A missense variant in CST3 exerts a recessive effect on susceptibility to age-related macular degeneration resembling its association with Alzheimer's disease

CST3 alleviates retinal vascular leakage by regulating the Rap1 signaling pathway

Retinal vascular leakage is a major event in several retinal diseases, including diabetic retinopathy (DR). In a previous study, we demonstrated that the aqueous humor concentration of Cystatin C (CST3), a physiological inhibitor of cysteine protease, is negatively correlated with the severity of diabetic macular edema. However, its function in the retina has not been clearly elucidated. In this study, we found a significant decrease in the aqueous humor concentration of CST3 with DR progression. Furthermore, we found that CST3 was expressed in retinal endothelial cells and that its expression was significantly downregulated in high glucose-treated human retinal microvascular endothelial cells (HRMECs) and the retinal vessels of oxygen-induced retinopathy (OIR) mice. Silencing CST3 expression resulted in decreased HRMEC migration and tubule formation ability. Exogenous addition of the CST3 protein significantly improved HRMEC migration and tubular formation. In-vivo experiments demonstrated that CST3 silencing induced retinal vascular leakage in WT mice, while its intravitreal injection significantly reduced retinal leakage in OIR mice. Mechanistically, CST3 promoted the expression of the downstream adhesion molecules, claudin5, VE-cadherin, and ZO-1, in retinal vascular cells by regulating the Rap1 signaling pathway. Therefore, this study revealed a novel mechanism by which CST3 improves retinal vascular function and provided evidence that it is a potential therapeutic target for retinal vascular leakage.

Association of biological age with health outcomes and its modifiable factors

Identifying the clinical implications and modifiable and unmodifiable factors of aging requires the measurement of biological age (BA) and age gap. Leveraging the biomedical traits involved with physical measures, biochemical assays, genomic data, and cognitive functions from the healthy participants in the UK Biobank, we establish an integrative BA model consisting of multi-dimensional indicators. Accelerated aging (age gap >3.2 years) at baseline is associated incident circulatory diseases, related chronic disorders, all-cause, and cause-specific mortality. We identify 35 modifiable factors for age gap (p < 4.81 × 10-4 ), where pulmonary functions, body mass, hand grip strength, basal metabolic rate, estimated glomerular filtration rate, and C-reactive protein show the most significant associations. Genetic analyses replicate the possible associations between age gap and health-related outcomes and further identify CST3 as an essential gene for biological aging, which is highly expressed in the brain and is associated with immune and metabolic traits. Our study profiles the landscape of biological aging and provides insights into the preventive strategies and therapeutic targets for aging.

Impact of Serum Cystatin C Level on Long-Term Cognitive Impairment After Acute Ischemic Stroke and Transient Ischemic Attack

Objective

Cognitive impairment after stroke/transient ischemic attack (TIA) has a high prevalence. Cystatin C (CysC) has been found as a novel biomarker of neurodegenerative diseases, such as dementia and Alzheimer's disease. We aimed to explore the possible correlations of serum CysC level with cognitive impairment in patients who had mild ischemic stroke and TIA after 1 year.

Methods

We measured serum CysC level in 1025 participants with a minor ischemic stroke/TIA from enrolled from the Impairment of Cognition and Sleep (ICONS) study of the China National Stroke Registry-3 (CNSR-3). They were divided into four groups according to quartiles of baseline CysC levels. Patients' cognitive functions were assessed by Montreal Cognitive Assessment (MoCA)-Beijing at day 14 and at 1 year. Multiple logistic regression models were performed to evaluate the relationship between CysC and post-stroke cognitive impairment (PSCI) at 1-year follow-up.

Results

Cognitive impairment was defined as MoCA-Beijing ≤22. Most patients were in 60s (61.52±10.97 years old) with a median (interquartile range) National Institute of Health Stroke Scale(NIHSS) score of 3.00 (4.00) and greater than primary school level of education, and 743 participants (72.49%) were male. Among the 1025 participants, 331 participants (32.29%) patients suffered PSCI at 1-year follow-up. A U-shaped association was observed between CysC and 1-year PSCI [quartile (Q)1 vs Q3: adjusted odds ratio (aOR) 2.69, 95% CI 1.67-4.34, p < 0.0001; Q2 vs Q3: aOR 1.63, 95% CI 1.03-2.57, p = 0.0354; Q4 vs Q3: aOR 1.83, 95% CI 1.16-2.87, p = 0.009]. Moreover, the U-shaped trends were also found between CysC level and the subscores of attention, recall, abstraction and language in MoCA.

