Progranulin Protein Levels Research Articles

Benzoxazole-derivatives enhance progranulin expression and reverse the aberrant lysosomal proteome caused by GRN haploinsufficiency

Heterozygous loss-of-function mutations in the GRN gene are a major cause of hereditary frontotemporal dementia. The mechanisms linking frontotemporal dementia pathogenesis to progranulin deficiency are not well understood, and there is currently no treatment. Our strategy to prevent the onset and progression of frontotemporal dementia in patients with GRN mutations is to utilize small molecule positive regulators of GRN expression to boost progranulin levels from the remaining functional GRN allele, thus restoring progranulin levels back to normal within the brain. This work describes a series of blood-brain-barrier-penetrant small molecules which significantly increase progranulin protein levels in human cellular models, correct progranulin protein deficiency in Grn+/− mouse brains, and reverse lysosomal proteome aberrations, a phenotypic hallmark of frontotemporal dementia, more efficiently than the previously described small molecule suberoylanilide hydroxamic acid. These molecules will allow further elucidation of the cellular functions of progranulin and its role in frontotemporal dementia and will also serve as lead structures for further drug development.

A systematic review of progranulin concentrations in biofluids in over 7,000 people—assessing the pathogenicity of GRN mutations and other influencing factors

BackgroundPathogenic heterozygous mutations in the progranulin gene (GRN) are a key cause of frontotemporal dementia (FTD), leading to significantly reduced biofluid concentrations of the progranulin protein (PGRN). This has led to a number of ongoing therapeutic trials aiming to treat this form of FTD by increasing PGRN levels in mutation carriers. However, we currently lack a complete understanding of factors that affect PGRN levels and potential variation in measurement methods. Here, we aimed to address this gap in knowledge by systematically reviewing published literature on biofluid PGRN concentrations.MethodsPublished data including biofluid PGRN concentration, age, sex, diagnosis and GRN mutation were collected for 7071 individuals from 75 publications. The majority of analyses (72%) had focused on plasma PGRN concentrations, with many of these (56%) measured with a single assay type (Adipogen) and so the influence of mutation type, age at onset, sex, and diagnosis were investigated in this subset of the data.ResultsWe established a plasma PGRN concentration cut-off between pathogenic mutation carriers and non-carriers of 74.8 ng/mL using the Adipogen assay based on 3301 individuals, with a CSF concentration cut-off of 3.43 ng/mL. Plasma PGRN concentration varied by GRN mutation type as well as by clinical diagnosis in those without a GRN mutation. Plasma PGRN concentration was significantly higher in women than men in GRN mutation carriers (p = 0.007) with a trend in non-carriers (p = 0.062), and there was a significant but weak positive correlation with age in both GRN mutation carriers and non-carriers. No significant association was seen with weight or with TMEM106B rs1990622 genotype. However, higher plasma PGRN levels were seen in those with the GRN rs5848 CC genotype in both GRN mutation carriers and non-carriers.ConclusionsThese results further support the usefulness of PGRN concentration for the identification of the large majority of pathogenic mutations in the GRN gene. Furthermore, these results highlight the importance of considering additional factors, such as mutation type, sex and age when interpreting PGRN concentrations. This will be particularly important as we enter the era of trials for progranulin-associated FTD.

ARKD‐104, A Potential Treatment of Frontotemporal Dementia and Other Neurodegenerative Disorders

