Alteration in cell cycle-related proteins in lymphoblasts from carriers of the c.709-1G>A PGRN mutation associated with FTLD-TDP dementia

Progranulin Deficiency Induces Mitochondrial Dysfunction in Frontotemporal Lobar Degeneration with TDP-43 Inclusions

Loss-of-function (LOF) mutations in GRN gene, which encodes progranulin (PGRN), cause frontotemporal lobar degeneration with TDP-43 inclusions (FTLD-TDP). FTLD-TDP is one of the most common forms of early onset dementia, but its pathogenesis is not fully understood. Mitochondrial dysfunction has been associated with several neurodegenerative diseases such as Alzheimer’s disease (AD), Parkinson’s disease (PD) and amyotrophic lateral sclerosis (ALS). Here, we have investigated whether mitochondrial alterations could also contribute to the pathogenesis of PGRN deficiency-associated FTLD-TDP. Our results showed that PGRN deficiency induced mitochondrial depolarization, increased ROS production and lowered ATP levels in GRN KD SH-SY5Y neuroblastoma cells. Interestingly, lymphoblasts from FTLD-TDP patients carrying a LOF mutation in the GRN gene (c.709-1G > A) also demonstrated mitochondrial depolarization and lower ATP levels. Such mitochondrial damage increased mitochondrial fission to remove dysfunctional mitochondria by mitophagy. Interestingly, PGRN-deficient cells showed elevated mitochondrial mass together with autophagy dysfunction, implying that PGRN deficiency induced the accumulation of damaged mitochondria by blocking its degradation in the lysosomes. Importantly, the treatment with two brain-penetrant CK-1δ inhibitors (IGS-2.7 and IGS-3.27), known for preventing the phosphorylation and cytosolic accumulation of TDP-43, rescued mitochondrial function in PGRN-deficient cells. Taken together, these results suggest that mitochondrial function is impaired in FTLD-TDP associated with LOF GRN mutations and that the TDP-43 pathology linked to PGRN deficiency might be a key mechanism contributing to such mitochondrial dysfunction. Furthermore, our results point to the use of drugs targeting TDP-43 pathology as a promising therapeutic strategy for restoring mitochondrial function in FTLD-TDP and other TDP-43-related diseases.

Helicobacter pylori-Induced Progranulin Promotes the Progression of the Gastric Epithelial Cell Cycle by Regulating CDK4

Helicobacter pylori, a group 1 carcinogen, colonizes the stomach and affects the development of stomach diseases. Progranulin (PGRN) is an autocrine growth factor that regulates multiple cellular processes and plays a tumorigenic role in many tissues. Nevertheless, the mechanism of action of PGRN in gastric cancer caused by H. pylori infection remains unclear. Here, we investigated the role of PGRN in cell cycle progression and the cell proliferation induced by H. pylori infection. We found that the increased PGRN was positively associated with CDK4 expression in gastric cancer tissue. PGRN was upregulated by H. pylori infection, thereby promoting cell proliferation, and that enhanced level of proliferation was reduced by PGRN inhibitor. CDK4, a target gene of PGRN, is a cyclin-dependent kinase that binds to cyclin D to promote cell cycle progression, which was upregulated by H. pylori infection. We also showed that knockdown of CDK4 reduced the higher cell cycle progression caused by upregulated PGRN. Moreover, when the PI3K/Akt signaling pathway (which is promoted by PGRN) was blocked, the upregulation of CDK4 mediated by PGRN was reduced. These results reveal the potential mechanism by which PGRN plays a major role through CDK4 in the pathological mechanism of H. pylori infection.