Conclusion

CysC showed a U-shaped correlation with 1-year overall cognitive function. It is probable that measurement of the serum CysC level would aid in the early diagnosis of PSCI.

Loss of cystatin C regulates permeability and inflammatory pathways in retina

Cystatin C has been linked to inflammation in other diseases, such as epilepsy and Alzheimer's disease. These studies were designed to investigate whether Cystatin C regulates retinal inflammation and permeability. To address this question, we used Cystatin C knockout mice in a retinal ischemia/reperfusion model to determine whether Cystatin C regulated retinal damage, as well as inflammatory mediators and retinal permeability. To support the mouse work, we also used primary retinal endothelial cells cultured in normal and high glucose. Ischemia/reperfusion in Cystatin C knockout mice caused increased formation of degenerate capillaries. Loss of Cystatin C increased fluorescein leakage in the retina, which was accompanied by reduced levels of zonula occludin 1 (ZO-1) and occludin proteins. When REC were grown in high glucose, recombinant Cystatin C decreased retinal permeability, while Cystatin C siRNA increased dextran flux compared to high glucose alone. Recombinant Cystatin C decreased levels of interleukin-1-beta (IL-1β) and high mobility group box 1 (HMGB1) levels. In conclusion, loss of Cystatin C increased vascular damage in response to ischemia/reperfusion. Cystatin C regulated permeability and inflammatory mediators in the retina in response to stressors. Cystatin C offers a new target for retinal disease therapeutic development.

Analysis of Wild Type and Variant B Cystatin C Interactome in Retinal Pigment Epithelium Cells Reveals Variant B Interacting Mitochondrial Proteins

Cystatin C, a secreted cysteine protease inhibitor, is abundantly expressed in retinal pigment epithelium (RPE) cells. A mutation in the protein's leader sequence, corresponding to formation of an alternate variant B protein, has been linked with an increased risk for both age-related macular degeneration (AMD) and Alzheimer's disease (AD). Variant B cystatin C displays intracellular mistrafficking with partial mitochondrial association. We hypothesized that variant B cystatin C interacts with mitochondrial proteins and impacts mitochondrial function. We sought to determine how the interactome of the disease-related variant B cystatin C differs from that of the wild-type (WT) form. For this purpose, we expressed cystatin C Halo-tag fusion constructs in RPE cells to pull down proteins interacting with either the WT or variant B form, followed by identification and quantification by mass spectrometry. We identified a total of 28 interacting proteins, of which 8 were exclusively pulled down by variant B cystatin C. These included 18 kDa translocator protein (TSPO) and cytochrome B5 type B, both of which are localized to the mitochondrial outer membrane. Variant B cystatin C expression also affected RPE mitochondrial function with increased membrane potential and susceptibility to damage-induced ROS production. The findings help us to understand how variant B cystatin C differs functionally from the WT form and provide leads to RPE processes adversely affected by the variant B genotype.

Bioinformatics Analysis of Next Generation Sequencing Data Identifies Molecular Biomarkers Associated With Type 2 Diabetes Mellitus

Background

Type 2 diabetes mellitus (T2DM) is the most common metabolic disorder. The aim of the present investigation was to identify gene signature specific to T2DM.

Methods

The next generation sequencing (NGS) dataset GSE81608 was retrieved from the gene expression omnibus (GEO) database and analyzed to identify the differentially expressed genes (DEGs) between T2DM and normal controls. Then, Gene Ontology (GO) and pathway enrichment analysis, protein-protein interaction (PPI) network, modules, miRNA (micro RNA)-hub gene regulatory network construction and TF (transcription factor)-hub gene regulatory network construction, and topological analysis were performed. Receiver operating characteristic curve (ROC) analysis was also performed to verify the prognostic value of hub genes.