AbstractBackgroundHeterozygous mutations in the gene encoding progranulin (GRN) that lead to haploinsufficiency of the progranulin protein (PGRN) cause the fatal neurodegenerative disease frontotemporal dementia (FTD‐GRN). A promising treatment approach for FTD‐GRN is to restore PGRN to levels detected in healthy individuals. In pursuit of this objective, Arkuda Therapeutics is developing brain‐penetrant, orally bioavailable small molecules that increase PGRN levels within the central nervous system (CNS).MethodA functional cell‐based assay was utilized to identify novel compounds that stimulate PGRN secretion from a murine microglial cell line. Compounds with good in vitro potency were further optimized through an iterative series of selectivity, ADME, pharmacokinetic (PK), safety and pharmacology assessments.ResultWhen applied to cells, ARKD‐104 increased PGRN and PSAP secretion and engaged lysosomal pathways as evidenced by intracellular changes in granulins, saposins, and lysosomal lipids including bis(monoacylglycero)phosphate (BMP). Oral administration of ARKD‐104 to cynomolgus monkeys resulted in a dose and exposure‐dependent increase in PGRN measured in cerebrospinal fluid (CSF). The exposure‐response relationship demonstrated that a systemic exposure of 8 nM ARKD‐104 in plasma (unbound) doubled the amount PGRN in CSF. PGRN levels were further increased to more than 4‐times pre‐dose levels at the highest tested dose. Elevation of PGRN levels was sustained with repeat dosing of ARKD‐104. ARKD‐104 was characterized for CNS drug‐like properties including PK, metabolism, brain penetration, selectivity, and safety. In these assessments, ARKD‐104 demonstrated a profile suggesting that beneficial increases in PGRN can be achieved with once daily oral dosing in human.ConclusionARKD‐104 has excellent CNS drug‐like properties, increases PGRN in the CNS of non‐human primates and increases important cofactors of lysosomal enzymes, . ARKD‐104 is therefore a promising candidate for continued development as a treatment for FTD‐GRN, Parkinson’s disease and other neurodegenerative disorders exhibiting lysosomal dysfunction.

Antisense oligonucleotides targeting the miR-29b binding site in the GRN mRNA increase progranulin translation

Heterozygous GRN (progranulin) mutations cause frontotemporal dementia (FTD) due to haploinsufficiency, and increasing progranulin levels is a major therapeutic goal. Several microRNAs, including miR-29b, negatively regulate progranulin protein levels. Antisense oligonucleotides (ASOs) are emerging as a promising therapeutic modality for neurological diseases, but strategies for increasing target protein levels are limited. Here, we tested the efficacy of ASOs as enhancers of progranulin expression by sterically blocking the miR-29b binding site in the 3' UTR of the human GRN mRNA. We found 16 ASOs that increase progranulin protein in a dose-dependent manner in neuroglioma cells. A subset of these ASOs also increased progranulin protein in iPSC-derived neurons and in a humanized GRN mouse model. In FRET-based assays, the ASOs effectively competed for miR-29b from binding to the GRN 3' UTR RNA. The ASOs increased levels of newly synthesized progranulin protein by increasing its translation, as revealed by polysome profiling. Together, our results demonstrate that ASOs can be used to effectively increase target protein levels by partially blocking miR binding sites. This ASO strategy may be therapeutically feasible for progranulin-deficient FTD as well as other conditions of haploinsufficiency.

Rare exonic variant affects GRN splicing and contributes to frontotemporal lobar degeneration

Heterozygous loss-of-function (LOF) mutations in the progranulin gene (GRN) cause frontotemporal lobar degeneration (FTLD) by a mechanism of haploinsufficiency. For most missense mutations, the contribution to FTLD is however unclear. We studied the pathogenicity of rare GRN missense mutations using patient biomaterials. We identified a new mutation in GRN, c.1178 A>C, in a patient with a diagnosis of primary progressive aphasia. Neuropathological examination of autopsied brain showed FTLD with TAR DNA-binding protein 43 (FTLD-TDP) type A pathology with concomitant Alzheimer’s disease pathology. Serum progranulin protein levels were reduced to levels comparable to known LOF mutations. The mutation is in the last codon of exon 10, in the splice donor sequence. Our data provide evidence that the mutation leads to aberrant splicing, resulting in a frameshift (p.(Glu393AlafsTer31)) and consequently nonsense-mediated mRNA decay. Our finding demonstrates that carefully examining sequencing data around splice sites is needed since this mutation was annotated as a missense mutation. Unraveling the pathogenicity of variants of unknown significance is important for clinical diagnosis and genetic counseling.

Antisense oligonucleotides targeting miR‐29b binding site increase translation of progranulin protein: potential therapeutic strategy for progranulin‐deficient frontotemporal dementia

