Hedgehog signalling as an antagonist of ageing and its associated diseases

Sonic hedgehog signalling pathway contributes in age-related disorders and Alzheimer's disease

Alzheimer's disease (AD) is caused by the aging process and manifested by cognitive deficits and progressive memory loss. During aging, several conditions, including hypertension, diabetes, and cholesterol, have been identified as potential causes of AD by affecting Sonic hedgehog (Shh) signalling. In addition to being essential for cell differentiation and proliferation, Shh signalling is involved in tissue repair and the prevention of neurodegeneration. Neurogenesis is dependent on Shh signalling; inhibition of this pathway results in neurodegeneration. Several protein-protein interactions that are involved in Shh signalling are implicated in the pathophysiology of AD like overexpression of the protein nexin-1 inhibits the Shh pathway in AD. A protein called Growth Arrest Specific-1 works with another protein called cysteine dioxygenase (CDO) to boost Shh signalling. CDO is involved in the development of the central nervous system (CNS). Shh signalling strengthened the blood brain barrier and therefore prevent the entry of amyloid beta and other toxins to the brain from periphery. Further, several traditional remedies used for AD and dementia, including Epigallocatechin gallate, yokukansan, Lycium barbarum polysaccharides, salvianolic acid, and baicalin, are known to stimulate the Shh pathway. In this review, we elaborated that the Shh signalling exerts a substantial influence on the pathogenesis of AD. In this article, we have tried to explore the various possible connections between the Shh signalling and various known pathologies of AD.

Devo-Aging: Intersections Between Development and Aging

There are two fundamental questions in developmental biology. How does a single fertilized cell give rise to a whole body? and how does this body later produce progeny? Synchronization of these embryonic and postembryonic developments ensures continuity of life from one generation to the next. An enormous amount of work has been done to unravel the molecular mechanisms behind these processes, but more recently, modern developmental biology has been expanded to study development in wider contexts, including regeneration, environment, disease, and even aging. However, we have just started to understand how the mechanisms that govern development also regulate aging. This review discusses examples of signaling pathways involved in development to elucidate how their regulation influences healthspan and lifespan. Therefore, a better knowledge of developmental signaling pathways stresses the possibility of using them as innovative biomarkers and targets for aging and age-related diseases.

Impact of neuroinflammation on epigenetic transcriptional control of Sonic Hedgehog members in the central nervous system

Sonic Hedgehog (Shh) signaling plays a critical role during central nervous system (CNS) development, and its dysregulation leads to neurological disorders. Nevertheless, little is known about Shh signaling regulation in the adult brain. Here, we investigated the contribution of DNA methylation on the transcriptional control of Shh signaling pathway members and its basal distribution impact on the brain, as well as its modulation by inflammation. The methylation status of the promoter regions of these members and the transcriptional profile of DNA-modifying enzymes (DNA Methyltransferases - DNMTs and Tet Methylcytosine Dioxygenase - TETs) were investigated in a murine model of neuroinflammation by qPCR. We showed that, in the adult brain, methylation in the CpG promoter regions of the Shh signaling pathway members was critical to determine the endogenous differential transcriptional pattern observed between distinct brain regions. We also found that neuroinflammation differentially modulates gene expression of DNA-modifying enzymes. This study reveals the basal transcriptional profile of DNMTs and TETs enzymes in the CNS and demonstrates the effect of neuroinflammation on the transcriptional control of members of the Shh Signaling pathway in the adult brain.

