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.

Soft-Lithographic Patterning of Luminescent Carbon Nanodots Derived from Collagen Waste

Luminescent carbon dots (Cdots) synthesized using inexpensive precursors have inspired tremendous research interest because of their superior properties and applicability in various fields. In this work, we report a simple, economical, green route for the synthesis of multifunctional fluorescent Cdots prepared from a natural, low-cost source: collagen extracted from animal skin wastes. The as-synthesized metal-free Cdots were found to be in the size range of ∼1.2-9 nm, emitting bright blue photoluminescence with a calculated Cdot yield of ∼63%. Importantly, the soft-lithographic method used was inexpensive and yielded a variety of Cdot patterns with different geometrical structures and significant cellular biocompatibility. This novel approach to Cdot production highlights innovative ways of transforming industrial biowastes into advanced multifunctional materials which offer exciting potential for applications in nanophotonics and nanobiotechnology using a simple and scalable technique.

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.

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

Numerous epidemiological studies have shown a significantly higher risk for development of Alzheimer's disease (AD) in patients affected by type 2 diabetes (T2D), but the molecular mechanism responsible for this association is presently unknown. Both diseases are considered protein misfolding disorders associated with the accumulation of protein aggregates; amyloid-beta (Aβ) and tau in the brain during AD, and islet amyloid polypeptide (IAPP) in pancreatic islets in T2D. Formation and accumulation of these proteins follows a seeding-nucleation model, where a misfolded aggregate or 'seed' promotes the rapid misfolding and aggregation of the native protein. Our underlying hypothesis is that misfolded IAPP produced in T2D potentiates AD pathology by cross-seeding Aβ, providing a molecular explanation for the link between these diseases. Here, we examined how misfolded IAPP affects Aβ aggregation and AD pathology in vitro and in vivo. We observed that addition of IAPP seeds accelerates Aβ aggregation in vitro in a seeding-like manner and the resulting fibrils are composed of both peptides. Transgenic animals expressing both human proteins exhibited exacerbated AD-like pathology compared with AD transgenic mice or AD transgenic animals with type 1 diabetes (T1D). Remarkably, IAPP colocalized with amyloid plaques in brain parenchymal deposits, suggesting that these peptides may directly interact and aggravate the disease. Furthermore, inoculation of pancreatic IAPP aggregates into the brains of AD transgenic mice resulted in more severe AD pathology and significantly greater memory impairments than untreated animals. These data provide a proof-of-concept for a new disease mechanism involving the interaction of misfolded proteins through cross-seeding events which may contribute to accelerate or exacerbate disease pathogenesis. Our findings could shed light on understanding the linkage between T2D and AD, two of the most prevalent protein misfolding disorders.

Interleukin33 deficiency causes tau abnormality and neurodegeneration with Alzheimer-like symptoms in aged mice

This corrects the article DOI: 10.1038/tp.2017.142.

Induction of IAPP amyloid deposition and associated diabetic abnormalities by a prion-like mechanism

In this article, Mukherjee et al. show that the pathologic and clinical alterations of type 2 diabetes can be induced in vitro and in vivo by prion-like transmission of IAPP misfolded aggregates, supporting an important role for IAPP aggregation in the disease.

Although a large proportion of patients with type 2 diabetes (T2D) accumulate misfolded aggregates composed of the islet amyloid polypeptide (IAPP), its role in the disease is unknown. Here, we show that pancreatic IAPP aggregates can promote the misfolding and aggregation of endogenous IAPP in islet cultures obtained from transgenic mouse or healthy human pancreas. Islet homogenates immunodepleted with anti-IAPP–specific antibodies were not able to induce IAPP aggregation. Importantly, intraperitoneal inoculation of pancreatic homogenates containing IAPP aggregates into transgenic mice expressing human IAPP dramatically accelerates IAPP amyloid deposition, which was accompanied by clinical abnormalities typical of T2D, including hyperglycemia, impaired glucose tolerance, and a substantial reduction on β cell number and mass. Finally, induction of IAPP deposition and diabetic abnormalities were also induced in vivo by administration of IAPP aggregates prepared in vitro using pure, synthetic IAPP. Our findings suggest that some of the pathologic and clinical alterations of T2D might be transmissible through a similar mechanism by which prions propagate in prion diseases.