Results

A total of 927 DEGs (461 were up regulated and 466 down regulated genes) were identified in T2DM. GO and REACTOME results showed that DEGs mainly enriched in protein metabolic process, establishment of localization, metabolism of proteins, and metabolism. The top centrality hub genes APP, MYH9, TCTN2, USP7, SYNPO, GRB2, HSP90AB1, UBC, HSPA5, and SQSTM1 were screened out as the critical genes. ROC analysis provides prognostic value of hub genes.

Conclusion

The potential crucial genes, especially APP, MYH9, TCTN2, USP7, SYNPO, GRB2, HSP90AB1, UBC, HSPA5, and SQSTM1, might be linked with risk of T2DM. Our study provided novel insights of T2DM into genetics, molecular pathogenesis, and novel therapeutic targets.

High-Fat Diet Alters the Retinal Transcriptome in the Absence of Gut Microbiota

The relationship between retinal disease, diet, and the gut microbiome has shown increasing importance over recent years. In particular, high-fat diets (HFDs) are associated with development and progression of several retinal diseases, including age-related macular degeneration (AMD) and diabetic retinopathy. However, the complex, overlapping interactions between diet, gut microbiome, and retinal homeostasis are poorly understood. Using high-throughput RNA-sequencing (RNA-seq) of whole retinas, we compare the retinal transcriptome from germ-free (GF) mice on a regular diet (ND) and HFD to investigate transcriptomic changes without influence of gut microbiome. After correction of raw data, 53 differentially expressed genes (DEGs) were identified, of which 19 were upregulated and 34 were downregulated in GF-HFD mice. Key genes involved in retinal inflammation, angiogenesis, and RPE function were identified. Enrichment analysis revealed that the top 3 biological processes affected were regulation of blood vessel diameter, inflammatory response, and negative regulation of endopeptidase. Molecular functions altered include endopeptidase inhibitor activity, protease binding, and cysteine-type endopeptidase inhibitor activity. Human and mouse pathway analysis revealed that the complement and coagulation cascades are significantly affected by HFD. This study demonstrates novel data that diet can directly modulate the retinal transcriptome independently of the gut microbiome.

Increased risk of Alzheimer's disease among patients with age-related macular degeneration: A nationwide population-based study

OBJECTIVE

This study aimed to investigate the risk of Alzheimer's disease among patients with age-related macular degeneration and its association with confounding comorbidities.

METHOD

This was a population-based, retrospective cohort study. By accessing data from the National Health Insurance Research Database of Taiwan, we identified 10,578 patients aged 50-100 years who were newly diagnosed with age-related macular degeneration between 2000 and 2012 and 10,578 non- age-related macular degeneration individuals. The comorbidities assessed were osteoporosis, diabetes, cirrhosis, cerebrovascular disease, chronic kidney disease, hypertension, hyperlipidemia, coronary artery disease, and chronic obstructive pulmonary disease.

RESULTS

Patients with age-related macular degeneration had a 1.23-fold increased risk of their condition advancing to Alzheimer's disease (aHR = 1.23, 95% CI = 1.04-1.46). The younger patients were diagnosed with age-related macular degeneration, the more likely patients got Alzheimer's disease (50-64 age group: aHR = 1.97, 95% CI = 1.04-3.73; 65-79 age group: aHR = 1.27, 95% CI = 1.02-1.58; 80-100 age group: aHR = 1.06, 95% CI = 0.78-1.45). In addition, there were significantly higher risks of Alzheimer's disease for patients with cirrhosis (aHR = 1.50, 95% CI = 1.09-2.06) in the age-related macular degeneration cohort than in the non-age-related macular degeneration cohort.

CONCLUSION

Patients with age-related macular degeneration may exhibit a higher risk of Alzheimer's disease than people without age-related macular degeneration.