TLR4 Modulates Senescence and Paracrine Action in Placental Mesenchymal Stem Cells via Inhibiting Hedgehog Signaling Pathway in Preeclampsia

Preeclampsia (PE) is a heterogeneous disease closely associated with the accelerated senescence of the placentas. Placental mesenchymal stem cells (PMSCs) modulate placental development, which is abnormally senescent in PE together with abnormal paracrine. Both pivotal in the placenta development, Toll-like receptor 4 (TLR4) and Hedgehog (HH) pathway are also tightly involved in regulating cellular senescence. This study was aimed at demonstrating that TLR4/HH pathway modulated senescence of placentas and PMSCs in vitro and in vivo. Preeclamptic and normal PMSCs were isolated. Smoothed agonist (SAG) and cyclopamine were used to activate and inhibit HH pathway, respectively. Lipopolysaccharide (LPS) was used to activate TLR4 in vitro and establish the classic PE-like rat model. qRT-PCR, Western blotting, and immunofluorescence were used to detect the expression of TLR4 and HH components (SHH, SMO, and Gli1). Cellular biological function such as proliferation, apoptosis, and migration was compared. Cell cycle analysis, β-galactosidase staining, and the protein expressions of p16 and p53 were detected to analyze the cellular senescence. The secretion levels of human matrix metalloproteinase 9 (MMP-9) and soluble fms-like tyrosine kinase-1 (sFlt-1) were measured in the conditioned medium. Cell migration, invasion, and tube formation were analyzed in HTR8/SVneo cells or human umbilical vein endothelial cells (HUVECs). Our study demonstrated that activation of TLR4 accelerated senescence of PMSCs via suppressing HH pathway both in vitro and in vivo, accompanied by the detrimental paracrine to impair the uterine spiral artery remodeling and placental angiogenesis. Meanwhile, induction of HH pathway could alleviate PE-like manifestations, improve pregnancy outcomes, and ameliorate multiorgan injuries, suggesting that strengthening the HH pathway may serve as a potential therapy in PE.

The bright side of fibroblasts: molecular signature and regenerative cues in major organs

Fibrosis is a pathologic process characterized by the replacement of parenchymal tissue by large amounts of extracellular matrix, which may lead to organ dysfunction and even death. Fibroblasts are classically associated to fibrosis and tissue repair, and seldom to regeneration. However, accumulating evidence supports a pro-regenerative role of fibroblasts in different organs. While some organs rely on fibroblasts for maintaining stem cell niches, others depend on fibroblast activity, particularly on secreted molecules that promote cell adhesion, migration, and proliferation, to guide the regenerative process. Herein we provide an up-to-date overview of fibroblast-derived regenerative signaling across different organs and discuss how this capacity may become compromised with aging. We further introduce a new paradigm for regenerative therapies based on reverting adult fibroblasts to a fetal/neonatal-like phenotype.

RhoA/ROCK signaling pathway and astrocytes in ischemic stroke

Ischemic stroke is one of the most common and undertreated cerebral diseases with high mortality and disability rate. Various intrinsic and extrinsic factors regulate the onset, severity, and progression of ischemic stroke. As an integral part of the neuronal glia system, astrocytes provide many housekeeping functions in nervous system, and perform multiple functions both beneficial and detrimental for neuronal survival after ischemic stroke. In addition, the small GTPase Rho and its downstream Rho kinase (ROCK) are associated with various neuronal functions such as dendrite development, migration and axonal extension, and numerous central nervous system (CNS) diseases. The aim of this review is to summarize the role of RhoA/ROCK signaling pathway and astrocytes on neurological function after ischemic stroke. We also discuss the interaction of RhoA/ROCK signaling pathway and astrocytes on the tissue repair after brain injury.

Transcriptomic and epigenomic profiling of young and aged spermatogonial stem cells reveals molecular targets regulating differentiation

Spermatogonial stem cells (SSC), the foundation of spermatogenesis and male fertility, possess lifelong self-renewal activity. Aging leads to the decline in stem cell function and increased risk of paternal age-related genetic diseases. In the present study, we performed a comparative genomic analysis of mouse SSC-enriched undifferentiated spermatogonia (Oct4-GFP+/KIT-) and differentiating progenitors (Oct4-GFP+/KIT+) isolated from young and aged testes. Our transcriptome data revealed enormous complexity of expressed coding and non-coding RNAs and alternative splicing regulation during SSC differentiation. Further comparison between young and aged undifferentiated spermatogonia suggested these differentiation programs were affected by aging. We identified aberrant expression of genes associated with meiosis and TGF-β signaling, alteration in alternative splicing regulation and differential expression of specific lncRNAs such as Fendrr. Epigenetic profiling revealed reduced H3K27me3 deposition at numerous pro-differentiation genes during SSC differentiation as well as aberrant H3K27me3 distribution at genes in Wnt and TGF-β signaling upon aging. Finally, aged undifferentiated spermatogonia exhibited gene body hypomethylation, which is accompanied by an elevated 5hmC level. We believe this in-depth molecular analysis will serve as a reference for future analysis of SSC aging.

