples were obtained at the time of cataract surgery from 15 patients with PES, 15 patients with PEG, and 15 control patients. All of the samples were analyzed using enzyme-linked immunosorbent assay to evaluate the levels of ET-1 and Klotho protein.

RESULT

Aqueous and serum levels of Klotho in PES patients (49.02±10.97, 56.32±10.25 ng/mL) and PEG patients (34.53±4.87, 50.49±2.63 ng/mL) were lower than in control patients (56.31±7.68, 65.06±12.32 ng/mL). Both aqueous and serum levels of Klotho in the PEG group were lower than in the PES group (P=0.001). Mean aqueous and serum levels of ET-1 in the PES (1.28±0.09, 1.65±0.75 pg/mL) and the PEG groups (1.45±0.07, 1.58±0.58 pg/mL) were significantly higher than that measured in the control group (1.17±0.09, 1.16±0.34 pg/mL). Aqueous levels of ET-1 in the PEG group were higher than the PES group (P=0.04), but there were no significant difference in serum levels of ET-1 between the PES and the PEG groups (P=0.83).

CONCLUSIONS

Aqueous and serum levels of Klotho decreased both in PES and PEG patients, and this decrease in the PEG group was more significant. In contrast, aqueous and serum levels of ET-1 increased in the PES and the PEG patients, and the increase in the aqueous level of ET-1 in PEG patients was more significant.

Tissue expression and source of circulating αKlotho

αKlotho (Klotho), a type I transmembrane protein and a coreceptor for Fibroblast Growth Factor-23, was initially thought to be expressed only in a limited number of tissues, most importantly the kidney, parathyroid gland and choroid plexus. Emerging data may suggest a more ubiquitous Klotho expression pattern which has prompted reevaluation of the restricted Klotho paradigm. Herein we systematically review the evidence for Klotho expression in various tissues and cell types in humans and other mammals, and discuss potential reasons behind existing conflicting data. Based on current literature and tissue expression atlases, we propose a classification of tissues into high, intermediate and low/absent Klotho expression. The functional relevance of Klotho in organs with low expression levels remain uncertain and there is currently limited data on a role for membrane-bound Klotho outside the kidney. Finally, we review the evidence for the tissue source of soluble Klotho, and conclude that the kidney is likely to be the principal source of circulating Klotho in physiology.

The role of the anti-ageing protein Klotho in vascular physiology and pathophysiology

Klotho is an anti-ageing protein that functions in many pathways that govern ageing, like regulation of phosphate homeostasis, insulin signaling, and Wnt signaling. Klotho expression levels and levels in blood decline during ageing. The vascular phenotype of Klotho deficiency features medial calcification, intima hyperplasia, endothelial dysfunction, arterial stiffening, hypertension, and impaired angiogenesis and vasculogenesis, with characteristics similar to aged human arteries. Klotho-deficient phenotypes can be prevented and rescued by Klotho gene expression or protein supplementation. High phosphate levels are likely to be directly pathogenic and are a prerequisite for medial calcification, but more important determinants are pathways that regulate cellular senescence, suggesting that deficiency of Klotho renders cells susceptible to phosphate toxicity. Overexpression of Klotho is shown to ameliorate medial calcification, endothelial dysfunction, and hypertension. Endogenous vascular Klotho expression is a controversial subject and, currently, no compelling evidence exists that supports the existence of vascular membrane-bound Klotho expression, as expressed in kidney. In vitro, Klotho has been shown to decrease oxidative stress and apoptosis in both SMCs and ECs, to reduce SMC calcification, to maintain the contractile SMC phenotype, and to prevent μ-calpain overactivation in ECs. Klotho has many protective effects with regard to the vasculature and constitutes a very promising therapeutic target. The purpose of this review is to explore the etiology of the vascular phenotype of Klotho deficiency and the therapeutic potential of Klotho in vascular disease.

