Molecular interaction between type 2 diabetes and Alzheimer's disease through cross-seeding of protein misfolding

Fundamentals of cross-seeding of amyloid proteins: an introduction

Misfolded protein aggregates formed by the same (homologous) or different (heterologous/cross) sequences are the pathological hallmarks of many protein misfolding diseases (PMDs) including Alzheimer's disease (AD) and type 2 diabetes (T2D). Different from homologous-amyloid aggregation that is solely associated with a specific PMD, cross-amyloid aggregation (i.e. cross-seeding) of different amyloid proteins is more fundamentally and biologically important for understanding and untangling not only the pathological process of each PMD, but also a potential molecular cross-talk between different PMDs. However, the cross-amyloid aggregation is still a subject poorly explored and little is known about its sequence/structure-dependent aggregation mechanisms, as compared to the widely studied homo-amyloid aggregation. Here, we review the most recent and important findings of amyloid cross-seeding behaviors from in vitro, in vivo, and in silico studies. Some typical cross-seeding phenomena between Aβ/hIAPP, Aβ/tau, Aβ/α-synuclein, and tau/α-synuclein are selected and presented, and the underlying specific or general cross-seeding mechanisms are also discussed to better reveal their sequence-structure-property relationships. The potential use of the cross-seeding concept to design amyloid inhibitors is also proposed. Finally, we offer some personal perspectives on current major challenges and future research directions in this less-studied yet important field, and hopefully this work will stimulate more research to explore all possible fundamental and practical aspects of amyloid cross-seeding.

Transplantation of bone marrow derived macrophages reduces markers of neuropathology in an APP/PS1 mouse model

Background

We investigated early hallmarks of putative therapeutic effects following systemic transplantation of bone marrow derived macrophages (BM-M) in APP/PS1 transgenic mice.

Method

BM-M were transplanted into the tail vein and the animals analysed 1 month later.

Results

BM-M transplantation promoted the reduction of the amyloid beta [37-42] plaque number and size in the cortex and hippocampus of the treated mice, but no change in the more heavily modified pyroglutamate amyloid beta E3 plaques. The number of phenotypically 'small' microglia increased in the hippocampus. Astrocyte size decreased overall, indicating a reduction of activated astrocytes. Gene expression of interleukin 6 and 10, interferon-gamma, and prostaglandin E receptor 2 was significantly lower in the hippocampus, while interleukin 10 expression was elevated in the cortex of the treated mice.

Conclusions

BM-M systemically transplanted, promote a decrease in neuroinflammation and a limited reversion of amyloid pathology. This exploratory study may support the potential of BM-M or microglia-like cell therapy and further illuminates the mechanisms of action associated with such transplants.

Amylin as a potential link between type 2 diabetes and alzheimer disease

OBJECTIVE

Alzheimer disease (AD) is the leading cause of dementia, and although its etiology remains unclear, it seems that type 2 diabetes mellitus (T2DM) and other prediabetic states of insulin resistance could contribute to the appearance of sporadic AD. As such, we have assessed whether tau and β-amyloid (Aβ) deposits might be present in pancreatic tissue of subjects with AD, and whether amylin, an amyloidogenic protein deposited in the pancreas of T2DM patients, might accumulate in the brain of AD patients.

METHODS

We studied pancreatic and brain tissue from 48 individuals with no neuropathological alterations and from 87 subjects diagnosed with AD. We examined Aβ and tau accumulation in the pancreas as well as that of amylin in the brain. Moreover, we performed proximity ligation assays to ascertain whether tau and/or Aβ interact with amylin in either the pancreas or brain of these subjects.

RESULTS

Cytoplasmic tau and Aβ protein deposits were detected in pancreatic β cells of subjects with AD as well as in subjects with a normal neuropathological examination but with a history of T2DM and in a small cohort of control subjects without T2DM. Furthermore, we found amylin deposits in the brain of these subjects, providing histological evidence that amylin can interact with Aβ and tau in both the pancreas and hippocampus.

INTERPRETATION

The presence of both tau and Aβ inclusions in pancreatic β cells, and of amylin deposits in the brain, provides new evidence of a potential overlap in the mechanisms underlying the pathogenesis of T2DM and AD. ANN NEUROL 2019;86:539-551.

Targeting the IL-1β/IL-1Ra pathways for the aggregation of human islet amyloid polypeptide in an ex vivo organ culture system of the intervertebral disc

Intervertebral disc degeneration (IDD) is characterized by excessive apoptosis of nucleus pulposus (NP) cells and hyperactive extracellular matrix (ECM) catabolism. Our previous studies revealed the relationship between human islet amyloid polypeptide (hIAPP) and NP cell apoptosis. However, the role of hIAPP aggregates in IDD has not yet been investigated. This study aimed to determine whether the accumulation of hIAPP aggregates promotes IDD progression. The aggregation of hIAPP increased in human NP tissues during IDD. The deposition of hIAPP aggravated the compression-induced IDD that promoted NP cell apoptosis and ECM degradation via IL-1β/IL-1Ra signaling in an ex vivo rat disc model. Moreover, neutralizing IL-1β augmented the protective effects of hIAPP overexpression by decreasing hIAPP aggregation in human NP cells. These results suggest that the aggregation of hIAPP promotes NP cell apoptosis and ECM degradation ex vivo and in vitro by disrupting the balance of IL-1β/IL-1Ra signaling.

