M. Di Luca

Mutation within TARDBP leads to Frontotemporal Dementia without motor neuron disease

It has been recently demonstrated that the 43‐kDa transactive response (TAR)‐DNA‐binding protein (TARDBP) is the neuropathological hallmark of Frontotemporal Dementia (FTD) with ubiquitin‐positive and tau‐negative inclusions. Large series of FTD patients without motor neuron disease have been previously analysed, but no TARDBP mutation was identified. The aim of the present study was to evaluate whether TARDBP gene mutations may be associated with FTD. We report that a pathogenetic TARDBP mutation is causative of behavioural variant FTD (bvFTD). An aged woman in her seventies initially started to present apathy and depression associated with impairment in executive functions. The diagnosis of bvFTD (apathetic syndrome) was accomplished by three‐year follow‐up, and structural and functional neuroimaging. By five‐years after onset, extensive electrophysiological investigations excluded subclinical motor neuron disease. In this patient, a single base substitution c.800A>G of TARDBP gene was identified. This mutation, already described as causative of ALS, predicted the amino acidic change arginine to serine at position 267 (N267S). In silico analysis demonstrated that this substitution generates a new phosphorylation site, and western blot analysis on lymphoblastoid cells reported a decrease of protein expression in N267S mutation carrier. Our study suggests that TARDBP mutations can be pathogenetic of bvFTD without motor neuron disease. TARDBP screening needs to be considered in FTD cases.

Calcium/Calmodulin‐Dependent Protein Kinase II Is Associated with NR2A/B Subunits of NMDA Receptor in Postsynaptic Densities

Abstract: NMDA receptors and Ca2+/calmodulin‐dependent kinase II (CaMKII) have been reported to be highly concentrated in the postsynaptic density (PSD). Although the possibility that CaMKII in PSD might be associated with specific proteins has been put forward, the protein or proteins determining the targeting of the kinase in PSD have not yet been identified. Here we report that CaMKII binds to NR2A and NR2B subunits of NMDA receptors in PSD isolated from cortex and hippocampus. The association of NMDA receptor subunits and CaMKII was assessed by immunoprecipitating PSD proteins with antibodies specific for NR2A/B and CaMKII: CaMKII coprecipitated with NR2A/B and NR1 but not with other glutamate ionotropic receptor subunits, such as GluR1 and GluR2‐3. A direct association between CaMKII and NR2A/B subunits was further confirmed by overlay experiments using either 32P‐autophosphorylated CaMKII or 32P‐NR2A/B and by evaluating the formation of a CaMKII‐NR2A/B complex by means of the cross‐linker disuccimidyl suberate. These data demonstrate an association between the NMDA receptor complex and CaMKII in the postsynaptic compartment, suggesting that this colocalization may be relevant for synaptic plasticity.

Combined 99mTc-ECD SPECT and neuropsychological studies in MCI for the assessment of conversion to AD

Identifying pre-clinical Alzheimers disease (AD) in subjects with mild cognitive impairment (MCI) is a major issue in clinical diagnosis. Establishing a combination of predictive markers from different fields of research might help in increasing the diagnostic accuracy. Aim of this study was to evaluate the potential role of 99mTc-ECD single photon emission computed tomography (SPECT) and memory scores in predicting conversion to AD in MCI subjects. Thirty-one MCI subjects underwent a clinical and neuropsychological examination, and a regional cerebral blood flow (rCBF) SPECT scan at baseline. Subjects had been followed periodically through 2 years in order to monitor the progression of cognitive symptoms. Canonical variate analysis of principal components was able to separate all subjects who converted to AD from those who remained stable, the former being characterized by a specific hypometabolic pattern, involving the parietal and temporal lobes, precuneus, and posterior cingulate cortex. Canonical correlation analysis of combined baseline memory deficits and rCBF SPECT images identified pre-clinical AD with a sensitivity and specificity of 77.8%. The pattern of hypoperfusion 99mTc-ECD SPECT and the severity of memory deficits predict the risk of progression to probable AD dementia in MCI subjects.

Platelet APP, ADAM 10 and BACE alterations in the early stages of Alzheimer disease

Amyloid precursor protein (APP), ADAM 10, and β-site-APP cleaving enzyme (BACE) alterations were evaluated in platelets of 31 patients with Alzheimer disease (AD) and 15 age-matched controls. A significant modification of these proteins and enzymes involved in the amyloid cascade was detected from the earliest clinically detectable disease stage. This observation suggests that AD is associated with an early metabolic derangement toward amyloidogenic pathways and supports the potential value of APP and secretase measurements for early diagnosis of AD.