Longitudinal single-cell RNA-seq of hESCs-derived retinal organoids

Human retina development involves multiple well-studied signaling pathways that promote the genesis of a wide arrange of different cell types in a complex architectural structure. Human embryonic stem cells (hESCs)-derived retinal organoids could recapitulate the human retinal development. We performed single-cell RNA-seq of retinal organoids from 5 time points (D36, D66, D96, D126, D186) and identified 9 distinct populations of cells. In addition, we analyzed the molecular characteristics of each main population and followed them from genesis to maturity by pseudotime analysis and characterized the cell-cell interactions between different cell types. Interestingly, we identified insulin receptor (INSR) as a specifically expressed receptor involved in the genesis of photoreceptors, and pleiothropin (PTN)-protein tyrosine phosphatase receptor type Z1 (PTPRZ1) as a mediator of a previously unknown interaction between Müller and retinal progenitor cells. Taken together, these findings provide a rich transcriptome-based lineage map for studying human retinal development and modeling developmental disorders in retinal organoids.

Absence of miRNA-146a Differentially Alters Microglia Function and Proteome

Background: MiR-146a is an important regulator of innate inflammatory responses and is also implicated in cell death and survival.

Methods: By sorting CNS resident cells, microglia were the main cellular source of miR-146a. Therefore, we investigated microglia function and phenotype in miR-146a knock-out (KO) mice, analyzed the proteome of KO and wild-type (WT) microglia by LC-MS/MS, and examined miR-146a expression in different brain lesions of patients with multiple sclerosis (MS).

Results: When stimulated with LPS or myelin in vitro, microglia from KO mice expressed higher levels of IL-1β, TNF, IL-6, IL-10, CCL3, and CCL2 compared to WT. Stimulation increased migration and phagocytosis of WT but not KO microglia. CD11c⁺ microglia were induced by cuprizone (CPZ) in the WT mice but less in the KO. The proteome of ex vivo microglia was not different in miR-146a KO compared to WT mice, but CPZ treatment induced differential and reduced protein responses in the KO: GOT1, COX5b, CRYL1, and cystatin-C were specifically changed in KO microglia. We explored discriminative features of microglia proteomes: sparse Partial Least Squares-Discriminant Analysis showed the best discrimination when control and CPZ-treated conditions were compared. Cluster of ten proteins separated WT and miR-146a KO microglia after CPZ: among them were sensomes allowing to perceive the environment, Atp1a3 that belongs to the signature of CD11c⁺ microglia, and proteins related to inflammatory responses (S100A9, Ppm1g). Finally, we examined the expression of miR-146a and its validated target genes in different brain lesions of MS patients. MiR-146 was upregulated in all lesion types, and the highest expression was in active lesions. Nineteen of 88 validated target genes were significantly changed in active lesions, while none were changed in NAWM.

Conclusion: Our data indicated that microglia is the major source of miR-146a in the CNS. The absence of miR-146a differentially affected microglia function and proteome, and miR-146a may play an important role in gene regulation of active MS lesions.

Investigating APOE, APP-Aβ metabolism genes and Alzheimer's disease GWAS hits in brain small vessel ischemic disease

Alzheimer’s disease and small vessel ischemic disease frequently co-exist in the aging brain. However, pathogenic links between these 2 disorders are yet to be identified. Therefore we used Taqman genotyping, exome and RNA sequencing to investigate Alzheimer’s disease known pathogenic variants and pathways: APOE ε4 allele, APP-Aβ metabolism and late-onset Alzheimer’s disease main genome-wide association loci (APOE, BIN1, CD33, MS4A6A, CD2AP, PICALM, CLU, CR1, EPHA1, ABCA7) in 96 early-onset small vessel ischemic disease Caucasian patients and 368 elderly neuropathologically proven controls (HEX database) and in a mouse model of cerebral hypoperfusion. Only a minority of patients (29%) carried APOE ε4 allele. We did not detect any pathogenic mutation in APP, PSEN1 and PSEN2 and report a burden of truncating mutations in APP-Aß degradation genes. The single-variant association test identified 3 common variants with a likely protective effect on small vessel ischemic disease (0.54>OR > 0.32, adj. p-value <0.05) (EPHA1 p.M900V and p.V160A and CD33 p.A14V). Moreover, 5/17 APP-Aß catabolism genes were significantly upregulated (LogFC > 1, adj. p-val<0.05) together with Apoe, Ms4a cluster and Cd33 during brain hypoperfusion and their overexpression correlated with the ischemic lesion size. Finally, the detection of Aβ oligomers in the hypoperfused hippocampus supported the link between brain ischemia and Alzheimer’s disease pathology.

