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

Abstract

Frontotemporal lobar degeneration with neuronal inclusions containing TAR DNA binding protein 43 (TDP-43) is associated in most cases with null-mutations in the progranulin gene (PGRN). While the mechanisms by which PGRN haploinsufficiency leads to neurodegeneration remained speculative, increasing evidence support the hypothesis that cell cycle reentry of postmitotic neurons precedes many instances of neuronal death. Based in the mitogenic and neurotrophic activities of PGRN, we hypothesized that PGRN deficit may induce cell cycle disturbances and alterations in neuronal vulnerability. Because cell cycle dysfunction is not restricted to neurons, we studied the influence of PGRN haploinsufficiency, on cell cycle control in peripheral cells from patients suffering from frontotemporal dementia, bearing the PGRN mutation c.709-1G>A. Here we show that progranulin deficit increased cell cycle activity in immortalized lymphocytes. This effect was associated with increased levels of cyclin-dependent kinase 6 (CDK6) and phosphorylation of retinoblastoma protein (pRb), resulting in a G(1)/S regulatory failure. A loss of function of TDP-43 repressing CDK6 expression may result from altered subcellular TDP-43 distribution. The distinct functional features of lymphoblastoid cells from c.709-1 G>A carriers offer an invaluable, noninvasive tool to investigate the etiopathogenesis of frontotemporal lobar degeneration.

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

“…25,45 Because most of the asymptomatic carriers are younger than the patients with FTD, it is suggested that these features are probably early etiologically relevant events during the development of this disorder. These presymptomatic GRN mutation carriers showed no symptoms of disease, but previous studies have described poorer neuropsychological performance and distinctive agerelated cortical thinning in asymptomatic individuals compared with controls 74,75 that may reflect a presymptomatic phase of the disease.…”

“…Parametric tests were therefore used in the statistical analysis. Based on the expertise achieved in previous works 25,44,45 we expected that with the sample size that we used and the significance level that we established the variability within groups would be low enough and the power to detect differences between groups would be high enough to J Psychiatry Neurosci 2016;41(4) ensure a statistical power above 0.9. Statistical significance was estimated using the Student t test or, when appropriate, using 1-way and 2-way analyses of variance (ANOVA) followed by the Bonferroni test for multiple comparisons.…”

“…46,[52][53][54] For this reason, peripheral cells, such as fibroblasts or blood lymphocytes, have been used extensively in the search for useful biomarkers that may correlate with expression and/or progression of disease. [55][56][57][58] In this regard, it has been shown that peripheral cells from patients with neurodegenerative disorders display cell cycle disturbances, 45,[59][60][61][62] reflecting the unscheduled cell cycle re-entry of postmitotic neurons and leading to apoptotic cell death. [63][64][65] The present work was undertaken to elucidate possible mechanisms involved in the PGRN deficiencyinduced WNT5A expression and signalling in PGRNdeficient lymphoblasts from patients with FTLD-TDP that were considered responsible for the increased activation of the CDK6/pRb-mediated cell proliferation.…”

“…50 As already mentioned, PGRN-deficient lymphoblasts display increased levels and kinase activity of CDK6 protein. 44,45 On these grounds we considered the possibility that the enhanced CDK6 levels could contribute to increased NF-κB activity in these cell lines. Our results show that the treatment of PGRN-deficient cells with PD332991, a specific CDK6 kinase activity inhibitor, inhibited p65 NF-kB subunit phosphorylation, decreased WNT5A levels and blunted the enhanced proliferative response of the PGRN-deficient lymphoblasts.…”

“…45 Since it has been reported that CDK6 may affect the transcriptional activity of NF-kB by its ability to phosphorylate the p65 subunit at serine 536, 50,51 we considered it interesting to evaluate whether this kinase could influence total levels of WNT5A. To address this issue we treated the cells with a known CDK6 activity inhibitor (PD332991).…”