The Endoplasmic Reticulum Chaperone GRP78/BiP Modulates Prion Propagation in vitro and in vivo

Prion diseases are fatal neurodegenerative disorders affecting several mammalian species, characterized by the accumulation of the misfolded form of the prion protein, which is followed by the induction of endoplasmic reticulum (ER) stress and the activation of the unfolded protein response (UPR). GRP78, also called BiP, is a master regulator of the UPR, reducing ER stress levels and apoptosis due to an enhancement of the cellular folding capacity. Here, we studied the role of GRP78 in prion diseases using several in vivo and in vitro approaches. Our results show that a reduction in the expression of this molecular chaperone accelerates prion pathogenesis in vivo. In addition, we observed that prion replication in cell culture was inversely related to the levels of expression of GRP78 and that both proteins interact in the cellular context. Finally, incubation of PrP^Sc with recombinant GRP78 led to the dose-dependent reduction of protease-resistant PrP^Scin vitro. Our results uncover a novel role of GRP78 in reducing prion pathogenesis, suggesting that modulating its levels/activity may offer a novel opportunity for designing therapeutic approaches for these diseases. These findings may also have implications for other diseases involving the accumulation of misfolded proteins.

Amyloid-beta and tau pathology following repetitive mild traumatic brain injury

Neurodegenerative diseases are characterized by distinctive neuropathological alterations, including the cerebral accumulation of misfolded protein aggregates, neuroinflammation, synaptic dysfunction, and neuronal loss, along with behavioral impairments. Traumatic brain injury (TBI) is believed to be an important risk factor for certain neurodegenerative diseases, such as Alzheimer's disease (AD) and chronic traumatic encephalopathy (CTE). TBI represents a ubiquitous problem in the world and could play a major role in the pathogenesis and etiology of AD or CTE later in life. TBI events appear to trigger and exacerbate some of the pathological processes in these diseases, in particular, the formation and accumulation of misfolded protein aggregates composed of amyloid-beta (Aβ) and tau. Here, we describe the relationship between repetitive mild TBI and the development of Aβ and tau pathology in patients affected by AD or CTE on the basis of epidemiological and pathological studies in human cases, and a thorough overview of data obtained in experimental animal models. We also discuss the possibility that TBI may contribute to initiate the formation of misfolded oligomeric species that may subsequently spread the pathology through a prion-like process of seeding of protein misfolding.

Role of Prion Replication in the Strain-dependent Brain Regional Distribution of Prions

One intriguing feature of prion diseases is their strain variation. Prion strains are differentiated by the clinical consequences they generate in the host, their biochemical properties, and their potential to infect other animal species. The selective targeting of these agents to specific brain structures have been extensively used to characterize prion strains. However, the molecular basis dictating strain-specific neurotropism are still elusive. In this study, isolated brain structures from animals infected with four hamster prion strains (HY, DY, 139H, and SSLOW) were analyzed for their content of protease-resistant PrP(Sc) Our data show that these strains have different profiles of PrP deposition along the brain. These patterns of accumulation, which were independent of regional PrP(C) production, were not reproduced by in vitro replication when different brain regions were used as substrate for the misfolding-amplification reaction. On the contrary, our results show that in vitro replication efficiency depended exclusively on the amount of PrP(C) present in each part of the brain. Our results suggest that the variable regional distribution of PrP(Sc) in distinct strains is not determined by differences on prion formation, but on other factors or cellular pathways. Our findings may contribute to understand the molecular mechanisms of prion pathogenesis and strain diversity.

Amyloid-β reduces the expression of neuronal FAIM-L, thereby shifting the inflammatory response mediated by TNFα from neuronal protection to death

The brains of patients with Alzheimer's disease (AD) present elevated levels of tumor necrosis factor-α (TNFα), a cytokine that has a dual function in neuronal cells. On one hand, TNFα can activate neuronal apoptosis, and on the other hand, it can protect these cells against amyloid-β (Aβ) toxicity. Given the dual behavior of this molecule, there is some controversy regarding its contribution to the pathogenesis of AD. Here we examined the relevance of the long form of Fas apoptotic inhibitory molecule (FAIM) protein, FAIM-L, in regulating the dual function of TNFα. We detected that FAIM-L was reduced in the hippocampi of patients with AD. We also observed that the entorhinal and hippocampal cortex of a mouse model of AD (PS1_M146LxAPP_751sl) showed a reduction in this protein before the onset of neurodegeneration. Notably, cultured neurons treated with the cortical soluble fractions of these animals showed a decrease in endogenous FAIM-L, an effect that is mimicked by the treatment with Aβ-derived diffusible ligands (ADDLs). The reduction in the expression of FAIM-L is associated with the progression of the neurodegeneration by changing the inflammatory response mediated by TNFα in neurons. In this sense, we also demonstrate that the protection afforded by TNFα against Aβ toxicity ceases when endogenous FAIM-L is reduced by short hairpin RNA (shRNA) or by treatment with ADDLs. All together, these results support the notion that levels of FAIM-L contribute to determine the protective or deleterious effect of TNFα in neuronal cells.

