Dysregulation of stress granule dynamics by DCTN1 deficiency exacerbates TDP-43 pathology in Drosophila models of ALS/FTD.

The abnormal aggregation of TDP-43 into cytoplasmic inclusions in affected neurons is a major pathological hallmark of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Although TDP-43 is aberrantly accumulated in the neurons of most patients with sporadic ALS/FTD and other TDP-43 proteinopathies, how TDP-43 forms cytoplasmic aggregates remains unknown. In this study, we show that a deficiency in DCTN1, a subunit of the microtubule-associated motor protein complex dynactin, perturbs the dynamics of stress granules and drives the formation of TDP-43 cytoplasmic aggregation in cultured cells, leading to the exacerbation of TDP-43 pathology and neurodegeneration in vivo. We demonstrated using a Drosophila model of ALS/FTD that genetic knockdown of DCTN1 accelerates the formation of ubiquitin-positive cytoplasmic inclusions of TDP-43. Knockdown of components of other microtubule-associated motor protein complexes, including dynein and kinesin, also increased the formation of TDP-43 inclusions, indicating that intracellular transport along microtubules plays a key role in TDP-43 pathology. Notably, DCTN1 knockdown delayed the disassembly of stress granules in stressed cells, leading to an increase in the formation of pathological cytoplasmic inclusions of TDP-43. Our results indicate that a deficiency in DCTN1, as well as disruption of intracellular transport along microtubules, is a modifier that drives the formation of TDP-43 pathology through the dysregulation of stress granule dynamics.

Glasdegib with intensive/nonintensive chemotherapy in Japanese patients with untreated acute myeloid leukemia or high-risk myelodysplastic syndromes.

Glasdegib is a potent, selective, oral inhibitor of the hedgehog signaling pathway. In this phase I study, previously untreated Japanese patients with acute myeloid leukemia (AML) or high-risk myelodysplastic syndromes were treated with glasdegib (100 mg once daily) combinations: low-dose cytarabine (20 mg twice daily; cohort 1, n = 6; expansion cohort, n = 15); daunorubicin and cytarabine (60 mg/m2 i.v.; cohort 2, n = 6); or azacitidine (100 mg/m2 i.v.; cohort 3, n = 6). Patients, except cohort 2, were ineligible for intensive chemotherapy. The primary end-point was dose-limiting toxicity in cohorts 1-3 and disease-modifying response in the expansion cohort. Disease-modifying response rate was tested with the null hypothesis of 6.8%, which was set based on the results from the phase II BRIGHT AML 1003 study (NCT01546038). No dose-limiting toxicities were observed in cohorts 1 or 3; one patient in cohort 2 experienced a dose-limiting toxicity of grade 3 erythroderma. The most common grade ≥3 treatment-related adverse events were neutropenia and thrombocytopenia (66.7% each) in cohort 1 and thrombocytopenia (60.0%) in the expansion cohort. In the expansion cohort, the disease-modifying response rate was 46.7% (90% confidence interval, 24.4-70.0; p < 0.0001), with all patients achieving either a complete response or complete response with incomplete blood count recovery. Median overall survival was 13.9 months. In this study, the primary disease-modifying response end-point with glasdegib plus low-dose cytarabine was met. The study confirms the safety and efficacy of glasdegib plus low-dose cytarabine in Japanese patients with AML ineligible for intensive chemotherapy.

11C-Labeling of acyclic retinoid peretinoin by rapid C-[11C]methylation to disclose novel brain permeability and central nervous system activities hidden in antitumor agent.

