Retinitis Pigmentosa: over-expression of anti-ageing protein Klotho in degenerating photoreceptors

Absence of the Klotho Function Causes Cornea Degeneration with Specific Features Resembling Fuchs Endothelial Corneal Dystrophy and Bullous Keratopathy

The Klotho loss-of-function mutation is known to cause accelerated senescence in many organs, but its effects on the cornea have not been published. The present study aims to investigate the effects of the Klotho null mutation on cornea degeneration and to characterize the pathological features. Mouse corneas of Klotho homozygous, heterozygous, and wild-type mice at 8 weeks of age for both genders were subject to pathological and immunohistological examinations. The results show an irregular topography on the corneal surface with a Klotho null mutation. Histological examinations revealed a reduced corneal epithelial cell density, endothelial cell-shedding, and decreased cornea stromal layer thickness in the absence of the Klotho function. Furthermore, guttae formation and the desquamation of wing cells were significantly increased, which was comparable to the characteristics of Fuchs endothelial corneal dystrophy and bullous keratopathy. The mechanism analysis showed multi-fold abnormalities, including oxidative stress-induced cornea epithelium apoptosis and inflammation, extracellular matrix remodeling in the stroma, and a disruption of epithelial repair, presumably through the epithelial-mesenchymal transition. In conclusion, cornea degeneration was observed in the Klotho loss-of-function mutant mice. These pathological features support the use of Klotho mutant mice for investigating age-related cornea anomalies, including Fuchs endothelial corneal dystrophy, bullous keratopathy, and dry eye diseases.

[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.

Klotho: An Elephant in Aging Research

The year 2017 marked the 20th anniversary of the first publication describing Klotho. This single protein was and is remarkable in that its absence in mice conferred an accelerated aging, or progeroid, phenotype with a dramatically shortened life span. On the other hand, genetic overexpression extended both health span and life span by an impressive 30%. Not only has Klotho deficiency been linked to a number of debilitating age-related illnesses but many subsequent reports have lent credence to the idea that Klotho can compress the period of morbidity and extend the life span of both model organisms and humans. This suggests that Klotho functions as an integrator of organ systems, making it both a promising tool for advancing our understanding of the biology of aging and an intriguing target for interventional studies. In this review, we highlight advances in our understanding of Klotho as well as key challenges that have somewhat limited our view, and thus translational potential, of this potent protein.

Phenotypic characterization of P23H and S334ter rhodopsin transgenic rat models of inherited retinal degeneration

We produced 8 lines of transgenic (Tg) rats expressing one of two different rhodopsin mutations in albino Sprague-Dawley (SD) rats. Three lines were generated with a proline to histidine substitution at codon 23 (P23H), the most common autosomal dominant form of retinitis pigmentosa in the United States. Five lines were generated with a termination codon at position 334 (S334ter), resulting in a C-terminal truncated opsin protein lacking the last 15 amino acid residues and containing all of the phosphorylation sites involved in rhodopsin deactivation, as well as the terminal QVAPA residues important for rhodopsin deactivation and trafficking. The rates of photoreceptor (PR) degeneration in these models vary in proportion to the ratio of mutant to wild-type rhodopsin. The models have been widely studied, but many aspects of their phenotypes have not been described. Here we present a comprehensive study of the 8 Tg lines, including the time course of PR degeneration from the onset to one year of age, retinal structure by light and electron microscopy (EM), hemispheric asymmetry and gradients of rod and cone degeneration, rhodopsin content, gene dosage effect, rapid activation and invasion of the outer retina by presumptive microglia, rod outer segment disc shedding and phagocytosis by the retinal pigmented epithelium (RPE), and retinal function by the electroretinogram (ERG). The biphasic nature of PR cell death was noted, as was the lack of an injury-induced protective response in the rat models. EM analysis revealed the accumulation of submicron vesicular structures in the interphotoreceptor space during the peak period of PR outer segment degeneration in the S334ter lines. This is likely due to the elimination of the trafficking consensus domain as seen before as with other rhodopsin mutants lacking the C-terminal QVAPA. The 8 rhodopsin Tg lines have been, and will continue to be, extremely useful models for the experimental study of inherited retinal degenerations.