Klotho ameliorates oxidized low density lipoprotein (ox-LDL)-induced oxidative stress via regulating LOX-1 and PI3K/Akt/eNOS pathways

Background

Atherosclerosis is a common cardiovascular disease that causes myocardial infarction, heart failure, and stroke. Increased oxidized low density lipoprotein (ox-LDL) in the sub-endothelium is the characteristic origin of atherogenesis. Klotho, an anti-aging protein, has been reported to protect against atherosclerosis and ameliorate endothelial dysfunction in vivo. The aim of this study is to investigatethe anti-oxidative activity of Klothoin ox-LDL-treated human umbilical vein endothelial cells (HUVECs).

Methods

After pre-treatment with 200 pMKlotho for 1 h, HUVECs were stimulated with 50 μg/ml ox-LDL for 24 h. Reactive oxygen species (ROS) and superoxide dismutase (SOD) levels were analyzed in the cells. Nitric oxide (NO) concertation was measured in the medium supernatant. Related proteins or genes were detected with Western blot or real time PCR, respectively, in the cell lysates.

Results

Initially, oxidative damage in HUVECs was established by adding 50 μg/mL ox-LDL, which resulted in decreased cellular viability, SOD/Cu/Zn-SOD and endothelial NO synthase (eNOS) expression and NO production, as well as increased malondialdehyde (MDA) levels, ROS production, inducible NO synthase (iNOS), phosphatidyl inositol-3 kinase (PI3K), protein kinase B (Akt), gp91 phox, and lectin-like ox-LDL receptor (LOX-1) expression in HUVECs. Pre-incubation with recombinant Klotho (200 pM) significantly prevented all of these alterations. These results suggest that Klotho can attenuate ox-LDL-induced oxidative stress in HUVECs through upregulating oxidative scavengers (SOD and NO) viaactivating the PI3K/Akt/eNOS pathway and depressing LOX-1expression.

Conclusions

These results suggest that Klotho has a potential therapeutic effect on attenuating endothelial dysfunction and ameliorating atherosclerosis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12944-017-0447-0) contains supplementary material, which is available to authorized users.

Appropriately differentiated ARPE-19 cells regain phenotype and gene expression profiles similar to those of native RPE cells

PURPOSE

The RPE cell line ARPE-19 provides a dependable and widely used alternative to native RPE. However, replication of the native RPE phenotype becomes more difficult because these cells lose their specialized phenotype after multiple passages. Compounding this problem is the widespread use of ARPE-19 cells in an undifferentiated state to attempt to model RPE functions. We wished to determine whether suitable culture conditions and differentiation could restore the RPE-appropriate expression of genes and proteins to ARPE-19, along with a functional and morphological phenotype resembling native RPE. We compared the transcriptome of ARPE-19 cells kept in long-term culture with those of primary and other human RPE cells to assess the former's inherent plasticity relative to the latter.

METHODS

ARPE-19 cells at passages 9 to 12 grown in DMEM containing high glucose and pyruvate with 1% fetal bovine serum were differentiated for up to 4 months. Immunocytochemistry was performed on ARPE-19 cells grown on filters. Total RNA extracted from ARPE-19 cells cultured for either 4 days or 4 months was used for RNA sequencing (RNA-Seq) analysis using a 2 × 50 bp paired end protocol. The RNA-Seq data were analyzed to identify the affected pathways and recognize shared ontological classification among differentially expressed genes. RPE-specific mRNAs and miRNAs were assessed with quantitative real-time (RT)-PCR, and proteins with western blotting.

RESULTS

ARPE-19 cells grown for 4 months developed the classic native RPE phenotype with heavy pigmentation. RPE-expressed genes, including RPE65, RDH5, and RDH10, as well as miR-204/211, were greatly increased in the ARPE-19 cells maintained at confluence for 4 months. The RNA-Seq analysis provided a comprehensive view of the relative abundance and differential expression of the genes in the differentiated ARPE-19 cells. Of the 16,757 genes with detectable signals, nearly 1,681 genes were upregulated, and 1,629 genes were downregulated with a fold change of 2.5 or more differences between 4 months and 4 days of culture. Gene Ontology analysis showed that the upregulated genes were associated with visual cycle, phagocytosis, pigment synthesis, cell differentiation, and RPE-related transcription factors. The majority of the downregulated genes play a role in cell cycle and proliferation.