Recently, retinoid actions on the central nervous system (CNS) have attracted considerable attention from the perspectives of brain disease diagnosis and drug development. Firstly, we successfully synthesized [11C]peretinoin esters (methyl, ethyl, and benzyl) using a Pd(0)-mediated rapid C-[11C]methylation of the corresponding stannyl precursors without geometrical isomerization in 82%, 66%, and 57% radiochemical yields (RCYs). Subsequent hydrolysis of the 11C-labeled ester produced [11C]peretinoin in 13 ± 8% RCY (n = 3). After pharmaceutical formulation, the resulting [11C]benzyl ester and [11C]peretinoin had high radiochemical purity (>99% each) and molar activities of 144 and 118 ± 49 GBq µmol-1 at total synthesis times of 31 min and 40 ± 3 min, respectively. Rat brain PET imaging for the [11C]ester revealed a unique time-radioactivity curve, suggesting the participation of the acid [11C]peretinoin for the brain permeability. However, the curve of the [11C]peretinoin rose steadily after a shorter time lag to reach 1.4 standardized uptake value (SUV) at 60 min. These various phenomena between the ester and acid became more pronounced in the monkey brain (SUV of > 3.0 at 90 min). With the opportunity to identify high brain uptake of [11C]peretinoin, we discovered CNS activities of a drug candidate called peretinoin, such as the induction of a stem-cell to neuronal cell differentiation and the suppression of neuronal damages.

Cynomolgus macaque model of neuronal ceroid lipofuscinosis type 2 disease.

Neuronal ceroid lipofuscinoses (NCLs) are autosomal-recessive fatal neurodegenerative diseases that occur in children and young adults, with symptoms including ataxia, seizures and visual impairment. We report the discovery of cynomolgus macaques carrying the CLN2/TPP1 variant and our analysis of whether the macaques could be a new non-human primate model for NCL type 2 (CLN2) disease. Three cynomolgus macaques presented progressive neuronal clinical symptoms such as limb tremors and gait disturbance after about 2 years of age. Morphological analyses using brain MRI at the endpoint of approximately 3 years of age revealed marked cerebellar and cerebral atrophy of the gray matter, with sulcus dilation, gyrus thinning, and ventricular enlargement. Histopathological analyses of three affected macaques revealed severe neuronal loss and degeneration in the cerebellar and cerebral cortices, accompanied by glial activation and/or changes in axonal morphology. Neurons observed throughout the central nervous system contained autofluorescent cytoplasmic pigments, which were identified as ceroid-lipofuscin based on staining properties, and the cerebral cortex examined by transmission electron microscopy had curvilinear profiles, the typical ultrastructural pattern of CLN2. These findings are commonly observed in all forms of NCL. DNA sequencing analysis identified a homozygous single-base deletion (c.42delC) of the CLN2/TPP1 gene, resulting in a frameshifted premature stop codon. Immunohistochemical analysis showed that tissue from the affected macaques lacked a detectable signal against TPP1, the product of the CLN2/TPP1 gene. Analysis for transmission of the CLN2/TPP1 mutated gene revealed that 47 (49.5%) and 48 (50.5%) of the 95 individuals genotyped in the CLN2-affected macaque family were heterozygous carriers and homozygous wild-type individuals, respectively. Thus, we identified cynomolgus macaques as a non-human primate model of CLN2 disease. The CLN2 macaques reported here could become a useful resource for research and the development of drugs and methods for treating CLN2 disease, which involves severe symptoms in humans.

Age-related alterations in protein phosphatase 2A methylation levels in brains of cynomolgus monkeys: a pilot study.

The abnormal activity of PP2A, a dominant member of type 2A serine/threonine protein phosphatase, has been implicated in the development of Alzheimer's disease (AD) and dementia with Lewy bodies (DLB). PP2A is a holoenzyme, and protein methylation of the catalytic subunit, PP2Ac, alters the complex composition. A decrease in PP2Ac methylation levels has been reported in AD and DLB. Aging is the most common risk factor for AD and DLB, but the relationship between aging and PP2A has not been studied in detail. Cynomolgus monkey show increased phosphorylation levels of tau and α-synuclein with aging. In this study, we investigated the alterations in the PP2A activity regulation with aging in monkey brains from 2 to 43 years of age using fractionated proteins. We found that type 2A protein phosphatase activity decreased with aging in cytoplasmic and nuclear-soluble fractions. PP2Ac methylation level was decreased in cytoplasmic and sarkosyl-insoluble fractions. A principal component analysis using PP2Ac, demethylated PP2Ac and PP2A methylesterase PME-1 levels in cytoplasmic and nuclear-soluble fractions as attributes showed that aged monkeys were in the same cluster. Our results show that brain aging in cynomolgus monkeys is closely related to changes in PP2A methylation.

