What we can learn from animal models about cerebral multi-morbidity

Phenotypic evaluation of a childhood-onset parkinsonism-dystonia mouse model with inherent postural abnormalities

Mouse models that replicate facets of human neurological diseases are often used at the pre-clinical stage to better understand the underlying mechanisms of a disease and test the target engagement of potential therapeutic interventions. We recently characterized a mouse model of childhood-onset parkinsonism-dystonia, a disease caused by a homozygous loss-of-function mutation in the SLC39A14 gene. The disease manifests itself phenotypically by impairments in locomotor behaviour and postural abnormalities. Our initial characterization of the model revealed that the Slc39a14^-/- mice showed altered Mn homeostasis and compromised locomotor performance in vertical pole-descending, horizontal beam-traversing, and rotarod tests (Jenkitkasemwong et al., 2018). However, some of the mice also displayed torticollis and Straub tail. In this study, we investigated whether these postural abnormalities affected the performance in the above motility tests and consequently, biased and compromised the external validity of reported abnormal locomotor profiles. Our analyses showed that the Slc39a14^-/- mice displaying torticollis and/or Straub tail had tests scores comparable to scores of their counterparts that never displayed these postural abnormalities. The z-score general index of performance revealed that the Slc39a14^-/- model presents a complex pathological motor phenotype relevant to the complexity of phenotypes identified in childhood-onset parkinsonism-dystonia.

Protein Co-Aggregation Related to Amyloids: Methods of Investigation, Diversity, and Classification

Amyloids are unbranched protein fibrils with a characteristic spatial structure. Although the amyloids were first described as protein deposits that are associated with the diseases, today it is becoming clear that these protein fibrils play multiple biological roles that are essential for different organisms, from archaea and bacteria to humans. The appearance of amyloid, first of all, causes changes in the intracellular quantity of the corresponding soluble protein(s), and at the same time the aggregate can include other proteins due to different molecular mechanisms. The co-aggregation may have different consequences even though usually this process leads to the depletion of a functional protein that may be associated with different diseases. The protein co-aggregation that is related to functional amyloids may mediate important biological processes and change of protein functions. In this review, we survey the known examples of the amyloid-related co-aggregation of proteins, discuss their pathogenic and functional roles, and analyze methods of their studies from bacteria and yeast to mammals. Such analysis allow for us to propose the following co-aggregation classes: (i) titration: deposition of soluble proteins on the amyloids formed by their functional partners, with such interactions mediated by a specific binding site; (ii) sequestration: interaction of amyloids with certain proteins lacking a specific binding site; (iii) axial co-aggregation of different proteins within the same amyloid fibril; and, (iv) lateral co-aggregation of amyloid fibrils, each formed by different proteins.

Alpha-synucleinopathies

A neurodegenerative disorder displaying an altered α-synuclein (αS) in the brain tissue is called α-synucleinopathy (αS-pathy) and incorporates clinical entities such as Parkinson disease (PD), PD with dementia, dementia with Lewy bodies, and multiple-system atrophy. Neuroradiologic techniques visualizing αS pathology in the brain or assays of αS in the cerebrospinal fluid or blood are probably available and will be implemented in the near future but currently the definite diagnosis of αS-pathy relies on a postmortem examination of the brain. Since the 1980s immunohistochemical technique based on the use of antibodies directed to proteins of interest has become a method of choice for neuropathologic diagnosis. Furthermore, since the 1990s it has been acknowledged that progressions of most neurodegenerative pathologies follow a certain predictable time-related neuroanatomic distribution. Currently, for Lewy body disease, two staging techniques are commonly used: McKeith and Braak staging. Thus, the neuropathologic diagnosis of a αS-pathy is based on detection of altered αS in the tissue and registration of the neuroanatomic distribution of this alteration in the brain. The clinicopathologic correlation is not absolute due to the quite frequent observation of incidental and concomitant αS pathology.

Comorbidities

The term comorbidities or mixed pathologies is used when brain tissue, a surgical sample, or postmortem brain displays a mixture of protein alterations or other pathologies. Most of the alterations when seen in sufficient extent are considered causative, are related to a certain clinical phenotype, i.e., when hyperphosphorylated τ (HPτ) is observed in occipital cortex concomitant with β-amyloid (Aβ), the diagnosis is Alzheimer disease (AD). When HPτ is observed in hippocampal structures in a subject with extensive and widespread α-synuclein pathology, a Lewy body disease (LBD), the HPτ pathology is considered as a concomitant alteration. There are numerous reports indicating that when "concomitant" pathologies are seen in a subject with certain neurodegenerative diseases, the clinical phenotype might be altered. In addition there are those cases where many alterations are seen in a sparse extent, but jointly they lead to a clinical syndrome. Thus today it is not sufficient to confirm a certain pathology to be seen, i.e., AD- or LBD-related; in addition the concomitant aging-related alterations have to be looked for.