Complement C3 mediates early hippocampal neurodegeneration and memory impairment in experimental multiple sclerosis.

Memory impairment is one of the disabling manifestations of multiple sclerosis (MS) possibly present from the early stages of the disease and for which there is no specific treatment. Hippocampal synaptic dysfunction and dendritic loss, associated with microglial activation, can underlie memory deficits, yet the molecular mechanisms driving such hippocampal neurodegeneration need to be elucidated. In early-stage experimental autoimmune encephalomyelitis (EAE) female mice, we assessed the expression level of molecules involved in microglia-neuron interactions within the dentate gyrus and found overexpression of genes of the complement pathway. Compared to sham immunized mice, the central element of the complement cascade, C3, showed the strongest and 10-fold upregulation, while there was no increase of downstream factors such as the terminal component C5. The combination of in situ hybridization with immunofluorescence showed that C3 transcripts were essentially produced by activated microglia. Pharmacological inhibition of C3 activity, by daily administration of rosmarinic acid, was sufficient to prevent early dendritic loss, microglia-mediated phagocytosis of synapses in the dentate gyrus, and memory impairment in EAE mice, while morphological markers of microglial activation were still observed. In line, when EAE was induced in C3 deficient mice (C3KO), dendrites and spines of the dentate gyrus as well as memory abilities were preserved. Altogether, these data highlight the central role of microglial C3 in early hippocampal neurodegeneration and memory impairment in EAE and, therefore, pave the way toward new neuroprotective strategies in MS to prevent cognitive deficit using complement inhibitors.

Dissection of synaptic pathways through the CSF biomarkers for predicting Alzheimer disease.

OBJECTIVE: To assess the ability of a combination of synaptic CSF biomarkers to separate Alzheimer disease (AD) and non-AD disorders and to help in the differential diagnosis between neurocognitive diseases. METHODS: This was a retrospective cross-sectional monocentric study. All participants explored with CSF assessments for neurocognitive decline were invited to participate. After complete clinical and imaging evaluations, 243 patients were included. CSF synaptic (GAP-43, neurogranin, SNAP-25 total, SNAP-25aa40, synaptotagmin-1) and AD biomarkers were blindly quantified with ELISA or mass spectrometry. Statistical analysis compared CSF levels between the various groups of AD dementias (n = 81), mild cognitive impairment (MCI)-AD (n = 30), other MCI (n = 49), other dementias (OD) (n = 49), and neurologic controls (n = 35) and their discriminatory powers. RESULTS: All synaptic biomarkers were significantly increased in patients with MCI-AD and AD-dementia compared to the other groups. All synaptic biomarkers could efficiently discriminate AD dementias from OD (AUC ≥0.80). All but synaptotagmin were also able to discriminate patients with MCI-AD from controls (area under the curve [AUC] ≥0.85) and those with AD dementias from controls (AUC ≥0.80). Overall, CSF SNAP-25aa40 had the highest discriminative power (AUC 0.93 between patients with AD dementias and controls or OD, AUC 0.90 between those with MCI-AD and controls). Higher levels were associated with 2 alleles of APOE ε4. CONCLUSION: All synaptic biomarkers tested had a good discriminatory power to distinguish patients with AD abnormal CSF from those with non-AD disorders. SNAP25aa40 demonstrated the highest power to discriminate AD CSF-positive patients from patients without AD and neurologic controls in this cohort. CLASSIFICATION OF EVIDENCE: This retrospective study provides Class II evidence that CSF synaptic biomarkers discriminate patients with AD from those without AD.

PKR knockout in the 5xFAD model of Alzheimer's disease reveals beneficial effects on spatial memory and brain lesions.

Brain lesions in Alzheimer's disease (AD) include amyloid plaques made of Aß peptides and neurofibrillary tangles composed of hyperphosphorylated tau protein with synaptic and neuronal loss and neuroinflammation. Aß oligomers can trigger tau phosphorylation and neuronal alterations through activation of neuronal kinases leading to progressive cognitive decline. PKR is a ubiquitous pro-apoptotic serine/threonine kinase, and levels of activated PKR are increased in AD brains and AD CSF. In addition, PKR regulates negatively memory formation in mice. To assess the role of PKR in an AD in vivo model, we crossed 5xFAD transgenic mice with PKR knockout (PKRKO) mice and we explored the contribution of PKR on cognition and brain lesions in the 5xFAD mouse model of AD as well as in neuron-microglia co-cultures exposed to the innate immunity activator lipopolysaccharide (LPS). Nine-month-old double-mutant mice revealed significantly improved memory consolidation with the new object location test, starmaze test, and elevated plus maze test as compared to 5xFAD mice. Brain amyloid accumulation and BACE1 levels were statistically decreased in double-mutant mice. Apoptosis, neurodegeneration markers, and synaptic alterations were significantly reduced in double-mutant mice as well as neuroinflammation markers such as microglial load and brain cytokine levels. Using cocultures, we found that PKR in neurons was essential for LPS microglia-induced neuronal death. Our results demonstrate the clear involvement of PKR in abnormal spatial memory and brain lesions in the 5xFAD model and underline its interest as a target for neuroprotection in AD.