The Involvement of Peripheral and Brain Insulin Resistance in Late Onset Alzheimer's Dementia

Nowadays, Alzheimer's disease (AD) is a severe sociological and clinical problem. Since it was first described, there has been a constant increase in its incidence and, for now, there are no effective treatments since current approved medications have only shown short-term symptomatic benefits. Therefore, it is imperative to increase efforts in the search for molecules and non-pharmacological strategies that are capable of slowing or stopping the progress of the disease and, ideally, to reverse it. The amyloid cascade hypothesis based on the fundamental role of amyloid has been the central hypothesis in the last 30 years. However, since amyloid-directed treatments have shown no relevant beneficial results other theories have been postulated to explain the origin of the pathology. The brain is a highly metabolically active energy-consuming tissue in the human body. It has an almost complete dependence on the metabolism of glucose and uses most of its energy for synaptic transmission. Thus, alterations on the utilization or availability of glucose may be cause for the appearance of neurodegenerative pathologies like AD. In this review article, the hypothesis known as Type 3 Diabetes (T3D) will be evaluated by summarizing some of the data that has been reported in recent years. According to published research, the adherence over time to low saturated fatty acids diets in the context of the Mediterranean diet would reduce the inflammatory levels in brain, with a decrease in the pro-inflammatory glial activation and mitochondrial oxidative stress. In this situation, the insulin receptor pathway would be able to fine tune the mitochondrial biogenesis in neuronal cells, regulation the adenosine triphosphate/adenosine diphosphate intracellular balance, and becoming a key factor involved in the preservation of the synaptic connexions and neuronal plasticity. In addition, new targets and strategies for the treatment of AD will be considered in this review for their potential as new pharmacological or non-pharmacological approaches.

Diabetes-related Amylin Dyshomeostasis: a Contributing Factor to Cerebrovascular Pathology and Dementia

Type 2 diabetes (T2D) increases the risk for cerebrovascular disease (CVD) and dementia. The underlying molecular mechanisms remain elusive, which hampers the development of treatment or/and effective prevention strategies. Recent studies suggest that dyshomeostasis of amylin, a satiety hormone that forms pancreatic amyloid in patients with T2D, promotes accumulation of amylin in cerebral small blood vessels and interaction with Alzheimer's disease (AD) pathology. Overexpression of human amylin in rodents (rodent amylin does not form amyloid) leads to late-life onset T2D and neurologic deficits. In this Review, we discuss clinical evidence of amylin pathology in CVD and AD and identify critical characteristics of animal models that could help to better understand molecular mechanisms underlying the increased risk of CVD and AD in patients with prediabetes or T2D.

Traumatic Brain Injury Induces Tau Aggregation and Spreading

The misfolding and aggregation of tau protein into neurofibrillary tangles is the main underlying hallmark of tauopathies. Most tauopathies have a sporadic origin and can be associated with multiple risk factors. Traumatic brain injury (TBI) has been suggested as a risk factor for tauopathies by triggering disease onset and facilitating its progression. Several studies indicate that TBI seems to be a risk factor to development of Alzheimer disease and chronic traumatic encephalopathy, because there is a relationship of TBI severity and propensity to development of these illnesses. In this study, we evaluated whether moderate to severe TBI can trigger the initial formation of pathological tau that would induce the development of the pathology throughout the brain. To this end, we subjected tau transgenic mice to TBI and assessed tau phosphorylation and aggregation pattern to create a spatial heat map of tau deposition and spreading in the brain. Our results suggest that brain injured tau transgenic mice have an accelerated tau pathology in different brain regions that increases over time compared with sham mice. The appearance of pathological tau occurs in regions distant to the injury area that are connected synaptically, suggesting dissemination of tau aggregates. Overall, this work posits TBI as a risk factor for tauopathies through the induction of tau hyperphosphorylation and aggregation.

A systemic view of Alzheimer disease - insights from amyloid-β metabolism beyond the brain

Alzheimer disease (AD) is the most common type of dementia, and is currently incurable; existing treatments for AD produce only a modest amelioration of symptoms. Research into this disease has conventionally focused on the CNS. However, several peripheral and systemic abnormalities are now understood to be linked to AD, and our understanding of how these alterations contribute to AD is becoming more clearly defined. This Review focuses on amyloid-β (Aβ), a major hallmark of AD. We review emerging findings of associations between systemic abnormalities and Aβ metabolism, and describe how these associations might interact with or reflect on the central pathways of Aβ production and clearance. On the basis of these findings, we propose that these abnormal systemic changes might not only develop secondary to brain dysfunction but might also affect AD progression, suggesting that the interactions between the brain and the periphery have a crucial role in the development and progression of AD. Such a systemic view of the molecular pathogenesis of AD could provide a novel perspective for understanding this disease and present new opportunities for its early diagnosis and treatment.

A metabolic perspective of late onset Alzheimer's disease

After decades of research, the molecular neuropathology of Alzheimer's disease (AD) is still one of the hot topics in biomedical sciences. Some studies suggest that soluble amyloid β (Aβ) oligomers act as causative agents in the development of AD and could be initiators of its complex neurodegenerative cascade. On the other hand, there is also evidence pointing to Aβ oligomers as mere aggravators, with an arguable role in the origin of the disease. In this line of research, the relative contribution of soluble Aβ oligomers to neuronal damage associated with metabolic disorders such as Type 2 Diabetes Mellitus (T2DM) and obesity is being actively investigated. Some authors have proposed the endoplasmic reticulum (ER) stress and the induction of the unfolded protein response (UPR) as important mechanisms leading to an increase in Aβ production and the activation of neuroinflammatory processes. Following this line of thought, these mechanisms could also cause cognitive impairment. The present review summarizes the current understanding on the neuropathological role of Aβ associated with metabolic alterations induced by an obesogenic high fat diet (HFD) intake. It is believed that the combination of these two elements has a synergic effect, leading to the impairement of ER and mitochondrial functions, glial reactivity status alteration and inhibition of insulin receptor (IR) signalling. All these metabolic alterations would favour neuronal malfunction and, eventually, neuronal death by apoptosis, hence causing cognitive impairment and laying the foundations for late-onset AD (LOAD). Moreover, since drugs enhancing the activation of cerebral insulin pathway can constitute a suitable strategy for the prevention of AD, we also discuss the scope of therapeutic approaches such as intranasal administration of insulin in clinical trials with AD patients.