Aging induces abnormal accumulation of Aß in extracellular vesicle and/or intraluminal membrane vesicle-rich fractions in nonhuman primate brain.

Aß metabolism in the brain is mediated by endocytosis, one part of the intracellular membrane trafficking system. We previously showed that aging attenuates the interaction of dynein with dynactin, which disrupts the endosomal/lysosomal trafficking pathway involved in Aß metabolism, resulting in intracellular accumulation of Aß. Several studies have shown that in Alzheimer's disease (AD), intraneuronal accumulation of Aß precedes extracellular Aß depositions. However, it is unclear what accounts for this transition from intracellular to extracellular depositions. Accumulating evidence suggest that autophagy has an important role in AD pathology, and we observed that autophagy-related protein levels began to decrease before amyloid plaque formation in cynomolgus monkey brains. Surprisingly, experimental induction of autophagosome formation in Neuro2a cells significantly increased intracellular Aß and decreased extracellular release of Aß, accompanied by the prominent reduction of extracellular vesicle (EV) secretion. RNAi study confirmed that EV secretion affected intracellular and extracellular Aß levels, and siRNA-induced downregulation of autophagosome formation enhanced EV secretion to ameliorate intracellular Aß accumulation induced by dynein knockdown. In aged cynomolgus monkeys, Aß levels in EV/intraluminal membrane vesicle (ILV)-rich fractions isolated from temporal lobe parenchyma were drastically increased. Moreover, EV/ILV marker proteins overlapped spatially with amyloid plaques. These findings suggest that EV would be an important carrier of Aß in brain and abnormal accumulation of Aß in EVs/ILVs may be involved in the transition of age-dependent Aß pathology.

Molecular dissection of ALS-linked TDP-43 - involvement of the Gly-rich domain in interaction with G-quadruplex mRNA.

TDP-43 is the major pathogenic protein of amyotrophic lateral sclerosis (ALS). Previously, we identified that TDP-43 interacts with G-quadruplex (G4)-containing RNA and is involved in their long-distance transport in neurons. For the molecular dissection of the TDP-43 and G4-RNA interaction, we analyzed it here in vitro and in cultured cells using a set of 10 mutant TDP-43 proteins from familial and sporadic ALS patients as well as using the TDP-43 C-terminal Gly-rich domain alone. Our results altogether indicate the involvement of the Gly-rich region of TDP-43 in the initial recognition and binding of G4-RNA, which then induces tight binding of TDP-43 with target RNAs, supposedly in conjunction with its RNA recognition motifs.

Decrease in p3-Alcß37 and p3-Alcß40, products of Alcadein ß generated by γ-secretase cleavages, in aged monkeys and patients with Alzheimer's disease.

INTRODUCTION: Neuronal p3-Alcß peptides are generated from the precursor protein Alcadein ß (Alcß) through cleavage by α- and γ-secretases of the amyloid ß (Aß) protein precursor (APP). To reveal whether p3-Alcß is involved in Alzheimer's disease (AD) contributes for the development of novel therapy and/or drug targets. METHODS: We developed new sandwich enzyme-linked immunosorbent assay (sELISA) systems to quantitate levels of p3-Alcß in the cerebrospinal fluid (CSF). RESULTS: In monkeys, CSF p3-Alcß decreases with age, and the aging is also accompanied by decreased brain expression of Alcß. In humans, CSF p3-Alcß levels decrease to a greater extent in those with AD than in age-matched controls. Subjects carrying presenilin gene mutations show a significantly lower CSF p3-Alcß level. A cell study with an inverse modulator of γ-secretase remarkably reduces the generation of p3-Alcß37 while increasing the production of Aß42. DISCUSSION: Aging decreases the generation of p3-Alcß, and further significant decrease of p3-Alcß caused by aberrant γ-secretase activity may accelerate pathogenesis in AD.