AbstractBackground GRN mutations cause frontotemporal dementia (FTD) due to haploinsufficiency of progranulin. Several microRNAs (miRs), including miR‐29b, have been reported to negatively regulate progranulin protein levels. Here, we tested if antisense oligonucleotides (ASOs) – which are versatile modulators of target mRNA/protein levels – can be used to increase progranulin levels by sterically blocking the miR‐29b binding site.MethodWe designed 48 ASOs targeting the miR‐29b binding site in the 3’ UTR of the human GRN mRNA. We treated H4 neuroglioma cells and iPSC‐derived neurons with these ASOs and subsequently measured progranulin protein levels by western blot and ELISA. We performed further studies to determine the mechanism of action of these ASOs using ribosomal profiling, metabolic labeling, and FRET assays.ResultsWe identified 16 ASOs that increased progranulin protein levels in a dose‐dependent manner. Ribosomal profiling experiments revealed that cells treated with ASOs had marked enrichment in GRN mRNA in heavy polyribosome fractions, compared to cells treated with a scrambled control ASO, suggesting that the ASOs increase the rate of progranulin translation. Consistent with this, ASO treatment resulted in increased levels of newly synthesized progranulin protein. FRET‐based assays showed that ASOs can effectively compete miR‐29b from its binding site in the GRN 3’ UTR RNA under in vitro conditions.ConclusionsTogether, our results demonstrate that ASOs can be used to effectively increase target protein levels by partially blocking miR binding sites. This strategy may be therapeutically feasible for progranulin‐deficient FTD as well as other conditions of haploinsufficiency.

Progranulin upregulation by antisense oligonucleotides targeting regRNAs for treatment of FTD‐GRN

AbstractBackgroundHeterozygous mutations in progranulin (GRN) gene leading to progranulin protein (PGRN) haploinsufficieny are the major genetic cause of GRN‐related frontotemporal dementia (FTD‐GRN)1, 2 and 3. Decreased levels of PGRN disrupt lysosome homeostasis, cause aberrant microglia activation and neuronal cell death resulting in progressive behavioral changes, language deficits and memory impairment4. We hypothesize that upregulation of PGRN in both neuronal cells and microglia would be effective for treating FTD‐GRN patients.MethodRegulatory RNAs (regRNAs) are a class of noncoding RNAs that modulate gene transcription. We have developed an RNA Actuating Platform (RAPTM) that identified regRNAs and enables tunable upregulation of genes by specific targeting of regRNAs with antisense oligonucleotides (ASOs).ResultOur platform identified shared GRN regRNAs in human iPSC‐derived neuron and microglia like cells (iMGLs). ASOs targeting shared regRNAs were screened in a human neuroblastoma cell line to identify lead ASOs that upregulate GRN at least 2‐fold. We showed that the lead ASOs upregulate GRN in both human iPSC‐derived neurons and iMGL cells. Moreover, this level of GRN upregulation was sufficient to rescue staurosporine‐induced toxicity in FTD‐GRN patient iPSC‐derived neurons.Furthermore, we identified mouse Grn regRNA‐targeting ASOs that upregulate Grn transcription 2.5‐fold in mouse neuroblastoma cell lines and primary neurons. We tested these ASOs for efficacy in an FTD‐GRN mouse model (Grn+/tm1.1Far )5 by intracerebroventricular injection. Grn upregulation is observed across disease‐relevant brain regions, including cortex in the Grn haploinsufficient mice.ConclusionHere, we describe the development of oligonucleotide drug candidates that target regRNAs to upregulate GRN expression as a therapeutic approach for FTD‐GRN. We believe that our strategy will restore secreted and lysosomal PGRN levels in both microglia and neurons thereby decreasing neuroinflammation and neurotoxicity. We are developing these oligonucleotides as a disease modifying treatment for patients with FTD‐GRN.

Generation and Characterization of Novel iPSC Lines from a Portuguese Family Bearing Heterozygous and Homozygous GRN Mutations.

Mutations in granulin (GRN) have been associated with neurodegenerative diseases, such as frontotemporal lobar degeneration (FTLD) and neuronal ceroid lipofuscinosis (NCL). In Portugal, GRN mutations account for around half of all FTLD cases with known genetic origin. Here, we describe the generation and characterization of three human-induced pluripotent stem cell (hiPSC) lines from a Portuguese family harboring heterozygous and homozygous GRN mutation. hiPSCs were reprogrammed from human dermal fibroblasts by episomal nucleofection of the Yamanaka factors. The new generated lines were positive for pluripotency markers, could be further differentiated to cells expressing all trilineage markers, and presented a normal karyotype. They were also capable of differentiating into 3D brain organoids and presented a significant decrease in progranulin protein levels. Hence, these cell lines constitute suitable new tools to elucidate the pathophysiological mechanisms associated with the GRN mutations in the context of FTLD.

