Klotho regulates CA1 hippocampal synaptic plasticity

The role of P2X4R in regulating CA1 hippocampal synaptic impairment in LPS-induced depression

AIM

To study the role of the P2X4 receptor (P2X4R) in regulating hippocampal synaptic impairment in lipopolysaccharide (LPS)-induced depression.

METHODS

A rat model of depression was established by LPS injection. P2X4R expression was inhibited by 5-(3-bromophenyl)-1, 3-dihydro-2H-benzofuro[3,2-e]-1,4-diazepin-2-one (5-BDBD). Depressive symptoms were identified through behavioral tests. P2X4R and cytokine mRNA levels were measured by qRT-PCR, while synaptic protein levels were measured by Western blotting. Synaptic ultrastructure was assessed by transmission electron microscopy, and the colocalization of brain-derived neurotrophic factor (BDNF) with microglia, astrocytes, and neurons was determined by double immunofluorescence staining.

RESULTS

Injection of 5-BDBD alleviated LPS-induced depressive symptoms. LPS injection significantly increased the mRNA levels of P2X4R and proinflammatory cytokines in the hippocampus, especially in the CA1 region. The levels of synaptic proteins (BDNF, PSD95, and synapsin I) in the CA1 region were significantly lower than those in the other two regions of the hippocampus, and the synaptic ultrastructure in the hippocampal CA1 region was significantly altered. As expected, the Pearson's correlation R and the overlap coefficient R for the hippocampal colocalization of IBA-1 with BDNF were decreased, and 5-BDBD injection reversed these trends. Injection of 5-BDBD increased hippocampal BDNF mRNA expression.

CONCLUSIONS

P2X4R may induce synaptic impairment in the hippocampal CA1 region by influencing microglial BDNF expression in the context of LPS-induced depression in rats.

Potential Effects of Low-Level Toluene Exposure on the Nervous System of Mothers and Infants

In day-to-day living, individuals are exposed to various environmentally hazardous substances that have been associated with diverse diseases. Exposure to air pollutants can occur during breathing, posing a considerable risk to those with environmental health vulnerabilities. Among vulnerable individuals, maternal exposure can negatively impact the mother and child in utero. The developing fetus is particularly vulnerable to environmentally hazardous substances, with potentially greater implications. Among air pollutants, toluene is neurotoxic, and its effects have been widely explored. However, the impact of low-level toluene exposure in daily life remains unclear. Herein, we evaluated 194 mothers and infants from the Growing children's health and Evaluation of Environment (GREEN) cohort to determine the possible effects of early-life toluene exposure on the nervous system. Using Omics experiments, the effects of toluene were confirmed based on epigenetic changes and altered mRNA expression. Various epigenetic changes were identified, with upregulated expression potentially contributing to diseases such as glioblastoma and Alzheimer's, and downregulated expression being associated with structural neuronal abnormalities. These findings were detected in both maternal and infant groups, suggesting that maternal exposure to environmental hazardous substances can negatively impact the fetus. Our findings will facilitate the establishment of environmental health policies, including the management of environmentally hazardous substances for vulnerable groups.

The Importance of α-Klotho in Depression and Cognitive Impairment and Its Connection to Glutamate Neurotransmission-An Up-to-Date Review

Depression is a serious neuropsychiatric disease affecting an increasing number of people worldwide. Cognitive deficits (including inattention, poor memory, and decision-making difficulties) are common in the clinical picture of depression. Cognitive impairment has been hypothesized to be one of the most important components of major depressive disorder (MDD; referred to as clinical depression), although typical cognitive symptoms are less frequent in people with depression than in people with schizophrenia or bipolar disorder (BD; sometimes referred to as manic-depressive disorder). The importance of α-Klotho in the aging process has been well-documented. Growing evidence points to the role of α-Klotho in regulating other biological functions, including responses to oxidative stress and the modulation of synaptic plasticity. It has been proven that a Klotho deficit may contribute to the development of various nervous system pathologies, such as behavioral disorders or neurodegeneration. Given the growing evidence of the role of α-Klotho in depression and cognitive impairment, it is assumed that this protein may be a molecular link between them. Here, we provide a research review of the role of α-Klotho in depression and cognitive impairment. Furthermore, we propose potential mechanisms (related to oxidative stress and glutamatergic transmission) that may be important in α-Klotho-mediated regulation of mental and cognitive function.