Switching of vascular cells towards atherogenesis, and other factors contributing to atherosclerosis: a systematic review

Background

Onset, development and progression of atherosclerosis are complex multistep processes. Many aspects of atherogenesis are not yet properly known. This study investigates the changes in vasculature that contribute to switching of vascular cells towards atherogenesis, focusing mainly on ageing.

Methods

Databases including PubMed, MEDLINE and Google Scholar were searched for published articles without any date restrictions, involving atherogenesis, vascular homeostasis, aging, gene expression, signaling pathways, angiogenesis, vascular development, vascular cell differentiation and maintenance, vascular stem cells, endothelial and vascular smooth muscle cells.

Results

Atherogenesis is a complex multistep process that unfolds in a sequence. It is caused by alterations in: epigenetics and genetics, signaling pathways, cell circuitry, genome stability, heterotypic interactions between multiple cell types and pathologic alterations in vascular microenvironment. Such alterations involve pathological changes in: Shh, Wnt, NOTCH signaling pathways, TGF beta, VEGF, FGF, IGF 1, HGF, AKT/PI3K/ mTOR pathways, EGF, FOXO, CREB, PTEN, several apoptotic pathways, ET - 1, NF-κB, TNF alpha, angiopoietin, EGFR, Bcl - 2, NGF, BDNF, neurotrophins, growth factors, several signaling proteins, MAPK, IFN, TFs, NOs, serum cholesterol, LDL, ephrin, its receptor pathway, HoxA5, Klf3, Klf4, BMPs, TGFs and others.This disruption in vascular homeostasis at cellular, genetic and epigenetic level is involved in switching of the vascular cells towards atherogenesis. All these factors working in pathologic manner, contribute to the development and progression of atherosclerosis.

Conclusion

The development of atherosclerosis involves the switching of gene expression towards pro-atherogenic genes. This happens because of pathologic alterations in vascular homeostasis. When pathologic alterations in epigenetics, genetics, regulatory genes, microenvironment and vascular cell biology accumulate beyond a specific threshold, then the disease begins to express itself phenotypically. The process of biological ageing is one of the most significant factors in this aspect as it is also involved in the decline in homeostasis, maintenance and integrity.The process of atherogenesis unfolds sequentially (step by step) in an interconnected loop of pathologic changes in vascular biology. Such changes are involved in 'switching' of vascular cells towards atherosclerosis.

Emerging Roles of Inhibitor of Differentiation-1 in Alzheimer's Disease: Cell Cycle Reentry and Beyond

Inhibitor of DNA-binding/differentiation (Id) proteins, a family of helix-loop-helix (HLH) proteins that includes four members of Id1 to Id4 in mammalian cells, are critical for regulating cell growth, differentiation, senescence, cell cycle progression, and increasing angiogenesis and vasculogenesis, as well as accelerating the ability of cell migration. Alzheimer’s disease (AD), the most common neurodegenerative disease in the adult population, manifests the signs of cognitive decline, behavioral changes, and functional impairment. The underlying mechanisms for AD are not well-clarified yet, but the aggregation of amyloid-beta peptides (Aβs), the major components in the senile plaques observed in AD brains, contributes significantly to the disease progression. Emerging evidence reveals that aberrant cell cycle reentry may play a central role in Aβ-induced neuronal demise. Recently, we have shown that several signaling mediators, including Id1, hypoxia-inducible factor-1 (HIF-1), cyclin-dependent kinases-5 (CDK5), and sonic hedgehog (Shh), may contribute to Aβ-induced cell cycle reentry in postmitotic neurons; furthermore, Id1 and CDK5/p25 mutually antagonize the expression/activity of each other. Therefore, Id proteins may potentially have clinical applications in AD. In this review article, we introduce the underlying mechanisms for cell cycle dysregulation in AD and present some examples, including our own studies, to show different aspects of Id1 in terms of cell cycle reentry and other signaling that may be crucial to alter the neuronal fates in this devastating neurodegenerative disease. A thorough understanding of the underlying mechanisms may provide a rationale to make an earlier intervention before the occurrence of cell cycle reentry and subsequent apoptosis in the fully differentiated neurons during the progression of AD or other neurodegenerative diseases.

