Familial Alzheimer's Disease Fibroblasts Research Articles

Lysosomal TPCN (two pore segment channel) inhibition ameliorates beta-amyloid pathology and mitigates memory impairment in Alzheimer disease

ABSTRACT Impairment of the macroautophagy/autophagy-lysosomal pathway (ALP) can lead to amyloid plaque accumulation in Alzheimer disease (AD); however, the underlying mechanism remains unresolved. This study revealed a mechanism of ALP impairment mediated by gain-of-function of lysosomal TPCN2/TPC2 (two pore segment channel 2) and suggests a molecular target for AD intervention. Using mutant PSEN1/PS1 (presenilin 1)-expressing human neuroblastoma SH-SY5Y and familial AD fibroblasts collected from human patients, we showed lysosomal pH was increased in AD cells due to exaggerated TPCN2-mediated calcium (Ca2+) release which increases lysosomal pH and compromises ALP degradation. Genetic knockdown or pharmacological inhibition of the TPCN2 channel restored lysosomal Ca2+ homeostasis, acidity of the lysosome and ALP function. Furthermore, AD mice (5xFAD) that had received treatment with the TPCN2 inhibitor tetrandrine for 6 months or injection of AAV-shTpcn2 to knock down Tpcn2 showed reduction in amyloid plaques in cortical and hippocampal regions. These treatments also improved spine morphology and density and corrected cognitive deficits in 5xFAD mice assayed by immunohistochemistry, behavioral tests, and electrophysiological measurements, respectively. Taken together, these findings reveal a previously under-appreciated role of lysosomal TPCN2 in ALP impairment of AD. They also suggest targeting the lysosomal TPCN2 can serve as a therapeutic strategy for AD treatment in future drug development. Abbreviations Aβ: β-amyloid; AD: Alzheimer disease; AIF1/IBA1: allograft inflammatory factor 1; ALP: autophagy-lysosomal pathway; APP: amyloid beta precursor protein; ATP6V1B1/V-ATPase V1b1: ATPase H+ transporting V1 subunit B1; AVs: autophagy vacuoles; BAF: bafilomycin A1; CFC: contextual/cued fear conditioning assay; CHX: Ca2+/H+ exchanger; CTF-β: carboxy-terminal fragment derived from β-secretase; CTSD: cathepsin D; fAD: familial Alzheimer disease; GFAP: glial fibrillary acidic protein; LAMP1: lysosomal associated membrane protein 1; LTP: long‐term potentiation; MCOLN1/TRPML1: mucolipin 1; MAP1LC3B/LC3B: microtubule associated protein 1 light chain 3 beta; MAPT: microtubule associated protein tau; MWM: Morris water maze; NFT: neurofibrillary tangles; PFC: prefrontal cortex; PSEN1: presenilin 1; SQSTM1/p62: sequestosome 1; TBS: theta burst stimulation; TEM: transmission electronic microscopy; TPCN2/TPC2: two pore segment channel 2; WT: wild-type; V-ATPase: vacuolar type H+-ATPase

Fibroblasts from PS1 Mutated Pre-Symptomatic Subjects and Alzheimer's Disease Patients Share a Unique Protein Levels Profile

In Alzheimer's disease (AD), a major goal is to improve early detection, as the diagnosis cannot be made until patients exhibit a noticeable decline in cognition and the brain is irreversibly damaged. With this aim in mind, we performed proteome analysis of familial AD fibroblasts from both demented and pre-symptomatic subjects, using a 2D-PAGE based approach and then identifying proteins by mass spectrometry. We compared primary fibroblast cultures from skin biopsy of presenilin 1 (PS1) mutated patients, pre-symptomatic subjects carrying mutations in the PS1 gene but healthy at the time of skin biopsy, and age-matched individuals as control. 15 differentially expressed proteins were identified in PS1 mutated fibroblasts, related to cell adhesion and cytoskeleton, energy and glucose metabolism, stress response and ubiquitin-proteasome system, and signal transduction. Interestingly, many of these proteins have been previously associated with AD and neurodegeneration. Overall results indicated that a unique protein profile can be identified by peripheral cell analysis of PS1 mutated individuals, and showed that fibroblasts are a useful cell model for pathological investigations as well as identification of potential biomarkers for AD diagnosis at early stages.