The KL-VS polymorphism of KLOTHO gene is protective against retinopathy incidence in patients with type 1 diabetes

BACKGROUND AND AIMS

KLOTHO is an anti-ageing circulating hormone involved in insulin signaling, inflammation and vascular homeostasis through its protective effects on the endothelium and antioxidant actions. The common functional "KL-VS" variant of the KLOTHO gene is reproducibly associated with longevity in humans. Large number of studies have evaluated close relationship between KLOTHO protein and diabetes but the association between KL-VS variant and retinopathy in type 1 diabetes mellitus (T1D) is unknown. Therefore, in the present study we examined the association between the KL-VS polymorphism and the risk of diabetic retinopathy (DR) in patients with T1D.

METHODS

We examined 400 patients with T1D and 350 healthy age-matched controls. The analysis concerned KL-VS polymorphism along with the levels of serum inflammatory (CRP, TNF-α) and anti-inflammatory (IL-10) markers, pro-angiogenic (angiogenin) and anti-angiogenic interferon gamma-induced protein 10 (IP-10) factors as well as adhesion molecules (ICAM-1, ICAM-3).

RESULTS

We did not find significant association between T1D and KL-VS alleles. However, we observed that the incidence of KL-VS genotype is lower in a group with retinopathy in comparison to diabetic patients without this complication. Moreover, we established that KL-VS carriers had the lowest levels of inflammatory markers, pro-angiogenic factors and adhesion molecules. Simultaneously, the KL-VS carriers had increased serum levels of anti-inflammatory and anti-angiogenic cytokines than holders bearing wild type genotype.

CONCLUSIONS

In conclusion, the findings of our studies suggest that the functional KL-VS variant of the KLOTHO gene protects against the development of retinopathy in patients with T1D.

Comparison of Different Cell Culture Media in the Model of the Isolated and Superfused Bovine Retina: Investigating the Limits of More Physiological Perfusion Solutions

PURPOSE

The isolated superfused retina is a standardized tool in ophthalmological research. However, stable electroretinogram (ERG) responses can only be obtained for around eight hours; therefore, limiting its use. The aim of this study was to evaluate the short-term potential of different cell culture media and to promote long-term testing based on the results obtained.

MATERIALS AND METHODS

For the experimental procedure bovine retinae were prepared and perfused with the standard Sickel solution and an ERG was performed. After recording stable a- or b-waves, different media (Dulbecco's Modified Eagle's Medium (DMEM), MACS, and Neurobasal) were superfused for 45 minutes. ERG recovery was monitored overall for 75 minutes. Analysis of the mRNA expression of Thy-1, GFAP, Bax/Bcl-2-ratio, Rhodopsin, and Opsin via qRT-PCR was performed directly after ERG recording on the same retina.

RESULTS

None of the tested media had a negative effect on a-wave amplitudes, although b-wave amplitudes decreased (DMEM) or increased (MACS and Neurobasal) compared to the standard solution (Sickel) after 45 minutes of exposure. However, after 75 minutes of wash-out, no difference to the standard solution alone could be observed. Exposure to different media either had no effect or decreased the Opsin and Rhodopsin mRNA levels. Thy-1 expression was strongly diminished in DMEM and MACS (by 2-3-fold), whereas incubation in Neurobasal medium led to a slight increase compared to incubation with the standard solution. Furthermore, the Bax/Bcl-2 ratio indicated an anti-apoptotic effect (Bax/Bcl-2 = 0.16; p < 0.05) for Neurobasal.

CONCLUSION

Neurobasal medium displayed the best electrophysiological properties in the short-term and may be applicable for stable long-term escalation testing.

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 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.

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.