Regulation of Hedgehog signaling Offers A Novel Perspective for Bone Homeostasis Disorder Treatment

The hedgehog (HH) signaling pathway is central to the regulation of bone development and homeostasis. HH signaling is not only involved in osteoblast differentiation from bone marrow mesenchymal stem cells (BM-MSCs), but also acts upstream within osteoblasts via the OPG/RANK/RANKL axis to control the expression of RANKL. HH signaling has been found to up-regulate parathyroid hormone related protein (PTHrP) expression in osteoblasts, which in turn activates its downstream targets nuclear factor of activated T cells (NFAT) and cAMP responsive element binding protein (CREB), and as a result CREB and NFAT cooperatively increase RANKL expression and osteoclastogenesis. Osteoblasts must remain in balance with osteoclasts in order to avoid excessive bone formation or resorption, thereby maintaining bone homeostasis. This review systemically summarizes the mechanisms whereby HH signaling induces osteoblast development and controls RANKL expression through PTHrP in osteoblasts. Proper targeting of HH signaling may offer a therapeutic option for treating bone homeostasis disorders.

Emerging Therapeutic Targets for Metabolic Syndrome: Lessons from Animal Models

Background:

Metabolic syndrome is a cluster of medical conditions that synergistically increase the risk of heart diseases and diabetes. The current treatment strategy for metabolic syndrome focuses on treating its individual components. A highly effective agent for metabolic syndrome has yet to be developed. To develop a target for metabolic syndrome, the mechanism encompassing different organs - nervous system, pancreas, skeletal muscle, liver and adipose tissue - needs to be understood. Many animal models have been developed to understand the pathophysiology of metabolic syndrome. Promising molecular targets have emerged while characterizing these animals. Modulating these targets is expected to treat some components of metabolic syndrome.

Objective:

o discuss the emerging molecular targets in an animal model of metabolic syndrome.

Methods:

A literature search was performed for the retrieval of relevant articles.

Conclusion:

Multiple genes/pathways that play important role in the development of Metabolic Syndrome are discussed.

Emerging Roles of Sonic Hedgehog in Adult Neurological Diseases: Neurogenesis and Beyond

Sonic hedgehog (Shh), a member of the hedgehog (Hh) family, was originally recognized as a morphogen possessing critical characters for neural development during embryogenesis. Recently, however, Shh has emerged as an important modulator in adult neural tissues through different mechanisms such as neurogenesis, anti-oxidation, anti-inflammation, and autophagy. Therefore, Shh may potentially have clinical application in neurodegenerative diseases and brain injuries. In this article, we present some examples, including ours, to show different aspects of Shh signaling and how Shh agonists or mimetics are used to alter the neuronal fates in various disease models, both in vitro and in vivo. Other potential mechanisms that are discussed include alteration of mitochondrial function and anti-aging effect; both are critical for age-related neurodegenerative diseases. A thorough understanding of the protective mechanisms elicited by Shh may provide a rationale to design innovative therapeutic regimens for various neurodegenerative diseases.