Increased PKR level in human CADASIL brains.

Cerebral autosomal dominant arteriolopathy with subcortical infarcts and leucoencephalopathy (CADASIL) is the most common form of hereditary small vessel disease (SVD) of the brain. Neuronal apoptosis has been demonstrated in the cortex of patients. Whether it is associated with an activation of the pro-apoptotic protein PKR pathway is unknown. Similarly, activation of autophagy in CADASIL has never been explored. Immunostaining of four CADASIL brains previously analyzed for cortical neuronal apoptosis and five control brains for PKR (phosphoPKR) and autophagy (ATG5, LC3II) activation markers. Significant nuclear pPKR staining was observed in CADASIL neurons comparatively to controls (p = 0.001). No difference was observed between patients and controls with autophagy markers. We demonstrated the activation of PKR pathway in CADASIL. This was not associated with a detectable modulation of autophagy. These results open a new field to explore in order to better understand the mechanisms underlying cortical neurons apoptosis.

PKR modulates abnormal brain signaling in experimental obesity.

Metabolic disorders including obesity and type 2 diabetes are known to be associated with chronic inflammation and are obvious risk factors for Alzheimer's disease. Recent evidences concerning obesity and diabetes suggest that the metabolic inflammasome ("metaflammasome") mediates chronic inflammation. The double-stranded RNA-dependent protein kinase (PKR) is a central component of the metaflammasome. In wild type (WT) and PKR-/- mice, blood glucose, insulin and lipid levels and the brain expression of the phosphorylated components of the metaflammasome-PKR, JNK, IRS1 and IKKbeta-were studied after the induction of obesity by a high fat diet (HFD). The results showed significant increased levels of activated brain metaflammasome proteins in exposed WT mice but the changes were not significant in PKR-/- mice. In addition, gain weight was observed in WT mice and also in PKR-/- mice exposed to HFD. Increased blood insulin level was more accentuated in PKR -/- mice. The modulation of PKR activity could be an appropriate therapeutic approach, aimed at reducing abnormal brain metabolism and inflammation linked to metabolic disorders in order to reduce the risk of neurodegeneration.

PTK2B/Pyk2 overexpression improves a mouse model of Alzheimer's disease.

Pyk2 is a Ca2+-activated non-receptor tyrosine kinase enriched in forebrain neurons and involved in synaptic regulation. Human genetic studies associated PTK2B, the gene coding Pyk2, with risk for Alzheimer's disease (AD). We previously showed that Pyk2 is important for hippocampal function, plasticity, and spine structure. However, its potential role in AD is unknown. To address this question we used human brain samples and 5XFAD mice, an amyloid mouse model of AD expressing mutated human amyloid precursor protein and presenilin1. In the hippocampus of 5XFAD mice and in human AD patients' cortex and hippocampus, Pyk2 total levels were normal. However, Pyk2 Tyr-402 phosphorylation levels, reflecting its autophosphorylation-dependent activity, were reduced in 5XFAD mice at 8 months of age but not 3 months. We crossed these mice with Pyk2-/- mice to generate 5XFAD animals devoid of Pyk2. At 8 months the phenotype of 5XFAD x Pyk2-/- double mutant mice was not different from that of 5XFAD. In contrast, overexpression of Pyk2 in the hippocampus of 5XFAD mice, using adeno-associated virus, rescued autophosphorylated Pyk2 levels and improved synaptic markers and performance in several behavioral tasks. Both Pyk2-/- and 5XFAD mice showed an increase of potentially neurotoxic Src cleavage product, which was rescued by Pyk2 overexpression. Manipulating Pyk2 levels had only minor effects on Aß plaques, which were slightly decreased in hippocampus CA3 region of double mutant mice and increased following overexpression. Our results show that Pyk2 is not essential for the pathogenic effects of human amyloidogenic mutations in the 5XFAD mouse model. However, the slight decrease in plaque number observed in these mice in the absence of Pyk2 and their increase following Pyk2 overexpression suggest a contribution of this kinase in plaque formation. Importantly, a decreased function of Pyk2 was observed in 5XFAD mice, indicated by its decreased autophosphorylation and associated Src alterations. Overcoming this deficit by Pyk2 overexpression improved the behavioral and molecular phenotype of 5XFAD mice. Thus, our results in a mouse model of AD suggest that Pyk2 impairment may play a role in the symptoms of the disease.