Increased Rate of Retinal Pigment Epithelial Cell Migration and Pro-Angiogenic Potential Ensuing From Reduced Cystatin C Expression

Purpose

Variant B precursor cysteine protease inhibitor cystatin C, a known recessive risk factor for developing exudative age-related macular degeneration (AMD), presents altered intracellular trafficking and reduced secretion from retinal pigment epithelial (RPE) cells. Because cystatin C inhibits multiple extracellular matrix (ECM)-degrading cathepsins, this study evaluated the role of this mutation in inducing ECM-related functional changes in RPE cellular behavior.

Methods

Induced pluripotent stem cells gene-edited bi-allelically by CRISPR/Cas9 to express the AMD-linked cystatin C variant were differentiated to RPE cells and assayed for their ability to degrade fluorescently labeled ECM proteins. Cellular migration and adhesion on multiple ECM proteins, differences in transepithelial resistance and polarized protein secretion were tested. Vessel formation induced by gene edited cells-conditioned media was quantified using primary human dermal microvascular epithelial cells.

Results

Variant B cystatin C-expressing induced pluripotent stem cells-derived RPE cells displayed a significantly higher rate of laminin and fibronectin degradation 3 days after seeding on fluorescently labeled ECM (P < 0.05). Migration on matrigel, collagen IV and fibronectin was significantly faster for edited cells compared with wild-type (WT) cells. Both edited and WT cells displayed polarized secretion of cystatin C, but transepithelial resistance was lower in gene-edited cells after 6 weeks culture, with significantly lower expression of tight junction protein claudin-3. Media conditioned by gene-edited cells stimulated formation of significantly longer microvascular tubes (P < 0.05) compared with WT-conditioned media.

Conclusions

Reduced levels of cystatin C lead to changes in the RPE ability to degrade, adhere, and migrate supporting increased invasiveness and angiogenesis relevant for AMD pathology.

Secretory proteostasis of the retinal pigmented epithelium: Impairment links to age-related macular degeneration

Secretory proteostasis integrates protein synthesis, processing, folding and trafficking pathways that are essential for efficient cellular secretion. For the retinal pigment epithelium (RPE), secretory proteostasis is of vital importance for the maintenance of the structural and functional integrity of apical (photoreceptors) and basal (Bruch's membrane/choroidal blood supply) sides of the environment it resides in. This integrity is achieved through functions governed by RPE secreted proteins, which include extracellular matrix modelling/remodelling, angiogenesis and immune response modulation. Impaired RPE secretory proteostasis affects not only the extracellular environment, but leads to intracellular protein aggregation and ER-stress with subsequent cell death. Ample recent evidence implicates dysregulated proteostasis as a key factor in the development of age-related macular degeneration (AMD), the leading cause of blindness in the developed world, and research aiming to characterise the roles of various proteins implicated in AMD-associated dysregulated proteostasis unveiled unexpected facets of the mechanisms involved in degenerative pathogenesis. This review analyses cellular processes unveiled by the study of the top 200 transcripts most abundantly expressed by the RPE/choroid in the light of the specialised secretory nature of the RPE. Functional roles of these proteins and the mechanisms of their impaired secretion, due to age and genetic-related causes, are analysed in relation to AMD development. Understanding the importance of RPE secretory proteostasis in relation to maintaining retinal health and how it becomes impaired in disease is of paramount importance for the development and assessment of future therapeutic advancements involving gene and cell therapies.