Cerebrospinal fluid neuroinflammatory biomarkers along the Alzheimer disease continuum in Down syndrome

AbstractBackgroundAlzheimer’s disease (AD) is the main medical problem and cause of death for adults with Down syndrome (DS). Glial activation is an early phenomenon central to AD pathophysiology; however, whether glial biomarker profiles in DS differ from sporadic AD remains unanswered. We compared cerebrospinal fluid (CSF) glial biomarkers along the AD continuum between DS individuals and sporadic AD cases and its relationship with CSF neurodegeneration biomarkers.MethodSingle‐center cross‐sectional study. We classified individuals with DS into three clinical subgroups: without cognitive impairment (aDS), prodromal AD (pDS) or with AD dementia (dDS). We determined CSF‐YKL40 and progranulin protein (PGRN) levels by ELISA (Quidel and Adipogen, respectively) and we compare them along the AD continuum in DS. For comparisons, we included subjects with sporadic prodromal AD (pAD) and AD dementia (ADd) and healthy controls. We studied correlations of YKL40 and PGRN with CSF‐total‐tau (Fujirebio‐Europe), phospho‐tau (Fujirebio‐Europe) and NfL (UmanDiagnostics) within participants with DS. We used Mann‐Whitney tests corrected for multiple comparisons and Spearman coefficients for correlations.ResultParticipants included were 56 aDS, 17 pDS, 27 dDS, 28 pAD, 55 ADd and 147 controls. YKL40 levels were lower in aDS compared to controls (p<0.0001) and along the AD continuum in DS compared to sporadic cases (pDS vs pAD, p= 0.0004 and dDS vs ADd, p=0.0002) (Figure 1a). Symptomatic AD was associated with an 88.8% increase in YKL40 levels in DS and with a 69.9% increase in sporadic AD. There were no differences in PGRN levels along the AD continuum in DS or between DS and sporadic AD; however, PGRN levels were lower in aDS than in HC (Figure 1b). Both YKL40 and PGRN levels positively correlated with total‐tau (r=0.3, p<0.001; r=0.4, p<0.001), phospho‐tau (r=0.87, p<0.001; r=0.41, p<0.001) and NfL, (r=0.82, p<0.001; r=0.43 p<0.001) levels in the group with DS.ConclusionCSF glial biomarkers in subjects with DS differ from that in healthy controls and sporadic AD. However, symptomatic AD is characterized by similar changes in astrocyte and microglial activation markers such as YKL‐40 and PGRN. Differences in the immune system and response to AD might have important therapeutic implications and deserve further research.

Reduction of microglial progranulin does not exacerbate pathology or behavioral deficits in neuronal progranulin-insufficient mice

Loss-of-function mutations in progranulin (GRN), most of which cause progranulin haploinsufficiency, are a major autosomal dominant cause of frontotemporal dementia (FTD). Individuals with loss-of-function mutations on both GRN alleles develop neuronal ceroid lipofuscinosis (NCL), a lysosomal storage disorder. Progranulin is a secreted glycoprotein expressed by a variety of cell types throughout the body, including neurons and microglia in the brain. Understanding the relative importance of neuronal and microglial progranulin insufficiency in FTD pathogenesis may guide development of therapies. In this study, we used mouse models to investigate the role of neuronal and microglial progranulin insufficiency in the development of FTD-like pathology and behavioral deficits. Grn−/− mice model aspects of FTD and NCL, developing lipofuscinosis and gliosis throughout the brain, as well as deficits in social behavior. We have previously shown that selective depletion of neuronal progranulin disrupts social behavior, but does not produce lipofuscinosis or gliosis. We hypothesized that reduction of microglial progranulin would induce lipofuscinosis and gliosis, and exacerbate behavioral deficits, in neuronal progranulin-deficient mice. To test this hypothesis, we crossed Grnfl/fl mice with mice expressing Cre transgenes targeting neurons (CaMKII-Cre) and myeloid cells/microglia (LysM-Cre). CaMKII-Cre, which is expressed in forebrain excitatory neurons, reduced cortical progranulin protein levels by around 50%. LysM-Cre strongly reduced progranulin immunolabeling in many microglia, but did not reduce total brain progranulin levels, suggesting that, at least under resting conditions, microglia contribute less than neurons to overall brain progranulin levels. Mice with depletion of both neuronal and microglial progranulin failed to develop lipofuscinosis or gliosis, suggesting that progranulin from extracellular sources prevented pathology in cells targeted by the Cre transgenes. Reduction of microglial progranulin also did not exacerbate the social deficits of neuronal progranulin-insufficient mice. These results do not support the hypothesis of synergistic effects between progranulin-deficient neurons and microglia. Nearly complete progranulin deficiency appears to be required to induce lipofuscinosis and gliosis in mice, while partial progranulin insufficiency is sufficient to produce behavioral deficits.