Differential regulation of hippocampal transcriptome by circulating estrogen

Estrogen (E2) modulates the synaptic structure and plasticity in the hippocampus. Previous studies showed that E2 fluctuations during various phases of the menstrual cycle produce subtle neurosynaptic changes that impact women's behavior, emotion, and cognitive functions. In this study, we explored the transcriptome of the hippocampus via RNA-seq (RNA-sequencing) between proestrus (PE) and diestrus (DE) stages in young female rats to determine the effect of E2 of PE and DE stages on hippocampal gene expression. We identified 238 genes (at 1.5-fold-change selection criteria, FDR adjusted p-value < 0.05) as differentially expressed genes (DEGs) that responded to E2 between PE and DE stages. Functional analysis based on Gene Ontology (GO) revealed that a higher E2 level corresponded to an increase in gene transcription among most of the DEGs, suggesting biological mechanisms operating differentially in the hippocampus of female rats between PE and DE stages in the estrus cycle; while analysis with Kyoto Encyclopedia of Genes and Genomes database (KEGG) found that the DEGs involving neuroactive ligand-receptor interaction, antigen processing, cell adhesion molecules, and presentation were upregulated in PE stage, whereas DEGs in pathways relating to bile secretion, coagulation cascades, osteoclast differentiation, cysteine and methionine metabolism were upregulated in DE stage of the estrus cycle. The high-fold expression of DEGs was confirmed by a follow-up quantitative real-time PCR. Our findings in this current study have provided fundamental information for further dissection of neuro-molecular mechanisms in the hippocampus in response to E2 fluctuation and its relationship with disorders.

JAK2/STAT3 Signaling Pathway and Klotho Gene in Cadmium-induced Neurotoxicity In Vitro and In Vivo

Cadmium (Cd), a common heavy metal in the environment, is associated with cognitive impairment. In the present study, we carried out a preliminary inquiry to explore whether Cd causes neurotoxicity by regulating the JAK2/STAT3 signaling pathway and affecting the expression of klotho genes in vivo and in vitro, providing clues for the mechanism of Cd-induced cognitive dysfunction. The rat samples were injected with Cd chloride solution for 14 weeks, and the memory function of the rats was detected. Different concentrations of Cd and JAK2/STAT3 signaling pathway inhibitors were used to treat PC12 cells and thus detect the apoptosis rate. The protein expression levels of JAK2, p-JAK2, STAT3, p-STAT3, and klotho in rat and PC12 cell were detected by ELISA and Western blot, respectively. With the increase in exposure dose, the memory function of rats was severely impaired. The expression of p-JAK2 and p-STAT3 proteins was significantly up-regulated, whereas that of klotho was significantly down-regulated both in vivo and in vitro (p < 0.05). In comparison with the high-dose Cd exposure group, after adding tyrphostin AG490 (AG490), the apoptosis rate of PC12 cells increased, whereas the phosphorylation levels of JAK2 and STAT3 in the cells decreased significantly (p < 0.05). Cd exposure may cause neurotoxicity by regulating the JAK2/STAT3 signaling pathway and down-regulating klotho protein expression, leading to cognitive dysfunction.

The fibroblast growth factor system in cognitive disorders and dementia

Cognitive impairment is the core precursor to dementia and other cognitive disorders. Current hypotheses suggest that they share a common pathological basis, such as inflammation, restricted neurogenesis, neuroendocrine disorders, and the destruction of neurovascular units. Fibroblast growth factors (FGFs) are cell growth factors that play essential roles in various pathophysiological processes via paracrine or autocrine pathways. This system consists of FGFs and their receptors (FGFRs), which may hold tremendous potential to become a new biological marker in the diagnosis of dementia and other cognitive disorders, and serve as a potential target for drug development against dementia and cognitive function impairment. Here, we review the available evidence detailing the relevant pathways mediated by multiple FGFs and FGFRs, and recent studies examining their role in the pathogenesis and treatment of cognitive disorders and dementia.