CONCLUSIONS

The ARPE-19 cells cultured for 4 months developed a phenotype characteristic of native RPE and expressed proteins, mRNAs, and miRNAs characteristic of the RPE. Comparison of the ARPE-19 RNA-Seq data set with that of primary human fetal RPE, embryonic stem cell-derived RPE, and native RPE revealed an important overall similar expression ratio among all the models and native tissue. However, none of the cultured models reached the absolute values in the native tissue. The results of this study demonstrate that low-passage ARPE-19 cells can express genes specific to native human RPE cells when appropriately cultured and differentiated.

The neuroprotective effect of latanoprost acts via klotho-mediated suppression of calpain activation after optic nerve transection

Latanoprost was first developed for use in glaucoma therapy as an ocular hypotensive agent targeting the prostaglandin F2α (FP) receptor. Subsequently, latanoprost showed a neuroprotective effect, an additional pharmacological action. However, although it is well-known that latanoprost exerts an ocular hypotensive effect via the FP receptor, it is not known whether this is also true of its neuroprotective effect. Klotho was firstly identified as the gene linked to the suppression of aging phenotype: the defect of klotho gene in mice results aging phenotype such as hypokinesis, arteriosclerosis, and short lifespan. After that, the function of klotho was also reported to maintain calcium homeostasis and to exert a neuroprotective effect in various models of neurodegenerative disease. However, the function of klotho in eyes including retina is still poorly understood. Here, we show that klotho is a key factor underlying the neuroprotective effect of latanoprost during post-axotomy retinal ganglion cell (RGC) degeneration. Importantly, a quantitative RT-PCR gene expression analysis of klotho in sorted rat retinal cells revealed that the highest expression level of klotho in the retina was in the RGCs. Latanoprost acid, the biologically active form of latanoprost, inhibits post-traumatic calpain activation and concomitantly facilitates the expression and shedding of klotho in axotomized RGCs. This expression profile is a good match with the localization, not of the FP receptor, but of organic anion transporting polypeptide 2B1, known as a prostaglandin transporter, in the ocular tissue. Furthermore, an organic anion transporting polypeptide 2B1 inhibitor suppressed latanoprost acid-mediated klotho shedding ex vivo, whereas an FP receptor antagonist did not. The klotho fragments shed from the RGCs reduced the intracellular level of reactive oxygen species, and a specific klotho inhibitor accelerated and increased RGC death after axotomy. We conclude that the shed klotho fragments might contribute to the attenuation of axonal injury-induced calpain activation and oxidative stress, thereby protecting RGCs from post-traumatic neuronal degeneration.

Dysfunctional autophagy in RPE, a contributing factor in age-related macular degeneration

Age-related macular degeneration (AMD) is a devastating neurodegenerative disease and a major cause of blindness in the developed world. Owing to its complexity and the lack of an adequate human model that recapitulates key aspects of the disease, the molecular mechanisms of AMD pathogenesis remain poorly understood. Here we show that cultured human retinal pigment epithelium (RPE) from AMD donors (AMD RPE) are functionally impaired and exhibit distinct phenotypes compared with RPE cultured from normal donors (normal RPE). Accumulation of lipid droplets and glycogen granules, disintegration of mitochondria, and an increase in autophagosomes were observed in AMD RPE cultures. Compared with normal RPE, AMD RPE exhibit increased susceptibility to oxidative stress, produce higher levels of reactive oxygen species (ROS) under stress conditions, and showed reduced mitochondrial activity. Measurement of the ratio of LC3-II/ LC3-I, revealed impaired autophagy in AMD RPE as compared with normal RPE. Autophagic flux was also reduced in AMD RPE as compared with normal RPE, as shown by inability of AMD RPE to downregulate p62 levels during starvation. Impaired autophagic pathways were further shown by analyzing late autophagic vesicles; immunostaining with lysosome-associated membrane protein 1 (LAMP-1) antibody revealed enlarged and annular LAMP-1-positive organelles in AMD RPE as opposed to smaller discrete puncta observed in normal RPE. Our study provides insights into AMD cellular and molecular mechanisms, proposes dysfunctional autophagy as an underlying mechanism contributing to the pathophysiology of the disease, and opens up new avenues for development of novel treatment strategies.