G, Calderon O, Moreno-Gonzalez I. Modifiable Risk Factors for Alzheimer's Disease

Since first described in the early 1900s, Alzheimer's disease (AD) has risen exponentially in prevalence and concern. Research still drives to understand the etiology and pathogenesis of this disease and what risk factors can attribute to AD. With a majority of AD cases being of sporadic origin, the increasing exponential growth of an aged population and a lack of treatment, it is imperative to discover an easy accessible preventative method for AD. Some risk factors can increase the propensity of AD such as aging, sex, and genetics. Moreover, there are also modifiable risk factors-in terms of treatable medical conditions and lifestyle choices-that play a role in developing AD. These risk factors have their own biological mechanisms that may contribute to AD etiology and pathological consequences. In this review article, we will discuss modifiable risk factors and discuss the current literature of how each of these factors interplay into AD development and progression and if strategically analyzed and treated, could aid in protection against this neurodegenerative disease.

Tau underlies synaptic and cognitive deficits for type 1, but not type 2 diabetes mouse models

Diabetes mellitus (DM) is one of the most devastating diseases that currently affects the aging population. Recent evidence indicates that DM is a risk factor for many brain disorders, due to its direct effects on cognition. New findings have shown that the microtubule-associated protein tau is pathologically processed in DM; however, it remains unknown whether pathological tau modifications play a central role in the cognitive deficits associated with DM. To address this question, we used a gain-of-function and loss-of-function approach to modulate tau levels in type 1 diabetes (T1DM) and type 2 diabetes (T2DM) mouse models. Our study demonstrates that tau differentially contributes to cognitive and synaptic deficits induced by DM. On one hand, overexpressing wild-type human tau further exacerbates cognitive and synaptic impairments induced by T1DM, as human tau mice treated under T1DM conditions show robust deficits in learning and memory processes. On the other hand, neither a reduction nor increase in tau levels affects cognition in T2DM mice. Together, these results shine new light onto the different molecular mechanisms that underlie the cognitive and synaptic impairments associated with T1DM and T2DM.

Anti-prion systems in yeast

Yeast prions have become important models for the study of the basic mechanisms underlying human amyloid diseases. Yeast prions are pathogenic (unlike the [Het-s] prion of Podospora anserina), and most are amyloid-based with the same in-register parallel β-sheet architecture as most of the disease-causing human amyloids studied. Normal yeast cells eliminate the large majority of prion variants arising, and several anti-prion/anti-amyloid systems that eliminate them have been identified. It is likely that mammalian cells also have anti-amyloid systems, which may be useful in the same way humoral, cellular, and innate immune systems are used to treat or prevent bacterial and viral infections.

Structural elucidation and bioactivities of a novel arabinogalactan from Coreopsis tinctoria

Coreopsis tinctoria is being widely cultivated in Xinjiang of China, whose consumption is known to prevent diabetes and neurodegenerative diseases. To elucidate the bioactive ingredients responsible for these benefits, the alkaline soluble crude polysaccharide (CTB) was isolated from C. tinctoria. In vitro experiments showed that the inhibition of α-amylase and α-glucosidase by CTB was 13407-fold and 906-fold higher than that by positive control, respectively. Then, a novel arabinogalactan, CTBP-1, was isolated and purified from CTB. Structural analysis showed that CTBP-1 possessed a 1,6-linked β-d-Galp and 1,5-linked α-l-Araf backbone with branches substituted at the C-3 position of the 1,6-linked β-d-Galp, and the side chains included 1,5-linked α-l-Araf, T-linked β-d-Galp and T-linked α-l-Araf. The inhibitory effects of CTBP-1 on α-amylase and α-glucosidase were 2.7 and 17.9 times that of acarbose, respectively. CTBP-1 could avoid indigestion and similar side effects. In addition, CTBP-1 remarkably inhibited the release of nitric oxide (NO), tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) in lipopolysaccharide (LPS)-stimulated BV2 microglial cells. In summary, CTBP-1 is a novel arabinogalactan with great potential as a treatment for type 2 diabetes and Alzheimer's disease.

Next Generation Precision Medicine: CRISPR-mediated Genome Editing for the Treatment of Neurodegenerative Disorders

Despite significant advancements in the field of molecular neurobiology especially neuroinflammation and neurodegeneration, the highly complex molecular mechanisms underlying neurodegenerative diseases remain elusive. As a result, the development of the next generation neurotherapeutics has experienced a considerable lag phase. Recent advancements in the field of genome editing offer a new template for dissecting the precise molecular pathways underlying the complex neurodegenerative disorders. We believe that the innovative genome and transcriptome editing strategies offer an excellent opportunity to decipher novel therapeutic targets, develop novel neurodegenerative disease models, develop neuroimaging modalities, develop next-generation diagnostics as well as develop patient-specific precision-targeted personalized therapies to effectively treat neurodegenerative disorders including Alzheimer's disease, Parkinson's disease, Huntington's disease, Amyotrophic lateral sclerosis, Frontotemporal dementia etc. Here, we review the latest developments in the field of CRISPR-mediated genome editing and provide unbiased futuristic insights regarding its translational potential to improve the treatment outcomes and minimize financial burden. However, despite significant advancements, we would caution the scientific community that since the CRISPR field is still evolving, currently we do not know the full spectrum of CRISPR-mediated side effects. In the wake of the recent news regarding CRISPR-edited human babies being born in China, we urge the scientific community to maintain high scientific and ethical standards and utilize CRISPR for developing in vitro disease in a dish model, in vivo testing in nonhuman primates and lower vertebrates and for the development of neurotherapeutics for the currently incurable neurodegenerative disorders. Graphical Abstract.

Pre-structured hydrophobic peptide β-strands: A universal amyloid trap?