Obesity and Aging in the Drosophila Model

Being overweight increases the risk of many metabolic disorders, but how it affects lifespan is not completely clear. Not all obese people become ill, and the exact mechanism that turns excessive fat storage into a health-threatening state remains unknown. Drosophila melanogaster has served as an excellent model for many diseases, including obesity, diabetes, and hyperglycemia-associated disorders, such as cardiomyopathy or nephropathy. Here, we review the connections between fat storage and aging in different types of fly obesity. Whereas obesity induced by high-fat or high-sugar diet is associated with hyperglycemia, cardiomyopathy, and in some cases, shortening of lifespan, there are also examples in which obesity correlates with longevity. Transgenic lines with downregulations of the insulin/insulin-like growth factor (IIS) and target of rapamycin (TOR) signaling pathways, flies reared under dietary restriction, and even certain longevity selection lines are obese, yet long-lived. The mechanisms that underlie the differential lifespans in distinct types of obesity remain to be elucidated, but fat turnover, inflammatory pathways, and dysregulations of glucose metabolism may play key roles. Altogether, Drosophila is an excellent model to study the physiology of adiposity in both health and disease.

Adaptive Group-combined P-values Test for Two-sample Location Problem with Applications to Microarray Data

The purpose of this article is to propose a test for two-sample location problem in high-dimensional data. In general highdimensional case, the data dimension can be much larger than the sample size and the underlying distribution may be far from normal. Existing tests requiring explicit relationship between the data dimension and sample size or designed for multivariate normal distributions may lose power significantly and even yield type I error rates strayed from nominal levels. To overcome this issue, we propose an adaptive group p-values combination test which is robust against both high dimensionality and normality. Simulation studies show that the proposed test controls type I error rates correctly and outperforms some existing tests in most situations. An Ageing Human Brain Microarray data are used to further exemplify the method.

Insulin resistance adipocyte-derived exosomes aggravate atherosclerosis by increasing vasa vasorum angiogenesis in diabetic ApoE-/- mice

BACKGROUND

Vasa vasorum (VV) angiogenesis is increased in type 2 diabetes mellitus (T2DM) and may promote atherosclerotic plaque rupture. We sought to determine whether insulin resistance adipocyte-derived exosomes (IRADEs) played a major role in modulating VV angiogenesis and the mechanisms involved.

METHODS

The characterization of IRADEs was performed by electron microscopy, NTA (Nanoparticle Tracking Analysis) and western blot. The cellular effects of IRADEs on angiogenesis were explored in human umbilical vein endothelial cells (HUVECs) and murine aortic endothelial cells (MAECs) in vitro. The roles of IRADEs in angiogenesis were demonstrated with aortic ring and matrigel plug assays ex vivo and the plaque burden, plaque stability and angiogenesis-related protein expression in vivo were evaluated by ultrasonography, immunohistochemistry and western blot.

RESULTS

The IRADEs had a cup-shaped morphology, could be taken up by HUVECs and atherosclerotic plaques, and promoted tube formation by shh in vitro. In the aortic ring and matrigel plug assays, angiogenesis was significantly increased in the IRADEs group. Exogenously administered shh-containing IRADEs increased VV angiogenesis, the plaque burden, the vulnerability index and the expression of angiogenesis-related factors, whereas these effects were attenuated by silencing shh in IRADEs.

CONCLUSIONS

In conclusion, IRADEs promote plaque burden and plaque vulnerability partly by inducing VV angiogenesis, which occurs partly through shh. Accordingly, the application of IRADEs may serve as a novel therapeutic approach to treat diabetic atherosclerosis.

Age-associated DNA methylation changes in naive CD4+ T cells suggest an evolving autoimmune epigenotype in aging T cells

AIM

We sought to define age-associated DNA methylation changes in naive CD4⁺ T cells.

MATERIALS & METHODS

Naive CD4⁺ T cells were collected from 74 healthy individuals (age 19-66 years), and age-related DNA methylation changes were characterized.