Klotho Regulated by Estrogen Plays a Key Role in Sex Differences in Stress Resilience in Rats

Klotho (KL) is a glycosyl hydrolase and aging-suppressor gene. Stress is a risk factor for depression and anxiety, which are highly comorbid with each other. The aim of this study is to determine whether KL is regulated by estrogen and plays an important role in sex differences in stress resilience. Our results showed that KL is regulated by estrogen in rat hippocampal neurons in vivo and in vitro and is essential for the estrogen-mediated increase in the number of presynaptic vesicular glutamate transporter 1 (Vglut1)-positive clusters on the dendrites of hippocampal neurons. The role of KL in sex differences in stress response was examined in rats using 3-week chronic unpredictable mild stress (CUMS). CUMS produced a deficit in spatial learning and memory, anhedonic-like behaviors, and anxiety-like behaviors in male but not female rats, which was accompanied by a reduction in KL protein levels in the hippocampus of male but not female rats. This demonstrated the resilience of female rats to CUMS. Interestingly, the knockdown of KL protein levels in the rat hippocampus of both sexes caused a decrease in stress resilience in both sexes, especially in female rats. These results suggest that the regulation of KL by estrogen plays an important role in estrogen-mediated synapse formation and that KL plays a critical role in the sex differences in cognitive deficit, anhedonic-like behaviors, and anxiety-like behaviors induced by chronic stress in rats, highlighting an important role of KL in sex differences in stress resilience.

The Socio-Political Roles of Neuroethics and the Case of Klotho

An increasing amount of very diverse scholarship self-identifies as belonging to the field of neuroethics, illuminating a need to provide some reference points for what that field actually entails. We argue that neuroethics is a single field with distinct perspectives, roles, and subspecialties. We propose that-in addition to the three traditional perspectives delineated by Eric Racine-a fourth, socio-political perspective, must be recognized in neuroethics. The socio-political perspective in neuroethics focuses on the interplay between the behavioral as well as the brain sciences and the socio-political system; this interplay includes social regulation in addition to all other realistic elements of social and political neurodiscourses. Thus, defining what-if any-roles the socio-political perspective in neuroethics might have is a pressing issue. Doing so could provide guidance for defining the criteria for prospective ethical evaluations in neuroethics. A promising approach to doing this could be by describing the roles of neuroethics in terms of the more concrete examples of the roles of political philosophy in general, as in the tradition of John Rawls. We take klotho, the supposed "longevity protein," as a modern neuroethics case to exemplify the obstacles faced in securing neuroethics' legitimacy and how the Rawlsian framework we propose may be applied to handle cases such as this. Ultimately, the socio-political perspective in neuroethics should not be swayed by the media hype and ought to offer useful ethical guidance and articulation of genuine ethical concerns to policy makers and the public alike.

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.

Neuronal hibernation following hippocampal demyelination

Cognitive dysfunction occurs in greater than 50% of individuals with multiple sclerosis (MS). Hippocampal demyelination is a prominent feature of postmortem MS brains and hippocampal atrophy correlates with cognitive decline in MS patients. Cellular and molecular mechanisms responsible for neuronal dysfunction in demyelinated hippocampi are not fully understood. Here we investigate a mouse model of hippocampal demyelination where twelve weeks of treatment with the oligodendrocyte toxin, cuprizone, demyelinates over 90% of the hippocampus and causes decreased memory/learning. Long-term potentiation (LTP) of hippocampal CA1 pyramidal neurons is considered to be a major cellular readout of learning and memory in the mammalian brain. In acute slices, we establish that hippocampal demyelination abolishes LTP and excitatory post-synaptic potentials of CA1 neurons, while pre-synaptic function of Schaeffer collateral fibers is preserved. Demyelination also reduced Ca2+-mediated firing of hippocampal neurons in vivo. Using three-dimensional electron microscopy, we investigated the number, shape (mushroom, stubby, thin), and post-synaptic densities (PSDs) of dendritic spines that facilitate LTP. Hippocampal demyelination did not alter the number of dendritic spines. Surprisingly, dendritic spines appeared to be more mature in demyelinated hippocampi, with a significant increase in mushroom-shaped spines, more perforated PSDs, and more astrocyte participation in the tripartite synapse. RNA sequencing experiments identified 400 altered transcripts in demyelinated hippocampi. Gene transcripts that regulate myelination, synaptic signaling, astrocyte function, and innate immunity were altered in demyelinated hippocampi. Hippocampal remyelination rescued synaptic transmission, LTP, and the majority of gene transcript changes. We establish that CA1 neurons projecting demyelinated axons silence their dendritic spines and hibernate in a state that may protect the demyelinated axon and facilitates functional recovery following remyelination.