Amyloid fibril formation has long been studied because of the variety of proteins that are capable of adopting this structure despite sharing little sequence homology. This makes amyloid fibrils a challenging focus for inhibition studies because the peptides and proteins that form amyloid fibrils cannot be targeted based on a sequence motif. Most peptide inhibitors that target specific amyloidogenic proteins rely heavily on sequence recognition to ensure that the inhibitory peptide is able to bind its target. This approach is limited to targeting one amyloidogenic protein at a time. However, there is increasing evidence of cross-reactivity between amyloid-forming polypeptides. It has therefore become more useful to study the similarities between these proteins that goes beyond their sequence homology. Indeed, the observation that amyloidogenic proteins adopt similar secondary structures along the pathway to fibril formation opens the way to an interesting investigation: the development of inhibitors that could be universal amyloid traps. The review below will analyze two specific amyloidogenic proteins, α-synuclein and human amylin, and introduce a small number of peptides that have been shown to be capable of inhibiting the amyloidogenesis of both of these very dissimilar polypeptides. Some of the inhibitory peptide motifs may indeed, be applicable to Aβ and other amyloidogenic systems.

Diverse Misfolded Conformational Strains and Cross-seeding of Misfolded Proteins Implicated in Neurodegenerative Diseases

Numerous neurodegenerative diseases including prion, Alzheimer's and Parkinson's diseases are characterized by accumulation of protein aggregates in brain. Prion disease is unique in that the natively folded prion protein forms diverse misfolded aggregates with distinct molecular conformations (strains), which underlie different disease phenotypes. In addition, the conformational strains are able to self-propagate their unique conformations by recruiting normal protein monomers and converting their conformations to misfolded conformers. There is an increasing body of evidence that suggests other aggregation-prone proteins including tau and α-synuclein associated with Alzheimer's and Parkinson's diseases, respectively, also behave like a prion that has conformational strains with self-propagation (seeding) property. Moreover, misfolded protein aggregates can promote misfolding and aggregation of different proteins through cross-seeding, which might be associated with co-occurrence of multiple neurodegenerative diseases in the same patient. Elucidation of diverse conformational strains with self-propagation capability and of molecular basis for the cross-talk between misfolded proteins is essential to the development of effective therapeutic intervention.

Biomolecular Assemblies: Moving from Observation to Predictive Design

Biomolecular assembly is a key driving force in nearly all life processes, providing structure, information storage, and communication within cells and at the whole organism level. These assembly processes rely on precise interactions between functional groups on nucleic acids, proteins, carbohydrates, and small molecules, and can be fine-tuned to span a range of time, length, and complexity scales. Recognizing the power of these motifs, researchers have sought to emulate and engineer biomolecular assemblies in the laboratory, with goals ranging from modulating cellular function to the creation of new polymeric materials. In most cases, engineering efforts are inspired or informed by understanding the structure and properties of naturally occurring assemblies, which has in turn fueled the development of predictive models that enable computational design of novel assemblies. This Review will focus on selected examples of protein assemblies, highlighting the story arc from initial discovery of an assembly, through initial engineering attempts, toward the ultimate goal of predictive design. The aim of this Review is to highlight areas where significant progress has been made, as well as to outline remaining challenges, as solving these challenges will be the key that unlocks the full power of biomolecules for advances in technology and medicine.

Co-occurrence of chronic traumatic encephalopathy and prion disease

Chronic traumatic encephalopathy (CTE) is a neurodegenerative disease associated with repetitive traumatic brain injury (TBI). CTE is generally found in athletes participating in contact sports and military personnel exposed to explosive blasts but can also affect civilians. Clinically and pathologically, CTE overlaps with post-traumatic stress disorder (PTSD), a term mostly used in a clinical context. The histopathology of CTE is defined by the deposition of hyperphosphorylated tau protein in neurons and astrocytes preferentially with perivascular distribution and at the depths of the cortical sulci. In addition to hyperphosphorylated tau, other pathologic proteins are deposited in CTE, including amyloid β (Aβ), transactive response (TAR) DNA-binding protein 43 kDa (TDP-43) and α-synuclein. However, the coexistence of prion disease in CTE has not been observed. We report three cases of histopathologically validated CTE with co-existing sporadic prion disease. Two were identified in a cohort of 55 pathologically verified cases of CTE submitted to the CTE Center of Boston University. One was identified among brain tissues submitted to the National Prion Disease Pathology Surveillance Center of Case Western Reserve University. The histopathological phenotype and properties of the abnormal, disease-related prion protein (PrPD) of the three CTE cases were examined using lesion profile, immunohistochemistry, electrophoresis and conformational tests. Subjects with sporadic Creutzfeldt-Jakob disease (sCJD) matched for age, PrP genotype and PrPD type were used as controls. The histopathology phenotype and PrPD properties of the three CTE subjects showed no significant differences from their respective sCJD controls suggesting that recurring neurotrauma or coexisting CTE pathology did not detectably impact the prion disease phenotype and PrPD conformational characteristics. Based on the reported incidence of sporadic prion disease, the detection of two cases with sCJD in the CTE Center series of 55 CTE cases by chance alone would be highly unlikely (p = 8.93*10- 6). Nevertheless, examination of a larger cohort of CTE is required to conclusively determine whether the risk of CJD is significantly increased in patients with CTE.

Diabetes and Alzheimer's Disease: A Link not as Simple as it Seems

Type 2 diabetes mellitus is associated with an increased risk to develop Alzheimer disease, however, the underlying mechanisms for this association are still unclear. In this review we will provide a critical overview of the major findings coming from clinical studies and animal models.