Reduction of Ca2+ stores and capacitative Ca2+ entry is associated with the familial Alzheimer's disease presenilin-2 T122R mutation and anticipates the onset of dementia

Mutations in the presenilin genes PS1 and PS2, the major cause of familial Alzheimer's disease (FAD), are associated with alterations in Ca2+ signalling. In contrast to the majority of FAD-linked PS1 mutations, which cause an overload of intracellular Ca2+ pools, the FAD-linked PS2 mutation M239I reduces Ca2+ release from intracellular stores [Zatti, G., Ghidoni, R., Barbiero, L., Binetti, G., Pozzan, T., Fasolato, C., Pizzo, P., 2004. The presenilin 2 M239I mutation associated with Familial Alzheimer's Disease reduces Ca2+ release from intracellular stores. Neurobiol. Dis. 15/2, 269-278]. We here show that in human FAD fibroblasts another PS2 mutation (T122R) reduces both Ca2+ release and capacitative Ca2+ entry. The observation, done in two monozygotic twins, is of note since only one of the subjects showed overt signs of disease at the time of biopsy whereas the other one developed the disease 3 years later. This finding indicates that Ca2+ dysregulation anticipates the onset of dementia. A similar Ca2+ alteration occurred in HeLa and HEK293 cells transiently expressing PS2-T122R. Based on these data, the "Ca2+ overload" hypothesis in AD pathogenesis is here discussed and reformulated.

Fibroblasts from FAD-linked presenilin 1 mutations display a normal unfolded protein response but overproduce Aβ42 in response to tunicamycin

Many patients affected by early onset familial Alzheimer's disease (FAD), carry mutations in the presenilin 1 ( PS1) gene. Since it has been suggested that FAD-linked PS1 mutations impair the unfolded protein response (UPR) due to endoplasmic reticulum (ER) stress, we analyzed the UPR and amyloid β-protein processing in fibroblasts bearing various PS1 mutations. Neither in normal conditions nor after induction of ER stress with DTT or tunicamycin were the mRNA levels of UPR-responsive genes (BiP and PDI) significantly different in control and FAD fibroblasts. DTT, which blocked APP transport to the Golgi, caused a 30% decrease of secreted Aβ42 in wild type and PS1 mutant fibroblasts. In contrast, tunicamycin, which allowed exit of APP from the ER, increased secreted Aβ42 only in PS1 mutant fibroblasts. Our findings suggest that, although the UPR is active in fibroblasts from FAD patients, mutant PS1 may selectively increase Aβ42 secretion when N-glycosylation is impaired.

G protein subunit levels in fibroblasts from familial Alzheimer's disease patients: lower levels of the high molecular weight Gs α isoform in patients with decreased β-adrenergic receptor stimulated cAMP formation

Abnormalities in G protein linked signal transduction pathways have been detected in fibroblasts from individuals with familial and sporadic Alzheimer's disease. The present study used Gs α, Gi α, Gq α and Go α G protein subunit antisera, immunoblotting and densitometry to quantify levels of these proteins in control fibroblasts and in fibroblasts from individuals with familial Alzheimer's disease (FAD). The FAD fibroblasts were from individuals with the APP K670N,M671L mutation, different presenilin 1 (PS1) mutations and one fibroblast cell line from an individual with FAD of unknown genetic aetiology. Results revealed a significant reduction in the large Gs α subunit in fibroblasts with the PS1 mutations and in the fibroblast cell line of unknown genetic aetiology, when compared to control levels. This decrease was not apparent in the APP K670N,M671L FAD fibroblasts. Immunoreactivity for Go α was not detected in any of the fibroblast cell lines. No differences were observed in Gi α or Gq α levels when comparing any of the control and Alzheimer's disease fibroblast groups. We conclude that with the exception of decreased levels of the large Gs α subunit, gross alterations in the levels of the Gi α, Gq α and Go α are not associated with the G protein-coupled signal transduction disturbances described previously for some of these FAD fibroblasts.

Alteration of acylphosphatase levels in familial Alzheimer's disease fibroblasts with presenilin gene mutations

Acylphosphatase (ATPase), an enzyme that modulates the activity of Ca 2+-ATPase by hydrolysing its phosphorylated moiety, has been found to be significantly higher in cultured skin fibroblasts from donors affected by early onset familial Alzheimer's disease (EOFAD) with PS-1 and PS-2 gene mutations. Of the two known isoenzymes of acylphosphatase, only the erythrocyte one accounts for the total increase in activity. No relevant alteration was observed in phosphotyrosine phosphatase activity (PTPase), in Ca 2+-ATPase and Na +,K +-ATPase activities of the same cells as compared to age-matched controls. This finding could suggest a possible explanation for the calcium-dependent biochemical alterations previously described in Alzheimer's disease fibroblasts.

