Different Aβ43 deposition patterns in the brains of aged dogs, sea lions, and cats

Classification of amyloidosis and protein misfolding disorders in animals 2024: A review on pathology and diagnosis

Amyloidosis is a group of diseases in which proteins become amyloid, an insoluble fibrillar aggregate, resulting in organ dysfunction. Amyloid deposition has been reported in various animal species. To diagnose and understand the pathogenesis of amyloidosis, it is important to identify the amyloid precursor protein involved in each disease. Although 42 amyloid precursor proteins have been reported in humans, little is known about amyloidosis in animals, except for a few well-described amyloid proteins, including amyloid A (AA), amyloid light chain (AL), amyloid β (Aβ), and islet amyloid polypeptide-derived amyloid. Recently, several types of novel amyloidosis have been identified in animals using immunohistochemistry and mass spectrometry-based proteomic analysis. Certain species are predisposed to specific types of amyloidosis, suggesting a genetic background for its pathogenesis. Age-related amyloidosis has also emerged due to the increased longevity of captive animals. In addition, experimental studies have shown that some amyloids may be transmissible. Accurate diagnosis and understanding of animal amyloidosis are necessary for appropriate therapeutic intervention and comparative pathological studies. This review provides an updated classification of animal amyloidosis, including associated protein misfolding disorders of the central nervous system, and the current understanding of their pathogenesis. Pathologic features are presented together with state-of-the-art diagnostic methods that can be applied for routine diagnosis and identification of novel amyloid proteins in animals.

Alzheimer's Disease Neuropathological Change in Aged Non-Primate Mammals

Human brain aging is characterized by the production and deposition of β-amyloid (Aβ) in the form of senile plaques and cerebral amyloid angiopathy and the intracellular accumulation of hyper-phosphorylated tau (Hp-tau) to form neurofibrillary tangles (NFTs) and dystrophic neurites of senile plaques. The process progresses for years and eventually manifests as cognitive impairment and dementia in a subgroup of aged individuals. Aβ is produced and deposited first in the neocortex in most aged mammals, including humans; it is usually not accompanied by altered behavior and cognitive impairment. Hp-tau is less frequent than Aβ pathology, and NFTs are rare in most mammals. In contrast, NFTs are familiar from middle age onward in humans; NFTs first appear in the paleocortex and selected brain stem nuclei. NFTs precede for decades or years Aβ deposition and correlate with dementia in about 5% of individuals at the age of 65 and 25% at the age of 85. Based on these comparative data, (a) Aβ deposition is the most common Alzheimer's disease neuropathological change (ADNC) in the brain of aged mammals; (b) Hp-tau is less common, and NFTs are rare in most aged mammals; however, NFTs are the principal cytoskeletal pathology in aged humans; (c) NFT in aged humans starts in selected nuclei of the brain stem and paleocortical brain regions progressing to the most parts of the neocortex and other regions of the telencephalon; (d) human brain aging is unique among mammalian species due to the early appearance and dramatic progression of NFTs from middle age onward, matching with cognitive impairment and dementia in advanced cases; (e) neither mammalian nor human brain aging supports the concept of the amyloid cascade hypothesis.

Senile plaques and phosphorylated tau deposition in a super-aged rhesus monkey (Macaca mulatta)

The brain of a rhesus monkey that died at 43 years of age with symptoms of suspected cognitive dysfunction was analyzed. pathological analyses revealed characteristic Alzheimer's disease-related lesions: the aggregation of amyloid β (Aβ) in the form of senile plaques and phosphorylated tau proteins. We also revealed that Aβ43, which is prone to aggregation and toxicity in humans, is involved in senile plaques in the brain of the rhesus monkey, as well as several other Aβ species. Comparative studies of neuropathology using aged nonhuman primates lack behavioral descriptions compared to human medicine. This case report showed behavioral abnormalities and the detailed pathological changes that may have caused it in a super-aged rhesus monkey.

Metallothionein I/II Expression and Metal Ion Levels in Correlation with Amyloid Beta Deposits in the Aged Feline Brain

Brain aging has been correlated with high metallothionein I-II (MT-I/II) expression, iron and zinc dyshomeostasis, and Aβ deposition in humans and experimental animals. In the present study, iron and zinc accumulation, the expression of MT-I/II and Aβ42, and their potential association with aging in the feline brain were assessed. Tissue sections from the temporal and frontal grey (GM) and white (WM) matter, hippocampus, thalamus, striatum, cerebellum, and dentate nucleus were examined histochemically for the presence of age-related histopathological lesions and iron deposits and distribution. We found, using a modified Perl's/DAB method, two types of iron plaques that showed age-dependent accumulation in the temporal GM and WM and the thalamus, along with the age-dependent increment in cerebellar-myelin-associated iron. We also demonstrated an age-dependent increase in MT-I/II immunoreactivity in the feline brain. In cats over 7 years old, Aβ immunoreactivity was detected in vessel walls and neuronal somata; extracellular Aβ deposits were also evident. Interestingly, Aβ-positive astrocytes were also observed in certain cases. ICP-MS analysis of brain content regarding iron and zinc concentrations showed no statistically significant association with age, but a mild increase in iron with age was noticed, while zinc levels were found to be higher in the Mature and Senior groups. Our findings reinforce the suggestion that cats could serve as a dependable natural animal model for brain aging and neurodegeneration; thus, they should be further investigated on the basis of metal ion concentration changes and their effects on aging.

Going beyond established model systems of Alzheimer's disease: companion animals provide novel insights into the neurobiology of aging

Alzheimer's disease (AD) is characterized by brain plaques, tangles, and cognitive impairment. AD is one of the most common age-related dementias in humans. Progress in characterizing AD and other age-related disorders is hindered by a perceived dearth of animal models that naturally reproduce diseases observed in humans. Mice and nonhuman primates are model systems used to understand human diseases. Still, these model systems lack many of the biological characteristics of Alzheimer-like diseases (e.g., plaques, tangles) as they grow older. In contrast, companion animal models (cats and dogs) age in ways that resemble humans. Both companion animal models and humans show evidence of brain atrophy, plaques, and tangles, as well as cognitive decline with age. We embrace a One Health perspective, which recognizes that the health of humans is connected to those of animals, and we illustrate how such a perspective can work synergistically to enhance human and animal health. A comparative biology perspective is ideally suited to integrate insights across veterinary and human medical disciplines and solve long-standing problems in aging.