Disorders of Body Weight, Sleep and Circadian Rhythm as Manifestations of Hypothalamic Dysfunction in Alzheimer's Disease

While cognitive decline and memory loss are the major clinical manifestations of Alzheimer’s disease (AD), they are now recognized as late features of the disease. Recent failures in clinical drug trials highlight the importance of evaluating and treating patients with AD as early as possible and the difficulties in developing effective therapies once the disease progresses. Since the pathological hallmarks of AD including the abnormal aggregation of amyloid-beta (Aβ) and tau can occur decades before any significant cognitive decline in the preclinical stage of AD, it is important to identify the earliest clinical manifestations of AD and elucidate their underlying cellular and molecular mechanisms. Importantly, metabolic and non-cognitive manifestations of AD such as weight loss and alterations of peripheral metabolic signals can occur before the onset of cognitive symptoms and worsen with disease progression. Accumulating evidence suggests that the major culprit behind these early metabolic and non-cognitive manifestations of AD is AD pathology causing dysfunction of the hypothalamus, a brain region critical for integrating peripheral signals with essential homeostatic physiological functions. Here, we aim to highlight recent developments that address the role of AD pathology in the development of hypothalamic dysfunction associated with metabolic and non-cognitive manifestations seen in AD. Understanding the mechanisms underlying hypothalamic dysfunction in AD could give key new insights into the development of novel biomarkers and therapeutic targets.

The Early Events That Initiate β-Amyloid Aggregation in Alzheimer's Disease

Alzheimer’s disease (AD) is characterized by the development of amyloid plaques and neurofibrillary tangles (NFTs) consisting of aggregated β-amyloid (Aβ) and tau, respectively. The amyloid hypothesis has been the predominant framework for research in AD for over two decades. According to this hypothesis, the accumulation of Aβ in the brain is the primary factor initiating the pathogenesis of AD. However, it remains elusive what factors initiate Aβ aggregation. Studies demonstrate that AD has multiple causes, including genetic and environmental factors. Furthermore, genetic factors, many age-related events and pathological conditions such as diabetes, traumatic brain injury (TBI) and aberrant microbiota also affect the aggregation of Aβ. Here we provide an overview of the age-related early events and other pathological processes that precede Aβ aggregation.

Inhibition of protein misfolding and aggregation by natural phenolic compounds

Protein misfolding and aggregation into fibrillar deposits is a common feature of a large group of degenerative diseases affecting the central nervous system or peripheral organs, termed protein misfolding disorders (PMDs). Despite their established toxic nature, clinical trials aiming to reduce misfolded aggregates have been unsuccessful in treating or curing PMDs. An interesting possibility for disease intervention is the regular intake of natural food or herbal extracts, which contain active molecules that inhibit aggregation or induce the disassembly of misfolded aggregates. Among natural compounds, phenolic molecules are of particular interest, since most have dual activity as amyloid aggregation inhibitors and antioxidants. In this article, we review many phenolic natural compounds which have been reported in diverse model systems to have the potential to delay or prevent the development of various PMDs, including Alzheimer's and Parkinson's diseases, prion diseases, amyotrophic lateral sclerosis, systemic amyloidosis, and type 2 diabetes. The lower toxicity of natural compounds compared to synthetic chemical molecules suggest that they could serve as a good starting point to discover protein misfolding inhibitors that might be useful for the treatment of various incurable diseases.

Cognitive decline and dementia in diabetes mellitus: mechanisms and clinical implications

Cognitive dysfunction is increasingly recognized as an important comorbidity of diabetes mellitus. Different stages of diabetes-associated cognitive dysfunction exist, each with different cognitive features, affected age groups and prognoses and probably with different underlying mechanisms. Relatively subtle, slowly progressive cognitive decrements occur in all age groups. More severe stages, particularly mild cognitive impairment and dementia, with progressive deficits, occur primarily in older individuals (>65 years of age). Patients in the latter group are the most relevant for patient management and are the focus of this Review. Here, we review the evolving insights from studies on risk factors, brain imaging and neuropathology, which provide important clues on mechanisms of both the subtle cognitive decrements and the more severe stages of cognitive dysfunction. In the majority of patients, the cognitive phenotype is probably defined by multiple aetiologies. Although both the risk of clinically diagnosed Alzheimer disease and that of vascular dementia is increased in association with diabetes, the cerebral burden of the prototypical pathologies of Alzheimer disease (such as neurofibrillary tangles and neuritic plaques) is not. A major challenge for researchers is to pinpoint from the spectrum of diabetes-related disease processes those that affect the brain and contribute to development of dementia beyond the pathologies of Alzheimer disease. Observations from experimental models can help to meet that challenge, but this requires further improving the synergy between experimental and clinical scientists. The development of targeted treatment and preventive strategies will therefore depend on these translational efforts.

Protein misfolding, aggregation, and conformational strains in neurodegenerative diseases

A hallmark event in neurodegenerative diseases (NDs) is the misfolding, aggregation, and accumulation of proteins, leading to cellular dysfunction, loss of synaptic connections, and brain damage. Despite the involvement of distinct proteins in different NDs, the process of protein misfolding and aggregation is remarkably similar. A recent breakthrough in the field was the discovery that misfolded protein aggregates can self-propagate through seeding and spread the pathological abnormalities between cells and tissues in a manner akin to the behavior of infectious prions in prion diseases. This discovery has vast implications for understanding the mechanisms involved in the initiation and progression of NDs, as well as for the design of novel strategies for treatment and diagnosis. In this Review, we provide a critical discussion of the role of protein misfolding and aggregation in NDs. Commonalities and differences between distinct protein aggregates will be highlighted, in addition to evidence supporting the hypothesis that misfolded aggregates can be transmissible by the prion principle. We will also describe the molecular basis and implications for prion-like conformational strains, cross-interaction between different misfolded proteins in the brain, and how these concepts can be applied to the development of novel strategies for therapy and diagnosis.

