Amphiregulin normalizes altered circuit connectivity for social dominance of the CRTC3 knockout mouse.

Social hierarchy has a profound impact on social behavior, reward processing, and mental health. Moreover, lower social rank can lead to chronic stress and often more serious problems such as bullying victims of abuse, suicide, or attack to society. However, its underlying mechanisms, particularly their association with glial factors, are largely unknown. In this study, we report that astrocyte-derived amphiregulin plays a critical role in the determination of hierarchical ranks. We found that astrocytes-secreted amphiregulin is directly regulated by cAMP response element-binding (CREB)-regulated transcription coactivator 3 (CRTC3) and CREB. Mice with systemic and astrocyte-specific CRTC3 deficiency exhibited a lower social rank with reduced functional connectivity between the prefrontal cortex, a major social hierarchy center, and the parietal cortex. However, this effect was reversed by astrocyte-specific induction of amphiregulin expression, and the epidermal growth factor domain was critical for this action of amphiregulin. These results provide evidence of the involvement of novel glial factors in the regulation of social dominance and may shed light on the clinical application of amphiregulin in the treatment of various psychiatric disorders.

Tau acetylation at K280 regulates tau phosphorylation.

PURPOSE/AIM OF THE STUDY: Accumulation of hyperphosphorylated tau is a key pathological finding of Alzheimer's disease. Recently, acetylation of tau is emerging as another key pathogenic modification, especially regarding the acetylation of tau at K280 of the hexapeptide 275VQIINK280, a critical sequence in driving tau aggregation. However, the relationship between these two key post-translational modifications is not well known. In this study, effect of acetylation of tau at K280 on tau phosphorylation profile was investigated. MATERIALS AND METHODS: The human neuroblastoma cell line, SH-SY5Y, was transfected with p300 acetyltransferase and tau to induce acetylation of tau. Phosphorylation profile after acetylation was evaluated on western blot. K280A-mutant tau was transfected to investigate the effect of acetylation of tau at K280 on tau phosphorylation profile. RESULTS: Overexpression of p300 acetyltransferase in tau-transfected SH-SY5Y human neuroblastoma cells increased acetylation of tau. Meanwhile, tau and its phosphorylation also increased at various sites such as S199/202, S202/T205, T231, and S422, but not at S396. However, blocking acetylation only at K280 with K280A-mutant tau reversed the increased phosphorylation of tau at S202/T205, T231, and S422, but not at S199/202 or S396. CONCLUSION: Here we identified tau phosphorylation profile in the context of p300-induced acetylation and K280A-mutant tau, demonstrating that tau acetylation affects phosphorylation differently by residues and that acetylation at K280 is a determinant of phosphorylation at some residues in the context of pathologic acetyltransferase activity. Yet, our results suggest there is a complex interplay yet to be explored between tau acetylation with tau phosphorylation.

TLQP-21 mediated activation of microglial BV2 cells promotes clearance of extracellular fibril amyloid-ß.

ß-Amyloid (Aß) plaque in the brains of patients with Alzheimer's disease (AD) is mainly caused by impaired clearance of Aß by glial cells, including microglia and astrocytes. Because microglia play an important protective role in the central nervous system, many efforts have been made to identify agents that effectively improve microglial Aß phagocytosis. This study found that TLQP-21, which is cleaved from VGF (VGF nerve growth factor inducible) precursor protein, enhanced Aß phagocytosis and degradation by microglial BV2 cells. TLQP-21 also improved microglial phagocytic activity and promoted fibrillar amyloid-ß (fAß) uptake by microglial BV2 cells via a C3AR1-dependent mechanism. Moreover, TLQP-21 stimulated Aß degradation by enhancing lysosome activity, thereby enhancing fAß clearance. These results suggest that treatment with TLQP-21 may be a novel therapeutic strategy to efficiently enhance microglial Aß clearance in AD.

Ouabain activates transcription factor EB and exerts neuroprotection in models of Alzheimer's disease.

