Rs5848 variant influences GRN mRNA levels in brain and peripheral mononuclear cells in patients with Alzheimer's disease

Genetics screening in an Italian cohort of patients with Amyotrophic Lateral Sclerosis: the importance of early testing and its implication

INTRODUCTION

Amyotrophic Lateral Sclerosis (ALS) is a neurodegenerative disease with an elusive etiology. While environmental factors have been considered, familial ALS cases have raised the possibility of genetic involvement. This genetic connection is increasingly evident, even in patients with sporadic ALS. We allowed access to the genetic test to all patients attending our clinic to identify the prevalence and the role of genetic variants in the development of the disease and to identify patients with potentially treatable forms of the disease.

MATERIALS AND METHODS

194 patients with probable or definite ALS, were enrolled. A comprehensive genetic testing was performed, including sequencing all exons of the SOD1 gene and testing for hexanucleotide intronic repeat expansions (G4C2) in the C9orf72 gene using fluorescent repeat-primed PCR (RP-PCR). Whole Exome NGS Sequencing (WES) was performed, followed by an in silico multigene panel targeting neuromuscular diseases, spastic paraplegia, and motor distal neuropathies. We conducted statistical analyses to compare different patient groups.

RESULTS

Clinically significant pathogenetic variants were detected in 14.43% of cases. The highest prevalence of pathogenetic variants was observed in fALS patients, but a substantial proportion of sALS patients also displayed at least one variant, either pathogenetic or of uncertain significance (VUS). The most observed pathogenetic variant was the expansion of the C9orf72 gene, which was associated with a shorter survival. SOD1 variants were found in 1.6% of fALS and 2.5% of sALS patients.

DISCUSSION

The study reveals a significant number of ALS patients carrying pathogenic or likely pathogenic variants, with a higher prevalence in familial ALS cases. The expansion of the C9orf72 gene emerges as the most common genetic cause of ALS, affecting familial and sporadic cases. Additionally, SOD1 variants are detected at an unexpectedly higher rate, even in patients without a familial history of ALS, underscoring the crucial role of genetic testing in treatment decisions and potential participation in clinical trials. We also investigated variants in genes such as TARDBP, FUS, NEK1, TBK1, and DNAJC7, shedding light on their potential involvement in ALS. These findings underscore the complexity of interpreting variants of uncertain significance (VUS) and their ethical implications in patient communication and genetic counseling for patients' relatives.

CONCLUSION

This study emphasizes the diverse genetic basis of ALS and advocates for integrating comprehensive genetic testing into diagnostic protocols. The evolving landscape of genetic therapies requires identifying all eligible patients transcending traditional familial boundaries. The presence of VUS highlights the multifaceted nature of ALS genetics, prompting further exploration of complex interactions among genetic variants, environmental factors, and disease development.

Investigating the Role and Regulation of GPNMB in Progranulin-deficient Macrophages

Progranulin is a holoprotein that is critical for successful aging, and insufficient levels of progranulin are associated with increased risk for developing age-related neurodegenerative diseases like AD, PD, and FTD. Symptoms can vary widely, but a uniting feature among these different neurodegenerative diseases is prodromal peripheral immune cell phenotypes. However, there remains considerable gaps in the understanding of the function(s) of progranulin in immune cells, and recent work has identified a novel target candidate called GPNMB. We addressed this gap by investigating the peritoneal macrophages of 5-6-month-old Grn KO mice, and we discovered that GPNMB is actively increased as a result of insufficient progranulin and that MITF, a transcription factor, is also dysregulated in progranulin-deficient macrophages. These findings highlight the importance of early-stage disease mechanism(s) in peripheral cell populations that may lead to viable treatment strategies to delay disease progression at an early, prodromal timepoint and extend therapeutic windows.

Mutations in PGRN gene associated with the risk of psoriasis in Pakistan: a case control study

BACKGROUND

Psoriasis is a chronic, autoimmune, papulosquamous skin disorder, characterized by the formation of drop-like papules and silvery-white plaques surrounded by reddened or inflamed skin, existing predominantly on the scalp, knees and elbows. The characteristic inflammation and hyperproliferation of keratinocytes in psoriasis is regulated by progranulin (PGRN), which suppresses the expression and release of inflammatory cytokines, such as TNF-α.

METHODOLOGY

In this study mutation analysis of the PGRN gene was performed by extracting the genomic DNA from blood samples of 171 diagnosed psoriasis patients and controls through standard salting-out method, followed by amplification and sequencing of the targeted region of exon 5-7 of PGRN gene.

RESULTS

Three single nucleotide polymorphisms, rs25646, rs850713 and a novel point mutation 805A/G were identified in the PGRN gene with significant association with the disease. The variant alleles of the polymorphisms were significantly distributed among cases and controls, and statistical analysis suggested that the mutant genotypes conferred a higher risk of psoriasis development and progression. Multi-SNP haplotype analysis indicated that the CAA (OR = 8.085, 95% CI = 5.16-12.66) and the CAG (OR = 3.204, 95% CI = 1.97-5.21) haplotypes were significantly associated with psoriasis pathogenesis.

CONCLUSIONS

These findings demonstrate that polymorphisms in PGRN might act as potential molecular targets for early diagnosis of psoriasis in susceptible individuals.

Progranulin and GPNMB: interactions in endo-lysosome function and inflammation in neurodegenerative disease

BACKGROUND

Alterations in progranulin (PGRN) expression are associated with multiple neurodegenerative diseases (NDs), including frontotemporal dementia (FTD), Alzheimer's disease (AD), Parkinson's disease (PD), and lysosomal storage disorders (LSDs). Recently, the loss of PGRN was shown to result in endo-lysosomal system dysfunction and an age-dependent increase in the expression of another protein associated with NDs, glycoprotein non-metastatic B (GPNMB).

MAIN BODY

It is unclear what role GPNMB plays in the context of PGRN insufficiency and how they interact and contribute to the development or progression of NDs. This review focuses on the interplay between these two critical proteins within the context of endo-lysosomal health, immune function, and inflammation in their contribution to NDs.

SHORT CONCLUSION

PGRN and GPNMB are interrelated proteins that regulate disease-relevant processes and may have value as therapeutic targets to delay disease progression or extend therapeutic windows.

Targeting Progranulin as an Immuno-Neurology Therapeutic Approach

Immuno-neurology is an emerging therapeutic strategy for dementia and neurodegeneration designed to address immune surveillance failure in the brain. Microglia, as central nervous system (CNS)-resident myeloid cells, routinely perform surveillance of the brain and support neuronal function. Loss-of-function (LOF) mutations causing decreased levels of progranulin (PGRN), an immune regulatory protein, lead to dysfunctional microglia and are associated with multiple neurodegenerative diseases, including frontotemporal dementia caused by the progranulin gene (GRN) mutation (FTD-GRN), Alzheimer's disease (AD), Parkinson's disease (PD), limbic-predominant age-related transactivation response deoxyribonucleic acid binding protein 43 (TDP-43) encephalopathy (LATE), and amyotrophic lateral sclerosis (ALS). Immuno-neurology targets immune checkpoint-like proteins, offering the potential to convert aging and dysfunctional microglia into disease-fighting cells that counteract multiple disease pathologies, clear misfolded proteins and debris, promote myelin and synapse repair, optimize neuronal function, support astrocytes and oligodendrocytes, and maintain brain vasculature. Several clinical trials are underway to elevate PGRN levels as one strategy to modulate the function of microglia and counteract neurodegenerative changes associated with various disease states. If successful, these and other immuno-neurology drugs have the potential to revolutionize the treatment of neurodegenerative disorders by harnessing the brain's immune system and shifting it from an inflammatory/pathological state to an enhanced physiological/homeostatic state.

Converging links between adult-onset neurodegenerative Alzheimer's disease and early life neurodegenerative neuronal ceroid lipofuscinosis?