Deregulated expression of a longevity gene, Klotho, in the C9orf72 deletion mice with impaired synaptic plasticity and adult hippocampal neurogenesis

Hexanucleotide repeat expansion of C9ORF72 is the most common genetic cause of amyotrophic lateral sclerosis and frontotemporal dementia. Synergies between loss of C9ORF72 functions and gain of toxicities from the repeat expansions contribute to C9ORF72-mediated pathogenesis. However, how loss of C9orf72 impacts neuronal and synaptic functions remains undetermined. Here, we showed that long-term potentiation at the dentate granule cells and long-term depression at the Schaffer collateral/commissural synapses at the area CA1 were reduced in the hippocampus of C9orf72 knockout mice. Using unbiased transcriptomic analysis, we identified that Klotho, a longevity gene, was selectively dysregulated in an age-dependent manner. Specifically, Klotho protein expression in the hippocampus of C9orf72 knockout mice was incorrectly enriched in the dendritic regions of CA1 with concomitant reduction in granule cell layer of dentate gyrus at 3-month of age followed by an accelerating decline during aging. Furthermore, adult hippocampal neurogenesis was reduced in C9orf72 knockout mice. Taken together, our data suggest that C9ORF72 is required for synaptic plasticity and adult neurogenesis in the hippocampus and Klotho deregulations may be part of C9ORF72-mediated toxicity.

Local Klotho Enhances Neuronal Progenitor Proliferation in the Adult Hippocampus

Klotho is an aging-related protein associated with hippocampal cognitive performance in mammals. Klotho regulates progenitor cell proliferation in non-neuronal tissues, but its role in adult hippocampal neurogenesis (AHN) has not been explored. Klotho expression in the adult mouse hippocampus was examined by immunofluorescence and polymerase chain reaction. AHN was evaluated in the hippocampus of klotho knock-out mice (KO), klotho KO/vitamin D-receptor mutant mice, and in a model of local klotho hippocampal knockdown. The recombinant Klotho effect on proliferation was measured in mouse-derived hippocampal neural progenitor cells. Hippocampal-dependent memory was assessed by a dry-land version of the Morris water maze. Klotho was expressed in the granular cell layer of the adult Dentate Gyrus. AHN was increased in klotho KO mice, but not in klotho KO/vitamin D-receptor mutant mice. Inversely, local downregulation of hippocampal Klotho diminished AHN. Recombinant Klotho increased the proliferation rate of neural progenitors. Downregulation of hippocampal Klotho correlated with a decreased performance in hippocampal-dependent memory. These results suggest that Klotho directly participates in regulating AHN. Our observations indicate that Klotho promotes proliferation, AHN and hippocampal-dependent cognition. Increased neurogenesis in klotho KO mice may be secondary to the activation of other pathways altered in the model, such as vitamin D.

Estradiol Alters Hippocampal Gene Expression during the Estrous Cycle

Estrogen (E2) modulates a wide range of neural functions such as spine formation, synaptic plasticity, and neurotransmission in the hippocampus. Dendritic spines and synapse numbers in hippocampal neurons of female rats cyclically fluctuate across the estrous cycle, but the key genes responsible for these fluctuations are still unknown. In order to address this question, we explore the hippocampal transcriptome via RNA-sequencing (RNA-seq) at the proestrus (PE) and estrus (ES) stages in female rats. At standard fold-change selection criteria, 37 differentially expressed genes (DEGs) were found in PE vs. ES groups (FDR adjusted p-value (q)<0.05). The transcriptional changes identified by RNA-seq were confirmed by quantitative real-time PCR. To gain insight into the function of the DEGs, the E2-regulated genes were annotated by Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes database (KEGG). Based on GO and KEGG pathways, the identified DEGs of PE vs. ES stages are involved in extracellular matrix formation, regulation of actin cytoskeleton, oxidative stress, neuroprotection, immune system, oligodendrocyte maturation and myelination, signal transduction pathways, growth factor signaling, retinoid signaling, aging, cellular process, metabolism and transport. The profiles of the gene expression in the hippocampus identified at the PE vs. ES stages were compared with the gene expression profiles in ovariectomized (OVX) rats receiving E2 replacement via RNA-seq and qPCR. The profiles of gene expression between the OVX+E2 and the estrous cycle were different and the possible causes were discussed.