The number of neurofibrillary tangles containing abnormal hyperphosphorylated tau protein correlates with the degree of dementia in Alzheimer's disease (AD). In addition, autophagosome accumulation and disturbance of autophagy, the process by which toxic aggregate proteins are degraded in the cytosol, are also found in AD models. These indicate that regulation of the autophagy-lysosome system may be a potential therapeutic target for AD. Activation of transcription factor EB (TFEB), a master regulator of autophagy-lysosome system gene transcription, reduces the amount of tau in APP mice. Here, to identify potential therapeutic compounds for AD, we performed two types of screening to determine pharmacologically active compounds that increase 1) neuronal viability in okadaic acid-induced tau hyperphosphorylation-related neurodegeneration models and 2) nuclear localization of TFEB in high-contents screening. Ouabain, a cardiac glycoside, was discovered as a common hit compound in both screenings. It also exhibited a significant protective effect in tau transgenic fly and mouse models in vivo. This work demonstrates that ouabain enhances activation of TFEB through inhibition of the mTOR pathway and induces downstream autophagy-lysosomal gene expression and cellular restorative properties. Therefore, therapeutic approaches using ouabain reduce the accumulation of abnormal toxic tau in vitro and in vivo.

Small-molecule drug screening identifies drug Ro 31-8220 that reduces toxic phosphorylated tau in Drosophila melanogaster.

The intraneuronal aggregates of hyperphosphorylated and misfolded tau (neurofibrillary tangles, NFTs) cause a stereotypical spatiotemporal Alzheimer's disease (AD) progression that correlates with the severity of the associated cognitive decline. Kinase activity contributes to the balance between neuron survival and cell death. Hyperactivation of kinases including the conventional protein kinase C (PKC) is a defective molecular event accompanying associative memory loss, tau phosphorylation, and progression of AD or related neurodegenerative diseases. Here, we investigated the ability of small therapeutic compounds (a custom library) to improve tau-induced rough-eye phenotype in a Drosophila melanogaster model of frontotemporal dementia. We also assessed the tau phosphorylation in vivo and selected hit compounds. Among the potential hits, we investigated Ro 31-8220, described earlier as a potent PKCα inhibitor. Ro 31-8220 robustly improved the rough-eye phenotype, reduced phosphorylated tau species in vitro and in vivo, reversed tau-induced memory impairment, and improved the fly motor functions. In a human neuroblastoma cell line, Ro 31-8220 reduced the PKC activity and the tau phosphorylation pattern, but we also have to acknowledge the compound's wide range of biological activity. Nevertheless, Ro 31-8220 is a novel therapeutic mitigator of tau-induced neurotoxocity.

V232M substitution restricts a distinct O-glycosylation of PLD3 and its neuroprotective function.

The link between Val232Met variant of phospholipase D3 (PLD3) and late-onset Alzheimer's disease (AD) is still obscure. While it may not affect directly the amyloid precursor protein function, PLD3 could be regulating multiple cellular compartments. Here, we investigated the function of wild-type human PLD3 (PLD3WT) and the Val232Met variant (PLD3VM) in the presence of ß-amyloid (Aß) in a Drosophila melanogaster model of AD. We expressed PLD3WT in CNS of the Aß-model flies and monitored its effect on the ER stress, cell apoptosis and recovery the Aß-induced cognitive impairment. The expression reduced ER stress and neuronal apoptosis, which resulted in normalized antioxidative phospholipids levels and brain protection. A specific O-glycosylation at pT271 in PLD3 is essential for its normal trafficking and cellular localization. The V232 M substitution impairs this O-glycosylation, leading to enlarged lysosomes and plausibly aberrant protein recycling. PLD3VM was less neuroprotective, and while, PLD3WT expression enhances the lysosomal functions, V232 M attenuated PLD3's trafficking to the lysosomes. Thus, the V232 M mutation may affect AD pathogenesis. Further understanding of the mechanistic role of PLD3 in AD could lead to developing novel therapeutic agents.

Autophagy deficiency in myeloid cells exacerbates eosinophilic inflammation in chronic rhinosinusitis.