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

ObjectiveChanges 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).MethodsPeripheral 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.ResultsWe 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 (F 2,505 = 10.41, P = 3.72*10−5). This finding was replicated in the AddNeuroMed (F 2,271 = 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.InterpretationProgranulin 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.

An 8-week, open-label, dose-finding study of nimodipine for the treatment of progranulin insufficiency from GRN gene mutations

IntroductionFrontotemporal lobar degeneration–causing mutations in the progranulin (GRN) gene reduce progranulin protein (PGRN) levels, suggesting that restoring PGRN in mutation carriers may be therapeutic. Nimodipine, a Food and Drug Administration–approved blood-brain barrier-penetrant calcium channel blocker, increased PGRN levels in PGRN-deficient murine models. We sought to assess safety and tolerability of oral nimodipine in human GRN mutation carriers. MethodsWe performed an open-label, 8-week, dose-finding, phase 1 clinical trial in eight GRN mutation carriers to assess the safety and tolerability of nimodipine and assayed fluid and radiologic markers to investigate therapeutic endpoints. ResultsThere were no serious adverse events; however, PGRN concentrations (cerebrospinal fluid and plasma) did not change significantly following treatment (percent changes of −5.2 ± 10.9% in plasma and −10.2 ± 7.8% in cerebrospinal fluid). Measurable atrophy within the left middle frontal gyrus was observed over an 8-week period. DiscussionWhile well tolerated, nimodipine treatment did not alter PGRN concentrations or secondary outcomes.

Progranulin Levels in Plasma and Cerebrospinal Fluid in Granulin Mutation Carriers

Background: Pathogenic mutations in the granulin gene (GRN) are causative in 5-10% of patients with frontotemporal dementia (FTD), mostly leading to reduced progranulin protein (PGRN) levels. Upcoming therapeutic trials focus on enhancing PGRN levels. Methods: Fluctuations in plasma PGRN (n = 41) and its relationship with cerebrospinal fluid (CSF, n = 32) and specific single nucleotide polymorphisms were investigated in pre- and symptomatic GRN mutation carriers and controls. Results: Plasma PGRN levels were lower in carriers than in controls and showed a mean coefficient of variation of 5.3% in carriers over 1 week. Although plasma PGRN correlated with CSF PGRN in carriers (r = 0.54, p = 0.02), plasma only explained 29% of the variability in CSF PGRN. rs5848, rs646776 and rs1990622 genotypes only partly explained the variability of PGRN levels between subjects. Conclusions: Plasma PGRN is relatively stable over 1 week and therefore seems suitable for treatment monitoring of PGRN-enhancing agents. Since plasma PGRN only moderately correlated with CSF PGRN, CSF sampling will additionally be needed in therapeutic trials.

Prosaposin is a regulator of progranulin levels and oligomerization.

Progranulin (GRN) loss-of-function mutations leading to progranulin protein (PGRN) haploinsufficiency are prevalent genetic causes of frontotemporal dementia. Reports also indicated PGRN-mediated neuroprotection in models of Alzheimer's and Parkinson's disease; thus, increasing PGRN levels is a promising therapeutic for multiple disorders. To uncover novel PGRN regulators, we linked whole-genome sequence data from 920 individuals with plasma PGRN levels and identified the prosaposin (PSAP) locus as a new locus significantly associated with plasma PGRN levels. Here we show that both PSAP reduction and overexpression lead to significantly elevated extracellular PGRN levels. Intriguingly, PSAP knockdown increases PGRN monomers, whereas PSAP overexpression increases PGRN oligomers, partly through a protein–protein interaction. PSAP-induced changes in PGRN levels and oligomerization replicate in human-derived fibroblasts obtained from a GRN mutation carrier, further supporting PSAP as a potential PGRN-related therapeutic target. Future studies should focus on addressing the relevance and cellular mechanism by which PGRN oligomeric species provide neuroprotection.