Measurement of serum cystatin C: A valuable tool for evaluating dyskinesia in Parkinson's disease

Although cystatin C (Cys C) has been implicated in the pathophysiology of Parkinson's disease (PD), whether it can be used as a tool for evaluating dyskinesia is unknown. In the present study, the association of Cys C with dyskinesia in PD patients was investigated. Fasting serum Cys C levels were measured from 120 PD patients and 156 healthy controls. Demographic information was collected for all patients. In addition, levodopa (L-dopa)-equivalent dose, Unified Parkinson's Disease Rating Scale (UPDRS) score, Hoehn and Yahr (H&Y) stage, and dyskinesia were assessed in PD patients. Receiver operating characteristic (ROC) curves were adopted to assess the evaluating accuracy of Cys C levels for distinguishing dyskinesia in PD patients. Patients with PD exhibited significantly higher serum Cys C levels compared with heathy controls. Dyskinesia was observed in 32 patients (26.7%). Multiple logistic regression showed serum Cys C levels (odds ratio, OR 12.93; 95% confidence interval, CI 1.08-54.23; p = 0.043), duration of disease (OR 1.03, 95% CI 1.01-1.05, p = 0.001) and UPDRS II score (OR 1.07, 95% CI 1.01-1.14, p = 0.019) were independently associated with dyskinesia. The ROC curve for the Cys C levels yielded a valuable accuracy for distinguishing dyskinesia in PD patients. Serum Cys C levels were independently associated with dyskinesia and may be a valuable screening tool for differentiating dyskinesia in PD patients. Although the pathophysiological mechanism of PD is complicated, the results from our study provide a better understanding of the association between Cys C and dyskinesia in PD patients and may yield insights into the pathogenesis of PD.

CRISPR/Cas9-mediated one step bi-allelic change of genomic DNA in iPSCs and human RPE cells in vitro with dual antibiotic selection

CRISPR/Cas9 causes double-stranded DNA breaks that can undergo DNA repair either via non-homologous end joining (NHEJ) or, in the presence of a template, homology-directed repair (HDR). HDR is typically used to insert a specific genetic modification into the genome but has low efficiency compared to NHEJ, which is lowered even further when trying to create a homozygous change. In this study we devised a novel approach for homozygous single base editing based on utilising simultaneously two donor DNA templates cloned in plasmids with different antibiotic resistant genes. The donor templates were co-transfected alongside the CRISPR/Cas9 machinery into cells and a double antibiotic selection was optimised and allowed the isolation of viable desired clones. We applied the method for obtaining isogenic cells homozygous for variant B cystatin C, a recessive risk factor for age-related macular degeneration and Alzheimer's disease, in both induced Pluripotent Stem Cells (iPSCs) and a human RPE cell line. Bi-allelic gene edited clones were validated by sequencing, demonstrating that the double antibiotic templates approach worked efficiently for both iPSCs and human differentiated cells. We propose that this one step gene editing approach can be used to improve the specificity and frequency of introducing homozygous modifications in mammalian cells.

Combined measurement of plasma cystatin C and low-density lipoprotein cholesterol: A valuable tool for evaluating progressive supranuclear palsy

INTRODUCTION

Progressive supranuclear palsy (PSP) was previously thought as a cause of atypical Parkinsonism. Although Cystatin C (Cys C) and low-density cholesterol lipoprotein-C (LDL-C) are known to play critical roles in Parkinsonism, it is unknown whether they can be used as markers to distinguish PSP patients from healthy subjects and to determine disease severity.

METHODS

We conducted a cross-sectional study to determine plasma Cys C/HDL/LDL-C levels of 40 patients with PSP and 40 healthy age-matched controls. An extended battery of motor and neuropsychological tests, including the PSP-Rating Scale (PSPRS), the Non-Motor Symptoms Scale (NMSS), Geriatric Depression Scale (GDS) and Mini-Mental State Examination (MMSE), was used to evaluate the disease severity. Receiver operating characteristic (ROC) curves were adopted to assess the prognostic accuracy of Cys C/LDL-C levels in distinguishing PSP from healthy subjects.

RESULTS

Patients with PSP exhibited significantly higher plasma levels of Cys C and lower LDL-C. The levels of plasma Cys C were positively and inversely correlated with the PSPRS/NMSS and MMSE scores, respectively. The LDL-C/HDL-C ratio was positively associated with PSPRS/NMSS and GDS scores. The ROC curve for the combination of Cys C and LDL-C yielded a better accuracy for distinguishing PSP from healthy subjects than the separate curves for each parameter.

CONCLUSIONS

Plasma Cys C and LDL-C may be valuable screening tools for differentiating PSP from healthy subjects; while they could be useful for the PSP intensifies and severity evaluation. A better understanding of Cys C and LDL-C may yield insights into the pathogenesis of PSP.