Discovery of small molecules that normalize the transcriptome and enhance cysteine cathepsin activity in progranulin-deficient microglia

Patients with frontotemporal dementia (FTD) resulting from granulin (GRN) haploinsufficiency have reduced levels of progranulin and exhibit dysregulation in inflammatory and lysosomal networks. Microglia produce high levels of progranulin, and reduction of progranulin in microglia alone is sufficient to recapitulate inflammation, lysosomal dysfunction, and hyperproliferation in a cell-autonomous manner. Therefore, targeting microglial dysfunction caused by progranulin insufficiency represents a potential therapeutic strategy to manage neurodegeneration in FTD. Limitations of current progranulin-enhancing strategies necessitate the discovery of new targets. To identify compounds that can reverse microglial defects in Grn-deficient mouse microglia, we performed a compound screen coupled with high throughput sequencing to assess key transcriptional changes in inflammatory and lysosomal pathways. Positive hits from this initial screen were then further narrowed down based on their ability to rescue cathepsin activity, a critical biochemical readout of lysosomal capacity. The screen identified nor-binaltorphimine dihydrochloride (nor-BNI) and dibutyryl-cAMP, sodium salt (DB-cAMP) as two phenotypic modulators of progranulin deficiency. In addition, nor-BNI and DB-cAMP also rescued cell cycle abnormalities in progranulin-deficient cells. These data highlight the potential of a transcription-based platform for drug screening, and advance two novel lead compounds for FTD.

Therapeutic potential of novel Cell Division Cycle Kinase 7 inhibitors on TDP-43-related pathogenesis such as Frontotemporal Lobar Degeneration (FTLD) and amyotrophic lateral sclerosis (ALS)

TDP-43 has been identified as the major component of protein aggregates found in affected neurons in FTLD-TDP and amyotrophic lateral sclerosis (ALS) patients. TDP-43 is hyperphosphorylated, ubiquitinated, and cleaved in the C-terminus. CDC-7 was reported to phosphorylate TDP-43. There are no effective treatments for either FTLD-TDP or ALS, being a pressing need for the search of new therapies. We hypothesized that modulating CDC-7 activity with small molecules that are able to interfere with TDP-43 phosphorylation could be a good therapeutic strategy for these diseases. Here, we have studied the effects of novel brain penetrant, thiopurine-based, CDC-7 inhibitors in TDP-43 homeostasis in immortalized lymphocytes from FTLD-TDP patients, carriers of a loss-of-function GRN mutation, as well as in cells derived from sporadic ALS patients. We found that selective CDC-7 inhibitors, ERP1.14a and ERP1.28a, are able to decrease the enhanced TDP-43 phosphorylation in cells derived from FTLD-TDP and ALS patients and to prevent cytosolic accumulation of TDP-43. Moreover, treatment of FTLD-TDP lymphoblasts with CDC-7 inhibitors leads to recovering the nuclear function of TDP-43-inducing CDK6 repression. We suggest that CDC-7 inhibitors, mainly the heterocyclic compounds here shown, may be considered as promising drug candidates for the ALS/FTD spectrum.

Recapitulation of Pathological TDP-43 Features in Immortalized Lymphocytes from Sporadic ALS Patients

Amyotrophic lateral sclerosis (ALS) is a fatal progressive neurodegenerative disorder of still unknown etiology that results in loss of motoneurons, paralysis, and death, usually between 2 and 4 years from onset. There are no currently available ALS biomarkers to support early diagnosis and to facilitate the assessment of the efficacy of new treatments. Since ALS is considered a multisystemic disease, here we have investigated the usefulness of immortalized lymphocytes from sporadic ALS patients to study TDP-43 homeostasis as well as to provide a convenient platform to evaluate TDP-43 phosphorylation as a novel therapeutic approach for ALS. We report here that lymphoblasts from ALS patients recapitulate the hallmarks of TDP-43 processing in affected motoneurons, such as increased phosphorylation, truncation, and mislocalization of TDP-43. Moreover, modulation of TDP-43 by an in-house designed protein casein kinase-1δ (CK-1δ) inhibitor, IGS3.27, reduced phosphorylation of TDP-43, and normalized the nucleo-cytosol translocation of TDP-43 in ALS lymphoblasts. Therefore, we conclude that lymphoblasts, easily accessible cells, from ALS patients could be a useful model to study pathological features of ALS disease and a suitable platform to test the effects of potential disease-modifying drugs even in a personalized manner.