Evidence from genetics and from analyzing cellular and animal models have converged to suggest links between neurodegenerative disorders of early and late life. Here, we summarize emerging links between the most common late life neurodegenerative disease, Alzheimer's disease, and the most common early life neurodegenerative diseases, neuronal ceroid lipofuscinoses. Genetic studies reported an overlap of clinically diagnosed Alzheimer's disease and mutations in genes known to cause neuronal ceroid lipofuscinoses. Accumulating data strongly suggest dysfunction of intracellular trafficking mechanisms and the autophagy-endolysosome system in both types of neurodegenerative disorders. This suggests shared cytopathological processes underlying these different types of neurodegenerative diseases. A better understanding of the common mechanisms underlying the different diseases is important as this might lead to the identification of novel targets for therapeutic concepts, the transfer of therapeutic strategies from one disease to the other and therapeutic approaches tailored to patients with specific mutations. Here, we review dysfunctions of the endolysosomal autophagy pathway in Alzheimer's disease and neuronal ceroid lipofuscinoses and summarize emerging etiologic and genetic overlaps.

Preclinical Interventions in Mouse Models of Frontotemporal Dementia Due to Progranulin Mutations

Heterozygous loss-of-function mutations in progranulin (GRN) cause frontotemporal dementia (FTD), a leading cause of early-onset dementia characterized clinically by behavioral, social, and language deficits. There are currently no FDA-approved therapeutics for FTD-GRN, but this has been an active area of investigation, and several approaches are now in clinical trials. Here, we review preclinical development of therapies for FTD-GRN with a focus on testing in mouse models. Since most FTD-GRN-associated mutations cause progranulin haploinsufficiency, these approaches focus on raising progranulin levels. We begin by considering the disorders associated with altered progranulin levels, and then review the basics of progranulin biology including its lysosomal, neurotrophic, and immunomodulatory functions. We discuss mouse models of progranulin insufficiency and how they have been used in preclinical studies on a variety of therapeutic approaches. These include approaches to raise progranulin expression from the normal allele or facilitate progranulin production by the mutant allele, as well as approaches to directly increase progranulin levels by delivery across the blood-brain barrier or by gene therapy. Several of these approaches have entered clinical trials, providing hope that new therapies for FTD-GRN may be the next frontier in the treatment of neurodegenerative disease.

Serum progranulin is not associated with rs5848 polymorphism in Korean patients with neurodegenerative diseases

Low serum progranulin (PGRN) is known to be associated with granulin (GRN) gene mutation and T alleles of GRN rs5848 polymorphism. However, there have been only a few Asian studies exploring these. We investigated the serum PGRN levels, rs5848 genotypes, and their relations with cerebrospinal fluid (CSF) Alzheimer’s disease (AD) biomarkers in the Korean population. Serum PGRN levels, GRN rs5848 polymorphism, and GRN mutations were evaluated in 239 participants (22 cognitively unimpaired participants and 217 patients with neurodegenerative diseases). CSF AD biomarkers were also evaluated in 214 participants. There was no significant difference in the serum PGRN levels among the diagnostic groups. We could not find any GRN mutation carrier in our sample. The differences in the frequencies of the rs5848 genotypes among the clinical groups or the effects of the rs5848 genotypes on serum PGRN were not observed. There was no correlation between the serum PGRN level or rs5848 genotype and CSF AD biomarkers. Neither the T allele nor the TT genotype had an effect on the development of AD. Our results showed that serum PGRN levels were not associated with rs5848 genotypes, indicating that multiple single nucleotide polymorphisms might affect PGRN concentrations in an ethnicity-specific manner.

Uncovering the impact of noncoding variants in neurodegenerative brain diseases

Neurodegenerative brain diseases (NBDs) are characterized by cognitive decline and movement impairments caused by neuronal loss in different brain regions. A large fraction of the genetic heritability of NBDs is not explained by the current known mutations. Genome-wide association studies identified novel disease-risk loci, adding to the genetic basis of NBDs. Many of the associated variants reside in noncoding regions with distinct molecular functions. Genetic variation in these regions can alter functions and contribute to disease pathogenesis. Here, we discuss noncoding variants associated with NBDs. Methods for better functional interpretation of noncoding variation will expand our knowledge of the genetic architecture of NBDs and broaden the routes for therapeutic strategies.

Neurodegenerative Disease Risk in Carriers of Autosomal Recessive Disease

Genetics has driven significant discoveries in the field of neurodegenerative diseases (NDDs). An emerging theme in neurodegeneration warrants an urgent and comprehensive update: that carrier status of early-onset autosomal recessive (AR) disease, typically considered benign, is associated with an increased risk of a spectrum of late-onset NDDs. Glucosylceramidase beta (GBA1) gene mutations, responsible for the AR lysosomal storage disorder Gaucher disease, are a prominent example of this principle, having been identified as an important genetic risk factor for Parkinson disease. Genetic analyses have revealed further examples, notably GRN, TREM2, EIF2AK3, and several other LSD and mitochondria function genes. In this Review, we discuss the evidence supporting the strikingly distinct allele-dependent clinical phenotypes observed in carriers of such gene mutations and its impact on the wider field of neurodegeneration.

Sleep Characteristics and Cerebrospinal Fluid Progranulin in Older Adults: The CABLE Study

Cerebrospinal fluid (CSF) progranulin (PGRN) is related to various neurodegeneration diseases. And sleep problems can cause abnormality in protein metabolism in vivo. We aim to explore the potential associations between the self-reported sleep characteristics and CSF PGRN in cognitively intact older adults. Our study recruited 747 participants (mean (standard deviation (SD)) age, 61.99 (10.52) years, 329 (42.89%) females) who had normal cognition from the Chinese Alzheimer's Biomarker and LifestylE (CABLE) study with CSF PGRN and sleep characteristics measured. The multiple linear regression and nonlinear regression adjusted for age, gender, education, and apolipoprotein E-epsilon 4 gene (APOE4) status were used to assess the associations between sleep characteristics and PGRN. Interaction effects were explored between APOE4 status and sleep characteristics on CSF PGRN level. Sleep disturbances indicated lower CSF PGRN (β = - 0.0186, p = 0.0160). For detailed items in sleep disturbances, lower CSF PGRN was found in males who woke up during sleep (β = - 0.0121, p = 0.0062) and in females who had breathing difficulties (β = - 0.0258, p = 0.0271). Meanwhile, sleep efficiency was associated with CSF PGRN (β = - 0.0512, p = 0.0497). No significant interaction effects between sleep characteristics and APOE4 status were found. Meanwhile, we did not find a nonlinear relationship between nocturnal sleep duration and CSF PGRN. Sleep problems may influence the metabolism of PGRN, thus attenuating the protective effects of PGRN on neurodegeneration diseases.

Endosomal Trafficking in Alzheimer's Disease, Parkinson's Disease, and Neuronal Ceroid Lipofuscinosis

Neuronal ceroid lipofuscinosis (NCL) is one of the most prevalent neurodegenerative disorders of early life, Parkinson's disease (PD) is the most common neurodegenerative disorder of midlife, while Alzheimer's disease (AD) is the most common neurodegenerative disorder of late life. While they are phenotypically distinct, recent studies suggest that they share a biological pathway, retromer-dependent endosomal trafficking. A retromer is a multimodular protein assembly critical for sorting and trafficking cargo out of the endosome. As a lysosomal storage disease, all 13 of NCL's causative genes affect endolysosomal function, and at least four have been directly linked to retromer. PD has several known causative genes, with one directly linked to retromer and others causing endolysosomal dysfunction. AD has over 25 causative genes/risk factors, with several of them linked to retromer or endosomal trafficking dysfunction. In this article, we summarize the emerging evidence on the association of genes causing NCL with retromer function and endosomal trafficking, review the recent evidence linking NCL genes to AD, and discuss how NCL, AD, and PD converge on a shared molecular pathway. We also discuss this pathway's role in microglia and neurons, cell populations which are critical to proper brain homeostasis and whose dysfunction plays a key role in neurodegeneration.