Activity-dependent neuronal Klotho enhances astrocytic aerobic glycolysis

Mutations of the β-glucuronidase protein α-Klotho have been associated with premature aging, and altered cognitive function. Although highly expressed in specific areas of the brain, Klotho functions in the central nervous system remain unknown. Here, we show that cultured hippocampal neurons respond to insulin and glutamate stimulation by elevating Klotho protein levels. Conversely, AMPA and NMDA antagonism suppress neuronal Klotho expression. We also provide evidence that soluble Klotho enhances astrocytic aerobic glycolysis by hindering pyruvate metabolism through the mitochondria, and stimulating its processing by lactate dehydrogenase. Pharmacological inhibition of FGFR1, Erk phosphorylation, and monocarboxylic acid transporters prevents Klotho-induced lactate release from astrocytes. Taken together, these data suggest Klotho is a potential new player in the metabolic coupling between neurons and astrocytes. Neuronal glutamatergic activity and insulin modulation elicit Klotho release, which in turn stimulates astrocytic lactate formation and release. Lactate can then be used by neurons and other cells types as a metabolic substrate.

RIP at the Synapse and the Role of Intracellular Domains in Neurons

Regulated intramembrane proteolysis (RIP) occurs in a cell when transmembrane proteins are cleaved by intramembrane proteases such as secretases to generate soluble protein fragments in the extracellular environment and the cytosol. In the cytosol, these soluble intracellular domains (ICDs) have local functions near the site of cleavage or in many cases, translocate to the nucleus to modulate gene expression. While the mechanism of RIP is relatively well studied, the fate and function of ICDs for most substrate proteins remain poorly characterized. In neurons, RIP occurs in various subcellular compartments including at the synapse. In this review, we summarize current research on RIP in neurons, focusing specifically on synaptic proteins where the presence and function of the ICDs have been reported. We also briefly discuss activity-driven processing of RIP substrates at the synapse and the cellular machinery that support long-distance transport of ICDs from the synapse to the nucleus. Finally, we describe future challenges in this field of research in the context of understanding the contribution of ICDs in neuronal function.

Fibroblast growth factor 23 and α-Klotho co-dependent and independent functions

PURPOSE OF REVIEW

The current review examines what is known about the FGF-23/α-Klotho co-dependent and independent pathophysiological effects, and whether FGF-23 and/or α-Klotho are potential therapeutic targets.

RECENT FINDINGS

FGF-23 is a hormone derived mainly from bone, and α-Klotho is a transmembrane protein. Together they form a trimeric signaling complex with FGFRs in target tissues to mediate the physiological functions of FGF-23. Local and systemic factors control FGF-23 release from osteoblast/osteocytes in bone, and circulating FGF-23 activates FGFR/α-Klotho complexes in kidney proximal and distal renal tubules to regulate renal phosphate excretion, 1,25 (OH)2D metabolism, sodium and calcium reabsorption, and ACE2 and α-Klotho expression. The resulting bone-renal-cardiac-immune networks provide a new understanding of bone and mineral homeostasis, as well as identify other biological effects FGF-23. Direct FGF-23 activation of FGFRs in the absence of α-Klotho is proposed to mediate cardiotoxic and adverse innate immune effects of excess FGF-23, particularly in chronic kidney disease, but this FGF-23, α-Klotho-independent signaling is controversial. In addition, circulating soluble Klotho (sKl) released from the distal tubule by ectodomain shedding is proposed to have beneficial health effects independent of FGF-23.