Targeted proteomic analysis of cognitive dysfunction in remitted major depressive disorder: Opportunities of multi-omics approaches towards predictive, preventive, and personalized psychiatry

In order to accelerate the understanding of pathophysiological mechanisms and clinical biomarker discovery and in psychiatry, approaches that integrate multiple -omics platforms are needed. We introduce a workflow that investigates a narrowly defined psychiatric phenotype, makes use of the potent and cost-effective discovery technology of gene expression microarrays, applies Weighted Gene Co-Expression Network Analysis (WGCNA) to better capture complex and polygenic traits, and finally explores gene expression findings on the proteomic level using targeted mass-spectrometry (MS) technologies. To illustrate the effectiveness of the workflow, we present a proteomic analysis of peripheral blood plasma from patient's remitted major depressive disorder (MDD) who experience ongoing cognitive deficits. We show that co-expression patterns previous detected on the transcript level could be replicated for plasma proteins, as could the module eigengene correlation with cognitive performance. Further, we demonstrate that functional analysis of multi-omics data has the potential to point to cellular mechanisms and candidate biomarkers for cognitive dysfunction in MDD, implicating cell cycle regulation by cyclin D3 (CCND3), regulation of protein processing in the endoplasmatic reticulum by Thioredoxin domain-containing protein 5 (TXND5), and modulation of inflammatory cytokines by Tripartite Motif Containing 26 (TRI26).

SIGNIFICANCE

This paper discusses how data from multiple -omics platforms can be integrated to accelerate biomarker discovery in psychiatry. Using the phenotype of cognitive impairment in remitted major depressive disorder (MDD) as an example, we show that the application of a systems biology approach - weighted gene co-expression network analysis (WGCNA) - in the discovery phase, and targeted proteomic follow-up of results, provides a structured avenue towards uncovering novel candidate markers and pathways for personalized clinical psychiatry.

Genetics of Frontotemporal Lobar Degeneration: From the Bench to the Clinic

Frontotemporal lobar degeneration (FTLD) is a clinically heterogeneous neurodegenerative disease with a strong genetic component. In this review, we summarize most common mutations in MAPT, GRN, and C90RF72, as well as less common mutations in VCP, CHMP2B, TARDBP, FUS gene and so on. Several guidelines have been developed to help gene testing based on genotype-phenotype correlation, the underlying histopathological subtypes, and the neuroanatomic associations. Furthermore, we also summarize molecular pathways implicated by genes and novel targets for FTLD prevention and management in recent years.

Progranulin deficiency induces overactivation of WNT5A expression via TNF-α/NF-κB pathway in peripheral cells from frontotemporal dementia-linked granulin mutation carriers

BACKGROUND

Loss-of-function progranulin gene (GRN) mutations have been identified as the major cause of frontotemporal lobar degeneration with transactive response (TAR) DNA-binding protein 43 (TDP-43) pathology (frontotemporal lobar degeneration [FTLD]-TDP); however, little is known about the association between progranulin (PGRN) deficiency and neuronal loss in individuals with FTLD-TDP. Previously we reported enhanced proliferative activity associated with the activation of WNT5A/CDK6/pRb signalling in PGRN-deficient cells. The objective of this work was to elucidate the association between PGRN deficiency, WNT5A signalling and cell proliferation in immortalized lymphoblasts from carriers of the c.709-1G > A GRN mutation (asymptomatic and FTLD-TDP).

METHODS

We assessed cell proliferation in carriers of the c.709-1G > A GRN gene mutation and controls without GRN mutation and without sign of neurologic degeneration by cell counting or using an MTT assay. We used a luciferase assay to measure the nuclear factor-κ (NF-κ) activity. We evaluated messenger RNA levels using quantitative real-time polymerase chain reaction and protein levels by immunoblotting. Co-immunoprecipitation was used to analyze the interaction between PGRN and its receptors.

RESULTS

We enrolled 19 carriers of the GRN gene mutation and 10 controls in this study. The PGRN-deficient cells showed increased expression of WNT5A due to NF-κB signalling overactivation. We observed a competition between PGRN and tumour necrosis factor-α (TNF-α) for binding both TNF receptors (TNFR) I and II. Blocking NF-κB signalling using wedelolactone or specific antibodies against TNFRs inhibited WNT5A overexpression and proliferation of PGRN-deficient cells. Conversely, the activation of NF-κB signalling by TNF-α increased WNT5A-dependent proliferation of control cells.