Microglial Progranulin: Involvement in Alzheimer's Disease and Neurodegenerative Diseases

Neurodegenerative diseases such as Alzheimer’s disease have proven resistant to new treatments. The complexity of neurodegenerative disease mechanisms can be highlighted by accumulating evidence for a role for a growth factor, progranulin (PGRN). PGRN is a glycoprotein encoded by the GRN/Grn gene with multiple cellular functions, including neurotrophic, anti-inflammatory and lysosome regulatory properties. Mutations in the GRN gene can lead to frontotemporal lobar degeneration (FTLD), a cause of dementia, and neuronal ceroid lipofuscinosis (NCL), a lysosomal storage disease. Both diseases are associated with loss of PGRN function resulting, amongst other features, in enhanced microglial neuroinflammation and lysosomal dysfunction. PGRN has also been implicated in Alzheimer’s disease (AD). Unlike FTLD, increased expression of PGRN occurs in brains of human AD cases and AD model mice, particularly in activated microglia. How microglial PGRN might be involved in AD and other neurodegenerative diseases will be discussed. A unifying feature of PGRN in diseases might be its modulation of lysosomal function in neurons and microglia. Many experimental models have focused on consequences of PGRN gene deletion: however, possible outcomes of increasing PGRN on microglial inflammation and neurodegeneration will be discussed. We will also suggest directions for future studies on PGRN and microglia in relation to neurodegenerative diseases.

Genetic Risk Factors for Alzheimer Disease: Emerging Roles of Microglia in Disease Pathomechanisms

The accumulation of aggregated amyloid β (Aβ) peptides in the brain is deeply involved in Alzheimer disease (AD) pathogenesis. Mutations in APP and presenilins play major roles in Aβ pathology in rare autosomal-dominant forms of AD, whereas pathomechanisms of sporadic AD, accounting for the majority of cases, remain unknown. In this chapter, we review current knowledge on genetic risk factors of AD, clarified by recent advances in genome analysis technology. Interestingly, TREM2 and many genes associated with disease risk are predominantly expressed in microglia, suggesting that these risk factors are involved in pathogenicity through common mechanisms involving microglia. Therefore, we focus on factors closely associated with microglia and discuss their possible roles in pathomechanisms of AD. Furthermore, we review current views on the pathological roles of microglia and emphasize the importance of microglial changes in response to Aβ deposition and mechanisms underlying the phenotypic changes. Importantly, functional outcomes of microglial activation can be both protective and deleterious to neurons. We further describe the involvement of microglia in tau pathology and the activation of other glial cells. Through these topics, we shed light on microglia as a promising target for drug development for AD and other neurological disorders.

CSF progranulin increases in the course of Alzheimer's disease and is associated with sTREM2, neurodegeneration and cognitive decline

Progranulin (PGRN) is predominantly expressed by microglia in the brain, and genetic and experimental evidence suggests a critical role in Alzheimer's disease (AD). We asked whether PGRN expression is changed in a disease severity-specific manner in AD We measured PGRN in cerebrospinal fluid (CSF) in two of the best-characterized AD patient cohorts, namely the Dominant Inherited Alzheimer's Disease Network (DIAN) and the Alzheimer's Disease Neuroimaging Initiative (ADNI). In carriers of AD causing dominant mutations, cross-sectionally assessed CSF PGRN increased over the course of the disease and significantly differed from non-carriers 10 years before the expected symptom onset. In late-onset AD, higher CSF PGRN was associated with more advanced disease stages and cognitive impairment. Higher CSF PGRN was associated with higher CSF soluble TREM2 (triggering receptor expressed on myeloid cells 2) only when there was underlying pathology, but not in controls. In conclusion, we demonstrate that, although CSF PGRN is not a diagnostic biomarker for AD, it may together with sTREM2 reflect microglial activation during the disease.

Progranulin levels in blood in Alzheimer's disease and mild cognitive impairment

OBJECTIVE

Changes in progranulin (GRN) expression have been hypothesized to alter risk for Alzheimer's disease (AD). We investigated the relationship between GRN expression in peripheral blood and clinical diagnosis of AD and mild cognitive impairment (MCI).

METHODS

Peripheral blood progranulin gene expression was measured, using microarrays from Alzheimer's (n = 186), MCI (n = 118), and control (n = 204) subjects from the University of California San Francisco Memory and Aging Center (UCSF-MAC) and two independent published series (AddNeuroMed and ADNI). GRN gene expression was correlated with clinical, demographic, and genetic data, including APOE haplotype and the GRN rs5848 single-nucleotide polymorphism. Finally, we assessed progranulin protein levels, using enzyme-linked immunosorbent assay, and methylation status using methylation microarrays.

RESULTS

We observed an increase in blood progranulin gene expression and a decrease in GRN promoter methylation in males (P = 0.007). Progranulin expression was 13% higher in AD and MCI patients compared with controls in the UCSF-MAC cohort (F2,505 = 10.41, P = 3.72*10-5). This finding was replicated in the AddNeuroMed (F2,271 = 17.9, P = 4.83*10-8) but not the ADNI series. The rs5848 SNP (T-allele) predicted decreased blood progranulin gene expression (P = 0.03). The APOE4 haplotype was positively associated with progranulin expression independent of diagnosis (P = 0.04). Finally, we did not identify differences in plasma progranulin protein levels or gene methylation between diagnostic categories.

INTERPRETATION

Progranulin mRNA is elevated in peripheral blood of patients with AD and MCI and its expression is associated with numerous genetic and demographic factors. These data suggest a role in the pathogenesis of neurodegenerative dementias besides frontotemporal dementia.

Analysis of neurodegenerative Mendelian genes in clinically diagnosed Alzheimer Disease

Alzheimer disease (AD), Frontotemporal lobar degeneration (FTD), Amyotrophic lateral sclerosis (ALS) and Parkinson disease (PD) have a certain degree of clinical, pathological and molecular overlap. Previous studies indicate that causative mutations in AD and FTD/ALS genes can be found in clinical familial AD. We examined the presence of causative and low frequency coding variants in the AD, FTD, ALS and PD Mendelian genes, in over 450 families with clinical history of AD and over 11,710 sporadic cases and cognitive normal participants from North America. Known pathogenic mutations were found in 1.05% of the sporadic cases, in 0.69% of the cognitively normal participants and in 4.22% of the families. A trend towards enrichment, albeit non-significant, was observed for most AD, FTD and PD genes. Only PSEN1 and PINK1 showed consistent association with AD cases when we used ExAC as the control population. These results suggest that current study designs may contain heterogeneity and contamination of the control population, and that current statistical methods for the discovery of novel genes with real pathogenic variants in complex late onset diseases may be inadequate or underpowered to identify genes carrying pathogenic mutations.

Early-Onset Alzheimer Disease and Candidate Risk Genes Involved in Endolysosomal Transport

Importance

Mutations in APP, PSEN1, and PSEN2 lead to early-onset Alzheimer disease (EOAD) but account for only approximately 11% of EOAD overall, leaving most of the genetic risk for the most severe form of Alzheimer disease unexplained. This extreme phenotype likely harbors highly penetrant risk variants, making it primed for discovery of novel risk genes and pathways for AD.

Objective

To search for rare variants contributing to the risk for EOAD.

Design, Setting, and Participants

In this case-control study, whole-exome sequencing (WES) was performed in 51 non-Hispanic white (NHW) patients with EOAD (age at onset <65 years) and 19 Caribbean Hispanic families previously screened as negative for established APP, PSEN1, and PSEN2 causal variants. Participants were recruited from John P. Hussman Institute for Human Genomics, Case Western Reserve University, and Columbia University. Rare, deleterious, nonsynonymous, or loss-of-function variants were filtered to identify variants in known and suspected AD genes, variants in multiple unrelated NHW patients, variants present in 19 Hispanic EOAD WES families, and genes with variants in multiple unrelated NHW patients. These variants/genes were tested for association in an independent cohort of 1524 patients with EOAD, 7046 patients with late-onset AD (LOAD), and 7001 cognitively intact controls (age at examination, >65 years) from the Alzheimer's Disease Genetics Consortium. The study was conducted from January 21, 2013, to October 13, 2016.