Aggregate-depleted brain fails to induce Aβ deposition in a mouse model of Alzheimer's disease

Recent studies in animal models of Alzheimer's disease (AD) show that amyloid-beta (Aβ) misfolding can be transmissible; however, the mechanisms by which this process occurs have not been fully explored. The goal of this study was to analyze whether depletion of aggregates from an AD brain suppresses its in vivo "seeding" capability. Removal of aggregates was performed by using the Aggregate Specific Reagent 1 (ASR1) compound which has been previously described to specifically bind misfolded species. Our results show that pre-treatment with ASR1-coupled magnetic beads reduces the in vivo misfolding inducing capability of an AD brain extract. These findings shed light respect to the active principle responsible for the prion-like spreading of Alzheimer's amyloid pathology and open the possibility of using seeds-capturing reagents as a promising target for AD treatment.

Brains from non-Alzheimer's individuals containing amyloid deposits accelerate Aβ deposition in vivo

Background

One of the main features of Alzheimer’s disease (AD) is the presence of Aβ deposits, which accumulate in the brain years before the onset of symptoms. We and others have demonstrated that cerebral Aβ-amyloidosis can be induced in vivo by administration of AD-brain extracts into transgenic mice. However, it is currently unknown whether amyloid formation can be induced using extracts from individuals harboring Aβ deposits, but not clinical disease.

Results

In this study we analyzed the amyloid-inducing capability of samples from individuals affected by mild cognitive impairment (MCI) and Non-Demented persons with Alzheimer’s disease Neuropathology (NDAN). Our results show that inoculation of transgenic mice with MCI and NDAN brain samples accelerated Aβ pathology in a similar way as extracts from confirmed AD.

Conclusions

This data demonstrate that the sole presence of Aβ aggregates in a given sample, regardless of the clinical condition, is capable to accelerate Aβ deposition in vivo. These findings indicate that the amyloid-inducing activity may be present in the brain of people during pre-symptomatic or a-symptomatic stages of AD.

In vivo modification of Abeta plaque toxicity as a novel neuroprotective lithium-mediated therapy for Alzheimer's disease pathology

Background

Alzheimer’s disease (AD) is characterized by the abnormal accumulation of extracellular beta-amyloid (Abeta) plaques, intracellular hyperphosphorylated tau, progressive synaptic alterations, axonal dystrophies, neuronal loss and the deterioration of cognitive capabilities of patients. However, no effective disease-modifying treatment has been yet developed. In this work we have evaluated whether chronic lithium treatment could ameliorate the neuropathology evolution of our well characterized PS1M146LxAPPSwe-London mice model.

Results

Though beneficial effects of lithium have been previously described in different AD models, here we report a novel in vivo action of this compound that efficiently ameliorated AD-like pathology progression and rescued memory impairments by reducing the toxicity of Abeta plaques. Transgenic PS1M146LxAPPSwe-London mice, treated before the pathology onset, developed smaller plaques characterized by higher Abeta compaction, reduced oligomeric-positive halo and therefore with attenuated capacity to induce neuronal damage. Importantly, neuronal loss in hippocampus and entorhinal cortex was fully prevented. Our data also demonstrated that the axonal dystrophic area associated with lithium-modified plaques was highly reduced. Moreover, a significant lower accumulation of phospho-tau, LC3-II and ubiquitinated proteins was detected in treated mice. Our study highlights that this switch of plaque quality by lithium could be mediated by astrocyte activation and the release of heat shock proteins, which concentrate in the core of the plaques.

Conclusions

Our data demonstrate that the pharmacological in vivo modulation of the extracellular Abeta plaque compaction/toxicity is indeed possible and, in addition, might constitute a novel promising and innovative approach to develop a disease-modifying therapeutic intervention against AD.