LIMITATIONS

All cell lines were derived from individuals harboring the same splicing GRN mutation. Nevertheless, most of the known GRN mutations lead to haploinsufficiency of the protein.

CONCLUSION

Our results revealed an important role of NF-κB signalling in PGRN-associated FTLD-TDP and confirm that PGRN can bind to TNF-α receptors regulating the expression of WNT5A, suggesting novel targets for treatment of FTLD-TDP linked to GRN mutations.

Targeting TDP-43 phosphorylation by Casein Kinase-1δ inhibitors: a novel strategy for the treatment of frontotemporal dementia

Background

Mutations in the progranulin gene (GRN) are the most common cause of frontotemporal lobar degeneration with TDP-43 inclusions (FTLD-TDP). TDP-43 pathology is characterized by the hyperphosphorylation of the protein at Serine 409/410 residues. Casein kinase-1δ (CK-1δ) was reported to phosphorylate TDP-43 directly. Previous works from our laboratory described the presence of CDK6/pRb-dependent cell cycle alterations, and cytosolic accumulation of TDP-43 protein in lymphoblast from FTLD-TDP patients carriers of a loss-of function mutation in GRN gene (c.709-1G > A). In this work, we have investigated the effects of two brain penetrant CK-1δ inhibitors (IGS-2.7 and IGS-3.27) designed and synthetized in our laboratory on cell proliferation, TDP-43 phosphorylation and subcellular localization, as well as their effects on the known nuclear TDP-43 function repressing the expression of CDK6.

Results

We report here that both CK-1δ inhibitors (IGS-2.7 and IGS-3.27) normalized the proliferative activity of PGRN-deficient lymphoblasts by preventing the phosphorylation of TDP-43 fragments, its nucleo-cytosol translocation and the overactivation of the CDK6/pRb cascade. Moreover, ours results show neuroprotective effects of CK-1δ inhibitors in a neuronal cell model of induced TDP-43 phosphorylation.

Conclusions

Our results suggest that modulating CK-1δ activity could be considered a novel therapeutic approach for the treatment of FTLD-TDP and other TDP-43 proteinopathies.

Increased Wnt Signaling and Reduced Viability in a Neuronal Model of Progranulin-Deficient Frontotemporal Lobar Degeneration

Progranulin (PGRN) deficiency is considered the major cause of frontotemporal lobar degeneration with TDP-43 protein inclusions (FTLD-TDP). Recent work unveiled a relationship between Wnt signaling and PGRN in cellular models of FTLD and cells of patients carrying loss-of-function GRN mutations. This study was undertaken to explore the relationship between PGRN deficit and Wnt signaling in the regulation of survival of GRN knockdown neuroblastoma SH-SY5Y cells (GRN KD). We report here that both canonical and noncanonical Wnt signaling cascades are overactivated in GRN KD cells. We detected increased expression levels of Wnt1 and Wnt5a ligands of the Frizzled receptors, as well as evidence for increased signaling of the Wnt/β-catenin and Wnt/Ca²⁺ cascades in PGRN deficient cells, such as increased nuclear content of β-catenin and higher levels of cyclin D1, or increased levels of the active form of the NFAT1 transcription factor, respectively. Upregulation of either Wnt/β-catenin or Wnt/Ca²⁺ signaling in GRN KD cells leads to the stimulation of BrdU incorporation into DNA, hyperphosphorylation of the pRb family of proteins and reduced cell viability over time. Blocking the Wnt cascades by specific canonical or noncanonical inhibitors of Wnt-dependent signaling, normalized the rate of DNA synthesis, and what it is more important restored the viability of GRN KD cells. Our results suggest an important role of Wnt activation inducing cell cycle disturbance-mediated neuronal loss in the pathogenesis of PGRN deficiency-linked FTLD-TDP. Therefore, it is plausible that modulation of Wnt signaling could be a promising strategy for developing of new disease-modifying treatments for FTLD-TDP.