γKlotho is a novel marker and cell survival factor in a subset of triple negative breast cancers

Over the last decade, breast cancer mortality has declined. However, triple negative breast cancer (TNBC) remains a challenging problem mostly due to early recurrence and lack of molecularly driven treatments. There is a critical need to identify subgroups of TNBC with common molecular features that can be therapeutically targeted. Here we show that in contrast to Klotho and βKlotho, the third member of the Klotho protein family, γKlotho, is overexpressed in more than 60% of TNBCs and correlates with poorer disease progression. Furthermore, we find that γKlotho is expressed in a subset of TNBC cell lines promoting cell growth. Importantly, we demonstrate that in these cells γKlotho is necessary for cell survival and that its depletion leads to constitutive ERK activation, cell cycle arrest and apoptosis. Interestingly, we observe increased oxidative stress in γKlotho-depleted cells suggesting that γKlotho enables cancer cells to cope with an oxidative environment and that cells become dependent on its expression to maintain this survival advantage. These findings indicate that γKlotho might be a potential marker for patients that would benefit from treatments that alter oxidative stress and constitutes a novel drug target for a subset of TN breast cancers.

New Pathogenic Concepts and Therapeutic Approaches to Oxidative Stress in Chronic Kidney Disease

In chronic kidney disease inflammatory processes and stimulation of immune cells result in overproduction of free radicals. In combination with a reduced antioxidant capacity this causes oxidative stress. This review focuses on current pathogenic concepts of oxidative stress for the decline of kidney function and development of cardiovascular complications. We discuss the impact of mitochondrial alterations and dysfunction, a pathogenic role for hyperuricemia, and disturbances of vitamin D metabolism and signal transduction. Recent antioxidant therapy options including the use of vitamin D and pharmacologic therapies for hyperuricemia are discussed. Finally, we review some new therapy options in diabetic nephropathy including antidiabetic agents (noninsulin dependent), plant antioxidants, and food components as alternative antioxidant therapies.

NADPH oxidases: key modulators in aging and age-related cardiovascular diseases?

Reactive oxygen species (ROS) and oxidative stress have long been linked to aging and diseases prominent in the elderly such as hypertension, atherosclerosis, diabetes and atrial fibrillation (AF). NADPH oxidases (Nox) are a major source of ROS in the vasculature and are key players in mediating redox signalling under physiological and pathophysiological conditions. In this review, we focus on the Nox-mediated ROS signalling pathways involved in the regulation of 'longevity genes' and recapitulate their role in age-associated vascular changes and in the development of age-related cardiovascular diseases (CVDs). This review is predicated on burgeoning knowledge that Nox-derived ROS propagate tightly regulated yet varied signalling pathways, which, at the cellular level, may lead to diminished repair, the aging process and predisposition to CVDs. In addition, we briefly describe emerging Nox therapies and their potential in improving the health of the elderly population.