Interaction of amyloidogenic proteins in pancreatic β cells from subjects with synucleinopathies

Parkinson's disease patients experience a wide range of non-motor symptoms that may be provoked by deposits of phosphorylated α-synuclein in the peripheral nervous system. Pre-existing diabetes mellitus might be a risk factor for developing Parkinson's disease, and indeed, nearly 60% of Parkinson's disease patients are insulin resistant. Thus, we have investigated whether phosphorylated α-synuclein is deposited in pancreatic tissue of subjects with synucleinopathies. We studied pancreatic tissue from 39 subjects diagnosed with Parkinson's disease, Lewy body Dementia or incidental Lewy bodies disease, as well as that from 34 subjects with diabetes mellitus and a normal neuropathological examination, and 52 subjects with a normal neuropathological examination. We examined the pancreatic accumulation of phosphorylated α-synuclein and of the islet amyloid polypeptide precursor (IAPP), an amyloidogenic protein that plays an unknown role in diabetes mellitus, but that can promote α-synuclein amyloid deposition in vitro. Moreover, we performed proximity ligation assays to assess whether these two proteins interact in the pancreas of these subjects. Cytoplasmic phosphorylated α-synuclein deposits were found in the pancreatic β cells of 14 subjects with Parkinson's disease (93%), in 11 subjects with Lewy body Dementia (85%) and in 8 subjects with incidental Lewy body disease (73%). Furthermore, we found similar phosphorylated α-synuclein inclusions in 23 subjects with a normal neuropathological examination but with diabetes mellitus (68%) and in 9 control subjects (17%). In addition, IAPP/α-synuclein interactions appear to occur in patients with pancreatic inclusions of phosphorylated α-synuclein. The presence of phosphorylated α-synuclein inclusions in pancreatic β cells provides a new evidence of a mechanism that is potentially common to the pathogenesis of diabetes mellitus, PD and DLB. Moreover, the interaction of IAPP and α-synuclein in the pancreatic β cells of patients may represent a novel target for the development of strategies to treat these diseases.

Are Tanycytes the Missing Link Between Type 2 Diabetes and Alzheimer's Disease?

Tanycytes are highly specialized bipolar ependymal cells that line the ventrolateral wall and the floor of the third ventricle in the brain and form a blood-cerebrospinal fluid barrier at the level of the median eminence. They play a pivotal role in regulating metabolic networks that control body weight and energy homeostasis. Due to the glucosensing function of tanycytes, they could be considered as a critical player in the pathogenesis of type 2 diabetes. Genetic fate mapping studies have established the role of tanycytes for the newly detected adult hypothalamic neurogenesis with important implications for metabolism as well as pathophysiology of various neurodegenerative diseases. We believe that a comprehensive understanding of the physiological mechanisms underlying their neuroplasticity, glucosensing, and cross talk with endothelial cells will enable us to achieve metabolic homeostasis in type 2 diabetes patients and possibly delay the progression of Alzheimer's disease and hopefully improve cognitive function.

Islet Amyloid Polypeptide Promotes Amyloid-Beta Aggregation by Binding-Induced Helix-Unfolding of the Amyloidogenic Core

Amyloid aggregation of amyloid-beta (Aβ) and islet amyloid polypeptide (IAPP) is associated with Alzheimer's disease (AD) and type-2 diabetes (T2D), respectively. With T2D being the risk factor for AD and the ability of IAPP to cross the blood-brain barrier, the coaggregation of Aβ and IAPP has been explored to understand the cross-talk between the two diseases. Recent studies demonstrated that soluble IAPP could significantly accelerate the aggregation of Aβ while preformed amyloids of IAPP were poor "seeds" for Aβ aggregation. Here, we apply all-atom discrete molecular dynamics simulations to investigate possible molecular mechanisms for the accelerated coaggregation of IAPP and Aβ42 comparing to Aβ42 aggregation alone, which was confirmed by the complementary thioflavin-T fluorescence assay. Our simulation results suggest that peptides in the mixture tend to form heterodimers as the first step toward their coaggregation. Strong interpeptide interactions with IAPP in the heterodimer shift the helical conformation of Aβ42 in its amyloidogenic central hydrophobic core, residues 16-22 (Aβ16-22), to the extended conformation ready to form β-sheets. Our study suggests that the unfolding of Aβ16-22 helix contributes to the aggregation free-energy barrier and corresponds to the rate-limiting conformational change for Aβ42 aggregation. Therefore, we propose that soluble IAPP promotes the aggregation of Aβ42 by binding-induced conformational change of Aβ42 in its amyloidogenic core and thus reduced aggregation free-energy barrier.

Transactive DNA Binding Protein 43 Rather Than Other Misfolded Proteins in the Brain is Associated with Islet Amyloid Polypeptide in Pancreas in Aged Subjects with Diabetes Mellitus

A link between diabetes mellitus (DM) related islet amyloid polypeptide (IAPP) and Alzheimer’s disease (AD) related amyloid-β (Aβ) has been suggested in epidemiological and clinical studies. In 2017, proof for existing interaction between type 2 DM and AD on a molecular level was provided based on research carried out in experimental animal models. We assessed aging-related neurodegenerative lesions, i.e., misfolded proteins, associated with dementia such as hyperphosphorylated τ (HPτ), Aβ, α-synuclein (αS), and phosphorylated transactive DNA binding protein 43 (pTDP43) seen in the brain and IAPP seen in the pancreas in subjects with and without DM applying immunohistochemical techniques. HPτ in the brain and IAPP in the pancreas were observed in most subjects. The prevalence and the extent of all misfolded proteins increased with age but this increase was not influenced by DM. Interestingly the extent of misfolded proteins in the brain was higher in non-diabetics when compared with diabetics in demented. A significant correlation was observed between HPτ, Aβ, αS, and pTDP43, whereas IAPP showed no association with HPτ, Aβ, and αS. In subjects with DM, the extent of pTDP43 in brain correlated with the extent of IAPP in pancreas. Thus, there is no evidence of a link between AD-related pathology and DM in humans, whereas an association was found between pTDP43 and IAPP in DM. TDP43 is ubiquitously expressed in all organs but whether TDP43 is phosphorylated in other organs in DM or whether the phosphorylation of TDP43 is influenced by glucose metabolism is yet unknown.