Type II Diabetes Mellitus Accelerates Age-Dependent Aß Pathology in Cynomolgus Monkey Brain.

Accumulating evidence suggests that diabetes mellitus (DM) is one of the strongest risk factors for developing Alzheimer's disease (AD). However, it remains unclear how DM accelerates AD pathology in the brain. Cynomolgus monkey (Macaca fascicularis) is one of the nonhuman primates used for biomedical research, and we can observe spontaneous formation of AD pathology, such as senile plaques (SPs) and neurofibrillary tangles (NFTs), with the advance of aging. Furthermore, obesity is occasionally observed and frequently leads to development of type II DM (T2DM) in laboratory-housed cynomolgus monkeys. These findings suggest that cynomolgus monkey is a useful species to study the relationship between T2DM and AD pathology. In T2DM-affected monkey brains, SPs were observed in frontal and temporal lobe cortices almost 5 years earlier than healthy control monkeys. Moreover, age-related endocytic pathology, such as intraneuronal accumulation of enlarged endosomes, was exacerbated in T2DM-affected monkey brains. Since accumulating evidences suggest that endocytic dysfunction is involved in Aß pathology, T2DM may aggravate age-related endocytic dysfunction, leading to the acceleration of Aß pathology.

Efficacy and safety of sunitinib in Japanese patients with progressive, advanced/metastatic, well-differentiated, unresectable pancreatic neuroendocrine tumors: final analyses from a Phase II study.

BACKGROUND: In an interim analysis of a Phase II trial in Japanese patients with pancreatic neuroendocrine tumors (panNETs), sunitinib demonstrated antitumor activity with an objective response rate (ORR) of 50% (95% confidence interval [CI], 21-79) and a median progression-free survival (PFS) of 16.8 months (95% CI, 9.3-26.2). Here, we report the final analyses of efficacy and safety, as well as additional analyses, from this Phase II study. METHODS: This was a multicenter, open-label, Phase II trial (NCT01121562) of sunitinib in Japanese patients with panNETs. Patients received oral sunitinib 37.5 mg/day on a continuous daily dosing schedule. Dose modifications were permitted. The primary endpoint was clinical benefit rate (CBR). Secondary endpoints included ORR, PFS, overall survival (OS), safety and pharmacokinetics. RESULTS: Of 12 patients enrolled and treated, all discontinued treatment-the majority (n = 8) owing to disease progression. Most patients were male (n = 8), <65 years of age (n = 11) and had a non-functional tumor (n = 10). The median (range) number of days on drug was 323.5 (22-727). The CBR (95% CI) was 75.0% (42.8-94.5). ORR (95% CI) was 50.0% (21.1-78.9). Median (95% CI) PFS was 16.8 (9.3-26.2) months; however, median (95% CI) OS was not reached (22.0-not estimable). Most common adverse events (AEs; all-causality) were diarrhea (n = 10; 83.3%), hand-foot syndrome (n = 8; 66.7%) and hypertension (n = 8; 66.7%). CONCLUSIONS: These results support the efficacy and safety of sunitinib in Japanese patients with panNETs. Appropriate AE management through dose reduction and interruption may prolong sunitinib treatment and maximize its efficacy.

Correction to: Phase II study of sunitinib in Japanese patients with unresectable or metastatic, well-differentiated pancreatic neuroendocrine tumor.