Frontotemporal Lobar Degeneration: Mechanisms and Therapeutic Strategies

Frontotemporal lobar degeneration (FTLD) is characterized by progressive deterioration of frontal and anterior temporal lobes of the brain and often exhibits frontotemporal dementia (FTD) on clinic, in <65-year-old patients at the time of diagnosis. Interdisciplinary approaches combining genetics, molecular and cell biology, and laboratory animal science have revealed some of its potential molecular mechanisms. Although there is still no effective treatment to delay, prevent, and reverse the progression of FTD, emergence of agents targeting molecular mechanisms has been beginning to promote potential pharmaceutical development. Our review summarizes the latest new findings of FTLD and challenges in FTLD therapy.

Progranulin Deficiency Reduces CDK4/6/pRb Activation and Survival of Human Neuroblastoma SH-SY5Y Cells

Null mutations in GRN are associated with frontotemporal lobar degeneration with TDP-43 inclusions (FTLD-TDP). However, the influence of progranulin (PGRN) deficiency in neurodegeneration is largely unknown. In neuroblastoma cells, silencing of GRN gene causes significantly reduced cell survival after serum withdrawal. The following observations suggest that alterations of the CDK4/6/retinoblastoma protein (pRb) pathway, secondary to changes in PI3K/Akt and ERK1/2 activation induced by PGRN deficiency, are involved in the control of serum deprivation-induced apoptosis: (i) inhibiting CDK4/6 levels or their associated kinase activity by sodium butyrate or PD332991 sensitized control SH-SY5Y cells to serum deprivation-induced apoptosis without affecting survival of PGRN-deficient cells; (ii) CDK4/6/pRb seems to be downstream of the PI3K/Akt and ERK1/2 signaling pathways since their specific inhibitors, LY294002 and PD98059, were able to decrease CDK6-associated kinase activity and induce death of control SH-SY5Y cells; (iii) PGRN-deficient cells show reduced stimulation of PI3K/Akt, ERK1/2, and CDK4/6 activities compared with control cells in the absence of serum; and (iv) supplementation of recombinant human PGRN was able to rescue survival of PGRN-deficient cells. These observations highlight the important role of PGRN-mediated stimulation of the PI3K/Akt-ERK1/2/CDK4/6/pRb pathway in determining the cell fate survival/death under serum deprivation.

G1/S Cell Cycle Checkpoint Dysfunction in Lymphoblasts from Sporadic Parkinson's Disease Patients

Parkinson's disease (PD) is the second most prevalent neurodegenerative disease among aging individuals, affecting greatly the quality of their life. However, the pathogenesis of Parkinson's disease is still incompletely understood to date. Increasing experimental evidence suggests that cell cycle reentry of postmitotic neurons precedes many instances of neuronal death. Since cell cycle dysfunction is not restricted to neurons, we investigated this issue in peripheral cells from patients suffering from sporadic PD and age-matched control individuals. Here, we describe increased cell cycle activity in immortalized lymphocytes from PD patients that is associated to enhanced activity of the cyclin D3/CDK6 complex, resulting in higher phosphorylation of the pRb family protein and thus, in a G1/S regulatory failure. Decreased degradation of cyclin D3, together with increased p21 degradation, as well as elevated levels of CDK6 mRNA and protein were found in PD lymphoblasts. Inhibitors of cyclin D3/CDK6 activity like sodium butyrate, PD-332991, and rapamycin were able to restore the response of PD cells to serum stimulation. We conclude that lymphoblasts from PD patients are a suitable model to investigate cell biochemical aspects of this disease. It is suggested that cyclin D3/CDK6-associated kinase activity could be potentially a novel therapeutic target for the treatment of PD.