RESULTS

We identified 11,431 age-associated CpG sites, 57% of which were hypermethylated with age. Hypermethylated sites were enriched in CpG islands and repressive transcription factor binding sites, while hypomethylated sites showed T cell specific enrichment in active enhancers marked by H3K27ac and H3K4me1. Our data emphasize cancer-related DNA methylation changes with age, and also reveal age-associated hypomethylation in immune-related pathways, such as T cell receptor signaling, FCγR-mediated phagocytosis, apoptosis and the mammalian target of rapamycin signaling pathway. The MAPK signaling pathway was hypermethylated with age, consistent with a defective MAPK signaling in aging T cells.

CONCLUSION

Age-associated DNA methylation changes may alter regulatory mechanisms and signaling pathways that predispose to autoimmunity.

Hhip haploinsufficiency sensitizes mice to age-related emphysema

Genetic variants in Hedgehog interacting protein (HHIP) have consistently been associated with the susceptibility to develop chronic obstructive pulmonary disease and pulmonary function levels, including the forced expiratory volume in 1 s (FEV1), in general population samples by genome-wide association studies. However, in vivo evidence connecting Hhip to age-related FEV1 decline and emphysema development is lacking. Herein, using Hhip heterozygous mice (Hhip(+/-)), we observed increased lung compliance and spontaneous emphysema in Hhip(+/-) mice starting at 10 mo of age. This increase was preceded by increases in oxidative stress levels in the lungs of Hhip(+/-) vs. Hhip(+/+) mice. To our knowledge, these results provide the first line of evidence that HHIP is involved in maintaining normal lung function and alveolar structures. Interestingly, antioxidant N-acetyl cysteine treatment in mice starting at age of 5 mo improved lung function and prevented emphysema development in Hhip(+/-) mice, suggesting that N-acetyl cysteine treatment limits the progression of age-related emphysema in Hhip(+/-) mice. Therefore, reduced lung function and age-related spontaneous emphysema development in Hhip(+/-) mice may be caused by increased oxidative stress levels in murine lungs as a result of haploinsufficiency of Hhip.

A Systematic Investigation into Aging Related Genes in Brain and Their Relationship with Alzheimer's Disease

Aging, as a complex biological process, is accompanied by the accumulation of functional loses at different levels, which makes age to be the biggest risk factor to many neurological diseases. Even following decades of investigation, the process of aging is still far from being fully understood, especially at a systematic level. In this study, we identified aging related genes in brain by collecting the ones with sustained and consistent gene expression or DNA methylation changes in the aging process. Functional analysis with Gene Ontology to these genes suggested transcriptional regulators to be the most affected genes in the aging process. Transcription regulation analysis found some transcription factors, especially Specificity Protein 1 (SP1), to play important roles in regulating aging related gene expression. Module-based functional analysis indicated these genes to be associated with many well-known aging related pathways, supporting the validity of our approach to select aging related genes. Finally, we investigated the roles of aging related genes on Alzheimer's Disease (AD). We found that aging and AD related genes both involved some common pathways, which provided a possible explanation why aging made the brain more vulnerable to Alzheimer's Disease.

Ciliary abnormalities in senescent human fibroblasts impair proliferative capacity

Somatic cells senesce in culture after a finite number of divisions indefinitely arresting their proliferation. DNA damage and senescence increase the cellular number of centrosomes, the 2 microtubule organizing centers that ensure bipolar mitotic spindles. Centrosomes also provide the basal body from which primary cilia extend to sense and transduce various extracellular signals, notably Hedgehog. Primary cilium formation is facilitated by cellular quiescence a temporary cell cycle exit, but the impact of senescence on cilia is unknown. We found that senescent human fibroblasts have increased frequency and length of primary cilia. Levels of the negative ciliary regulator CP110 were reduced in senescent cells, as were levels of key elements of the Hedgehog pathway. Hedgehog inhibition reduced proliferation in young cells with increased cilium length accompanying cell cycle arrest suggesting a regulatory function for Hedgehog in primary ciliation. Depletion of CP110 in young cell populations increased ciliation frequencies and reduced cell proliferation. These data suggest that primary cilia are potentially novel determinants of the reduced cellular proliferation that initiates senescence.