SUMMARY

Separation of FGF-23 and α-Klotho independent functions has been difficult in mammalian systems and understanding FGF-23/α-Klotho co-dependent and independent effects are incomplete. Antagonism of FGF-23 is important in treatment of hypophosphatemic disorders caused by excess FGF-23, but its role in chronic kidney disease is uncertain. Administration of recombinant sKl is an unproven therapeutic strategy that theoretically could improve the healt span and lifespan of patients with α-Klotho deficiency.

Klotho deficiency affects the spine morphology and network synchronization of neurons

Klotho-deficient mice rapidly develop cognitive impairment and show some evidence of the onset of neurodegeneration. However, it is impossible to investigate the long-term consequences on the brain because of the dramatic shortening of lifespan caused by systemic klotho deficiency. As klotho expression is downregulated with advancing organismal age, understanding the mechanisms of klotho action is important for developing novel strategies to support healthy brain aging. Previously, we reported that klotho-deficient mice show enhanced long-term potentiation prior to the onset of cognitive impairment. To inform this unusual phenotype, herein, we examined neuronal structure and in vitro synaptic function. Our results indicate that klotho deficiency causes the population of dendritic spines to shift towards increased head diameter and decreased length consistent with mature, mushroom type spines. Multi-electrode array recordings from klotho-deficient neurons show increased synchronous firing and activity changes reflective of increased neuronal network activity. Supplementation of the neuronal growth media with recombinant shed klotho corrected some but not all of the activity changes caused by klotho deficiency. Last, in vivo we found that klotho-deficient mice have a decreased latency to induced seizure activity. Together these data show that klotho-deficient memory impairments are underpinned by structural and functional changes that may preclude ongoing normal cognition.

Role of fibroblast growth factor 23 and klotho cross talk in idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a chronic, progressive fibrosing interstitial pneumonia that mainly affects the elderly. Several reports have demonstrated that aging is involved in the underlying pathogenic mechanisms of IPF. α-Klotho (KL) has been well characterized as an "age-suppressing" hormone and can provide protection against cellular senescence and oxidative stress. In this study, KL levels were assessed in human plasma and primary lung fibroblasts from patients with idiopathic pulmonary fibrosis (IPF-FB) and in lung tissue from mice exposed to bleomycin, which showed significant downregulation when compared with controls. Conversely, transgenic mice overexpressing KL were protected against bleomycin-induced lung fibrosis. Treatment of human lung fibroblasts with recombinant KL alone was not sufficient to inhibit transforming growth factor-β (TGF-β)-induced collagen deposition and inflammatory marker expression. Interestingly, fibroblast growth factor 23 (FGF23), a proinflammatory circulating protein for which KL is a coreceptor, was upregulated in IPF and bleomycin lungs. To our surprise, FGF23 and KL coadministration led to a significant reduction in fibrosis and inflammation in IPF-FB; FGF23 administration alone or in combination with KL stimulated KL upregulation. We conclude that in IPF downregulation of KL may contribute to fibrosis and inflammation and FGF23 may act as a compensatory antifibrotic and anti-inflammatory mediator via inhibition of TGF-β signaling. Upon restoration of KL levels, the combination of FGF23 and KL leads to resolution of inflammation and fibrosis. Altogether, these data provide novel insight into the FGF23/KL axis and its antifibrotic/anti-inflammatory properties, which opens new avenues for potential therapies in aging-related diseases like IPF.

Enhanced Expression of Secreted α-Klotho in the Hippocampus Alters Nesting Behavior and Memory Formation in Mice

The klotho gene family consists of α-, β-, and γ-Klotho, which encode type I single-pass transmembrane proteins with large extracellular domains. α-Klotho exists as a full-length membrane-bound and as a soluble form after cleavage of the extracellular domain. Due to gene splicing, a short extracellular Klotho form can be expressed and secreted. Inactivation of α-Klotho leads to a phenotype that resembles accelerated aging, as the expression level of the α-Klotho protein in the hippocampal formation of mice decreases with age. Here, we show that intrahippocampal viral expression of secreted human α-Klotho alters social behavior and memory formation. Interestingly, overexpression of secreted human α-Klotho in the CA1 changed the nest-building behavior and improved object recognition, object location and passive avoidance memory. Moreover, α-Klotho overexpression increased hippocampal synaptic transmission in response to standardized stimulation strengths, altered paired-pulse facilitation of synaptic transmission, and enhanced activity-dependent synaptic plasticity. These results indicate that memory formation benefits from an augmented level of secreted α-Klotho.