Smoking exacerbates amyloid pathology in a mouse model of Alzheimer's disease

Several epidemiological studies have shown that cigarette smoking might alter the incidence of Alzheimer's disease. However, inconsistent results have been reported regarding the risk of Alzheimer's disease among smokers. Previous studies in experimental animal models have reported that administration of some cigarette components (for example, nicotine) alters amyloid-β aggregation, providing a possible link. However, extrapolation of these findings towards the in vivo scenario is not straightforward as smoke inhalation involves a number of other components. Here, we analysed the effect of smoking under more relevant conditions. We exposed transgenic mouse models of Alzheimer's disease to cigarette smoke and analysed the neuropathological alterations in comparison with animals not subjected to smoke inhalation. Our results showed that smoking increases the severity of some abnormalities typical of Alzheimer's disease, including amyloidogenesis, neuroinflammation and tau phosphorylation. Our findings suggest that cigarette smoking may increase Alzheimer's disease onset and exacerbate its features and thus, may constitute an important environmental risk factor for Alzheimer's disease.

Natural animal models of neurodegenerative protein misfolding diseases

Neurodegenerative diseases (NDs) are some of the most debilitating human illnesses. Research over the past 10 years has provided evidence for a common mechanism of neurodegeneration in which the critical event is the brain accumulation of misfolded protein aggregates. Although it is well established that misfolded proteins play an important role in these diseases, the mechanisms by which they cause cellular and tissue dysfunction are still unknown. To understand the molecular basis of NDs and to develop therapeutic strategies against them, numerous transgenic rodent models have been produced, which reproduce some (but not all) of the features of these diseases. Importantly, some NDs are not exclusive to human beings, such as transmissible spongiform encephalopathies. Moreover, other diseases which are associated to aging (e.g. Alzheimer's disease) could be studied in aged mammals, which could reproduce the human disease in a more natural way. Although the usefulness of transgenic mice is unquestionable, the information obtained from natural non-transgenic models could be very valuable to fully understand the pathogenesis of these devastating diseases.

Abnormal accumulation of autophagic vesicles correlates with axonal and synaptic pathology in young Alzheimer's mice hippocampus

Dystrophic neurites associated with amyloid plaques precede neuronal death and manifest early in Alzheimer's disease (AD). In this work we have characterized the plaque-associated neuritic pathology in the hippocampus of young (4- to 6-month-old) PS1(M146L)/APP(751SL) mice model, as the initial degenerative process underlying functional disturbance prior to neuronal loss. Neuritic plaques accounted for almost all fibrillar deposits and an axonal origin of the dystrophies was demonstrated. The early induction of autophagy pathology was evidenced by increased protein levels of the autophagosome marker LC3 that was localized in the axonal dystrophies, and by electron microscopic identification of numerous autophagic vesicles filling and causing the axonal swellings. Early neuritic cytoskeletal defects determined by the presence of phosphorylated tau (AT8-positive) and actin-cofilin rods along with decreased levels of kinesin-1 and dynein motor proteins could be responsible for this extensive vesicle accumulation within dystrophic neurites. Although microsomal Aβ oligomers were identified, the presence of A11-immunopositive Aβ plaques also suggested a direct role of plaque-associated Aβ oligomers in defective axonal transport and disease progression. Most importantly, presynaptic terminals morphologically disrupted by abnormal autophagic vesicle buildup were identified ultrastructurally and further supported by synaptosome isolation. Finally, these early abnormalities in axonal and presynaptic structures might represent the morphological substrate of hippocampal dysfunction preceding synaptic and neuronal loss and could significantly contribute to AD pathology in the preclinical stages.

Misfolded protein aggregates: mechanisms, structures and potential for disease transmission

Some of the most prevalent human degenerative diseases appear as a result of the misfolding and aggregation of proteins. Compelling evidence suggest that misfolded protein aggregates play an important role in cell dysfunction and tissue damage, leading to the disease. Prion protein (Prion diseases), amyloid-beta (Alzheimer's disease), alpha-synuclein (Parkinson's disease), Huntingtin (Huntington's disease), serum amyloid A (AA amyloidosis) and islet amyloid polypeptide (type 2 diabetes) are some of the proteins that trigger disease when they get misfolded. The recent understanding of the crucial role of misfolded proteins as well as the structural requirements and mechanism of protein misfolding have raised the possibility that these diseases may be transmissible by self-propagation of the protein misfolding process in a similar way as the infamous prions transmit prion diseases. Future research in this field should aim to clarify this possibility and translate the knowledge of the basic disease mechanisms into development of novel strategies for early diagnosis and efficient treatment.