Main Outcomes and Measures

Alzheimer disease diagnosed according to standard National Institute of Neurological and Communicative Disorders and Stroke and the Alzheimer Disease and Related Disorders Association criteria. Association between Alzheimer disease and genetic variants and genes was measured using logistic regression and sequence kernel association test-optimal gene tests, respectively.

Results

Of the 1524 NHW patients with EOAD, 765 (50.2%) were women and mean (SD) age was 60.0 (4.9) years; of the 7046 NHW patients with LOAD, 4171 (59.2%) were women and mean (SD) age was 77.4 (8.6) years; and of the 7001 NHW controls, 4215 (60.2%) were women and mean (SD) age was 77.4 (8.6) years. The gene PSD2, for which multiple unrelated NHW cases had rare missense variants, was significantly associated with EOAD (P = 2.05 × 10-6; Bonferroni-corrected P value [BP] = 1.3 × 10-3) and LOAD (P = 6.22 × 10-6; BP = 4.1 × 10-3). A missense variant in TCIRG1, present in a NHW patient and segregating in 3 cases of a Hispanic family, was more frequent in EOAD cases (odds ratio [OR], 2.13; 95% CI, 0.99-4.55; P = .06; BP = 0.413), and significantly associated with LOAD (OR, 2.23; 95% CI, 1.37-3.62; P = 7.2 × 10-4; BP = 5.0 × 10-3). A missense variant in the LOAD risk gene RIN3 showed suggestive evidence of association with EOAD after Bonferroni correction (OR, 4.56; 95% CI, 1.26-16.48; P = .02, BP = 0.091). In addition, a missense variant in RUFY1 identified in 2 NHW EOAD cases showed suggestive evidence of an association with EOAD as well (OR, 18.63; 95% CI, 1.62-213.45; P = .003; BP = 0.129).

Conclusions and Relevance

The genes PSD2, TCIRG1, RIN3, and RUFY1 all may be involved in endolysosomal transport-a process known to be important to development of AD. Furthermore, this study identified shared risk genes between EOAD and LOAD similar to previously reported genes, such as SORL1, PSEN2, and TREM2.

Progranulin haploinsufficiency reduces amyloid beta deposition in Alzheimer's disease model mice

Granulin (Grn) mutations were identified in familial frontotemporal lobar degeneration (FTLD) patients with TAR DNA-binding protein of 43 kd (TDP-43) pathology. Grn transcript haploinsufficiency is proposed as a disease mechanism that leads to the loss of functional progranulin (PGRN) protein. Thus, these mutations are strongly involved in FTLD pathogenesis. Moreover, recent findings indicate that Grn mutations are associated with other neurodegenerative disorders with tau pathology, including Alzheimer’s disease. To investigate the influence of PGRN on amyloid beta (Aβ) accumulation, amyloid precursor protein (APP) transgenic mice were interbred with Grn-deficient mice, producing APP transgenic mice harboring the Grn hemizygote (APP/Grn^+/−). Brains were collected from 16–18-month-old APP and APP/Grn^+/− mice and sequential extraction of proteins, immunoblotting and immunohistochemical analysis were performed. Immunohistochemical analysis showed that the number and area of Aβ plaque was significantly decreased in APP/Grn^+/− mice as compared to APP mice. Immunoblotting analysis revealed that Aβ was reduced in the sarkosyl-insoluble fraction of 16–18-month-old APP/Grn^+/− mice as compared with that of APP transgenic mice. Our data suggest that PGRN haploinsufficiency may decrease accumulation of Aβ.

Accumulation of multiple neurodegenerative disease-related proteins in familial frontotemporal lobar degeneration associated with granulin mutation

In 2006, mutations in the granulin gene were identified in patients with familial Frontotemporal Lobar Degeneration. Granulin transcript haploinsufficiency has been proposed as a disease mechanism that leads to the loss of functional progranulin protein. Granulin mutations were initially found in tau-negative patients, though recent findings indicate that these mutations are associated with other neurodegenerative disorders with tau pathology, including Alzheimer's disease and corticobasal degeneration. Moreover, a reduction in progranulin in tau transgenic mice is associated with increasing tau accumulation. To investigate the influence of a decline in progranulin protein on other forms of neurodegenerative-related protein accumulation, human granulin mutation cases were investigated by histochemical and biochemical analyses. Results showed a neuronal and glial tau accumulation in granulin mutation cases. Tau staining revealed neuronal pretangle forms and glial tau in both astrocytes and oligodendrocytes. Furthermore, phosphorylated α-synuclein-positive structures were also found in oligodendrocytes and the neuropil. Immunoblot analysis of fresh frozen brain tissues revealed that tau was present in the sarkosyl-insoluble fraction, and composed of three- and four-repeat tau isoforms, resembling Alzheimer's disease. Our data suggest that progranulin reduction might be the cause of multiple proteinopathies due to the accelerating accumulation of abnormal proteins including TDP-43 proteinopathy, tauopathy and α-synucleinopathy.

Opposing effects of progranulin deficiency on amyloid and tau pathologies via microglial TYROBP network

Progranulin (PGRN) is implicated in Alzheimer's disease (AD) as well as frontotemporal lobar degeneration. Genetic studies demonstrate an association of the common GRN rs5848 variant that results in reduced PGRN levels with increased risk for AD. However, the mechanisms by which PGRN reduction from the GRN AD risk variant or mutation exacerbates AD pathophysiology remain ill defined. Here, we show that the GRN AD risk variant has no significant effects on florbetapir positron emission tomographic amyloid imaging and cerebrospinal fluid (CSF) Aβ levels, whereas it is associated with increased CSF tau levels in human subjects of the Alzheimer's disease neuroimaging initiative studies. Consistent with the human data, subsequent analyses using the APPswe/PS1ΔE9 (APP/PS1) mouse model of cerebral amyloidosis show that PGRN deficiency has no exacerbating effects on Aβ pathology. In contrast and unexpectedly, PGRN deficiency significantly reduces diffuse Aβ plaque growth in these APP/PS1 mice. This protective effect is due, at least in part, to enhanced microglial Aβ phagocytosis caused by PGRN deficiency-induced expression of TYROBP network genes (TNG) including an AD risk factor Trem2. PGRN-deficient APP/PS1 mice also exhibit less severe axonal dystrophy and partially improved behavior phenotypes. While PGRN deficiency reduces these amyloidosis-related phenotypes, other neuronal injury mechanisms are increased by loss of PGRN, revealing a multidimensional interaction of GRN with AD. For example, C1q complement deposition at synapses is enhanced in APP/PS1 mice lacking PGRN. Moreover, PGRN deficiency increases tau AT8 and AT180 pathologies in human P301L tau-expressing mice. These human and rodent data suggest that global PGRN reduction induces microglial TNG expression and increases AD risk by exacerbating neuronal injury and tau pathology, rather than by accelerating Aβ pathology.

CSF protein changes associated with hippocampal sclerosis risk gene variants highlight impact of GRN/PGRN

OBJECTIVE

Hippocampal sclerosis of aging (HS-Aging) is a common cause of dementia in older adults. We tested the variability in cerebrospinal fluid (CSF) proteins associated with previously identified HS-Aging risk single nucleotide polymorphisms (SNPs).