Differential expression and regulation of Klotho by paricalcitol in the kidney, parathyroid, and aorta of uremic rats

Klotho plays an important role in the pathogenesis of cardiovascular disease in chronic kidney disease (CKD). Klotho is highly expressed in the kidney and parathyroid glands, but its presence in the vasculature is debated. Renal Klotho is decreased in CKD, but the effect of uremia on Klotho in other tissues is not defined. The effect of vitamin D receptor activator therapy in CKD on expression of Klotho in various tissues is also in debate. In uremic rats (surgical 5/6^th nephrectomy model), we compared 3-months of treatment with and without paricalcitol on Klotho immunostaining in the kidney, parathyroid glands and aorta. With uremia, Klotho was unchanged in the parathyroid, significantly decreased in the kidney (66%) and the intimal-medial area of the aorta (69%), and significantly increased in the adventitial area of the aorta (67%) compared with controls. Paricalcitol prevented the decrease in Klotho in the kidney, increased expression in the parathyroid (31%), had no effect in the aortic media, but blunted the increase of Klotho in aortic adventitia. We propose that fibroblasts are responsible for expression of Klotho in the adventitia. In hyperplastic human parathyroid tissue from uremic patients, Klotho was higher in oxyphil compared with chief cells. Thus, under our conditions of moderate CKD and mild-to-moderate hyperphosphatemia in rats, the differential expression of Klotho and its regulation by paricalcitol in uremia is tissue-dependent.

Klotho regulates retinal pigment epithelial functions and protects against oxidative stress

The retinal pigment epithelium (RPE) is a highly specialized CNS tissue that plays crucial roles in retinal homeostasis. Age-related morphological changes in the RPE have been associated with retinal degenerative disorders; our understanding of the underlying molecular mechanisms, however, remains incomplete. Here we report on a key role of Klotho (Kl), an aging-suppressor gene, in retinal health and RPE physiology. Kl(-/-) mice show RPE and photoreceptor degeneration, reduced pigment synthesis in the RPE, and impaired phagocytosis of the outer segment of the photoreceptors. Klotho protein (KL) is expressed in primary cultured human RPE, and regulates pigment synthesis by increasing the expression of MITF (microphthalmia transcription factor) and TYR (tyrosinase), two pivotal genes in melanogenesis. Importantly, KL increases phagocytosis in cultured RPE by inducing gene expression of MERTK/AXL/TYRO3. These effects of KL are mediated through cAMP-PKA-dependent phosphorylation of transcription factor CREB. In cultured human RPE, KL increases the l-3,4-dihydroxyphenylalanine synthesis and inhibits vascular endothelial growth factor (VEGF) secretion from basal membrane by inhibiting IGF-1 signaling and VEGF receptor 2 phosphorylation. KL also regulates the expression of stress-related genes in RPE, lowers the production of reactive oxygen species, and thereby, protects RPE from oxidative stress. Together, our results demonstrate a critical function for KL in mouse retinal health in vivo, and a protective role toward human RPE cells in vitro. We conclude that KL is an important regulator of RPE homeostasis, and propose that an age-dependent decline of KL expression may contribute to RPE degeneration and retinal pathology.

The age-regulating protein klotho is vital to sustain retinal function

PURPOSE

To determine whether the age-regulating protein klotho was expressed in the retina and determine whether the absence of klotho affected retinal function.

METHODS

Immunohistochemistry and qPCR of klotho knockout and wild-type mice were used to detect klotho expression in retina. Immunohistochemistry was used to probe for differences in expression of proteins important in synaptic function, retinal structure, and ionic flux. Electroretinography (ERG) was conducted on animals across lifespan to determine whether decreased klotho expression affects retinal function.

RESULTS

Klotho mRNA and protein were detected in the wild-type mouse retina, with protein present in all nuclear layers. Over the short lifespan of the knockout mouse (∼8 weeks), no overt photoreceptor cell loss was observed, however, function was progressively impaired. At 3 weeks of age neither protein expression levels (synaptophysin and glutamic acid decarboxylase [GAD67]) nor retinal function were distinguishable from wild-type controls. However, by 7 weeks of age expression of synaptophysin, glial fibrillary acidic protein (GFAP), and transient receptor potential cation channel subfamily member 1 (TRPM1) decreased while GAD67, post synaptic density 95 (PSD95), and wheat germ agglutinin staining, representative of glycoprotein sialic acid residues, were increased relative to wild-type mice. Accompanying these changes, profound functional deficits were observed as both ERG a-wave and b-wave amplitudes compared with wild-type controls.

CONCLUSIONS

Klotho is expressed in the retina and is important for healthy retinal function. Although the mechanisms for the observed abnormalities are not known, they are consistent with the accelerating aging phenotype seen in other tissues.