Brimapitide Reduced Neuronal Stress Markers and Cognitive Deficits in 5XFAD Transgenic Mice.

Alzheimer's disease (AD) is characterized by accumulations of amyloid-ß (Aß42) and hyperphosphorylated tau proteins, associated with neuroinflammation, synaptic loss, and neuronal death. Several studies indicate that c-Jun N-terminal kinase (JNK) is implicated in the pathological features of AD. We have investigated in 5XFAD mice, the therapeutic effects of Brimapitide, a JNK-specific inhibitory peptide previously tested with higher concentrations in another AD model (TgCRND8). Three-month-old 5XFAD and wild-type littermate mice were treated by intravenous injections of low doses (10 mg/kg) of Brimapitide every 3 weeks, for 3 or 6 months (n = 6-9 per group). Cognitive deficits and brain lesions were assessed using Y-maze, fear-conditioning test, and histological and biochemical methods. Chronic treatment of Brimapitide for 3 months resulted in a reduction of Aß plaque burden in the cortex of 5XFAD treated mice. After 6 months of treatment, cognitive deficits were reduced but also a significant reduction of cell death markers and the pro-inflammatory IL-1ß cytokine in treated mice were detected. The Aß plaque burden was not anymore modified by the 6 months of treatment. In addition to modulating cognition and amyloid plaque accumulation, depending on the treatment duration, Brimapitide seems experimentally to reduce neuronal stress in 5XFAD mice.

Inhibition of the inflammatory response to stress by targeting interaction between PKR and its cellular activator PACT.

PKR is a cellular kinase involved in the regulation of the integrative stress response (ISR) and pro-inflammatory pathways. Two N-terminal dsRNA Binding Domains (DRBD) are required for activation of PKR, by interaction with either dsRNA or PACT, another cellular DRBD-containing protein. A role for PKR and PACT in inflammatory processes linked to neurodegenerative diseases has been proposed and raised interest for pharmacological PKR inhibitors. However, the role of PKR in inflammation is subject to controversy. We identified the flavonoid luteolin as an inhibitor of the PKR/PACT interaction at the level of their DRBDs using high-throughput screening of chemical libraries by homogeneous time-resolved fluorescence. This was further validated using NanoLuc-Based Protein Complementation Assay. Luteolin inhibits PKR phosphorylation, the ISR and the induction of pro-inflammatory cytokines in human THP1 macrophages submitted to oxidative stress and toll-like receptor (TLR) agonist. Similarly, luteolin inhibits induction of pro-inflammatory cytokines in murine microglial macrophages. In contrast, luteolin increased activation of the inflammasome, in a PKR-independent manner. Collectively, these data delineate the importance of PKR in the inflammation process to the ISR and induction of pro-inflammatory cytokines. Pharmacological inhibitors of PKR should be used in combination with drugs targeting directly the inflammasome.

Neuroinflammation and Aß accumulation linked to systemic inflammation are decreased by genetic PKR down-regulation.

Alzheimer's disease (AD) is a neurodegenerative disorder, marked by senile plaques composed of amyloid-ß (Aß) peptide, neurofibrillary tangles, neuronal loss and neuroinflammation. Previous works have suggested that systemic inflammation could contribute to neuroinflammation and enhanced Aß cerebral concentrations. The molecular pathways leading to these events are not fully understood. PKR is a pro-apoptotic kinase that can trigger inflammation and accumulates in the brain and cerebrospinal fluid of AD patients. The goal of the present study was to assess if LPS-induced neuroinflammation and Aß production could be altered by genetic PKR down regulation. The results show that, in the hippocampus of LPS-injected wild type mice, neuroinflammation, cytokine release and Aß production are significantly increased and not in LPS-treated PKR knock-out mice. In addition BACE1 and activated STAT3 levels, a putative transcriptional regulator of BACE1, were not found increased in the brain of PKR knock-out mice as observed in wild type mice. Using PET imaging, the decrease of hippocampal metabolism induced by systemic LPS was not observed in LPS-treated PKR knock-out mice. Altogether, these findings demonstrate that PKR plays a major role in brain changes induced by LPS and could be a valid target to modulate neuroinflammation and Aß production.