BACKGROUND: Eosinophilic inflammation is a major pathologic feature of chronic rhinosinusitis (CRS) and is frequently associated with severe refractory disease. Prostaglandin (PG) D2 levels are increased in patients with CRS, and PGD2 is an important contributing factor to eosinophilic inflammation. Autophagy has a pleiotropic effect on immune responses and disease pathogenesis. Recent studies suggest the potential involvement of autophagy in patients with CRS and the PG pathway. OBJECTIVE: We sought to investigate whether altered function of autophagy is associated with eosinophilic inflammation and dysregulated production of PGD2 in patients with CRS. METHODS: We used myeloid cell-specific deletion of autophagy-related gene 7 (Atg7), which is vital for autophagy, and investigated the effects of impaired autophagy on eosinophilic inflammation in a murine model of eosinophilic chronic rhinosinusitis (ECRS). The effect of autophagy on PGD2 production and gene expression profiles associated with allergy and the PG pathway were assessed. RESULTS: We found that impaired autophagy in myeloid cells aggravated eosinophilia, epithelial hyperplasia, and mucosal thickening in mice with ECRS. This aggravation was associated with gene expression profiles that favor eosinophilic inflammation, TH2 response, mast cell infiltration, and PGD2 dysregulation. Supporting this, PGD2 production was also increased significantly by impaired autophagy. Among other myeloid cells, macrophages were associated with autophagy deficiency, leading to increased IL-1ß levels. Macrophage depletion or blockade of IL-1 receptor led to alleviation of eosinophilic inflammation and sinonasal anatomic abnormalities associated with autophagy deficiency. CONCLUSION: Our results suggest that impaired autophagy in myeloid cells, particularly macrophages, has a causal role in eosinophilic inflammation and ECRS pathogenesis.

Disease-Associated Mutations of TREM2 Alter the Processing of N-Linked Oligosaccharides in the Golgi Apparatus.

The triggering receptor expressed on myeloid cells 2 (TREM2) is an immune-modulatory receptor involved in phagocytosis and inflammation. Mutations of Q33X, Y38C and T66M cause Nasu-Hakola disease (NHD) which is characterized by early onset of dementia and bone cysts. A recent, genome-wide association study also revealed that single nucleotide polymorphism of TREM2, such as R47H, increased the risk of Alzheimer's disease (AD) similar to ApoE4. However, how these mutations affect the trafficking of TREM2, which may affect the normal functions of TREM2, was not known. In this study, we show that TREM2 with NHD mutations are impaired in the glycosylation with complex oligosaccharides in the Golgi apparatus, in the trafficking to plasma membrane and further processing by γ-secretase. Although R47H mutation in AD affected the glycosylation and normal trafficking of TREM2 less, the detailed pattern of glycosylated TREM2 differs from that of the wild type, thus suggesting that precise regulation of TREM2 glycosylation is impaired when arginine at 47 is mutated to histidine. Our results suggest that the impaired glycosylation and trafficking of TREM2 from endoplasmic reticulum/Golgi to plasma membrane by mutations may inhibit its normal functions in the plasma membrane, which may contribute to the disease.

ß-Amyloid is transmitted via neuronal connections along axonal membranes.

OBJECTIVE: ß-amyloid plaque is a critical pathological feature of Alzheimer disease. Pathologic studies suggest that neurodegeneration may occur in a retrograde fashion from axon terminals near ß-amyloid plaques, and that plaque may spread through brain regions. However, there is no direct experimental evidence to show transmission of ß-amyloid. METHODS: Microscopic imaging data of ß-amyloid transmission was acquired in cortical neuron cultures from Sprague-Dawley rat embryos using polydimethylsiloxane (PDMS) microfluidic culture chambers and in brain sections from in vivo ß-amyloid injection. RESULTS: We present direct imaging evidence in cultured cortical neurons, using PDMS microfluidic culture chambers, that ß-amyloid is readily absorbed by axonal processes and retrogradely transported to neuronal cell bodies. Transmission of ß-amyloid via neuronal connections was also confirmed in mouse brain. ß-Amyloid absorbed by distal axons accumulates in axonal swellings, mitochondria, and lysosomes of the cell bodies. Interestingly, dynasore, an inhibitor of dynamin, which is a protein indispensable for endocytosis, did not prevent retrograde transport of ß-amyloid, indicating that ß-amyloid is absorbed onto axonal membranes and transmitted via them to the cell body. Dynasore did decrease the transneuronal transmission of ß-amyloid, suggesting that this requires the internalization and secretion of ß-amyloid. INTERPRETATION: Our findings provide direct in vitro and in vivo evidence for spreading of ß-amyloid through neuronal connections, and suggest possible therapeutic approaches to blocking this spread.