Genetics of age-related macular degeneration (AMD)

Age-related macular degeneration (AMD) is a progressive blinding disease and represents the leading cause of visual impairment in the aging population. AMD affects central vision which impairs one's ability to drive, read and recognize faces. There is no cure for this disease and current treatment modalities for the exudative form of the disease require repeated intravitreal injections which may be painful, are incompletely efficacious, and represent a significant treatment burden for both the patient and physician. As such, AMD represents a significant and important clinical problem.It is anticipated that in three years' time, 196 million individuals will be affected with AMD. Over 250 billion dollars per year are spent on care for AMD patients in the US. Over half of the heritability is explained by two major loci, thus AMD is considered the most well genetically defined of the complex disorders. A recent GWAS on 43,566 subjects identified novel loci and pathways associated with AMD risk, which has provided an excellent platform for additional functional studies. Genetic variants have been investigated, particularly with respect to anti-VEGF treatment, however to date, no pharmacogenomic associations have been consistently identified across these studies. It may be that if the goal of personalized medicine is to be realized and biomarkers are to have predictive value for determining the magnitude of risk for AMD at the genetic level, one will need to examine the relationships between these pathways across disease state and relative to modifiable risk factors such as hypertension, smoking, body mass index, and hypercholesterolemia. Further studies investigating protective alleles in populations with low AMD prevalence may lead to this goal.

Unraveling the genes implicated in Alzheimer's disease

Alzheimer's disease (AD) is a heterogeneous neurodegenerative disorder and it is the most common form of dementia in the elderly. Early onset AD is caused by mutations in three genes: Amyloid-β precursor protein, presenilin 1 (PSEN1) and PSEN2. Late onset AD (LOAD) is complex and apolipoprotein E is the only unanimously accepted genetic risk factor for its development. Various genes implicated in AD have been identified using advanced genetic technologies, however, there are many additional genes that remain unidentified. The present review highlights the genetics of early and LOAD and summarizes the genes involved in different signaling pathways. This may provide insight into neurodegenerative disease research and will facilitate the development of effective strategies to combat AD.

Cystatin C as a potential therapeutic mediator against Parkinson's disease via VEGF-induced angiogenesis and enhanced neuronal autophagy in neurovascular units

Cystatin C (CYS C, Cst3) is an endogenous cysteine protease inhibitor that plays neuroprotective roles in neurodegenerative diseases. We aimed to explore the association of CYS C with Parkinson’s disease (PD) models and investigate its involvement in the role of neurovascular units (NVUs) in PD neuro-pathogenesis. We used A53T α-synuclein (SNCA) transgenic mice and 6-hydroxydopamine-lesioned DAergic PC12 cells as experimental PD models to investigate the mechanisms behind this association. The injections of CYS C were administered to the right substantia nigra (SN) of A53T SNCA transgenic mice to measure the effects of CYS C in transgenic A53T SNCA mice. To explore the angiogenesis in vivo and in vitro, we used the chick embryo chorioallantoic membrane (CAM) assay and tube formation (TF) assay. We found that CYS C has a neuroprotective effect in this in vivo PD model. We observed increased VEGF, NURR1 and autophagy markers LC3B and decreased SNCA and apoptosis marker cleaved CASP3 in different brain regions of CYS C-treated A53T SNCA transgenic mice. In vitro, we observed that CYS C-induced VEGF, a secreted protein, attenuated 6-OHDA-lesioned DAergic PC12 cell degeneration by regulating p-PKC-α/p-ERK1/2-Nurr1 signaling and inducing autophagy. VEGF-mediated angiogenesis was markedly enhanced in the conditioned media of 6-OHDA-lesioned PC12 cells with CYS C-overexpression, whereas blockage of autophagy in CYS C-overexpressing PC12 cells significantly downregulated VEGF expression and the associated angiogenesis. Our data indicate that CYS C displays dual neuronal–vascular functions, promoting PC12 cell survival and angiogenesis via regulating the level of secreted VEGF in NVUs. Our study provides evidence that may aid in the development of an alternative approach for the treatment of PD through modulation of CYS C-mediated neuronal-vascular pathways.