MicroRNAs as non-invasive biomarkers of heart transplant rejection.

AIM: Rejection is one of the major causes of late cardiac allograft failure and at present can only be diagnosed by invasive endomyocardial biopsies. We sought to determine whether microRNA profiling could serve as a non-invasive biomarker of cardiac allograft rejection. METHODS: We included 113 heart transplant recipients from four referral French institutions (test cohort, n = 60, validation cohort, n = 53). In the test cohort, we compared patients with acute biopsy-proven allograft rejection (n = 30) to matched control patients without rejection (n = 30), by assessing microRNAs expression in the heart allograft tissue and patients concomitant serum using RNA extraction and qPCR analysis. Fourteen miRNAs were selected on the basis of their implication in allograft rejection, endothelial activation, and inflammation and tissue specificity. RESULTS: We identified seven miRNAs that were differentially expressed between normal and rejecting heart allografts: miR-10a, miR-21, miR-31, miR-92a, miR-142-3p miR-155, and miR-451 (P < 0.0001 for all comparisons). Four out of seven miRNAs also showed differential serological expression (miR-10a, miR-31, miR-92a, and miR-155) with strong correlation with their tissular expression. The receiver-operating characteristic analysis showed that these four circulating miRNAs strongly discriminated patients with allograft rejection from patients without rejection: miR-10a (AUC = 0.975), miR-31 (AUC = 0.932), miR-92a (AUC = 0.989), and miR-155 (AUC = 0.998, P < 0.0001 for all comparisons). We confirmed in the external validation set that these four miRNAs highly discriminated patients with rejection from those without. The discrimination capability of the four miRNAs remained significant when stratified by rejection diagnosis (T-cell-mediated rejection or antibody-mediated rejection) and time post-transplant. CONCLUSION: This study demonstrates that a differential expression of miRNA occurs in rejecting allograft patients, not only at the tissue level but also in the serum, suggesting their potential relevance as non-invasive biomarkers in heart transplant rejection.

Pathologic classification of antibody-mediated rejection correlates with donor-specific antibodies and endothelial cell activation.

BACKGROUND: Humoral immune responses during heart transplantation may result in antibody-mediated rejection (AMR), which is now taken into account on endomyocardial biopsy (EMB) specimens and ranked according to the pathologic AMR (pAMR) grades of the International Society for Heart and Lung Transplantation classification. This classification might benefit from new immunohistological markers and validation by others biomarkers, namely donor-specific antibodies (DSA). METHODS: From the 293 protocol EMBs performed in 113 patients in our institution during a 1-year period for this prospective study, 280 EMB specimens were available with both histology and immunohistochemistry. C4d and labeling of intravascular cells by cluster of differentiation (CD) 68 were performed on paraffin sections. Available sera (n = 150) concomitant of EMB specimens were tested for the presence of DSA. All of the pAMR+ EMB specimens, along with a set of randomized pAMR0 EMB specimens, were immunolabeled for mammalian target of rapamycin (mTOR) effectors, phosphorylated 70 S6-kinase (p70S6K) and phosphorylated S6 ribosomal protein (pS6RP). RESULTS: AMR was diagnosed in 37 EMB specimens (13.2%): 1 pAMR1(I+), 27 pAMR1(H+), and 9 pAMR2. The proportion of DSA-positive EMB varied according to the pAMR grade, with pAMR0, pAMR1(H+), and pAMR2 EMB presenting 17.6%, 77.3%, and 100% of DSA-positivity, respectively. Among the 30 pAMR+ specimens with available DSA testing and the 30 pAMR0 randomized specimens, mTOR pathway immunohistochemistry showed endothelial cell positivity for p70S6K in 17 pAMR+ EMB specimens (56.7%) and in 1 pAMR0 EMB specimen (3.3%). pS6RP was detected in 8 pAMR+ EMB specimens (26.7%) and in 1 pAMR0 EMB specimen (3.3%). CONCLUSIONS: p70S6K and pS6RP immunohistochemistry afford new markers of AMR on EMB specimens because their expression is correlated with microcirculation inflammation and DSA. The correlation of DSA with pAMR grade suggests that this grading system is valid.