FGF-23 Deficiency Impairs Hippocampal-Dependent Cognitive Function

Fibroblast growth factor receptor (FGFR) and α-Klotho transduce FGF-23 signaling in renal tubules to maintain systemic phosphate/vitamin D homeostasis. Mice deficient for either the ligand, FGF-23, or the co-receptor, Klotho, are phenocopies with both showing rapid and premature development of multiple aging-like abnormalities. Such similarity in phenotype, suggests that FGF-23 and Klotho have co-dependent systemic functions. Recent reports revealed inverse central nervous system (CNS) effects of Klotho deficiency or Klotho overexpression on hippocampal synaptic, neurogenic, and cognitive functions. However, it is unknown whether FGF-23 deficiency effects function of the hippocampus. We report that, similar to Klotho-deficient mice, FGF-23-deficient mice develop dose-dependent, hippocampal-dependent cognitive impairment. However, FGF-23-deficient brains had no gross structural or developmental defects, no change in hippocampal synaptic plasticity, and only minor impairment to postnatal hippocampal neurogenesis. Together, these data provide evidence that FGF-23 deficiency impairs hippocampal-dependent cognition but otherwise results in a brain phenotype that is distinct from the KL-deficient mouse.

[α-Klotho protein in neurodegenerative and mental diseases]

The review aims to attract attention of psychiatrists and neurologists to a role of α-Klotho protein in biochemical mechanisms that counteract pathogenic processes of neurodegenerative and psychiatric diseases and to possible therapeutic potential of the protein. Basing on the analysis of contemporary literature, the authors summarized the results of model experiments and a few clinical trials (in psychiatry and neurology) indicating the role of α-Klotho protein in the brain processes of neurogenesis, dendrite growth, myelination (oligodendroglia differentiation and activity), regulation of antioxidant system, and synthesis of glutamate neurotransmitter system components, regulation of the activity and synthesis of ion channel protein components and membrane transporters, synaptic plasticity. It is concluded that α-Klotho protein can be used for therapeutic purposes in diseases associated with pathological brain aging, and/or in diseases associated with insufficient synthesis of this protein.

Klotho allele status is not associated with Aβ and APOE ε4-related cognitive decline in preclinical Alzheimer's disease

The longevity gene Klotho (KL), specifically the functional KL-VS variant, has previously been associated with cognition and rates of cognitive decline. This study aimed to determine whether KL-VS associations with cognition were observable in preclinical Alzheimer's disease (AD). The study also aimed to determine whether there was a combined influence of KL-VS, neocortical amyloid-β (Aβ) burden, and carriage of the apolipoprotein E (APOE) ε4 allele on cognitive decline. This study involved 581 Aβ-imaged, cognitively normal older adults, enrolled in the Australian Imaging, Biomarkers and Lifestyle Study of Aging. Linear mixed effects models revealed no significant associations between KL-VS and cognitive decline independently or in combination with Aβ burden and APOE ε4 genotype. Overall, previous associations reported between KL-VS and cognitive decline are not observed at the preclinical stages of AD. Furthermore, the results do not support the hypothesis that KL-VS has a modifying effect on Aβ burden and APOE ε4-driven cognitive decline in preclinical AD.