METHODS

Alzheimer's Disease Neuroimaging Initiative cohort (ADNI; n=237) data, combining both multiplexed proteomics CSF and genotype data, were used to assess the association between CSF analytes and risk SNPs in four genes (SNPs): GRN (rs5848), TMEM106B (rs1990622), ABCC9 (rs704180), and KCNMB2 (rs9637454). For controls, non-HS-Aging SNPs in APOE (rs429358/rs7412) and MAPT (rs8070723) were also analyzed against Aβ1-42 and total tau CSF analytes.

RESULTS

The GRN risk SNP (rs5848) status correlated with variation in CSF proteins, with the risk allele (T) associated with increased levels of AXL Receptor Tyrosine Kinase (AXL), TNF-Related Apoptosis-Inducing Ligand Receptor 3 (TRAIL-R3), Vascular Cell Adhesion Molecule-1 (VCAM-1) and clusterin (CLU) (all p<0.05 after Bonferroni correction). The TRAIL-R3 correlation was significant in meta-analysis with an additional dataset (p=5.05×10^-5). Further, the rs5848 SNP status was associated with increased CSF tau protein - a marker of neurodegeneration (p=0.015). These data are remarkable since this GRN SNP has been found to be a risk factor for multiple types of dementia-related brain pathologies.

Cerebrospinal Fluid Progranulin, but Not Serum Progranulin, Is Reduced in GRN-Negative Frontotemporal Dementia

BACKGROUND AND OBJECTIVE

Reduced progranulin levels are a hallmark of frontotemporal dementia (FTD) caused by loss-of-function (LoF) mutations in the progranulin gene (GRN). However, alterations of central nervous progranulin expression also occur in neurodegenerative disorders unrelated to GRN mutations, such as Alzheimer's disease. We hypothesised that central nervous progranulin levels are also reduced in GRN-negative FTD.

METHODS

Progranulin levels were determined in both cerebrospinal fluid (CSF) and serum in 75 subjects (37 FTD patients and 38 controls). All FTD patients were assessed by whole-exome sequencing for GRN mutations, yielding a target cohort of 34 patients without pathogenic mutations in GRN (GRN-negative cohort) and 3 GRN mutation carriers (2 LoF variants and 1 novel missense variant).

RESULTS

Not only the GRN mutation carriers but also the GRN-negative patients showed decreased CSF levels of progranulin (serum levels in GRN-negative patients were normal). The decreased CSF progranulin levels were unrelated to patients' increased CSF levels of total tau, possibly indicating different destructive neuronal processes within FTD neurodegeneration. The patient with the novel GRN missense variant (c.1117C>T, p.P373S) showed substantially decreased CSF levels of progranulin, comparable to the 2 patients with GRN LoF mutations, suggesting a pathogenic effect of this missense variant.

CONCLUSIONS

Our results indicate that central nervous progranulin reduction is not restricted to the relatively rare cases of FTD caused by GRN LoF mutations, but also contributes to the more common GRN-negative forms of FTD. Central nervous progranulin reduction might reflect a partially distinct pathogenic mechanism underlying FTD neurodegeneration and is not directly linked to tau alterations.

"New Old Pathologies": AD, PART, and Cerebral Age-Related TDP-43 With Sclerosis (CARTS)

The pathology-based classification of Alzheimer's disease (AD) and other neurodegenerative diseases is a work in progress that is important for both clinicians and basic scientists. Analyses of large autopsy series, biomarker studies, and genomics analyses have provided important insights about AD and shed light on previously unrecognized conditions, enabling a deeper understanding of neurodegenerative diseases in general. After demonstrating the importance of correct disease classification for AD and primary age-related tauopathy, we emphasize the public health impact of an underappreciated AD "mimic," which has been termed "hippocampal sclerosis of aging" or "hippocampal sclerosis dementia." This pathology affects >20% of individuals older than 85 years and is strongly associated with cognitive impairment. In this review, we provide an overview of current hypotheses about how genetic risk factors (GRN, TMEM106B, ABCC9, and KCNMB2), and other pathogenetic influences contribute to TDP-43 pathology and hippocampal sclerosis. Because hippocampal sclerosis of aging affects the "oldest-old" with arteriolosclerosis and TDP-43 pathologies that extend well beyond the hippocampus, more appropriate terminology for this disease is required. We recommend "cerebral age-related TDP-43 and sclerosis" (CARTS). A detailed case report is presented, which includes neuroimaging and longitudinal neurocognitive data. Finally, we suggest a neuropathology-based diagnostic rubric for CARTS.

PGRN Is Associated with Late-Onset Alzheimer's Disease: a Case-Control Replication Study and Meta-analysis

Progranulin (PGRN) plays an important role in Alzheimer's disease (AD) through participating in altering neurite outgrowth and neuronal survival. Previous studies identified that rs5848 in the 3'-untranslated region (3'-UTR) of the PGRN gene (GRN) is strongly associated with AD in Caucasians. In order to assess the involvement of the GRN polymorphism in the risk of late-onset AD (LOAD), we analyzed the genotype and allele distributions of rs5848 in 2350 Han Chinese subjects (AD, 992; control, 1358). The minor T allele of rs5848 was significantly associated with an increased risk of LOAD (P = 0.005, odds ratio (OR) = 1.197, 95 % confidence interval (CI) = 1.057-1.355). Moreover, the association was further validated in the multivariate logistic regression analysis (dominant model: OR = 1.195, P = 0.038, recessive model: OR = 1.386, P = 0.025; additive model: OR = 1.187, P = 0.009). Interestingly, we observed that the interaction between apolipoprotein E (APOE) and rs5848 significantly altered the risk for AD. The rs5848 polymorphism was only significantly associated with LOAD in APOE ε4 allele carriers. Then we included five studies (including the present study) and conducted a meta-analysis which consisted of 3236 cases (male, 1152; female, 2084) and 3405 (male, 1436; female, 1969) controls. The result of the meta-analysis supported T allele of rs5848 within GRN as a risk factor for AD. In conclusion, our results demonstrated that rs5848 polymorphism within GRN was associated with LOAD.

Brain pathologies in extreme old age

With an emphasis on evolving concepts in the field, we evaluated neuropathologic data from very old research volunteers whose brain autopsies were performed at the University of Kentucky Alzheimer's Disease Center, incorporating data from the Georgia Centenarian Study (n = 49 cases included), Nun Study (n = 17), and University of Kentucky Alzheimer's Disease Center (n = 11) cohorts. Average age of death was 102.0 (range: 98-107) years overall. Alzheimer's disease pathology was not universal (62% with "moderate" or "frequent" neuritic amyloid plaque densities), whereas frontotemporal lobar degeneration was absent. By contrast, some hippocampal neurofibrillary tangles (including primary age-related tauopathy) were observed in every case. Lewy body pathology was seen in 16.9% of subjects and hippocampal sclerosis of aging in 20.8%. We describe anatomic distributions of pigment-laden macrophages, expanded Virchow-Robin spaces, and arteriolosclerosis among Georgia Centenarians. Moderate or severe arteriolosclerosis pathology, throughout the brain, was associated with both hippocampal sclerosis of aging pathology and an ABCC9 gene variant. These results provide fresh insights into the complex cerebral multimorbidity, and a novel genetic risk factor, at the far end of the human aging spectrum.

Progranulin genetic polymorphisms influence progression of disability and relapse recovery in multiple sclerosis

BACKGROUND

Progranulin (GRN) is a multifunctional protein involved in inflammation and repair, and also a neurotrophic factor critical for neuronal survival. Progranulin is strongly expressed in multiple sclerosis (MS) brains by macrophages and microglia.

METHODS

In this study we evaluated GRN genetic variability in 400 MS patients, in correlation with clinical variables such as disease severity and relapse recovery. We also evaluated serum progranulin levels in the different groups of GRN variants carriers.