Peripheral Progranulin Levels Do Not Reflect Brain Progranulin Levels

EVALUATION OF: Nicholson AM, Finch NA, Thomas CS et al. Progranulin protein levels are differently regulated in plasma and CSF. Neurology 82(21), 1871–1878 (2014). Nicholson et al. report the first population-based comparative study of progranulin (GRN) levels in plasma and cerebrospinal fluid (CSF) in a large human cohort. Age, sex and rs5848 were found to be important modifiers of GRN levels in both plasma and CSF. The correlation between plasma and CSF levels was rather weak. Moreover, a differential regulation of GRN levels in plasma and CSF was noted. Although blood GRN measurements can be used to predict GRN mutation status, this study provides compelling evidence not to rely exclusively on plasma GRN measurements to assess the efficacy of future CNS-targeted GRN-modulating therapies. Further studies should assess the correlation between CSF and brain GRN levels in a longitudinal fashion and try to correlate CSF GRN levels with clinical parameters.

Progranulin protein levels are differently regulated in plasma and CSF.

We aimed to investigate the relationship between plasma and CSF progranulin (PGRN) levels. Plasma and CSF PGRN were measured in a cohort of 345 subjects from the Mayo Clinic Study of Aging by ELISA. Single nucleotide polymorphism genotyping was performed using TaqMan assays. Associations between PGRN and sex, age at sample collection, diagnosis, single nucleotide polymorphism genotypes (GRN, SORT1, and APOE), and Pittsburgh compound B score were explored separately in CSF and plasma using single variable linear regression models. Pearson partial correlation coefficient was used to estimate the correlation of PGRN in CSF and plasma. Plasma (p = 0.0031) and CSF (p = 0.0044) PGRN significantly increased with age, whereas plasma PGRN levels were 7% lower (p = 0.0025) and CSF PGRN levels 5% higher (p = 0.0024) in male compared with female participants. Correcting for age and sex, higher plasma PGRN was associated with higher CSF PGRN (partial r = 0.17, p = 0.004). In plasma, both rs5848 (GRN; p = 0.002) and rs646776 (SORT1; p = 3.56E-7) were associated with PGRN, while only rs5848 showed highly significant association in CSF (p = 5.59E-14). Age, sex, rs5848 genotype, and plasma PGRN together accounted for only 18% of the variability observed in CSF PGRN. While some correlation exists between plasma and CSF PGRN, age, sex, and genetic factors differently affect PGRN levels. Therefore, caution should be taken when using plasma PGRN to predict PGRN changes in the brain. These findings further highlight that plasma PGRN levels may not accurately predict clinical features or response to future frontotemporal lobar degeneration therapies.

TMEM106B p.T185S regulates TMEM106B protein levels: implications for frontotemporal dementia

Frontotemporal lobar degeneration (FTLD) is the second leading cause of dementia in individuals under age 65. In many patients, the predominant pathology includes neuronal cytoplasmic or intranuclear inclusions of ubiquitinated TAR DNA binding protein 43 (FTLD-TDP). Recently, a genome-wide association study identified the first FTLD-TDP genetic risk factor, in which variants in and around the TMEM106B gene (top SNP rs1990622) were significantly associated with FTLD-TDP risk. Intriguingly, the most significant association was in FTLD-TDP patients carrying progranulin (GRN) mutations. Here, we investigated to what extent the coding variant, rs3173615 (p.T185S) in linkage disequilibrium with rs1990622, affects progranulin protein (PGRN) biology and transmembrane protein 106 B (TMEM106B) regulation. First, we confirmed the association of TMEM106B variants with FTLD-TDP in a new cohort of GRN mutation carriers. We next generated and characterized a TMEM106B-specific antibody for investigation of this protein. Enzyme-linked immunoassay analysis of progranulin protein levels showed similar effects upon T185 and S185 TMEM106B over-expression. However, over-expression of T185 consistently led to higher TMEM106B protein levels than S185. Cycloheximide treatment experiments revealed that S185 degrades faster than T185 TMEM106B, potentially due to differences in N-glycosylation at residue N183. Together, our results provide a potential mechanism by which TMEM106B variants lead to differences in FTLD-TDP risk. We studied the p.T185S TMEM106B genetic variant previously implicated in frontotemporal dementia with TAR DNA binding protein 43 pathology caused by progranulin mutations. Our cell culture studies provide evidence that the protective S185 isoform is degraded more rapidly than T185 TMEM106B, potentially due to differences in glycosylation. These findings suggest that low TMEM106B levels might protect against FTLD-TDP in these patients.

