Insight into the Dissociation of Behavior from Histology in Synucleinopathies and in Related Neurodegenerative Diseases

Interpretable deep learning of myelin histopathology in age-related cognitive impairment

Age-related cognitive impairment is multifactorial, with numerous underlying and frequently co-morbid pathological correlates. Amyloid beta (Aβ) plays a major role in Alzheimer's type age-related cognitive impairment, in addition to other etiopathologies such as Aβ-independent hyperphosphorylated tau, cerebrovascular disease, and myelin damage, which also warrant further investigation. Classical methods, even in the setting of the gold standard of postmortem brain assessment, involve semi-quantitative ordinal staging systems that often correlate poorly with clinical outcomes, due to imperfect cognitive measurements and preconceived notions regarding the neuropathologic features that should be chosen for study. Improved approaches are needed to identify histopathological changes correlated with cognition in an unbiased way. We used a weakly supervised multiple instance learning algorithm on whole slide images of human brain autopsy tissue sections from a group of elderly donors to predict the presence or absence of cognitive impairment (n = 367 with cognitive impairment, n = 349 without). Attention analysis allowed us to pinpoint the underlying subregional architecture and cellular features that the models used for the prediction in both brain regions studied, the medial temporal lobe and frontal cortex. Despite noisy labels of cognition, our trained models were able to predict the presence of cognitive impairment with a modest accuracy that was significantly greater than chance. Attention-based interpretation studies of the features most associated with cognitive impairment in the top performing models suggest that they identified myelin pallor in the white matter. Our results demonstrate a scalable platform with interpretable deep learning to identify unexpected aspects of pathology in cognitive impairment that can be translated to the study of other neurobiological disorders.

Adiponectin Paradox as a Therapeutic Target in Alzheimer's Disease

Despite the apparent neurotoxicity of amyloid-β (Aβ), recent clinical trials of Aβ immunotherapy have not shown any clinical benefit in Alzheimer’s disease (AD). Given this, clarification of the next generation therapeutic strategy in AD is warranted. Hypothetically, adiponectin might be involved in promoting amyloidogenic evolvability in reproduction, which may result in the adiponectin paradox through antagonistic pleiotropy mechanism in aging, leading to AD. Accordingly, preventing the adiponectin paradox by suppressing adiponectin signaling might prove therapeutic in AD.

Evolvability and Neurodegenerative Disease: Antagonistic Pleiotropy Phenomena Derived from Amyloid Aggregates

At present, the precise physiological role of neurodegenerative disease-related amyloidogenic proteins (APs), including α-synuclein in Parkinson’s disease and β-amyloid in Alzheimer’s disease, remains unclear. Because of similar adaptability of both human brain neurons and yeast cells to diverse environmental stressors, we previously proposed that the concept of evolvability in yeast prion could also be applied to APs in human brain. However, the mechanistic relevance of evolvability to neurodegenerative disorders is elusive. Therefore, our objective is to discuss our hypothesis that evolvability and neurodegenerative disease may represent a form of antagonistic pleiotropy derived from the aggregates of APs. Importantly, such a perspective may provide an outlook of the entire course of sporadic neurodegenerative diseases.

Dual-therapy strategy for modification of adiponectin receptor signaling in aging-associated chronic diseases

Given the paradigm of anti-insulin resistance in therapies for metabolic syndrome, there has been considerable interest in adiponectin (APN), an adipocyte-derived sensitizer of insulin receptor signaling. In contrast to hypoadiponectinemia in metabolic syndrome, evidence suggests that Alzheimer's disease (AD) and other diseases, including chronic heart failure (CHF) and chronic kidney disease (CKD), are characterized by hyperadiponectinemia as well as the APN/obesity paradoxes, indicating that a decrease in APN might also be beneficial for these diseases. Thus, distinct from metabolic syndrome, it is anticipated that APN receptor antagonists rather than agonists might be effective in therapy for some chronic diseases.

Evolvability of Amyloidogenic Proteins in Human Brain

Currently, the physiological roles of amyloidogenic proteins (APs) in human brain, such as amyloid-β and α-synuclein, are elusive. Given that many APs arose by gene duplication and have been resistant against the pressures of natural selection, APs may be associated with some functions that are advantageous for survival of offspring. Nonetheless, evolvability is the sole physiological quality of APs that has been characterized in microorganisms such as yeast. Since yeast and human brain may share similar strategies in coping with diverse range of critical environmental stresses, the objective of this paper was to discuss the potential role of evolvability of APs in aging-associated neurodegenerative disorders, including Alzheimer's disease and Parkinson's disease. Given the heterogeneity of APs in terms of structure and cytotoxicity, it is argued that APs might be involved in preconditioning against diverse stresses in human brain. It is further speculated that these stress-related APs, most likely protofibrillar forms, might be transmitted to offspring via the germline, conferring preconditioning against forthcoming stresses. Thus, APs might represent a vehicle for the inheritance of the acquired characteristics against environmental stresses. Curiously, such a characteristic of APs is reminiscent of Charles Darwin's 'gemmules', imagined molecules of heritability described in his pangenesis theory. We propose that evolvability might be a physiological function of APs during the reproductive stage and neurodegenerative diseases could be a by-product effect manifested later in aging. Collectively, our evolvability hypothesis may play a complementary role in the pathophysiology of APs with the conventional amyloid cascade hypothesis.