RESULTS

We found that incomplete recovery after a relapse is correlated with an increased frequency of the rs9897526 A allele (odds ratio (OR) 4.367, p = 0.005). A more severe disease course (Multiple Sclerosis Severity Score > 5) is correlated with an increased frequency of the rs9897526 A allele (OR 1.886, p = 0.002) and of the rs5848 T allele (OR 1.580, p = 0.019). Carriers of the variants associated with a more severe disease course (rs9897526 A, rs5848 T) have significantly lower levels of circulating progranulin (80.5 ± 9.1 ng/mL vs. 165.7 ng/mL, p = 0.01).

CONCLUSION

GRN genetic polymorphisms likely influence disease course and relapse recovery in MS.

Association analysis of the GRN rs5848 and MAPT rs242557 polymorphisms in Parkinson's disease and multiple system atrophy: a large-scale population-based study and meta-analysis

BACKGROUND

Previous studies have found an association between the granulin gene rs5848 and microtubule-associated protein tau gene (MAPT) rs242557 polymorphisms and susceptibility to Parkinson's disease (PD). However, the results of association studies between the two polymorphisms and PD have been inconsistent. Given the overlap in clinical and pathological characteristics of PD and multiple system atrophy (MSA), we examined the associations of these two polymorphisms with PD and MSA in a subset of the Chinese population.

METHODS

In total, 1270 PD patients, 360 MSA patients and 830 healthy controls (HCs) were included in the study. All subjects were genotyped for the two polymorphisms using Sequenom iPLEX Assay technology. After combining our results with the available published data, a meta-analysis was conducted to investigate the association between MAPT rs242557 and the risk of PD.

RESULTS

The minor allele "T" of GRN rs5848 decreased the risk for PD (p = 0.0309, odds radio [OR], 0.86; 95% CI, 0.76-0.99). No differences in the genotype distributions and minor allele frequency (MAF) of MAPT rs242557 were observed between the PD and the HCs in our Chinese population. Our meta-analysis revealed an association between MAPT rs242557 and PD in Caucasian and Asian population in a recessive model (p = 0.049 and p = 0.046, respectively). However, no significant differences in the genotype distributions and MAFs of the two polymorphisms were found between the MSA patients and HCs.

CONCLUSION

Our results indicate that GRN rs5458 may decrease the risk of PD in Chinese individuals, and the MAPT rs242557 is marginally associated with PD.

Progranulin reduction is associated with increased tau phosphorylation in P301L tau transgenic mice

Granulin (GRN) mutations have been identified in familial frontotemporal lobar degeneration patients with ubiquitin pathology. GRN transcript haploinsufficiency is proposed as a disease mechanism that leads to the loss of functional progranulin (PGRN) protein. Thus, these mutations are strongly involved in frontotemporal lobar degeneration pathogenesis. Moreover, recent findings indicate that GRN mutations are associated with other neurodegenerative disorders with tau pathology, including Alzheimer disease and corticobasal degeneration. To investigate the potential influence of a decline in PGRN protein on tau accumulation, P301L tau transgenic mice were interbred with GRN-deficient mice, producing P301L tau transgenic mice harboring the GRN hemizygote. Brains were collected from 13- and 19-month-old mice, and sequential extraction of proteins, immunoblotting, and immunohistochemical analyses were performed. Immunoblotting analysis revealed that tau phosphorylation was accelerated in the Tris-saline soluble fraction of 13-month-old and in the sarkosyl-insoluble fraction of 19-month-old P301L tau/GRN hemizygotes compared with those in fractions from P301L tau transgenic mice. Activity of cyclin-dependent kinases was also upregulated in the brains of P301L tau/GRN hemizygote mice. Although the mechanisms involved in these findings remain unknown, our data suggest that a reduction in PGRN protein might contribute to phosphorylation and intraneuronal accumulation of tau.

Association of progranulin polymorphism rs5848 with neurodegenerative diseases: a meta-analysis

The purpose of this meta-analysis was to investigate the association between progranulin polymorphism rs5848 and risk of the neurodegenerative diseases frontotemporal lobar degeneration (FTLD), Alzheimer's disease (AD), Parkinson's disease (PD), and amyotrophic lateral sclerosis (ALS). Published literature from PubMed and other databases were retrieved, and 16 case-control studies were identified as eligible: 5 on FTLD (1,439 cases, 4,461 controls), 5 on AD (2,502 cases, 2,162 controls), 3 on PD (1,605 cases, 1,591 controls), and 3 on ALS (663 cases, 811 controls). The pooled odds ratio (OR) and 95% confidence interval (CI) were calculated. We found that rs5848 was associated with an increased risk of neurodegenerative diseases in the homozygous (TT vs. CC: OR, 1.24; 95% CI, 1.10-1.39; P < 0.001) and recessive models (TT vs. CC + CT: OR, 1.23; 95% CI, 1.10-1.37; P < 0.001). Stratified analyses showed associations of rs5848 with increased risk of AD and PD in the homozygous and recessive models. Our data indicate that rs5848 is associated with risk of AD and PD, suggesting important roles of progranulin in neurodegenerative processes.

Disease-related mutations among Caribbean Hispanics with familial dementia

Pathogenic mutations in the three known genes – the amyloid precursor protein (APP), presenilin 1 (PSEN1), presenilin 2 (PSEN2) – are known to cause familial Alzheimer's disease (AD) and tend to be associated with early-onset AD. However, the frequency and risk associated with these mutations vary widely. In addition, mutations in the frontotemporal lobar degeneration (FTLD) genes – the microtubule-associated protein tau (MAPT), granulin (GRN) – have also been found to be associated with clinical AD. Here, we conducted targeted resequencing of the exons in genes encoding APP, PSEN1, PSEN2, GRN, and MAPT in 183 individuals from families with four or more affected relatives, presumed to be AD, and living in the Dominican Republic and Puerto Rico. We then performed linkage and family-based association analyses in carrier families, and genotyped 498 similarly aged unrelated controls from the same ethnic background. Twelve potentially pathogenic mutations were found to be associated with disease in 53 individuals in the five genes. The most frequently observed mutation was the p.Gly206Ala variant in PSEN1 present in 30 (57%) of those sequenced. In the combined linkage and association analyses several rare variants were associated with dementia. In Caribbean Hispanics with familial AD, potentially pathogenic variants were present in 29.2%, four were novel mutations, while eight had been previously observed. In addition, some family members carried variants in the GRN and MAPT genes which are associated with FTLD.

Evidence of the innate antiviral and neuroprotective properties of progranulin

BACKGROUND

Compelling data exist that show that normal levels of progranulin (PGRN) are required for successful CNS aging. PGRN production is also modulated by inflammation and infection, but no data are available on the production and role of PGRN during CNS HIV infection.

METHODS

To determine the relationships between PGRN and HIV disease, neurocognition, and inflammation, we analyzed 107 matched CSF and plasma samples from CHARTER, a well-characterized HIV cohort. Levels of PGRN were determined by ELISA and compared to levels of several inflammatory mediators (IFNγ, IL-6, IL-10, IP-10, MCP-1, TNFα, IL-1β, IL-4 and IL-13), as well as clinical, virologic and demographic parameters. The relationship between HIV infection and PGRN was also examined in HIV-infected primary human microglial cultures.

RESULTS

In plasma, PGRN levels correlated with the viral load (VL, p<0.001). In the CSF of subjects with undetectable VL, lower PGRN was associated with neurocognitive impairment (p = 0.046). CSF PGRN correlated with CSF IP-10, TNFα and IL-10, and plasma PGRN correlated with plasma IP-10. In vitro, microglial HIV infection increased PGRN production and PGRN knockdown increased HIV replication, demonstrating that PGRN is an innate antiviral protein.

CONCLUSIONS

We propose that PGRN plays dual roles in people living with HIV disease. With active HIV replication, PGRN is induced in infected macrophages and microglia and functions as an antiviral protein. In individuals without active viral replication, decreased PGRN production contributes to neurocognitive dysfunction, probably through a diminution of its neurotrophic functions. Our results have implications for the pathogenesis, biomarker studies and therapy for HIV diseases including HIV-associated neurocognitive dysfunction (HAND).