Progranulin axis and recent developments in frontotemporal lobar degeneration

Frontotemporal lobar degeneration (FTLD) is a devastating neurodegenerative disease that is the second most common form of dementia affecting individuals under age 65. The most common pathological subtype, FTLD with transactive response DNA-binding protein with a molecular weight of 43 kDa inclusions (FTLD-TDP), is often caused by autosomal dominant mutations in the progranulin gene (GRN) encoding the progranulin protein (PGRN). GRN pathogenic mutations result in haploinsufficiency, usually by nonsense-mediated decay of the mRNA. Since the discovery of these mutations in 2006, several groups have published data and animal models that provide further insight into the genetic and functional relevance of PGRN in the context of FTLD-TDP. These studies were critical in initiating our understanding of the role of PGRN in neural development, degeneration, synaptic transmission, cell signaling, and behavior. Furthermore, recent publications have now identified the receptors for PGRN, which will hopefully lead to additional therapeutic targets. Additionally, drug screens have been conducted to identify pharmacological regulators of PGRN levels to be used as potential treatments for PGRN haploinsufficiency. Here we review recent literature describing relevant data on GRN genetics, cell culture experiments describing the potential role and regulators of PGRN in the central nervous system, animal models of PGRN deficiency, and potential PGRN-related FTLD therapies that are currently underway. The present review aims to underscore the necessity of further elucidation of PGRN biology in FTLD-related neurodegeneration.

Upregulation of progranulin byHelicobacter pyloriin human gastric epithelial cells via p38MAPK and MEK1/2 signaling pathway: role in epithelial cell proliferation and migration

Helicobacter pylori is a major human pathogen associated with gastric diseases such as chronic active gastritis, peptic ulcer, and gastric carcinoma. The growth factor progranulin (PGRN) is a secreted glycoprotein that functions as an important regulator of cell growth, migration, and transformation. We aimed to determine the molecular mechanisms by which H. pylori upregulates the expression of PGRN and the relationship between H. pylori infection and production of PGRN in controlling cell proliferation and migration. Levels of PGRN were examined in gastric tissues from patients and in vitro in gastric epithelial cells. Cell proliferation was measured by colony formation assay. Cell migration was monitored by wound healing migration assay. PGRN protein levels were increased in patients with gastritis and gastric cancer tissue. Infection of gastric epithelial cells with H. pylori significantly increased PGRN expression in a time-dependent manner. Blockade of the p38 and MEK1/2 pathway by inhibitor inhibited H. pylori-mediated PGRN upregulation. Activation of p38 and MEK1/2 pathway by H. pylori was also identified. Knockdown of PGRN attenuated the H. pylori-induced proliferative activity and migration of cancer cells. These findings suggest that the upregulation of PGRN in H. pylori-infected gastric epithelial cells may contribute to the carcinogenic process.

Mucosal Progranulin expression is induced by H. pylori, but independent of Secretory Leukocyte Protease Inhibitor (SLPI) expression

BackgroundMucosal levels of Secretory Leukocyte Protease Inhibitor (SLPI) are specifically reduced in relation to H. pylori-induced gastritis. Progranulin is an epithelial growth factor that is proteolytically degraded into fragments by elastase (the main target of SLPI). Considering the role of SLPI for regulating the activity of elastase, we studied whether the H. pylori-induced reduction of SLPI and the resulting increase of elastase-derived activity would reduce the Progranulin protein levels both ex vivo and in vitro.MethodsThe expression of Progranulin was studied in biopsies of H. pylori-positive, -negative and -eradicated subjects as well as in the gastric tumor cell line AGS by ELISA, immunohistochemistry and real-time RT-PCR.ResultsH. pylori-infected subjects had about 2-fold increased antral Progranulin expression compared to H. pylori-negative and -eradicated subjects (P < 0.05). Overall, no correlations between mucosal Progranulin and SLPI levels were identified. Immunohistochemical analysis confirmed the upregulation of Progranulin in relation to H. pylori infection; both epithelial and infiltrating immune cells contributed to the higher Progranulin expression levels. The H. pylori-induced upregulation of Progranulin was verified in AGS cells infected by H. pylori. The down-regulation of endogenous SLPI expression in AGS cells by siRNA methodology did not affect the Progranulin expression independent of the infection by H. pylori.ConclusionsTaken together, Progranulin was identified as novel molecule that is upregulated in context to H. pylori infection. In contrast to other diseases, SLPI seems not to have a regulatory role for Progranulin in H. pylori-mediated gastritis.