Critical appraisal of pathology transmission in the α-synuclein fibril model of Lewy body disorders

Lewy body disorders are characterized by the emergence of α-synucleinopathy in many parts of the central and peripheral nervous systems, including in the telencephalon. Dense α-synuclein+ pathology appears in regio inferior of the hippocampus in both Parkinson's disease and dementia with Lewy bodies and may disturb cognitive function. The preformed α-synuclein fibril model of Parkinson's disease is growing in use, given its potential for seeding the self-propagating spread of α-synucleinopathy throughout the mammalian brain. Although it is often assumed that the spread occurs through neuroanatomical connections, this is generally not examined vis-à-vis the uptake and transport of tract-tracers infused at precisely the same stereotaxic coordinates. As the neuronal connections of the hippocampus are historically well defined, we examined the first-order spread of α-synucleinopathy three months following fibril infusions centered in the mouse regio inferior (CA2+CA3), and contrasted this to retrograde and anterograde transport of the established tract-tracers FluoroGold and biotinylated dextran amines (BDA). Massive hippocampal α-synucleinopathy was insufficient to elicit memory deficits or loss of cells and synaptic markers in this model of early disease processes. However, dense α-synuclein+ inclusions in the fascia dentata were negatively correlated with memory capacity. A modest compensatory increase in synaptophysin was evident in the stratum radiatum of cornu Ammonis in fibril-infused animals, and synaptophysin expression correlated inversely with memory function in fibril but not PBS-infused mice. No changes in synapsin I/II expression were observed. The spread of α-synucleinopathy was somewhat, but not entirely consistent with FluoroGold and BDA axonal transport, suggesting that variables other than innervation density also contribute to the materialization of α-synucleinopathy. For example, layer II entorhinal neurons of the perforant pathway exhibited somal α-synuclein+ inclusions as well as retrogradely labeled FluoroGold+ somata. However, some afferent brain regions displayed dense retrograde FluoroGold label and no α-synuclein+ inclusions (e.g. medial septum/diagonal band), supporting the selective vulnerability hypothesis. The pattern of inclusions on the contralateral side was consistent with specific spread through commissural connections (e.g. stratum pyramidale of CA3), but again, not all commissural projections exhibited α-synucleinopathy (e.g. hilar mossy cells). The topographical extent of inclusions is displayed here in high-resolution images that afford viewers a rich opportunity to dissect the potential spread of pathology through neural circuitry. Finally, the results of this expository study were leveraged to highlight the challenges and limitations of working with preformed α-synuclein fibrils.

Importance of adiponectin activity in the pathogenesis of Alzheimer's disease

A recent study suggested that insulin resistance may play a central role in the pathogenesis of Alzheimer's disease (AD). In this regard, it is of note that upregulation of plasma adiponectin (APN), a benign adipokine that sensitizes the insulin receptor signaling pathway and suppresses inflammation, has recently been associated with the severities of amyloid deposits and cognitive deficits in the elderly, suggesting that APN may enhance the risk of AD. These results are unanticipated because AD has been linked to type II diabetes and other metabolic disorders in which hypoadiponectinemia has been firmly established, and because APN ameliorated neuropathological features in a mouse model of neurodegeneration. Therefore, the objective of this study is to discuss the possible mechanisms underlying the biological actions of APN in the context of AD. Given that insulin receptor signaling is required for normal function of the nervous system, we predict that APN may be upregulated to compensate for compromised activity of the insulin receptor signaling pathway. However, increased APN might be sequestered by tau in the brain, leading to neurotoxic protein aggregation in AD. Alternatively, misfolding of APN may result in downregulation of the insulin/APN signal transduction network, leading to decreased neuroprotective and neurotrophic activities. Thus, it is possible that both ‘gain of function’ and ‘loss of function’ of APN may underlie synaptic dysfunction and neuronal cell death in AD. Such a unique biological mechanism underlying APN function in AD may require a novel therapeutic strategy that is distinct from previous treatment for metabolic disorders.

Combined immunotherapy with "anti-insulin resistance" therapy as a novel therapeutic strategy against neurodegenerative diseases

Protein aggregation is a pathological hallmark of and may play a central role in the neurotoxicity in age-associated neurodegenerative diseases, such as Alzheimer's disease and Parkinson's disease. Accordingly, inhibiting aggregation of amyloidogenic proteins, including amyloid β and α-synuclein, has been a main therapeutic target for these disorders. Among various strategies, amyloid β immunotherapy has been extensively investigated in Alzheimer's disease, followed by similar studies of α-synuclein in Parkinson's disease. Notably, a recent study of solanezumab, an amyloid β monoclonal antibody, raises hope for the further therapeutic potential of immunotherapy, not only in Alzheimer's disease, but also for other neurodegenerative disorders, including Parkinson's disease. Thus, it is expected that further refinement of immunotherapy against neurodegenerative diseases may lead to increasing efficacy. Meanwhile, type II diabetes mellitus has been associated with an increased risk of neurodegenerative disease, such as Alzheimer's disease and Parkinson's disease, and studies have shown that metabolic dysfunction and abnormalities surrounding insulin signaling may underlie disease progression. Naturally, "anti-insulin resistance" therapy has emerged as a novel paradigm in the therapy of neurodegenerative diseases. Indeed, incretin agonists, which stimulate pancreatic insulin secretion, reduce dopaminergic neuronal loss and suppress Parkinson's disease disease progression in clinical trials. Similar studies are ongoing also in Alzheimer's disease. This paper focuses on critical issues in "immunotherapy" and "anti-insulin resistance" therapy in relation to therapeutic strategies against neurodegenerative disease, and more importantly, how they might merge mechanistically at the point of suppression of protein aggregation, raising the possibility that combined immunotherapy and "anti-insulin resistance" therapy may be superior to either monotherapy.