The long-lived Octodon degus as a rodent drug discovery model for Alzheimer's and other age-related diseases

Alzheimer's disease (AD) is a multifactorial progressive neurodegenerative disease. Despite decades of research, no disease modifying therapy is available and a change of research objectives and/or development of novel research tools may be required. Much AD research has been based on experimental models using animals with a short lifespan that have been extensively genetically manipulated and do not represent the full spectrum of late-onset AD, which make up the majority of cases. The aetiology of AD is heterogeneous and involves multiple factors associated with the late-onset of the disease like disturbances in brain insulin, oxidative stress, neuroinflammation, metabolic syndrome, retinal degeneration and sleep disturbances which are all progressive abnormalities that could account for many molecular, biochemical and histopathological lesions found in brain from patients dying from AD. This review is based on the long-lived rodent Octodon degus (degu) which is a small diurnal rodent native to South America that can spontaneously develop cognitive decline with concomitant phospho-tau, β-amyloid pathology and neuroinflammation in brain. In addition, the degu can also develop several other conditions like type 2 diabetes, macular and retinal degeneration and atherosclerosis, conditions that are often associated with aging and are often comorbid with AD. Long-lived animals like the degu may provide a more realistic model to study late onset AD.

Common fibrillar spines of amyloid-β and human islet amyloid polypeptide revealed by microelectron diffraction and structure-based inhibitors

Amyloid-β (Aβ) and human islet amyloid polypeptide (hIAPP) aggregate to form amyloid fibrils that deposit in tissues and are associated with Alzheimer's disease (AD) and type II diabetes (T2D), respectively. Individuals with T2D have an increased risk of developing AD, and conversely, AD patients have an increased risk of developing T2D. Evidence suggests that this link between AD and T2D might originate from a structural similarity between aggregates of Aβ and hIAPP. Using the cryoEM method microelectron diffraction, we determined the atomic structures of 11-residue segments from both Aβ and hIAPP, termed Aβ(24-34) WT and hIAPP(19-29) S20G, with 64% sequence similarity. We observed a high degree of structural similarity between their backbone atoms (0.96-Å root mean square deviation). Moreover, fibrils of these segments induced amyloid formation through self- and cross-seeding. Furthermore, inhibitors designed for one segment showed cross-efficacy for full-length Aβ and hIAPP and reduced cytotoxicity of both proteins, although by apparently blocking different cytotoxic mechanisms. The similarity of the atomic structures of Aβ(24-34) WT and hIAPP(19-29) S20G offers a molecular model for cross-seeding between Aβ and hIAPP.

Impaired peripheral glucose homeostasis and Alzheimer's disease

Alzheimer's disease (AD) is the most common type of dementia. Recent studies suggest that metabolic disturbances, particularly type 2 diabetes (T2D) increase the risk of cognitive decline and AD. AD is also a risk factor for T2D, and a growing body of evidence indicates that these diseases are connected both at clinical and molecular levels. In T2D, peripheral insulin resistance, hyperglycemia and eventually insulin deficiency develops, leading to an overall decline in tissue health. More recently, brain insulin resistance has been shown to be a key feature of AD that is linked to neuronal dysfunction and cognitive impairment. Furthermore, both AD and T2D are amyloidogenic diseases, with abnormal aggregation of amyloid-β peptide (Aβ) and islet amyloid polypeptide (IAPP) respectively contributing to cellular death and disease pathogenesis. Emerging data suggests that Aβ may have peripheral effects including its co-deposition in the pancreas. In this review, we discuss how peripheral effects of Aβ and metabolic disturbances may impact AD pathogenesis. This article is part of the Special Issue entitled 'Metabolic Impairment as Risk Factors for Neurodegenerative Disorders.'

Practical considerations for managing patients with diabetes and dementia

Diabetes and dementia appear to be linked epidemiologically and share a common pathogenetic mechanism. The development of dementia in older people with diabetes will have a significant impact on diabetes self-care and will increase the risk of hypoglycaemia and frailty which ultimately lead to disability and poor outcome. Areas covered: We performed a Medline and Embase search from 1997 to present on relevant dementia and diabetes studies published in English language. Expert commentary: Older people with comorbid diabetes and dementia are functionally heterogeneous and interventions should be proportionate to patients 'functional capacity. Metabolic targets can be tightened in fit persons and relaxed when cognitive abilities continue to decline and overall function deteriorates. A holistic multidisciplinary team approach that involves patients, their carers and integrated primary and secondary care services at one point of care that focuses on improving function and maintaining quality of life is needed.

Functional Amyloids and their Possible Influence on Alzheimer Disease

Amyloids play critical roles in human diseases but have increasingly been recognized to also exist naturally. Shared physicochemical characteristics of amyloids and of their smaller oligomeric building blocks offer the prospect of molecular interactions and crosstalk amongst these assemblies, including the propensity to mutually influence aggregation. A case in point might be the recent discovery of an interaction between the amyloid β peptide (Aβ) and somatostatin (SST). Whereas Aβ is best known for its role in Alzheimer disease (AD) as the main constituent of amyloid plaques, SST is intermittently stored in amyloid-form in dense core granules before its regulated release into the synaptic cleft. This review was written to introduce to readers a large body of literature that surrounds these two peptides. After introducing general concepts and recent progress related to our understanding of amyloids and their aggregation, the review focuses separately on the biogenesis and interactions of Aβ and SST, before attempting to assess the likelihood of encounters of the two peptides in the brain, and summarizing key observations linking SST to the pathobiology of AD. While the review focuses on Aβ and SST, it is to be anticipated that crosstalk amongst functional and disease-associated amyloids will emerge as a general theme with much broader significance in the etiology of dementias and other amyloidosis.