In the original publication of this article, the license subtype should be CC BY and not CC BY-NC.

Elevated Membrane Cholesterol Disrupts Lysosomal Degradation to Induce ß-Amyloid Accumulation: The Potential Mechanism Underlying Augmentation of ß-Amyloid Pathology by Type 2 Diabetes Mellitus.

The endocytic membrane trafficking system is altered in the brains of early-stage Alzheimer disease (AD) patients, and endocytic disturbance affects the metabolism of ß-amyloid (Aß) protein, a key molecule in AD pathogenesis. It is widely accepted that type 2 diabetes mellitus (T2DM) is one of the strongest risk factors for development of AD. Supporting this link, experimentally induced T2DM enhances AD pathology in various animal models. Spontaneous T2DM also enhances Aß pathology with severe endocytic pathology, even in nonhuman primate brains. However, it remains unclear how T2DM accelerates Aß pathology. Herein, we demonstrate that cholesterol metabolism-related protein levels are increased and that membrane cholesterol level is elevated in spontaneous T2DM-affected cynomolgus monkey brains. Moreover, in vitro studies that manipulate cellular cholesterol reveal that elevated membrane cholesterol disrupts lysosomal degradation and enhances chemical-induced endocytic disturbance, resulting in great accumulation of Aß in Neuro2a cells. These findings suggest that an alteration of cerebral cholesterol metabolism may be responsible for augmentation of Aß pathology in T2DM-affected brains, which, in turn, may increase the risk for developing AD.

Traffic jam hypothesis: Relationship between endocytic dysfunction and Alzheimer's disease.

Membrane trafficking pathways, like the endocytic pathway, carry out fundamental cellular processes that are essential for normal functioning. One such process is regulation of cell surface receptor signaling. A growing body of evidence suggests that ß-amyloid protein (Aß) plays a key role in Alzheimer's disease (AD) pathogenesis. Cleavage of Aß from its precursor, ß-amyloid precursor protein (APP), occurs through the endocytic pathway in neuronal cells. In early-stage AD, intraneuronal accumulation of abnormally enlarged endosomes is common, indicating that endosome trafficking is disrupted. Strikingly, genome-wide association studies reveal that several endocytosis-related genes are associated with AD onset. Also, recent studies demonstrate that alteration in endocytosis induces not only Aß pathology but also the propagation of tau protein pathology, another key pathological feature of AD. Endocytic dysfunction can disrupt neuronal physiological functions, such as synaptic vesicle transport and neurotransmitter release. Thus, "traffic jams" in the endocytic pathway may be involved in AD pathogenesis and may serve as a novel target for the development of new therapeutics.

Tau pathology in aged cynomolgus monkeys is progressive supranuclear palsy/corticobasal degeneration- but not Alzheimer disease-like -Ultrastructural mapping of tau by EDX.

Concomitant deposition of amyloid -beta protein (Aß) and neuronal tau as neurofibrillary tangles in the human brain is a hallmark of Alzheimer disease (AD). Because these deposits increase during normal aging, it has been proposed that aging brains may also undergo AD-like changes. To investigate the neuropathological changes that occur in the aging primate brain, we examined 21 brains of cynomolgus monkeys (7-36 years old) for Aß- and tau-positive lesions. We found, 1) extensive deposition of Aß in brains of cynomolgus monkeys over 25 years of age, 2) selective deposition of 4-repeat tau as pretangles in neurons, and as coiled body-like structures in oligodendroglia-like cells and astrocytes, 3) preferential distribution of tau in the basal ganglia and neocortex rather than the hippocampus, and 4) age-associated increases in 30-34 kDa AT8- and RD4-positive tau fragments in sarkosyl-insoluble fractions. We further labeled tau-positive structures using diaminobezidine enhanced with nickel, and visualized nickel-labeled structures by energy-dispersive X-ray (EDX) analysis of ultrathin sections. This allowed us to distinguish between nickel-labeled tau and background electron-dense structures, and we found that tau localized to 20-25 nm straight filaments in oligodendroglia-like cells and neurons. Our results indicate that the cytopathology and distribution of tau deposits in aged cynomolgus brains resemble those of progressive supranuclear palsy (PSP) and corticobasal degeneration (CBD) rather than AD. Thus, even in the presence of Aß, age-associated deposition of tau in non-human primates likely does not occur through AD-associated mechanisms.