Upregulation of klotho and erythropoietin contributes to the neuroprotection induced by curcumin-loaded nanoparticles in experimental model of chronic epilepsy

Klotho, which is a life extension factor, and erythropoietin (EPO) have been introduced as effective neuroprotective factors in several neurological disorders. The present study is an attempt to examine the potential role of klotho and EPO in therapeutic effect of curcumin-loaded nanoparticles (NPs) in pentylenetetrazol (PTZ)-induced kindling model. In order to induce the kindling model, PTZ was administrated intraperitoneally (i.p.) at dose of 36.5 mg/kg every other day for 20 days. Male NMRI mice received pre-treatment of free curcumin or curcumin-loaded NPs (12.5 mg/kg, i.p.) 10 days before PTZ injection and this was continued until 1 h before each PTZ injection. Immunostaining against NeuN, as a marker of neuronal maturation, and EPO was performed on hippocampal brain sections. Quantitative real time polymerase chain reaction (qRT-PCR) was conducted to assess the expression levels of tumor necrosis factor-α (TNF-α), klotho and EPO in the hippocampus. Immunostaining data indicated that treatment with curcumin-loaded NPs significantly alleviates the neuronal cell death in PTZ receiving animals. Curcumin-loaded NPs effectively upregulated the levels of EPO and klotho in PTZ receiving animals. Furthermore, mRNA level of TNF-α was considerably reduced in animals undergone curcumin-loaded NPs treatment. Overall, the results of this study suggest that downregulation of TNF-α and consequent upregulation of klotho and EPO might contribute to the neuroprotective effect of curcumin-loaded NPs in experimental model of epilepsy.

Klotho, the Key to Healthy Brain Aging?

Brain expression of klotho was first described with the initial discovery of the klotho gene. The prominent age-regulating effects of klotho are attributed to regulation of ion homeostasis through klotho function in the kidney. However, recent advances identified brain functions and cell populations, including adult hippocampal neural progenitors, which require klotho. As well, both human correlational studies and mouse models of disease show that klotho is protective against multiple neurological and psychological disorders. This review focuses on current knowledge as to how the klotho protein effects the brain.

Fibroblast growth factor 23 and Klotho contribute to airway inflammation

Circulating levels of fibroblast growth factor (FGF)23 are associated with systemic inflammation and increased mortality in chronic kidney disease. α-Klotho, a co-receptor for FGF23, is downregulated in chronic obstructive pulmonary disease (COPD). However, whether FGF23 and Klotho-mediated FGF receptor (FGFR) activation delineates a pathophysiological mechanism in COPD remains unclear. We hypothesised that FGF23 can potentiate airway inflammation via Klotho-independent FGFR4 activation.FGF23 and its effect were studied using plasma and transbronchial biopsies from COPD and control patients, and primary human bronchial epithelial cells isolated from COPD patients as well as a murine COPD model.Plasma FGF23 levels were significantly elevated in COPD patients. Exposure of airway epithelial cells to cigarette smoke and FGF23 led to a significant increase in interleukin-1β release via Klotho-independent FGFR4-mediated activation of phospholipase Cγ/nuclear factor of activated T-cells signalling. In addition, Klotho knockout mice developed COPD and showed airway inflammation and elevated FGFR4 expression in their lungs, whereas overexpression of Klotho led to an attenuation of airway inflammation.Cigarette smoke induces airway inflammation by downregulation of Klotho and activation of FGFR4 in the airway epithelium in COPD. Inhibition of FGF23 or FGFR4 might serve as a novel anti-inflammatory strategy in COPD.

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

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

Peripheral Elevation of a Klotho Fragment Enhances Brain Function and Resilience in Young, Aging, and α-Synuclein Transgenic Mice

Cognitive dysfunction and decreased mobility from aging and neurodegenerative conditions, such as Parkinson and Alzheimer diseases, are major biomedical challenges in need of more effective therapies. Increasing brain resilience may represent a new treatment strategy. Klotho, a longevity factor, enhances cognition when genetically and broadly overexpressed in its full, wild-type form over the mouse lifespan. Whether acute klotho treatment can rapidly enhance cognitive and motor functions or induce resilience is a gap in our knowledge of its therapeutic potential. Here, we show that an α-klotho protein fragment (αKL-F), administered peripherally, surprisingly induced cognitive enhancement and neural resilience despite impermeability to the blood-brain barrier in young, aging, and transgenic α-synuclein mice. αKL-F treatment induced cleavage of the NMDAR subunit GluN2B and also enhanced NMDAR-dependent synaptic plasticity. GluN2B blockade abolished αKL-F-mediated effects. Peripheral αKL-F treatment is sufficient to induce neural enhancement and resilience in mice and may prove therapeutic in humans.