Modulating protein amyloid aggregation with nanomaterials

Direct exposure or intake of nanopaticles (NPs) to the human body can invoke a series of biological responses, some of which are deleterious, and as such the role of NPs in vivo requires thorough examination. Over the past decade, it has been established that biomolecules such as proteins can bind NPs to form a 'corona', where the structures and dynamics of NP-associated proteins can assign new functionality, systemic distribution and toxicity. However, the behavior and fate of NPs in biological systems are still far from being fully understood. Growing evidence has shown that some natural or artificial NPs could either up- or down-regulate protein amyloid aggregation, which is associated with neurodegenerative diseases like Alzheimer's and Parkinson's diseases, as well as metabolic diseases such as type 2 diabetes. These effects can be either indirect (e.g., through a crowding effect) or direct, depending on the NP composition, size, shape and surface chemistry. However, efforts to design anti-amyloid NPs for biomedical applications have been largely hindered by insufficient understanding of the complex processes, even though proof-of-concept experiments have been conducted. Therefore, exploring the general mechanisms of NP-meditated protein aggregation marks an emerging field in bio-nano research and a new stage of handling nanotechnology that not only aids in elucidating the origin of nanotoxicity, but also provides a foundation for engineering de novo anti-amyloid nanomedicines. In this review, we summarize research on NP-mediated protein amyloid aggregation, with the goal of contributing to sustained nanotechnology and safe nanomedicine against amyloid diseases.

Brain microvascular injury and white matter disease provoked by diabetes-associated hyperamylinemia

OBJECTIVE

The brain blood vessels of patients with type 2 diabetes and dementia have deposition of amylin, an amyloidogenic hormone cosecreted with insulin. It is not known whether vascular amylin deposition is a consequence or a trigger of vascular injury. We tested the hypothesis that the vascular amylin deposits cause endothelial dysfunction and microvascular injury and are modulated by amylin transport in the brain via plasma apolipoproteins.

METHODS

Rats overexpressing amyloidogenic (human) amylin in the pancreas (HIP rats) and amylin knockout (AKO) rats intravenously infused with aggregated amylin were used for in vivo phenotyping. We also carried out biochemical analyses of human brain tissues and studied the effects of the aggregated amylin on endothelial cells ex vivo.

RESULTS

Amylin deposition in brain blood vessels is associated with vessel wall disruption and abnormal surrounding neuropil in patients with type 2 diabetes and dementia, in HIP rats, and in AKO rats infused with aggregated amylin. HIP rats have brain microhemorrhages, white matter injury, and neurologic deficits. Vascular amylin deposition provokes loss of endothelial cell coverage and tight junctions. Intravenous infusion in AKO rats of human amylin, or combined human amylin and apolipoprotein E4, showed that amylin binds to plasma apolipoproteins. The intravenous infusion of apolipoprotein E4 exacerbated the brain accumulation of aggregated amylin and vascular pathology in HIP rats.

INTERPRETATION

These data identify vascular amylin deposition as a trigger of brain endothelial dysfunction that is modulated by plasma apolipoproteins and represents a potential therapeutic target in diabetes-associated dementia and stroke. Ann Neurol 2017;82:208-222.

Heterologous prion-forming proteins interact to cross-seed aggregation in Saccharomyces cerevisiae

The early stages of protein misfolding remain incompletely understood, as most mammalian proteinopathies are only detected after irreversible protein aggregates have formed. Cross-seeding, where one aggregated protein templates the misfolding of a heterologous protein, is one mechanism proposed to stimulate protein aggregation and facilitate disease pathogenesis. Here, we demonstrate the existence of cross-seeding as a crucial step in the formation of the yeast prion [PSI ⁺], formed by the translation termination factor Sup35. We provide evidence for the genetic and physical interaction of the prion protein Rnq1 with Sup35 as a predominant mechanism leading to self-propagating Sup35 aggregation. We identify interacting sites within Rnq1 and Sup35 and determine the effects of breaking and restoring a crucial interaction. Altogether, our results demonstrate that single-residue disruption can drastically reduce the effects of cross-seeding, a finding that has important implications for human protein misfolding disorders.

Amylin Receptor: A Potential Therapeutic Target for Alzheimer's Disease

Alzheimer'sdisease (AD) is a progressive neurodegenerative disorder, characterized by senile plaques constituting extracellular deposits of β-amyloid (Aβ) fibrils. Since Aβ accumulation in the brain is considered an early event preceding, by decades, cognitive dysfunction, disease-modifying treatments are aimed at facilitating clearance of this protein from the brain or ameliorating its toxic effects. Recent studies have identified the amylin receptor as a capable mediator of the deleterious actions of Aβ and furthermore, administration of amylin receptor-based peptides has been shown to improve spatial memory and learning in transgenic mouse models of AD. Here, by discussing available evidence, we posit that the amylin receptor could be considered a potential therapeutic target for AD, and present the rationale for using amylin receptor antagonists to treat this debilitating condition.

Network analysis of common genes related to esophageal, gastric, and colon cancers

AIM

The aim of this study was to provide a biomarker panel for esophageal, gastric and colorectal cancers. It can help introducing some diagnostic biomarkers for these diseases.

BACKGROUND

Gastrointestinal cancers (GICs) including esophageal, gastric and colorectal cancers are the most common cancers in the world which are usually diagnosed in the final stages and due to heterogeneity of these diseases, the treatments usually are not successful. For this reason, many studies have been conducted to discover predictive biomarkers.

METHODS

In the present study, 507 genes related to esophageal, gastric and colon cancers were extracted.. The network was constructed by Cytoscape software (version 3.4.0). Then a main component of the network was analyzed considering centrality parameters including degree, betweenness, closeness and stress. Three clusters of the protein network accompanied with their seed nodes were determined by MCODE application in Cytoscape software. Furthermore, Gene Ontology (GO) analysis of the key genes in combination to the seed nodes was performed.

RESULTS

The network of 17 common differential expressed genes in three esophageal, gastric and colon adenocarcinomas including 1730 nodes and 9188 edges were constructed. Eight crucial genes were determined. Three Clusters of the network were analyzed by GO analysis.

CONCLUSION

The analyses of common genes of the three cancers showed that there are some common crucial genes including TP53, EGFR, MYC, AKT1, CDKN2A, CCND1 and HSP90AA1 which are tightly related to gastrointestinal cancers and can be predictive biomarkers for these cancers.