Molecular cloning, regulation, and functional analysis of two GHS-R genes in zebrafish.

Mammalian ghrelin is derived from stomach and regulates growth hormone release and appetite by modulating GHS-R (Growth hormone secretagogue receptor) activity. Zebrafish has been developed as a forward genetic screening model system and previous screening identified a number of genes involved in multiple signaling pathways. In this system, ghrelin has been identified and its function and regulation have been shown to be highly conserved to that of mammals. Here, we identified three isoforms of zGHS-R1 and one of zGHS-R2 (zGHS-R2a), and characterized their expression, regulation and function. Three isoforms of zGHS-R1, which we named zGHS-R1a, zGHS-R1b, and zGHS-R1c, are generated by alternative splicing. The expression of zGHS-R1 is highly enriched in brain, intestine tissue, and skin tissues. Compared to zGHS-R1, the expression pattern of zGHS-R2a is rather evenly distributed. A 15 day fasting elevated expression of zGHS-R1 and zGHS-R2 transcripts in anterior intestine tissues, but not in brain. Whereas zGHS-R1a, zGHS-R1c, and zGHS-R2a appear to be presented on the plasma membrane, the localization of zGHS-R1b seems to be restricted in the intracellular region. Treatment of ghrelin agonist, L692,585 or goldfish ghrelin peptides but not rat ghrelin, elevated intracellular Ca(2+) level and phosphorylation of ERK in HEK-293 cells expressing zGHS-R1a, but not zGHS-R1b, zGHS-R1c, or zGHS-R2a. It appears that besides core ghrelin peptide sequence of GS/TSF additional amino acids are required for the activation of zGHS-R1a, as rat ghrelin induces neither intracellular Ca(2+) mobilization nor ERK phosphrylation. These results suggest that ghrelin system in zebrafish is highly conserved to that of mammals, and thus is an ideal in vivo model for dissecting ghrelin system.

Attenuation of natural killer cell functions by capsaicin through a direct and TRPV1-independent mechanism.

The assessment of the biological activity of capsaicin, the compound responsible for the spicy flavor of chili pepper, produced controversial results, showing either carcinogenicity or cancer prevention. The innate immune system plays a pivotal role in cancer pathology and prevention; yet, the effect of capsaicin on natural killer (NK) cells, which function in cancer surveillance, is unclear. This study found that capsaicin inhibited NK cell-mediated cytotoxicity and cytokine production (interferon-γ and tumor necrosis factor-α). Capsaicin impaired the cytotoxicity of NK cells, thereby inhibiting lysis of standard target cells and gastric cancer cells by modulating calcium mobilization in NK cells. Capsaicin also induced apoptosis in gastric cancer cells, but that effect required higher concentrations and longer exposure times than those required to trigger NK cell dysfunction. Furthermore, capsaicin inhibited the cytotoxicity of isolated NK cells and of an NK cell line, suggesting a direct effect on NK cells. Antagonists of transient receptor potential vanilloid subfamily member 1 (TRPV1), a cognate capsaicin receptor, or deficiency in TRPV1 expression failed to prevent the defects induced by capsaicin in NK cells expressing functional TRPV1. Thus, the mechanism of action of capsaicin on NK cells is largely independent of TRPV1. Taken together, capsaicin may have chemotherapeutic potential but may impair NK cell function, which plays a central role in tumor surveillance.

PTX3 stimulates osteoclastogenesis by increasing osteoblast RANKL production.