Calretinin interneurons are early targets of extracellular amyloid-beta pathology in PS1/AbetaPP Alzheimer mice hippocampus

Specific neuronal networks are preferentially affected in the early stages of Alzheimer's disease (AD). The distinct subpopulations of hippocampal inhibitory GABAergic system have been shown to display differential vulnerability to neurodegeneration in AD. We have previously reported a substantial loss of SOM/NPY interneurons, whereas those expressing parvalbumin were unaltered, in the hippocampus of 6 month-old PS1/AbetaPP transgenic mice. In the present study, we now investigated the pathological changes of hippocampal calretinin (CR) interneurons in this PS1/AbetaPP model from 2 to 12 months of age. The total number of CR-immunoreactive inhibitory cells was determined by stereology in CA1 and CA2/3 subfields. Our findings show a substantial decrease (35%-45%) of CR-positive interneurons in both hippocampal subfields of PS1/AbetaPP mice at very early age (4 months) compared to age-matched control mice. This decrease was accompanied by a reduced CR mRNA content as determined by quantitative RT-PCR. However, the number of another hippocampal CR-positive population (belonging to Cajal-Retzius cells) was not affected. The selective early loss of CR-interneurons was parallel to the appearance of extracellular Abeta deposits, preferentially in CR-axonal fields, and the formation of dystrophic neurites. This specific GABAergic subpopulation plays a crucial role in the generation of synchronous rhythmic activity in hippocampus by controlling other interneurons. Therefore, early alterations of hippocampal inhibitory functionality in AD, caused by select CR-cells neurodegeneration, could result in cognitive impairments seen in initial stages of the disease.

Extracellular amyloid-beta and cytotoxic glial activation induce significant entorhinal neuron loss in young PS1(M146L)/APP(751SL) mice

Here we demonstrated that extracellular, not intracellular, amyloid-beta (Abeta) and the associated cytotoxic glial neuroinflammatory response are major contributors to early neuronal loss in a PS1xAPP model. A significant loss of principal (27%) and SOM/NPY (56-46%) neurons was found in the entorhinal cortex at 6 months of age. Loss of principal cells occurred selectively in deep layers (primarily layer V) whereas SOM/NPY cell loss was evenly distributed along the cortical column. Neither layer V pyramidal neurons nor SOM/NPY interneurons displayed intracellular Abeta immunoreactivity, even after formic acid retrieval; thus, extracellular factors should be preferentially implicated in this selective neurodegeneration. Amyloid deposits were mainly concentrated in deep layers at 4-6 months, and of relevance was the existence of a potentially cytotoxic inflammatory response (TNFalpha, TRAIL, and iNOS mRNAs were upregulated). Moreover, non-plaque associated activated microglial cells and reactive astrocytes expressed TNFalpha and iNOS, respectively. At this age, in the hippocampus of same animals, extracellular Abeta induced a non-cytotoxic glial activation. The opposite glial activation, at the same chronological age, in entorhinal cortex and hippocampus strongly support different mechanisms of disease progression in these two regions highly affected by Abeta pathology.

Inter-individual variability in the expression of the mutated form of hPS1M146L determined the production of Abeta peptides in the PS1xAPP transgenic mice

The detection of the early phenotypic modifications of Alzheimer's disease (AD) models is fundamental to understand the progression and identify pharmacologic targets of this pathology. However, a large variability within different models and between age-matched mice from the same model has been observed. This variability could be due to heterogeneity in the Abeta production. Present results showed the existence of a large variability in the Abeta deposition in both hippocampus and cortex in 6-month-old PS1xAPP mice. This variability was not due to the expression of hAPP751SL, however, linear relationship between hPS1M146L mRNA and Abeta production was identified. The Abeta content was related to the incorporation of the hPS1M146L into functional gamma-secretase complexes, detected by the presence of the corresponding human or endogenous PS1-CTFs. Animals expressing low amount of hPS1M146L mRNA, displayed low hPS1-CTF incorporation and produced a low amount of Abeta peptides. Conversely, mice with relatively high hPS1 mRNA expression displayed high hPS1-CTF and high Abeta deposition. Furthermore, the Abeta total and Abeta1-42 content was increased dramatically by the expression of hPS1M146L (as compared with transgenic APPsl littermates). Therefore, variations in the expression of transgenic form of hPS1M146L in this model, or even between different models, influenced strongly the incorporation of the mutated PS1 into functional gamma-secretase complexes, the production of Abeta peptides and, in consequence, the detrimental effects of Abeta peptides. These data might implicate an "apparent gain-of-function" of the gamma-secretase complex by the expression of the mutated PS1M146L.