785 Familial Alzheimer's disease fibroblasts with presenilin genes mutations: Alteration'of Acylphosphatase levels

785 Familial Alzheimer's disease fibroblasts with presenilin genes mutations: Alteration'of Acylphosphatase levels

226 Effect of fibroblast growth factor and insulin on β-amyloid production in normal and familial Alzheimer's disease fibroblasts

226 Effect of fibroblast growth factor and insulin on β-amyloid production in normal and familial Alzheimer's disease fibroblasts

Abnormality of the α‐ketoglutarate dehydrogenase complex in fibroblasts from familial Alzheimer's disease

To test whether previously demonstrated reductions in the activity of the alpha-ketoglutarate dehydrogenase complex (KGDHC) in Alzheimer's disease (AD) brain also occur in morphologically normal AD tissues, we examined KGDHC in cultured skin fibroblasts from patients with familial AD (FAD). KGDHC activity was reduced by 44% in the FAD cells (p < 0.002) from the 4 families studied, including a within-kindred comparison of affected and escapee subjects in the chromosome 14q24.3-linked Nova Scotia kindred. The activities of several other glutamate- and glutamine-metabolizing enzymes were normal in the FAD cells, as was the activity of another mitochondrial multienzyme dehydrogenase complex, that for pyruvate. Mixing experiments indicated that the abnormality of KGDHC activity in FAD fibroblasts was not due to an inhibitor or to excess protease activity. KGDHC is a complex of three proteins. Immunoblots for the E2k component under conditions of optimal protease inhibition revealed the expected 46-kd species in both AD and non-AD fibroblasts, but the patient cells also regularly contained an additional 29-kd species that was absent or present in minimal amounts in the controls. Immunoblotting demonstrated no abnormalities in the E1k and E3 components. Other studies indicate that the human gene for E2k residues on chromosome 14q24.3, in a region associated with FAD in a number of families including the KGDHC-deficient Nova Scotia kindred. The persistence of abnormalities in KGDHC and particularly in its E2k component in FAD fibroblasts indicates that abnormalities of this autosomally coded nuclear component are an intrinsic part of the AD process, and the possible role of this abnormality in the pathogenesis of AD is discussed.

Growth properties and in vitro life span of Alzheimer disease and Down syndrome fibroblasts. A blind study

A blind study was set up to examine the in vitro growth characteristics of skin fibroblasts from 2 individuals with and 9 at risk for familial Alzheimer disease, 4 individuals with sporadic Alzheimer disease, 18 with Down syndrome as well as 5 younger and 6 older controls. Several variables (biopsy size, number of explants, medium, passage procedure) were standardized. Two growth characteristics were examined quantitatively; (i) the actual in vitro replicating life span was determined by counting the number of cells plated the previous week at 500000 cells/flask (cumulative population doublings); and (ii) the growth potential was examined by a colony size distribution assay. A difference from the age-matched controls in the growth characteristics of skin fibroblasts was only observed for two patients with and one older individual at risk for familial Alzheimer disease. The growth properties of skin fibroblast cultures from patients with sporadic Alzheimer disease or Down syndrome were not at variance with their age-matched controls. The decrease in the growth potential observed in the familial Alzheimer disease fibroblasts is however modest and needs confirmation. It is clear that the growth properties of skin fibroblasts, as examined in this study, do not provide a good marker for any form of Alzheimer disease, nor do they provide an appropriate in vitro system to study factors which may contribute to the etiopathogenesis of Alzheimer disease or Down syndrome.

Decreased adhesiveness of Alzheimer's disease fibroblasts: is amyloid beta-protein precursor involved?

The adhesiveness of fibroblasts derived from Alzheimer's disease (AD) patients to a plastic substratum was assessed as the proportion of cells attached to a plastic dish bottom after a 30-minute incubation in culture medium of cells dissociated in ethylenediaminetetraacetic acid and was compared with the adhesiveness of normal fibroblasts from non-AD controls. It was found that the normal fibroblasts adhered better to plastic than did AD cells. This reduced adhesiveness was observed in fibroblasts derived from both sporadic and familial AD patients. Because of the possible involvement of amyloid beta-protein precursor (ABPP) in the process of cellular adhesion, the amount of ABPP messenger RNA was measured in these fibroblasts and was found to be decreased in the familial AD fibroblasts, although not in cells from sporadic AD patients. Furthermore, there were fewer molecules detected by an anti-ABPP antibody in conditioned media from familial AD fibroblasts as compared with media from control fibroblasts. Therefore, although it is possible that the reduced adhesiveness of familial AD fibroblasts may result from genetic deficits in ABPP gene expression, the reduced adhesiveness of sporadic AD fibroblasts most likely results from certain deficits in molecules other than the ABPP.

Deficient repair of DNA lesions in Alzheimer's disease fibroblasts

DNA strand breaks, resulting from treatment with N-methyl-N′-nitro-N-nitrosoguanidine, were repaired more slowly in four strains of familial Alzheimer's disease fibroblasts than in five strains of fibroblasts from age-matched normals. These results were not due to differences between the two cell types in in vitro ages, in the initial DNA damage or in drug-induced cell lysis. Bleomycin-induced DNA double-strand breaks were repaired equally efficiently by both types of cells. Alzheimer's disease cells may have a DNA repair defect, which may be involved in the pathogenesis of this disease.