Pentraxin-3 (PTX3), also known as tumor necrosis factor-stimulated gene 14 (TSG-14), is produced by immune and vascular cells in response to pro-inflammatory signals and is therefore a multipotent inflammatory mediator. The present study showed that during human osteoblast (OB) differentiation, precursor OBs (pOBs), but not mature OB, highly expressed PTX3. TNFα treatment elevated the PTX3 expression of pOBs. When mice were injected with lipopolysaccharide, which induces an inflammatory osteolytic condition characterized by trabecular bone destruction and high osteoclastogenesis, their bone marrow cells expressed elevated levels of PTX3 protein. Exogenous PTX3 did not directly affect osteoclast (OC) or OB differentiation. However, when pOBs and precursor OCs were co-cultured, exogenous PTX3 significantly increased the number of tartrate-resistant acid phosphatase-positive multinucleated cells (i.e., OC cells) by increasing the pOB mRNA expression and protein secretion of RANK ligand (RANKL). This was accompanied with increased Runt-related transcription factor 2 (Runx2) expression in the pOBs. Knock-down of endogenous PTX3 with small-interfering RNA did not change the osteogenic potential of pOBs but suppressed their production of RANKL and reduced osteoclastogenesis. Finally, TNFα treatment of the co-culture elevated PTX3 expression by the pOBs and increased OC formation. This effect was suppressed by PTX3 knock-down by decreasing RANKL expression. Thus, the PTX3-driven increase in the osteoclastogenic potential of pOBs appears to be mediated by the effect of PTX3 on pOB RANKL production. These findings suggest that PTX3 is an inflammatory mediator that contributes to the deteriorating osteolytic condition of inflamed bone. J. Cell. Physiol. 229: 1744-1752, 2014. © 2014 Wiley Periodicals, Inc.

Beclin-1 is required for RANKL-induced osteoclast differentiation.

Beclin-1 plays a critical role in autophagy; however, it also contributes to other biological processes in a non-autophagic manner. Although studies have examined the non-autophagic role of autophagy proteins in the secretory function of osteoclasts (OC), the role of Beclin-1 is unclear. Here, we examined the role of Beclin-1 in OC differentiation, and found that mouse bone marrow macrophages (BMMs) showed increased expression of Beclin-1 upon RANKL stimulation in a p38- and NF-kappa B-dependent manner. During OC differentiation, Beclin-1 localized to the mitochondria, where it was involved in the production of mitochondrial intracellular reactive oxygen species. Knockdown of Beclin-1 in RANKL-primed BMMs led to a significant reduction in RANKL-dependent osteoclastogenesis, which was accompanied by reduced NFATc1 induction. Furthermore, knockdown of Beclin-1 inhibited RANKL-mediated activation of JNK and p38, both of which act downstream of reactive oxygen species, resulting in the suppression of NFATc1 induction. Finally, overexpression of constitutively active NFATc1 rescued the phenotype induced by Beclin-1 knockdown, indicating that Beclin-1 mediates RANKL-induced osteoclastogenesis by regulating NFATc1 expression. These findings show that Beclin-1 plays a non-autophagic role in RANKL-induced osteoclastogenesis by inducing the production of reactive oxygen species and NFATc1.

Panax red ginseng extract regulates energy expenditures by modulating PKA dependent lipid mobilization in adipose tissue.

Regulation of balance between lipid accumulation and energy consumption is a critical step for the maintenance of energy homeostasis. Here, we show that Panax red ginseng extract treatments increased energy expenditures and prevented mice from diet induced obesity. Panax red ginseng extracts strongly activated Hormone Specific Lipase (HSL) via Protein Kinase A (PKA). Since activation of HSL induces lipolysis in WAT and fatty acid oxidation in brown adipose tissue (BAT), these results suggest that Panax red ginseng extracts reduce HFD induced obesity by regulating lipid mobilization.

Secretory clusterin inhibits osteoclastogenesis by attenuating M-CSF-dependent osteoclast precursor cell proliferation.