Retinal pigment epithelial cell multinucleation in the aging eye - a mechanism to repair damage and maintain homoeostasis

Retinal pigment epithelial (RPE) cells are central to retinal health and homoeostasis. Dysfunction or death of RPE cells underlies many age-related retinal degenerative disorders particularly age-related macular degeneration. During aging RPE cells decline in number, suggesting an age-dependent cell loss. RPE cells are considered to be postmitotic, and how they repair damage during aging remains poorly defined. We show that RPE cells increase in size and become multinucleate during aging in C57BL/6J mice. Multinucleation appeared not to be due to cell fusion, but to incomplete cell division, that is failure of cytokinesis. Interestingly, the phagocytic activity of multinucleate RPE cells was not different from that of mononuclear RPE cells. Furthermore, exposure of RPE cells in vitro to photoreceptor outer segment (POS), particularly oxidized POS, dose-dependently promoted multinucleation and suppressed cell proliferation. Both failure of cytokinesis and suppression of proliferation required contact with POS. Exposure to POS also induced reactive oxygen species and DNA oxidation in RPE cells. We propose that RPE cells have the potential to proliferate in vivo and to repair defects in the monolayer. We further propose that the conventionally accepted 'postmitotic' status of RPE cells is due to a modified form of contact inhibition mediated by POS and that RPE cells are released from this state when contact with POS is lost. This is seen in long-standing rhegmatogenous retinal detachment as overtly proliferating RPE cells (proliferative vitreoretinopathy) and more subtly as multinucleation during normal aging. Age-related oxidative stress may promote failure of cytokinesis and multinucleation in RPE cells.

Targeting the cAMP and Transforming Growth Factor-β Pathway Increases Proliferation to Promote Re-Epithelialization of Human Stem Cell-Derived Retinal Pigment Epithelium

Retinal pigment epithelium (RPE) cell integrity is critical to the maintenance of retinal function. Many retinopathies such as age-related macular degeneration (AMD) are caused by the degeneration or malfunction of the RPE cell layer. Replacement of diseased RPE with healthy, stem cell-derived RPE is a potential therapeutic strategy for treating AMD. Human embryonic stem cells (hESCs) differentiated into RPE progeny have the potential to provide an unlimited supply of cells for transplantation, but challenges around scalability and efficiency of the differentiation process still remain. Using hESC-derived RPE as a cellular model, we sought to understand mechanisms that could be modulated to increase RPE yield after differentiation. We show that RPE epithelialization is a density-dependent process, and cells seeded at low density fail to epithelialize. We demonstrate that activation of the cAMP pathway increases proliferation of dissociated RPE in culture, in part through inhibition of transforming growth factor-β (TGF-β) signaling. This results in enhanced uptake of epithelial identity, even in cultures seeded at low density. In line with these findings, targeted manipulation of the TGF-β pathway with small molecules produces an increase in efficiency of RPE re-epithelialization. Taken together, these data highlight mechanisms that promote epithelial fate acquisition in stem cell-derived RPE. Modulation of these pathways has the potential to favorably impact scalability and clinical translation of hESC-derived RPE as a cell therapy.

SIGNIFICANCE

Stem cell-derived retinal pigment epithelium (RPE) is currently being evaluated as a cell-replacement therapy for macular degeneration. This work shows that the process of generating RPE in vitro is regulated by the cAMP and transforming growth factor-β signaling pathway. Modulation of these pathways by small molecules, as identified by phenotypic screening, leads to an increased efficiency of generating RPE cells with a higher yield. This can have a potential impact on manufacturing transplantation-ready cells at large scale and is advantageous for clinical studies using this approach in the future.