Dynein Dysfunction Reproduces Age-Dependent Retromer Deficiency: Concomitant Disruption of Retrograde Trafficking Is Required for Alteration in ß-Amyloid Precursor Protein Metabolism.

It is widely accepted that ß-amyloid (Aß) protein plays a pivotal role in Alzheimer disease pathogenesis, and accumulating evidence suggests that endocytic dysfunction is involved in Aß pathology. Retromer, a conserved multisubunit complex, mediates the retrograde transport of numerous kinds of cargo from endosomes to the trans-Golgi network. Several studies have found that retromer deficiency enhances Aß pathology both in vitro and in vivo. Cytoplasmic dynein, a microtubule-based motor protein, mediates minus-end-directed vesicle transport via interactions with dynactin, another microtubule-associated protein that also interacts with retromer. Aging attenuates the dynein-dynactin interaction, and dynein dysfunction reproduces age-dependent endocytic disturbance, resulting in the intracellular accumulation of beta-amyloid precursor protein (APP) and its ß-cleavage products, including Aß. Here, we report that aging itself affects retromer trafficking in cynomolgus monkey brains. In addition, dynein dysfunction reproduces this type of age-dependent retromer deficiency (ie, the endosomal accumulation of retromer-related proteins and APP. Moreover, we found that knockdown of Rab7, Rab9, or Rab11 did not alter endogenous APP metabolism, such as that observed in aged monkey brains and in dynein-depleted cells. These findings suggest that dynein dysfunction can cause retromer deficiency and that concomitant disruption of retrograde trafficking may be the key factor underlying age-dependent Aß pathology.

Diabetes Mellitus Induces Alzheimer's Disease Pathology: Histopathological Evidence from Animal Models.

Alzheimer's disease (AD) is the major causative disease of dementia and is characterized pathologically by the accumulation of senile plaques (SPs) and neurofibrillary tangles (NFTs) in the brain. Although genetic studies show that ß-amyloid protein (Aß), the major component of SPs, is the key factor underlying AD pathogenesis, it remains unclear why advanced age often leads to AD. Interestingly, several epidemiological and clinical studies show that type II diabetes mellitus (DM) patients are more likely to exhibit increased susceptibility to AD. Moreover, growing evidence suggests that there are several connections between the neuropathology that underlies AD and DM, and there is evidence that the experimental induction of DM can cause cognitive dysfunction, even in rodent animal models. This mini-review summarizes histopathological evidence that DM induces AD pathology in animal models and discusses the possibility that aberrant insulin signaling is a key factor in the induction of AD pathology.

TDP-43 binds and transports G-quadruplex-containing mRNAs into neurites for local translation.

Growth and differentiation of the neurites depends on long-distance transport of a specific set of mRNAs to restricted area and their local translation. Here, we found that a TAR DNA-binding protein of 43 kDa in size (TDP-43) plays an essential role in intracellular transport of mRNA. For identification of target RNAs recognized by TDP-43, we purified TDP-43 in soluble dimer form and subjected to in vitro systematic evolution of ligands by exponential enrichment (SELEX) screening. All the TDP-43-bound RNAs were found to contain G-quadruplex (G4). Using a double-fluorescent probe system, G4-containing RNAs were found to be transported, together with TDP-43, into the distal neurites. Two lines of evidence indicated that loss of function of TDP-43 results in the neurodegenerative disorder: (i) amyotrophic lateral sclerosis (ALS)-linked mutant TDP-43M337V lacks the activity of binding and transport of G4-containing mRNAs; and (ii) RNA containing G4-forming GGGGCC repeat expansion from the ALS-linked C9orf72 gene absorbs TDP-43, thereby reducing the intracellular pool of functional TDP-43. Taken together, we propose that TDP-43 within neurons plays an essential role of mRNA transport into distal neurites for local translation, and thus, dysfunctions of TDP-43 cause neural diseases such as ALS and frontotemporal lobar degeneration.