Secretory clusterin (sCLU)/apolipoprotein J is a multifunctional glycoprotein that is ubiquitously expressed in various tissues. Reduced sCLU in the joints of patients with bone erosive disease is associated with disease activity; however, its exact role has yet to be elucidated. Here, we report that CLU is expressed and secreted during osteoclastogenesis in mouse bone marrow-derived macrophages (BMMs) that are treated with receptor activator of nuclear factor kappa-B ligand (RANKL) and macrophage colony-stimulating factor (M-CSF). CLU-deficient BMMs obtained from CLU(-/-) mice exhibited no significant alterations in OC differentiation in comparison with BMMs obtained from wild-type mice. In contrast, exogenous sCLU treatment significantly inhibited OC formation in both BMMs and OC precursor cultures. The inhibitory effect of sCLU was more prominent in BMMs than OC precursor cultures. Interestingly, treating BMMs with sCLU decreased the proliferative effects elicited by M-CSF and suppressed M-CSF-induced ERK activation of OC precursor cells without causing apoptotic cell death. This study provides the first evidence that sCLU reduces OC formation by inhibiting the actions of M-CSF, thereby suggesting its protective role in bone erosion.

Neuronal MHC-I complex is destabilized by amyloid-ß and its implications in Alzheimer's disease.

BACKGROUNDS: The expression of major histocompatibility complex I (MHC-I) in neurons has recently been shown to regulate neurite outgrowth and synaptic plasticity. However, its contribution to neurodegenerative diseases such as Alzheimer's disease (AD) remains largely unknown. METHODS: In this study, we investigated the relationship between impaired MHC-I-ß2M complex and AD in vitro and human AD samples. Interaction between protein was identified by liquid chromatography-tandem mass spectrometry and confirmed by immunoprecipitation. Single-chain trimer of MHC-I-ß2M was generated to study the effect of stabilization of MHC-I-ß2M complex on NCAM1 signaling. RESULTS: MHC-I is destabilized in the brains of AD patients and neuronal cells treated with oligomeric ß-amyloid (Aß). Specifically, Aß oligomers disassemble the MHC-I-ß2-microglobulin (ß2M) complex, leading to reduced interactions with neural cell adhesion molecule 1 (NCAM1), a novel interactor of neuronal MHC-I, and decreased signaling. Inhibition of MHC-I-ß2M complex destabilization by non-dissociable MHC-I-ß2M-peptide complex restored MHC-I-NCAM1 signaling in neuronal cells. CONCLUSIONS: The current study demonstrated that disruption of MHC-1-NCAM1 signaling by Aß induced disassembly of MHC-I-ß2M complex is involved in the pathophysiology of AD. Moreover, our findings suggest modulation of MHC-I stability may be a potential therapeutic target for restoring synaptic function in AD.

Monoclonal antibody Y01 prevents tauopathy progression induced by lysine 280-acetylated tau in cell and mouse models.

The spatiotemporal pattern of the spread of pathologically modified tau through brain regions in Alzheimer's disease (AD) can be explained by prion-like cell-to-cell seeding and propagation of misfolded tau aggregates. Hence, to develop targeted therapeutic antibodies, it is important to identify the seeding- and propagation-competent tau species. The hexapeptide 275VQIINK280 of tau is a critical region for tau aggregation, and K280 is acetylated in various tauopathies, including AD. However, the mechanism that links tau acetylated on lysine 280 (tau-acK280) to subsequent progression to neurodegenerative disease remains unclear. Here, we demonstrate that tau-acK280 is critical for tau propagation processes including secretion, aggregation, and seeding. We developed an antibody, Y01, that specifically targets tau-acK280 and solved the crystal structure of Y01 in complex with an acK280 peptide. The structure confirmed that Y01 directly recognizes acK280 and the surrounding residues. Strikingly, upon interaction with acetylated tau aggregates, Y01 prevented tauopathy progression and increased neuronal viability in neuron cultures and in tau-Tg mice through antibody-mediated neutralization and phagocytosis, respectively. Based on our observations that tau-acK280 is a core species involved in seeding and propagation activities, the Y01 antibody that specifically recognizes acK280 represents a promising therapeutic candidate for AD and other neurodegenerative diseases associated with tauopathy.

Sitagliptin increases tau phosphorylation in the hippocampus of rats with type 2 diabetes and in primary neuron cultures.