Klotho Is a Neuroprotective and Cognition-Enhancing Protein

In this chapter, we will describe what has been learned about Klotho and its potential functions in the brain. Klotho is localized in the choroid plexus and, to a lesser extent, in hippocampal neurons. Cognitive decline is a common issue in human aging affecting over 50% of the population. This cognitive decline can also be seen in animal models such as the Rhesus monkey. A long-term study undertaken by our lab demonstrated that normal brain aging in rhesus monkeys and other animal models is associated with a significant downregulation of Klotho expression. This observation substantiates data from other laboratories that have reported that loss of Klotho accelerates the development of aging-like phenotypes, including cognitive deficits, whereas Klotho overexpression extends life span and enhances cognition in mice and humans. Klotho is a type 1 transmembrane pleiotropic protein predominantly expressed in kidney and brain and shed by ADAM 10 and 17 into the blood and cerebral spinal fluid, respectively. While the renal functions of Klotho are well known, its roles in the brain remain to be fully elucidated. We recently demonstrated that Klotho protects hippocampal neurons from amyloid and glutamate toxicity via the activation of an antioxidant enzymatic system suggesting Klotho is a neuroprotective protein. Furthermore, Klotho is necessary for oligodendrocyte maturation and myelin integrity. Through its diverse roles in the brain, Klotho has become a new therapeutic target for neurodegenerative diseases such as Alzheimer's disease and demyelinating diseases like multiple sclerosis. Discovery of small molecule Klotho enhancers may lead to novel treatments for these incurable disorders.

Atrasentan increased the expression of klotho by mediating miR-199b-5p and prevented renal tubular injury in diabetic nephropathy

Atrasentan is a promising therapy for treating diabetic nephropathy (DN). Here we evaluated whether atrasentan down-regulated the miR-199b-5p expression, thereby increasing klotho and preventing renal tubular injury in DN. One-hundred patients with type 2 diabetes mellitus (T2DM) and 40 healthy subjects were included. A DN mice model was established by an injection of streptozotocin (STZ). Human renal proximal tubular epithelial HK-2 cells were exposed to high glucose (20 mmol/L). Treated the mice and HK-2 cells with atrasentan, and we then investigated whether and how miR-199b-5p and Klotho were involved in preventing renal tubular injury in DN. In patients, the serum miR-199b-5p level increased and the klotho concentration decreased in accordance with elevated albuminuria. Atrasentan down-regulated miR-199b-5p and up-regulated klotho of the DN mice and HK-2 cells exposed to high glucose. High glucose promoted the binding of histone H3 to the miR-199b-5p promoter, and atrasentan canceled this effect. MiR-199b-5p targeted the 3′ UTR of klotho. Overexpression of miR-199b-5p canceled the effects of atrasentan on klotho expression and apoptosis of renal tubular cells in both in vivo and in vitro. The increased serum klotho, mediated by miR-199b-5p, is a possible mechanism by which atrasentan prevents renal tubular injury in DN.

Soluble extracellular Klotho decreases sensitivity to cigarette smoke induced cell death in human lung epithelial cells

Chronic obstructive pulmonary disease (COPD) is currently the third leading cause of death in the US and is associated with an abnormal inflammatory response to cigarette smoke (CS). Exposure to CS induces oxidative stress and can result in cellular senescence in the lung. Cellular senescence can then lead to decreased proliferation of epithelial cells, the destruction of alveolar structure and pulmonary emphysema. The anti-aging gene, klotho, encodes a membrane bound protein that has been shown to be a key regulator of oxidative stress and cellular senescence. In this study the role of Klotho (KL) with regard to oxidative stress and cellular senescence was investigated in human pulmonary epithelial cells exposed to cigarette smoke. Individual clones that stably overexpress Klotho were generated through retroviral transfection and geneticin selection. Klotho overexpression was confirmed through RT-qPCR, Western blotting and ELISA. Compared to control cells, constitutive Klotho overexpression resulted in decreased sensitivity to cigarette smoke induced cell death in vitro via a reduction of reactive oxygen species and a decrease in the expression of p21. Our results suggest that increasing Klotho level in pulmonary epithelial cells may be a promising strategy to reduce cellular senescence and mitigate the risk for the development of COPD.