An overview of hedgehog signaling in fibrosis

The Hedgehog (Hh) signaling pathway plays a key role during embryogenesis and tissue regeneration. Recently, studies revealed that overactivated Hh signaling leads to fibrogenesis in many types of tissues. The activation of Hh signaling is involved in the epithelial-mesenchymal transition and excessive extracellular matrix deposition. Blockade of Hh signaling abolishes the induction of the epithelial-mesenchymal transition and ameliorates tissue fibrosis. Therefore, new therapeutic targets to alleviate fibrosis based on the Hh signaling have attracted a great deal of attention. This is a new strategy for treating fibrosis and other related diseases. In this review, we discuss the crucial role of Hh signaling in fibrogenesis to provide a better understanding of their relationship and to encourage the study of novel targeted therapies.

Sexual dimorphism in epigenomic responses of stem cells to extreme fetal growth

Extreme fetal growth is associated with increased susceptibility to a range of adult diseases through an unknown mechanism of cellular memory. We tested whether heritable epigenetic processes in long-lived CD34+ hematopoietic stem/progenitor cells (HSPCs) showed evidence for re-programming associated with the extremes of fetal growth. Here we show that both fetal growth restriction and over-growth are associated with global shifts towards DNA hypermethylation, targeting cis-regulatory elements in proximity to genes involved in glucose homeostasis and stem cell function. We find a sexually dimorphic response; intrauterine growth restriction (IUGR) is associated with substantially greater epigenetic dysregulation in males, whereas large for gestational age (LGA) growth predominantly affects females. The findings are consistent with extreme fetal growth interacting with variable fetal susceptibility to influence cellular aging and metabolic characteristics through epigenetic mechanisms, potentially generating biomarkers that could identify infants at higher risk for chronic disease later in life.

Using zebrafish models to explore genetic and epigenetic impacts on evolutionary developmental origins of aging

Can we reset, reprogram, rejuvenate, or reverse the organismal aging process? Certain genetic manipulations could at least reset and reprogram epigenetic dynamics beyond phenotypic plasticity and elasticity in cells, which can be manipulated further into organisms. However, in a whole complex aging organism, how can we rejuvenate intrinsic resources and infrastructures in an intact and noninvasive manner? The incidence of diseases increases exponentially with age, accompanied by progressive deteriorations of physiological functions in organisms. Aging-associated diseases are sporadic but essentially inevitable complications arising from senescence. Senescence is often considered the antithesis of early development, but yet there may be factors and mechanisms in common between these 2 phenomena to rejuvenate over the dynamic process of aging. The association between early development and late-onset disease with advancing age is thought to come from a consequence of developmental plasticity, the phenomenon by which one genotype can give rise to a range of physiologically and/or morphologically adaptive states based on diverse epigenotypes in response to intrinsic or extrinsic environmental cues and genetic perturbations. We hypothesized that the future aging process can be predictive based on adaptivity during the early developmental period. Modulating the thresholds and windows of plasticity and its robustness by molecular genetic and chemical epigenetic approaches, we have successfully conducted experiments to isolate zebrafish mutants expressing apparently altered senescence phenotypes during their embryonic and/or larval stages ("embryonic/larval senescence"). Subsequently, at least some of these mutant animals were found to show a shortened life span, whereas others would be expected to live longer into adulthood. We anticipate that previously uncharacterized developmental genes may mediate the aging process and play a pivotal role in senescence. On the other hand, unexpected senescence-related genes might also be involved in the early developmental process and its regulation. The ease of manipulation using the zebrafish system allows us to conduct an exhaustive exploration of novel genes, genotypes, and epigenotypes that can be linked to the senescence phenotype, which facilitates searching for the evolutionary and developmental origins of aging in vertebrates.