Retromer and Rab2-dependent trafficking mediate PS1 degradation by proteasomes in endocytic disturbance.

Accumulating evidence suggests that endocytic pathway deficits are involved in Alzheimer's disease pathogenesis. Several reports show that endocytic disturbance affects ß-amyloid peptide (Aß) cleavage from ß-amyloid precursor protein (APP). Presenilin-1 (PS1) is the catalytic core of the γ-secretase complex required for Aß generation. Previously, we showed that aging induces endocytic disturbance, resulting in the accumulation of Aß and APP in enlarged endosomes. It remains unclear, however, whether PS1 localization and function are affected with endocytic disturbance. Here, we report that in endocytic disturbance, PS1 is transported from endosomes to ER/Golgi compartments via retromer trafficking, and that PS1 interacts with vacuolar protein sorting-associated protein 35 both in vitro and in vivo. Moreover, PS1 is degraded by proteasomes via a Rab2-dependent trafficking pathway, only during endocytic disturbance. These findings suggest that PS1 levels and localization in endosomes are regulated by retromer trafficking and ER-associated degradation system, even if endocytic disturbance significantly induces the endosomal accumulation of APP and ß-site APP-cleaving enzyme 1. Results of this study also suggest that retromer deficiency can affect PS1 localization in endosomes, where Aß cleavage mainly occurs, possibly leading to enhanced Aß pathology. We proposed the following mechanism for intracellular transport of presenilin-1 (PS1). When endosome/lysosome trafficking is disturbed, PS1 is transported from endosome to endoplasmic reticulum (ER)/Golgi compartments via retromer and Rab2-mediated trafficking, and then degraded by endoplasmic reticulum-associated degradation (ERAD). Perturbations in this trafficking can cause abnormal endosomal accumulation of PS1, and then may lead to exacerbated Aß pathology. Cover Image for this issue: doi: 10.1111/jnc.13318.

Diabetes mellitus accelerates Aß pathology in brain accompanied by enhanced GAß generation in nonhuman primates.

Growing evidence suggests that diabetes mellitus (DM) is one of the strongest risk factors for developing Alzheimer's disease (AD). However, it remains unclear why DM accelerates AD pathology. In cynomolgus monkeys older than 25 years, senile plaques (SPs) are spontaneously and consistently observed in their brains, and neurofibrillary tangles are present at 32 years of age and older. In laboratory-housed monkeys, obesity is occasionally observed and frequently leads to development of type 2 DM. In the present study, we performed histopathological and biochemical analyses of brain tissue in cynomolgus monkeys with type 2 DM to clarify the relationship between DM and AD pathology. Here, we provide the evidence that DM accelerates Aß pathology in vivo in nonhuman primates who had not undergone any genetic manipulation. In DM-affected monkey brains, SPs were observed in frontal and temporal lobe cortices, even in monkeys younger than 20 years. Biochemical analyses of brain revealed that the amount of GM1-ganglioside-bound Aß (GAß)--the endogenous seed for Aß fibril formation in the brain--was clearly elevated in DM-affected monkeys. Furthermore, the level of Rab GTPases was also significantly increased in the brains of adult monkeys with DM, almost to the same levels as in aged monkeys. Intraneuronal accumulation of enlarged endosomes was also observed in DM-affected monkeys, suggesting that exacerbated endocytic disturbance may underlie the acceleration of Aß pathology due to DM.