Phosphodiesterase 4D acts downstream of Neuropilin to control Hedgehog signal transduction and the growth of medulloblastoma

Alterations in Hedgehog (Hh) signaling lead to birth defects and cancers including medulloblastoma, the most common pediatric brain tumor. Although inhibitors targeting the membrane protein Smoothened suppress Hh signaling, acquired drug resistance and tumor relapse call for additional therapeutic targets. Here we show that phosphodiesterase 4D (PDE4D) acts downstream of Neuropilins to control Hh transduction and medulloblastoma growth. PDE4D interacts directly with Neuropilins, positive regulators of Hh pathway. The Neuropilin ligand Semaphorin3 enhances this interaction, promoting PDE4D translocation to the plasma membrane and cAMP degradation. The consequent inhibition of protein kinase A (PKA) enhances Hh transduction. In the developing cerebellum, genetic removal of Neuropilins reduces Hh signaling activity and suppresses proliferation of granule neuron precursors. In mouse medulloblastoma allografts, PDE4D inhibitors suppress Hh transduction and inhibit tumor growth. Our findings reveal a new regulatory mechanism of Hh transduction, and highlight PDE4D as a promising target to treat Hh-related tumors.

DOI:http://dx.doi.org/10.7554/eLife.07068.001

A communication system in cells called the Hedgehog signaling pathway plays an essential role in the formation of tissues and organs in animal embryos. The activity of the pathway is carefully controlled during development and if Hedgehog signaling is disrupted it can lead to developmental defects and particular types of cancer. Some of these cancers can be treated with a drug called vismodegib, which targets a particular molecule in the Hedgehog signaling pathway. However, tumor cells can become resistant to this drug, so researchers are hoping to find new therapies that target other aspects of the signaling pathway.

Hedgehog signaling promotes the division of brain cells called granule neuron precursor cells (or GNP cells for short). If the signaling pathway is over-active it can trigger the GNP cells to divide more than they should. This can lead to medulloblastoma, which is the most common type of brain tumor that affects children. Proteins called Neuropilins—which bind to molecules known as Semaphorins—promote Hedgehog signaling and the formation of medulloblastoma, but it was not clear how this works.

Here Ge et al. studied the role of Neuropilin in cultured cells and in the cerebellum of mice. The experiments show that Semaphorin 3 promotes the accumulation of an enzyme called PDE4D at the cell membrane. PDE4D interacts with Neuropilin and blocks the activity of another enzyme that normally inhibits Hedgehog signaling. In mice that lack Neuropilin and Semophorin 3, the GNP cells are less able to divide, which leads to abnormal development of the cerebellum.

Further experiments show that drugs that target PDE4D inhibit both the Hedgehog pathway and the growth of tumors that are resistant to vismodegib treatment. Ge et al.'s findings uncover a new way in which Hedgehog signaling is regulated and highlight a potential new strategy for treating medulloblastoma and other similar tumors. Current PDE4D inhibitors are associated with severe side effects, so the next challenge is to develop new drugs that have fewer side effects.

DOI:http://dx.doi.org/10.7554/eLife.07068.002

Axl as a mediator of cellular growth and survival

The control of cellular growth and proliferation is key to the maintenance of homeostasis. Survival, proliferation, and arrest are regulated, in part, by Growth Arrest Specific 6 (Gas6) through binding to members of the TAM receptor tyrosine kinase family. Activation of the TAM receptors leads to downstream signaling through common kinases, but the exact mechanism within each cellular context varies and remains to be completely elucidated. Deregulation of the TAM family, due to its central role in mediating cellular proliferation, has been implicated in multiple diseases. Axl was cloned as the first TAM receptor in a search for genes involved in the progression of chronic to acute-phase leukemia, and has since been established as playing a critical role in the progression of cancer. The oncogenic nature of Axl is demonstrated through its activation of signaling pathways involved in proliferation, migration, inhibition of apoptosis, and therapeutic resistance. Despite its recent discovery, significant progress has been made in the development of effective clinical therapeutics targeting Axl. In order to accurately define the role of Axl in normal and diseased processes, it must be analyzed in a cell type-specific context.