NMDA receptor subunits are modified transcriptionally and post-translationally in the brain of streptozotocin-diabetic rats

Aims/hypothesis. Moderate disturbances of learning and memory were recognized as a complication of diabetes mellitus in patients. The streptozotocin-diabetic rat, an animal model of insulin-dependent diabetes, shows impairments in spatial memory and in long-term potentiation expression. We have studied the effect of experimental diabetes on expression of post-synaptic glutamate N-Methyl-D-Aspartate ionotropic receptors and of other key proteins regulating synaptic transmission at the post-synaptic compartment. Methods. In situ hybridization and Western blot analysis were used to assess expression and protein concentration of N-Methyl-D-Aspartate receptors and α-calcium-calmodulin-dependent kinase II. Receptor subunits αCaMKII-dependent phosphorylation was studied in post-synaptic densities obtained from the hippocampus and cortex of control, streptozotocin-diabetic and insulin-treated rats. Results. The transcript levels of NR1 and NR2A subunits of N-Methyl-D-Aspartate were unchanged in rats with a diabetic duration of 3 months when compared with age-matched control rats. Accordingly, NR1 and NR2A as well as GluR1, GluR2/3, PSD-95 and αCaMKII protein concentrations in post-synaptic densities were the same in both control and diabetic rats, whereas the immunoreactivity for NR2B was reduced by about 40 %. In addition, the activity of αCaMKII on exogenous substrates, such as syntide-2, and the phosphorylation of NR2A/B subunits of N-Methyl-D-Aspartate receptor was reduced in hippocampal post-synaptic densities of streptozotocin-diabetic rats as compared with control rats. Furthermore, we show that insulin intervention for 3 months after diabetic duration partially restored both αCaMKII activity and NR2B levels. Conclusion/interpretation. N-Methyl-D-Aspartate receptor expression and phosphorylation is possibly involved in behavioural and electrophysiological abnormalities observed in streptozotocin-diabetic rats. [Diabetologia (1999) 42: 693–701]

Effects of streptozotocin-diabetes on the hippocampal NMDA receptor complex in rats

In animal models of diabetes mellitus, such as the streptozotocin‐diabetic rat (STZ‐rat), spatial learning impairments develop in parallel with a reduced expression of long‐term potentiation (LTP) and enhanced expression of long‐term depression (LTD) in the hippocampus. This study examined the time course of the effects of STZ‐diabetes and insulin treatment on the hippocampal post‐synaptic glutamate N‐methyl‐d‐aspartate (NMDA) receptor complex and other key proteins regulating hippocampal synaptic transmission in the post‐synaptic density (PSD) fraction. In addition, the functional properties of the NMDA‐receptor complex were examined. One month of STZ‐diabetes did not affect the NMDA receptor complex. In contrast, 4 months after induction of diabetes NR2B subunit immunoreactivity, CaMKII and Tyr‐dependent phosphorylation of the NR2A/B subunits of the NMDA receptor were reduced and αCaMKII autophosphorylation and its association to the NMDA receptor complex were impaired in STZ‐rats compared with age‐matched controls. Likewise, NMDA currents in hippocampal pyramidal neurones measured by intracellular recording were reduced in STZ‐rats. Insulin treatment prevented the reduction in kinase activities, NR2B expression levels, CaMKII–NMDA receptor association and NMDA currents. These findings strengthen the hypothesis that altered post‐synaptic glutamatergic transmission is␣related to deficits in learning and plasticity in this animal model.

αCaMKII binding to the C-terminal tail of NMDA receptor subunit NR2A and its modulation by autophosphorylation

Ca2+/calmodulin‐dependent protein kinase II (CaMKII), a multifunctional, widely distributed enzyme, is enriched in post‐synaptic densities (PSDs). Here, we demonstrate that CaMKII binds to a discrete C‐terminal region of the NR2A subunit of NMDA receptors and promotes the phosphorylation of a Ser residue of this NMDA receptor subunit. Glutathione S‐transferase (GST)‐NR2A(1349‐1464) binds native CaMKII from solubilised hippocampal PSDs in ‘pull‐out’ and overlay experiments and this binding is competed by recombinant αCaMKII(1‐315). The longer GST‐NR2A(1244‐1464), although containing the CaMKII phosphosite Ser‐1289, binds the kinase with a lower efficacy. CaMKII association to NR2A(1349‐1464) is positively modulated by kinase autophosphorylation in the presence of Ca2+/calmodulin. These data provide direct evidence for a mechanism modulating the synaptic strength.

Amyloid precursor protein in platelets A peripheral marker for the diagnosis of sporadic AD

Background: An altered pattern of amyloid precursor protein (APP) forms consisting in a reduced ratio between the upper (130 kDa) and the lower (106 to 110 kDa) immunoreactivity bands has been described in platelets of patients with AD. Objective: To evaluate the sensitivity and the specificity of platelet APP forms’ ratio (APPr) as a marker for AD. Methods: Eighty-five patients with probable AD and 95 control subjects (CON), including healthy individuals and neurologic patients, entered the study. Platelet APPr was evaluated by means of Western Blot analysis and immunostaining in the whole platelet homogenate, and calculated by the ratio between the optical density (OD) of the upper (130 kDa) and the lower (106 to 110 kDa) APP immunoreactive bands. Results: Mean APPr levels were decreased in AD patients (mean OD ± SD = 0.35 ± 0.18) compared with the CON group (mean OD ± SD = 0.92 ± 0.38) (DF 1, 178, p < 0.0001). Accuracy levels measured by Receiver Operating Curve analysis showed that a cut-off level of 0.57 resulted in a sensitivity of 88.2% and a specificity of 89.4%, with an area under the curve of 0.945. APPr levels were significantly associated with disease severity (mild AD versus moderate AD: p < 0.0001; moderate AD versus severe AD: p < 0.05). Conclusion: Platelet APPr allowed to differentiate AD from normal aging and other dementing disorders with high sensitivity and specificity. These findings suggest that platelet APPr may be of help as an adjunctive diagnostic tool in clinical practice.