Cystatin C Shifts APP Processing from Amyloid-β Production towards Non-Amyloidgenic Pathway in Brain Endothelial Cells

Amyloid-β (Aβ), the major component of neuritic plaques in Alzheimer's disease (AD), is derived from sequential proteolytic cleavage of amyloid protein precursor (APP) by secretases. In this study, we found that cystatin C (CysC), a natural cysteine protease inhibitor, is able to reduce Aβ40 secretion in human brain microvascular endothelial cells (HBMEC). The CysC-induced Aβ40 reduction was caused by degradation of β-secretase BACE1 through the ubiquitin/proteasome pathway. In contrast, we found that CysC promoted secretion of soluble APPα indicating the activated non-amyloidogenic processing of APP in HBMEC. Further results revealed that α-secretase ADAM10, which was transcriptionally upregulated in response to CysC, was required for the CysC-induced sAPPα secretion. Knockdown of SIRT1 abolished CysC-triggered ADAM10 upregulation and sAPPα production. Taken together, our results demonstrated that exogenously applied CysC can direct amyloidogenic APP processing to non-amyloidgenic pathway in brain endothelial cells, mediated by proteasomal degradation of BACE1 and SIRT1-mediated ADAM10 upregulation. Our study unveils previously unrecognized protective role of CysC in APP processing.

Amyloid properties of the leader peptide of variant B cystatin C: implications for Alzheimer and macular degeneration

Variant B (VB) of cystatin C has a mutation in its signal peptide (A25T), which interferes with its processing leading to reduced secretion and partial retention in the vicinity of the mitochondria. There are genetic evidences of the association of VB with Alzheimer's disease (AD) and age-related macular degeneration (AMD). Here, we investigated aggregation and amyloid propensities of unprocessed VB combining computational and in vitro studies. Aggregation predictors revealed the presence of four aggregation-prone regions, with a strong one at the level of the signal peptide, which indeed formed toxic aggregates and mature amyloid fibrils in solution. In light of these results, we propose for the first time the role of the signal peptide in pathogenesis of AD and AMD.

Evidence of Alternative Cystatin C Signal Sequence Cleavage Which Is Influenced by the A25T Polymorphism

Cystatin C (Cys C) is a small, potent, cysteine protease inhibitor. An Ala25Thr (A25T) polymorphism in Cys C has been associated with both macular degeneration and late-onset Alzheimer's disease. Previously, studies have suggested that this polymorphism may compromise the secretion of Cys C. Interestingly, we found that untagged A25T, A25T tagged C-terminally with FLAG, or A25T FLAG followed by green fluorescent protein (GFP), were all secreted as efficiently from immortalized human cells as their wild-type (WT) counterparts (e.g., 112%, 100%, and 88% of WT levels from HEK-293T cells, respectively). Supporting these observations, WT and A25T Cys C variants also showed similar intracellular steady state levels. Furthermore, A25T Cys C did not activate the unfolded protein response and followed the same canonical endoplasmic reticulum (ER)-Golgi trafficking pathway as WT Cys C. WT Cys C has been shown to undergo signal sequence cleavage between residues Gly26 and Ser27. While the A25T polymorphism did not affect Cys C secretion, we hypothesized that it may alter where the Cys C signal sequence is preferentially cleaved. Under normal conditions, WT and A25T Cys C have the same signal sequence cleavage site after Gly26 (referred to as 'site 2' cleavage). However, in particular circumstances when the residues around site 2 are modified (such as by the presence of an N-terminal FLAG tag immediately after Gly26, or by a Gly26Lys (G26K) mutation), A25T has a significantly higher likelihood than WT Cys C of alternative signal sequence cleavage after Ala20 ('site 1') or even earlier in the Cys C sequence. Overall, our results indicate that the A25T polymorphism does not cause a significant reduction in Cys C secretion, but instead predisposes the protein to be cleaved at an alternative signal sequence cleavage site if site 2 is hindered. Additional N-terminal amino acids resulting from alternative signal sequence cleavage may, in turn, affect the protease inhibition function of Cys C.