Titration of GLI3 repressor activity by sonic hedgehog signaling is critical for maintaining multiple adult neural stem cell and astrocyte functions

Sonic hedgehog (SHH), a key regulator of embryonic neurogenesis, signals directly to neural stem cells (NSCs) in the subventricular zone (SVZ) and to astrocytes in the adult mouse forebrain. The specific mechanism by which the GLI2 and GLI3 transcriptional activators (GLI2(A) and GLI3(A)) and repressors (GLI2(R) and GLI3(R)) carry out SHH signaling has not been addressed. We found that the majority of slow-cycling NSCs express Gli2 and Gli3, whereas Gli1 is restricted ventrally and all three genes are downregulated when NSCs transition into proliferating progenitors. Surprisingly, whereas conditional ablation of Smo in postnatal glial fibrillary acidic protein-expressing cells results in cell-autonomous loss of NSCs and a progressive reduction in SVZ proliferation, without an increase in glial cell production, removal of Gli2 or Gli3 does not alter adult SVZ neurogenesis. Significantly, removing Gli3 in Smo conditional mutants largely rescues neurogenesis and, conversely, expression of a constitutive GLI3(R) in the absence of normal Gli2 and Gli3 abrogates neurogenesis. Thus unattenuated GLI3(R) is a primary inhibitor of adult SVZ NSC function. Ablation of Gli2 and Gli3 revealed a minor role for GLI2(R) and little requirement for GLI(A) function in stimulating SVZ neurogenesis. Moreover, we found that similar rules of GLI activity apply to SHH signaling in regulating SVZ-derived olfactory bulb interneurons and maintaining cortical astrocyte function. Namely, fewer superficial olfactory bulb interneurons are generated in the absence of Gli2 and Gli3, whereas astrocyte partial gliosis results from an increase in GLI3(R). Thus precise titration of GLI(R) levels by SHH is critical to multiple functions of adult NSCs and astrocytes.

Molecular and chemical genetic approaches to developmental origins of aging and disease in zebrafish

The incidence of diseases increases rapidly with age, accompanied by progressive deteriorations of physiological functions in organisms. Aging-associated diseases are sporadic but mostly inevitable complications arising from senescence. Senescence is often considered the antithesis of early development, but yet there may be factors and mechanisms in common between these two phenomena over the dynamic process of aging. The association between early development and late-onset disease with advancing age is thought to come from a consequence of developmental plasticity, the phenomenon by which one genotype can give rise to a range of physiologically and/or morphologically adaptive states in response to different environmental or genetic perturbations. On the one hand, we hypothesized that the future aging process can be predictive based on adaptivity during the early developmental period. Modulating the thresholds of adaptive plasticity by chemical genetic approaches, we have been investigating whether any relationship exists between the regulatory mechanisms that function in early development and in senescence using the zebrafish (Danio rerio), a small freshwater fish and a useful model animal for genetic studies. We have successfully conducted experiments to isolate zebrafish mutants expressing apparently altered senescence phenotypes during embryogenesis ("embryonic senescence"), subsequently showing shortened lifespan in adulthoods. We anticipate that previously uncharacterized developmental genes may mediate the aging process and play a pivotal role in senescence. On the other hand, unexpected senescence-related genes might also be involved in the early developmental process and regulation. The ease of manipulation using the zebrafish system allows us to conduct an exhaustive exploration of novel genes and small molecular compounds that can be linked to the senescence phenotype, and thereby facilitates searching for the evolutionary and developmental origins of aging in vertebrates. This article is part of a Special Issue entitled: Animal Models of Disease.

Hedgehog signaling pathway in ovarian cancer

Despite advances in surgical and chemotherapeutic treatment options, less than 50% of patients with advanced-stage ovarian cancer survive five years after initial diagnosis. In this regard, novel treatment approaches are warranted utilizing molecularly targeted therapies directed against particular components of specific signaling pathways which are required for tumor development and progression. One molecular pathway of interest is the hedgehog (Hh) signaling pathway. Activation of the Hh pathway has been observed in several cancer types, including ovarian cancer. This review highlights the crucial role of Hh signaling in the development and progression of ovarian cancer and might lead to a better understanding of the Hh signaling in ovarian tumorigenesis, thus encouraging the investigation of novel targeted therapies.