Progranulin in neurodegenerative disease

Loss-of-function mutations in the progranulin gene are a common cause of familial frontotemporal dementia (FTD). The purpose of this review is to summarize the role of progranulin in health and disease, because the field is now poised to begin examining therapeutics that alter endogenous progranulin levels. We first review the clinical and neuropathological phenotype of FTD patients carrying mutations in the progranulin gene, which suggests that progranulin-mediated neurodegeneration is multifactorial and influenced by other genetic and/or environmental factors. We then examine evidence for the role of progranulin in the brain with a focus on mouse model systems. A better understanding of the complexity of progranulin biology in the brain will help guide the development of progranulin-modulating therapies for neurodegenerative disease.

Progranulin polymorphism rs5848 is associated with increased risk of Alzheimer's disease

Progranulin is the precursor of granulins, and its down-regulation leads to neurodegeneration. Recent studies have indicated an association of progranulin polymorphism rs5848 with Alzheimer's disease (AD) risk, but the results remain controversial. To verify the association between rs5848 and AD risk, we retrieved the published literature from PubMed and other databases, and performed a meta-analysis by pooling all five studies containing 2502 AD cases and 2162 controls. The results showed that rs5848 is associated with increased risk of AD in homozygous (TT vs. CC: OR, 1.36; 95% CI, 1.11-1.66; P=0.003) and recessive models (TT vs. CC+CT: OR, 1.31; 95% CI, 1.08-1.58; P=0.006). This association was remained in Caucasian (2227 cases and 1902 controls). Our data indicate that TT allele of rs5848 is associated with increased risk of AD, suggesting that genetic variant of progranulin gene may play an important role in AD development.

Potential roles of microglial cell progranulin in HIV-associated CNS pathologies and neurocognitive impairment

Progranulin (PGRN) is a highly unusual molecule with both neuronal and microglial expression with two seemingly unrelated functions, i.e., as a neuronal growth factor and a modulator of neuroinflammation. Haploinsufficiency due to loss of function mutations lead to a fatal presenile dementing illness (frontotemporal lobar degeneration), indicating that adequate expression of PGRN is essential for successful aging. PGRN might be a particularly relevant factor in the pathogenesis of HIVencephalitis (HIVE) and HIV-associated neurocognitive disorders (HAND). We present emerging data and a review of the literature which show that cells of myeloid lineage such as macrophages and microglia are the primary sources of PGRN and that PGRN expression contributes to pathogenesis of CNS diseases. We also present evidence that PGRN is a macrophage antiviral cytokine. For example, PGRN mRNA and protein expression are significantly upregulated in brain specimens with HIVE, and in HIV infected microglia in vitro. Paradoxically, our preliminary CHARTER data analyses indicate that lower PGRN levels in CSF trended towards an association with HAND, particularly in those without detectable virus. Based upon these findings, we introduce the hypothesis that PGRN plays dual roles in modulating antiviral immunity and neuronal dysfunction in the context of HIV infection. In the presence of active viral replication, PGRN expression is increased functioning as an anti-viral factor as well as a neuroprotectant. In the absence of active HIV replication, ongoing inflammation or other stressors suppress PGRN production from macrophages/microglia contributing to neurocognitive dysfunction. We propose.

Progranulin mutations as risk factors for Alzheimer disease

IMPORTANCE

Mutations in the progranulin gene are known to cause diverse clinical syndromes, all attributed to frontotemporal lobar degeneration. We describe 2 patients with progranulin gene mutations and evidence of Alzheimer disease (AD) pathology. We also conducted a literature review.

OBSERVATIONS

This study focused on case reports of 2 unrelated patients with progranulin mutations at the University of California, San Francisco, Memory and Aging Center. One patient presented at age 65 years with a clinical syndrome suggestive of AD and showed evidence of amyloid aggregation on positron emission tomography. Another patient presented at age 54 years with logopenic progressive aphasia and, at autopsy, showed both frontotemporal lobar degeneration with TDP-43 inclusions and AD.

CONCLUSIONS AND RELEVANCE

In addition to autosomal-dominant frontotemporal lobar degeneration, mutations in the progranulin gene may be a risk factor for AD clinical phenotypes and neuropathology.

Progranulin does not bind tumor necrosis factor (TNF) receptors and is not a direct regulator of TNF-dependent signaling or bioactivity in immune or neuronal cells

Progranulin (PGRN) is a secreted glycoprotein expressed in neurons and glia that is implicated in neuronal survival on the basis that mutations in the GRN gene causing haploinsufficiency result in a familial form of frontotemporal dementia (FTD). Recently, a direct interaction between PGRN and tumor necrosis factor receptors (TNFR I/II) was reported and proposed to be a mechanism by which PGRN exerts anti-inflammatory activity, raising the possibility that aberrant PGRN-TNFR interactions underlie the molecular basis for neuroinflammation in frontotemporal lobar degeneration pathogenesis. Here, we report that we find no evidence for a direct physical or functional interaction between PGRN and TNFRs. Using coimmunoprecipitation and surface plasmon resonance (SPR) we replicated the interaction between PGRN and sortilin and that between TNF and TNFRI/II, but not the interaction between PGRN and TNFRs. Recombinant PGRN or transfection of a cDNA encoding PGRN did not antagonize TNF-dependent NFκB, Akt, and Erk1/2 pathway activation; inflammatory gene expression; or secretion of inflammatory factors in BV2 microglia and bone marrow-derived macrophages (BMDMs). Moreover, PGRN did not antagonize TNF-induced cytotoxicity on dopaminergic neuroblastoma cells. Last, co-addition or pre-incubation with various N- or C-terminal-tagged recombinant PGRNs did not alter lipopolysaccharide-induced inflammatory gene expression or cytokine secretion in any cell type examined, including BMDMs from Grn+/- or Grn-/- mice. Therefore, the neuroinflammatory phenotype associated with PGRN deficiency in the CNS is not a direct consequence of the loss of TNF antagonism by PGRN, but may be a secondary response by glia to disrupted interactions between PGRN and Sortilin and/or other binding partners yet to be identified.

Hippocampal sclerosis of aging, a prevalent and high-morbidity brain disease

Hippocampal sclerosis of aging (HS-Aging) is a causative factor in a large proportion of elderly dementia cases. The current definition of HS-Aging rests on pathologic criteria: neuronal loss and gliosis in the hippocampal formation that is out of proportion to AD-type pathology. HS-Aging is also strongly associated with TDP-43 pathology. HS-Aging pathology appears to be most prevalent in the oldest-old: autopsy series indicate that 5-30 % of nonagenarians have HS-Aging pathology. Among prior studies, differences in study design have contributed to the study-to-study variability in reported disease prevalence. The presence of HS-Aging pathology correlates with significant cognitive impairment which is often misdiagnosed as AD clinically. The antemortem diagnosis is further confounded by other diseases linked to hippocampal atrophy including frontotemporal lobar degeneration and cerebrovascular pathologies. Recent advances characterizing the neurocognitive profile of HS-Aging patients have begun to provide clues that may help identify living individuals with HS-Aging pathology. Structural brain imaging studies of research subjects followed to autopsy reveal hippocampal atrophy that is substantially greater in people with eventual HS-Aging pathology, compared to those with AD pathology alone. Data are presented from individuals who were followed with neurocognitive and neuroradiologic measurements, followed by neuropathologic evaluation at the University of Kentucky. Finally, we discuss factors that are hypothesized to cause or modify the disease. We conclude that the published literature on HS-Aging provides strong evidence of an important and under-appreciated brain disease of aging. Unfortunately, there is no therapy or preventive strategy currently available.