Limited role of free TDP-43 as a diagnostic tool in neurodegenerative diseases

TAR DNA-binding protein 43 (TDP-43) is one of the neuropathological hallmarks in amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD). It is present in patients' blood and cerebrospinal fluid (CSF); however, the source and clinical relevance of TDP-43 measurements in body fluids is uncertain. We investigated paired CSF and serum samples, blood lymphocytes, brain urea fractions and purified exosomes from CSF for TDP-43 by one- (1D), and two-dimensional (2D) Western immunoblotting (WB) and quantitative mass spectrometry (MRM) in patients with ALS, FTLD and non-neurodegenerative diseases. By means of 2D-WB we were able to demonstrate a similar isoform pattern of TDP-43 in lymphocytes, serum and CSF in contrast to that of brain urea fractions with TDP-43 pathology. We found that the TDP-43 CSF to blood concentration ratio is about 1:200. As a possible brain specific fraction we found TDP-43 in exosome preparations from CSF by immunoblot and MRM. We conclude that TDP-43 in CSF originates mainly from blood. Measurements of TDP-43 in CSF and blood are of minor importance as a diagnostic tool, but may be important for monitoring therapy effects of TDP-43 modifying drugs.

Calmodulin levels in blood cells as a potential biomarker of Alzheimer's disease

Introduction

The clinical features of Alzheimer’s disease (AD) overlap with a number of other dementias and conclusive diagnosis is only achieved at autopsy. Accurate in-life diagnosis requires finding biomarkers suitable for early diagnosis, as well as for discrimination from other types of dementia. Mounting evidence suggests that AD-dependent processes may also affect peripheral cells. We previously reported that calmodulin (CaM) signaling is impaired in AD lymphoblasts. Here, we address the issue as to whether the assessment of CaM levels in peripheral cells could serve as a diagnostic biomarker.

Methods

A total of 165 subjects were enrolled in the study, including 56 AD patients, 15 patients with mild cognitive impairment, 7 with frontotemporal dementia associated with progranulin mutations, 4 with dementia with Lewy bodies, 20 patients with Parkinson’s disease, 10 with amyotrophic lateral sclerosis, 5 with progressive supranuclear palsy, and 48 cognitively normal individuals. CaM levels were then analyzed in lymphoblasts, peripheral blood mononuclear cells and plasma. Receiver operating characteristic (ROC) curve analyses were employed to evaluate the diagnostic performance of CaM content in identifying AD patients.

Results

Compared with control individuals, CaM levels were significantly increased in AD cells, but not in the other neurodegenerative disorders. CaM levels differentiated AD from control with a sensitivity of 0.89 and a specificity of 0.82 and were not dependent on disease severity or age. MCI patients also showed higher levels of the protein.

Conclusions

CaM levels could be considered a peripheral biomarker for AD in its early stage and help to discriminate from other types of dementia.

Inactivation of CDK/pRb pathway normalizes survival pattern of lymphoblasts expressing the FTLD-progranulin mutation c.709-1G>A

BACKGROUND

Mutations in the progranulin (PGRN) gene, leading to haploinsufficiency, cause familial frontotemporal lobar degeneration (FTLD-TDP), although the pathogenic mechanism of PGRN deficit is largely unknown. Allelic loss of PGRN was previously shown to increase the activity of cyclin-dependent kinase (CDK) CDK6/pRb pathway in lymphoblasts expressing the c.709-1G>A PGRN mutation. Since members of the CDK family appear to play a role in neurodegenerative disorders and in apoptotic death of neurons subjected to various insults, we investigated the role of CDK6/pRb in cell survival/death mechanisms following serum deprivation.

METHODOLOGY/PRINCIPAL FINDINGS

We performed a comparative study of cell viability after serum withdrawal of established lymphoblastoid cell lines from control and carriers of c.709-1G>A PGRN mutation, asymptomatic and FTLD-TDP diagnosed individuals. Our results suggest that the CDK6/pRb pathway is enhanced in the c.709-1G>A bearing lymphoblasts. Apparently, this feature allows PGRN-deficient cells to escape from serum withdrawal-induced apoptosis by decreasing the activity of executive caspases and lowering the dissipation of mitochondrial membrane potential and the release of cytochrome c from the mitochondria. Inhibitors of CDK6 expression levels like sodium butyrate or the CDK6 activity such as PD332991 were able to restore the vulnerability of lymphoblasts from FTLD-TDP patients to trophic factor withdrawal.

CONCLUSION/SIGNIFICANCE

The use of PGRN-deficient lymphoblasts from FTLD-TDP patients may be a useful model to investigate cell biochemical aspects of this disease. It is suggested that CDK6 could be potentially a therapeutic target for the treatment of the FTLD-TDP.