Tau forms in CSF as a reliable biomarker for progressive supranuclear palsy

Objective: In CSF, extended (55 kDa) and truncated (33 kDa) tau forms have been previously recognized, and the tau 33 kDa/55 kDa ratio has been found significantly reduced in progressive supranuclear palsy (PSP) vs in other neurodegenerative disorders. The aim of this study was to evaluate the diagnostic value of the CSF tau form ratio as a biomarker of PSP and to correlate the structural anatomic changes as measured by means of voxel-based morphometry (VBM) to CSF tau form ratio decrease. Methods: A total of 166 subjects were included in the study (21 PSP, 20 corticobasal degeneration syndrome, 44 frontotemporal dementia, 29 Alzheimer disease, 10 Parkinson disease, 15 dementia with Lewy bodies, and 27 individuals without any neurodegenerative disorder). Each patient underwent a standardized clinical and neuropsychological evaluation. In CSF, a semiquantitative immunoprecipitation was developed to evaluate CSF tau 33 kDa/55 kDa ratio. MRI assessment and VBM analysis was carried out. Results: Tau form ratio was significantly reduced in patients with PSP (0.504 ± 0.284) when compared to age-matched controls (0.989 ± 0.343), and to patients with other neurodegenerative conditions (range = 0.899–1.215). The area under the curve (AUC) of the receiver operating characteristic analysis in PSP vs other subgroups ranged from 0.863 to 0.937 (PSP vs others, AUC = 0.897, p < 0.0001). VBM study showed that CSF tau form ratio decrease correlated significantly with brainstem atrophy. Conclusions: Truncated tau production, which selectively affects brainstem neuron susceptibility, can be considered a specific and reliable marker for PSP. Tau form ratio was the lowest in progressive supranuclear palsy with no overlap with any other neurodegenerative illness. GLOSSARY: AD = Alzheimer disease; AUC = area under the curve; BADL = Basic Activity of Daily Living; CBDS = corticobasal degeneration; CON = controls; DLB = dementia with Lewy bodies; DSM-IV = Diagnostic and Statistical Manual of Mental Disorders, 4th edition; FTD = frontotemporal dementia; IADL = Instrumental Activities of Daily Living; MMSE = Mini-Mental State Examination; MSA = multiple system atrophy; PD = Parkinson disease; PSP = progressive supranuclear palsy; ROC = receiver operating characteristic; UPDRS = Unified Parkinson’s Disease Rating Scale; VBM = voxel-based morphometry.

Pattern of Tau forms in CSF is altered in progressive supranuclear palsy

Cerebrospinal fluid (CSF) total Tau levels vary widely in neurodegenerative disorders, thus being not useful in their discrimination over Alzheimer disease. No CSF marker for progressive supranuclear palsy (PSP) is currently available. The aim of this study was to characterise and measure Tau forms in order to verify the differential patterns among neurodegenerative disorders. Seventy-eight patients with neurodegenerative disorders and 26 controls were included in the study. Each patient underwent a standardised clinical and neuropsychological evaluation, MRI, and CSF total-Tau and phospho-Tau dosage. In CSF and cerebral cortex, a quantitative immunoprecipitation was developed. An extended (55 kDa), and a truncated (33 kDa) forms of Tau were recognised. CSF samples were assayed, the optical density of the two Tau forms was measured, and the ratio calculated (Tau ratio, 33 kDa/55 kDa forms). Tau ratio 33 kDa/55 kDa was significantly decreased in patients with PSP (0.46+/-0.16) when compared to controls, including healthy subjects (1.16+/-0.46, P=0.002) and Alzheimer disease (1.38+/-0.68, P<0.001), and when compared to frontotemporal dementia (0.98+/-0.30, P=0.008) or corticobasal degeneration syndrome (0.98+/-0.48, P=0.02). Moreover, in PSP patients Tau form ratio was lower than in other neurodegenerative extrapyramidal disorders, such as Parkinson disease (1.16+/-0.26, P=0.002) and dementia with lewy bodies (1.44+/-0.48, P<0.001). Tau ratio 33 kDa/55 kDa did not correlate either with demographic characteristics, cognitive performances or with motor impairment severity. Truncated Tau production shows a different pattern in PSP compared to other neurodegenerative disorders, supporting the view of disease-specific pathological pathways. These findings are promising in suggesting the identification of a marker for PSP diagnosis in clinical practice.