Polymorphisms affecting miRNA regulation: a new level of genetic variation affecting disorders and diseases of the human CNS

The recognition of people and/or populations at a high risk for the development of various types of neurological disorders and diseases is not only key to improved screening programs and earlier detection, but it also provides hope for appropriate treatment and care. Genetic alterations that change gene-expression levels have long been investigated for association with the development of pathological neurological conditions. Gene regulation by miRNAs is a relatively new area of study, and published evidence suggests that alterations in this process may be associated with increased disease risk. Here, the authors review the current data for association between single nucleotide polymorphisms (SNPs) and miRNA-mediated gene regulation (miR-SNPs) in human neuropsychiatric and neurodegenerative diseases. Additionally, we present an approach to detect and identify functional miR-SNPs for the purpose of carrying out large-scale genetic association studies. The growing body of literature suggests that miR-SNPs are emerging as a powerful tool, both to study the pathobiology of diseases, as well as aiding in its diagnosis and prognosis.

Epidemiology and genetics of frontotemporal dementia: a door-to-door survey in southern Italy

The objectives of this study were to estimate frontotemporal dementia (FTD) prevalence, identify FTD-related mutations, and correlate FTD phenotype with mutations in a southern Italian population. The study population consisted of subjects ≥ 50 years of age residing in the Community of Biv. on January 1, 2004, and a door-to-door 2-phase design was used. Genetic and biochemical analyses were done on samples collected from 32 patients. Prevalence rates were 0.6 for Alzheimer's disease, 0.4 for vascular dementia (VD), 3.5 for FTD, 0.2 for Parkinson dementia, and 1.2 for unspecified dementia. Three GRN (1 known and 2 novel) mutations with reduced plasma protein levels were found associated to 3 distinct phenotypes (behavioral, affective, and delirious type). We report an unusually high FTD prevalence in the investigated population, but a low prevalence of Alzheimer's disease. We confirm the heterogeneity of FTD phenotype associated with different GRN mutations.

Progranulin gene (GRN) promoter methylation is increased in patients with sporadic frontotemporal lobar degeneration

Mutations in progranulin gene (GRN) are the most common cause of autosomal dominant familial frontotemporal lobar degeneration (FTLD). In addition, GRN variability influences the risk to develop the disease in non-carriers (sporadic FTLD). We evaluated progranulin gene (GRN) promoter methylation levels in peripheral blood mononuclear cells isolated from 38 patients with sporadic FTLD compared with 38 controls, and correlate them with GRN mRNA expression rate. The percentage of methylation of the GRN promoter was increased in patients with FTLD compared with controls (61.5 vs. 46.3 %, P < 0.001). A trend towards decreased GRN relative expression was observed in patients compared with controls (threefold decrease over controls, P > 0.05), together with a negative correlation between the degree of GRN promoter methylation and mRNA GRN levels (ρ = -0.1, P > 0.05). GRN promoter methylation was not correlated with age. In conclusion, the degree of methylation of the GRN promoter is increased in patients with FTLD as compared with controls, likely leading to a decreased expression of GRN.

Psychotropic drug effects on gene transcriptomics relevant to Alzheimer disease

Psychotropics are widely prescribed in Alzheimer disease (AD) without regard to their pathobiological effects. Results summarize a comprehensive survey of psychotropic effects on messenger ribonucleic acid (mRNA) expression for 52 genes linked to AD. Pending future investigations, current data indicate that atypical antipsychotics, lithium, and fluoxetine reduce AD risk, whereas other drug classes promote risk. Risk may be attenuated by antipsychotics and lithium (down-regulate TNF), atypical antipsychotics (down-regulate TF), risperidone (down-regulates IL1B), olanzapine (up-regulates TFAM, down-regulates PRNP), fluoxetine (up-regulates CLU, SORCS1, NEDD9, GRN, and ECE1), and lithium coadministered with antipsychotics (down-regulates IL1B). Risk may be enhanced by neuroleptics (up-regulate TF), haloperidol (up-regulates IL1B and PION), olanzapine (down-regulates THRA and PRNP, up-regulates IL1A), and chlorpromazine, imipramine, maprotiline, fluvoxamine, and diazepam (up-regulate IL1B). There were no results for dextromethorphan-plus-quinidine. Fluoxetine effects on CLU, NEDD9, and GRN were statistically robust. Drug effects on specific variants, polymorphisms, genotypes, and other genes (CCR2, TF, and PRNP) are detailed. Translational AD risk applications and their limitations related to specific genes, mutations, variants, polymorphisms, genotypes, brain site, sex, clinical population, AD stage, and other factors are discussed. This report provides an initial summary and framework to understand the potential impact of psychotropic drugs on AD-relevant genes.

Progranulin gene variability and plasma levels in bipolar disorder and schizophrenia

Basing on the assumption that frontotemporal lobar degeneration (FTLD), schizophrenia and bipolar disorder (BPD) might share common aetiological mechanisms, we analyzed genetic variation in the FTLD risk gene progranulin (GRN) in a German population of patients with schizophrenia (n = 271) or BPD (n = 237) as compared with 574 age-, gender- and ethnicity-matched controls. Furthermore, we measured plasma progranulin levels in 26 German BPD patients as well as in 61 Italian BPD patients and 29 matched controls.

A significantly decreased allelic frequency of the minor versus the wild-type allele was observed for rs2879096 (23.2 versus 34.2%, P<0.001, OR:0.63, 95%CI:0.49–0.80), rs4792938 (30.7 versus 39.7%, P = 0.005, OR: 0.70, 95%CI: 0.55–0.89) and rs5848 (30.3 versus 36.8, P = 0.007, OR: 0.71, 95%CI: 0.56–0.91). Mean±SEM progranulin plasma levels were significantly decreased in BPD patients, either Germans or Italians, as compared with controls (89.69±3.97 and 116.14±5.80 ng/ml, respectively, versus 180.81±18.39 ng/ml P<0.001) and were not correlated with age.

In conclusion, GRN variability decreases the risk to develop BPD and schizophrenia, and progranulin plasma levels are significantly lower in BPD patients than in controls. Nevertheless, a larger replication analysis would be needed to confirm these preliminary results.

Progranulin: an emerging target for FTLD therapies

Frontotemporal lobar degeneration (FTLD), a neurodegenerative disease primarily affecting the frontal and temporal lobes, is one of the most common types of dementia. While the majority of FTLD cases are sporadic, approximately 10-40% of patients have an inherited form of FTLD. Mutations in the progranulin gene (GRN) have recently been identified as a major cause of FTLD with ubiquitin positive inclusions (FTLD-U). Because over 70 disease-linked GRN mutations cause abnormal deficiencies in the production of PGRN, a protein that plays a crucial role in embryogenesis, cell growth and survival, wound repair and inflammation, researchers now aim to design therapies that would increase PGRN levels in affected individuals, thereby alleviating the symptoms associated with disease. Several compounds and genetic factors, as well as PGRN receptors, have recently been identified because of their ability to regulate PGRN levels. Strict quality control measures are needed given that extreme PGRN levels at either end of the spectrum - too low or too high - can lead to neurodegeneration or cancer, respectively. The aim of this review is to highlight what is known regarding PGRN biology; to improve understanding of the mechanisms involved in regulating PGRN levels and highlight studies that are laying the groundwork for the development of effective therapeutic modulators of PGRN. This article is part of a Special Issue entitled RNA-Binding Proteins.

rs5848 variant of progranulin gene is a risk of Alzheimer's disease in the Taiwanese population

Progranulin is the precursor of granulins, and its downregulation may lead to neurodegeneration. The single-nucleotide polymorphism rs5848 increases the risk of Alzheimer's disease (AD). We explored the association between alleles of rs5848 and the risk of AD in the Taiwanese population. The frequency of the homozygous TT genotype (16.4 vs. 10.0%) increased in AD subjects by an odds ratio (OR) of 1.87 (p = 0.03) corrected for APOE ε4, age and gender. Interaction between age and homozygous TT genotype accentuated the risk of AD (OR 4.44, p < 0.001). The homozygous TT genotype of rs5848 may play a role in the genetic risk of AD development, especially in the elderly.