Increasing evidence supports an association between Alzheimer's disease (AD) and diabetes. In this context, anti-diabetic agents such as rosiglitazone and glucagon-like peptide (GLP)-1 have been reported to reduce pathologies associated with AD, including tau hyperphosphorylation, suggesting that such agents might be used to treat AD. One such anti-diabetic agent is sitagliptin, which acts through inhibition of dipeptidyl peptidase (DPP)-IV to increase GLP-1 levels. Given this action, sitagliptin would be predicted to reduce AD pathology. Accordingly, we investigated whether sitagliptin is effective in attenuating AD pathologies, focusing on tau phosphorylation in the OLETF type 2 diabetic rat model. Unexpectedly, we found that sitagliptin was not effective against pathological tau phosphorylation in the hippocampus of OLETF type 2 diabetes rats, and instead aggravated it. This paradoxically increased tau phosphorylation was attributed to activation of the tau kinase, GSK3ß (glycogen synthase kinase 3ß). Sitagliptin also increased ser-616 phosphorylation of the insulin receptor substrate (IRS)-1, suggesting increased insulin resistance in the brain. These phenomena were recapitulated in primary rat cortical neurons treated with sitagliptin, further confirming sitagliptin's effects on AD-related pathologies in neurons. These results highlight the need for caution in considering the use of sitagliptin in AD therapy.

Rosiglitazone reduces tau phosphorylation via JNK inhibition in the hippocampus of rats with type 2 diabetes and tau transfected SH-SY5Y cells.

Increasing evidence supports an association between Alzheimer's disease (AD) and diabetes. Rosiglitazone, a peroxisome proliferator-activated receptor-γ (PPARγ) agonist, which is an anti-diabetic agent against type 2 diabetes, is currently in Phase III clinical trials in AD patients because rosiglitazone reduces ß-amyloid (Aß) pathology and inflammation. However, few studies have investigated whether rosiglitazone affects tau phosphorylation, another critical pathological feature of AD. Thus, we investigated it using OLETF type 2 diabetic rats and streptozotocin-injected type 1 diabetic mice. Interestingly, rosiglitazone reduced tau phosphorylation only in the hippocampus of OLETF type 2 diabetes rats, and not in that of STZ-injected type 1 diabetes mice. The activity of JNK was reduced in the hippocampus of rosiglitazone-treated OLETF rats, correlating with a reduction in tau phosphorylation, however, which was not correlated with GSK3ß activity. In human tau-transfected SH-SY5Y neuronal cell line, reduction of tau phosphorylation was also associated with reduction of JNK activity, not of GSK3ß activity. Hence, rosiglitazone could be used in reducing tau phosphorylation through JNK inactivation for therapeutic effects in type 2 diabetes related Alzheimer's disease.

Maintained activity of glycogen synthase kinase-3beta despite of its phosphorylation at serine-9 in okadaic acid-induced neurodegenerative model.

Glycogen synthase kinase-3beta (GSK3beta) is recognized as one of major kinases to phosphorylate tau in Alzheimer's disease (AD), thus lots of AD drug discoveries target GSK3beta. However, the inactive form of GSK3beta which is phosphorylated at serine-9 is increased in AD brains. This is also inconsistent with phosphorylation status of other GSK3beta substrates, such as beta-catenin and collapsin response mediator protein-2 (CRMP2) since their phosphorylation is all increased in AD brains. Thus, we addressed this paradoxical condition of AD in rat neurons treated with okadaic acid (OA) which inhibits protein phosphatase-2A (PP2A) and induces tau hyperphosphorylation and cell death. Interestingly, OA also induces phosphorylation of GSK3beta at serine-9 and other substrates including tau, beta-catenin and CRMP2 like in AD brains. In this context, we observed that GSK3beta inhibitors such as lithium chloride and 6-bromoindirubin-3'-monoxime (6-BIO) reversed those phosphorylation events and protected neurons. These data suggest that GSK3beta may still have its kinase activity despite increase of its phosphorylation at serine-9 in AD brains at least in PP2A-compromised conditions and that GSK3beta inhibitors could be a valuable drug candidate in AD.