Diffusion Tensor Imaging for Assessing Brain Gray and White Matter Abnormalities in a Feline Model of α-Mannosidosis

Widespread correction of brain pathology in feline alpha-mannosidosis by dose escalation of intracisternal AAV vector injection

Alpha-mannosidosis is caused by a genetic deficiency of lysosomal alpha-mannosidase, leading to the widespread presence of storage lesions in the brain and other tissues. Enzyme replacement therapy is available but is not approved for treating the CNS, since the enzyme does not penetrate the blood-brain barrier. However, intellectual disability is a major manifestation of the disease; thus, a complimentary treatment is needed. While enzyme replacement therapy into the brain is technically feasible, it requires ports and frequent administration over time that are difficult to manage medically. Infusion of adeno-associated viral vectors into the cerebrospinal fluid is an attractive route for broadly targeting brain cells. We demonstrate here the widespread post-symptomatic correction of the globally distributed storage lesions by infusion of a high dose of AAV1-feline alpha-mannosidase (fMANB) into the CSF via the cisterna magna in the gyrencephalic alpha-mannosidosis cat brain. Significant improvements in clinical parameters occurred, and widespread global correction was documented pre-mortem by non-invasive magnetic resonance imaging. Postmortem analysis demonstrated high levels of MANB activity and reversal of lysosomal storage lesions throughout the brain. Thus, CSF treatment by adeno-associated viral vector gene therapy appears to be a suitable complement to systemic enzyme replacement therapy to potentially treat the whole patient.

Investigated regional apparent diffusion coefficient values of the morphologically normal feline brain

OBJECTIVES

Diffusion-weighted imaging (DWI) MRI is increasingly available in veterinary medicine for investigation of the brain. However, apparent diffusion coefficient (ADC) values have only been reported in a small number of cats or in research settings. The aim of this study was to investigate the ADC values of different anatomical regions of the morphologically normal brain in a feline patient population. Additionally, we aimed to assess the possible influence on the ADC values of different patient-related factors, such as sex, body weight, age, imaging of the left and right side of the cerebral hemispheres and white vs grey matter regions.

METHODS

This retrospective study included cats undergoing an MRI (3T) examination with DWI sequences of the head at the Vetsuisse Faculty of the University Zurich between 2015 and 2021. Only cats with morphologically normal brains were included. On the ADC maps, 10 regions of interest (ROIs) were manually drawn on the following anatomical regions: caudate nucleus; internal capsule (two locations); piriform lobe; thalamus; hippocampus; cortex cerebri (two locations); cerebellar hemisphere; and one ROI in the centre of the cerebellar vermis. Except for the ROI at the cerebellar vermis, each ROI was drawn in the left and right hemisphere. The ADC values were calculated by the software and recorded.

RESULTS

A total of 129 cats were included in this study. The ADC varied in the different ROIs, with the highest mean ADC value in the hippocampus and the lowest in the cerebellar hemisphere. ADC was significantly lower in the white cerebral matter compared with the grey matter. ADC values were not influenced by age, with the exception of the hippocampus and the cingulate gyrus.

CONCLUSION AND RELEVANCE

ADC values of different anatomical regions of the morphologically normal feline brain in a patient population of 129 cats in a clinical setting are reported for the first time.

Early life adversity in male mice sculpts reward circuits

Early life adversity (ELA) comprises a wide variety of negative experiences during early life and has been linked to cognitive impairments, reduced experiences of pleasure (anhedonia), and other long-term consequences implying that ELA impacts the reward circuitry. In this study, we focused on the projections from the dorsal raphe (DR) to the ventral tegmental area (VTA) and on to the nucleus accumbens (NAcc), an important pathway within the reward circuit. We hypothesized that ELA alters connectivity within the DR-VTA-NAcc pathway, associated with deficient reward seeking behaviors in adulthood. We used the limited bedding and nesting model to induce ELA in mice and measured reward-related behaviors in adulthood using the three-chamber social interaction and sucrose preference tests. High resolution ex vivo diffusion tensor imaging (DTI) was acquired and processed for regional DTI metrics, including tractography to assess circuit organization. We found brain-wide changes in radial diffusivity (RD) and altered connectivity of the reward circuit in the ELA group. DR-VTA-NAcc circuit tractography and axial diffusivity (AD) along this tract exhibited dispersed organization where AD was increased in the VTA segment. Behaviorally, ELA elicited a social anhedonia-like phenotype in adulthood with decreased direct social approach and time spent with peers in the three-chamber task, and no overt differences in sucrose preference. Our findings suggest that reward circuits, assessed using DTI, are altered following ELA and that these changes may reflect enduring reward deficits.

Tacrolimus Protects against Age-Associated Microstructural Changes in the Beagle Brain

The overexpression of calcineurin leads to astrocyte hyperactivation, neuronal death, and inflammation, which are characteristics often associated with pathologic aging and Alzheimer's disease. In this study, we tested the hypothesis that tacrolimus, a calcineurin inhibitor, prevents age-associated microstructural atrophy, which we measured using higher-order diffusion MRI, in the middle-aged beagle brain (n = 30, male and female). We find that tacrolimus reduces hippocampal (p = 0.001) and parahippocampal (p = 0.002) neurite density index, as well as protects against an age-associated increase in the parahippocampal (p = 0.007) orientation dispersion index. Tacrolimus also protects against an age-related decrease in fractional anisotropy in the prefrontal cortex (p < 0.0001). We also show that these microstructural alterations precede cognitive decline and gross atrophy. These results support the idea that calcineurin inhibitors may have the potential to prevent aging-related pathology if administered at middle age.SIGNIFICANCE STATEMENT Hyperactive calcineurin signaling causes neuroinflammation and other neurobiological changes often associated with pathologic aging and Alzheimer's disease (AD). Controlling the expression of calcineurin before gross cognitive deficits are observable might serve as a promising avenue for preventing AD pathology. In this study, we show that the administration of the calcineurin inhibitor, tacrolimus, over 1 year prevents age- and AD-associated microstructural changes in the hippocampus, parahippocampal cortex, and prefrontal cortex of the middle-aged beagle brain, with no noticeable adverse effects. Tacrolimus is already approved by the Food and Drug Administration for use in humans to prevent solid organ transplant rejection, and our results bolster the promise of this drug to prevent AD and aging-related pathology.

White matter alteration and cerebellar atrophy are hallmarks of brain MRI in alpha-mannosidosis

OBJECTIVE

Despite profound neurological symptomatology there are only few MRI studies focused on the brain abnormalities in alpha-mannosidosis (AM). Our aim was to characterize brain MRI findings in a large cohort of AM patients along with clinical manifestations.

METHODS

Twenty-two brain MRIs acquired in 13 untreated AM patients (8 M/5F; median age 17 years) were independently assessed by three experienced readers and compared to 16 controls.

RESULTS

Focal and/or diffuse hyperintense signals in the cerebral white matter were present in most (85%) patients. Cerebellar atrophy was common (62%), present from the age of 5 years. Progression was observed in two out of 6 patients with follow-up scans. Cortical atrophy (62%) and corpus callosum thinning (23%) were already present in a 13-month-old child. The presence of low T₂ signal intensity in basal ganglia and thalami was excluded by the normalized signal intensity profiling. The enlargement of perivascular spaces in white matter (38%), widening of perioptic CSF spaces (62%), and enlargement of cisterna magna (85%) were also observed. Diploic space thickening (100%), mucosal thickening (69%) and sinus hypoplasia (54%) were the most frequent non-CNS abnormalities.

CONCLUSION

White matter changes and cerebellar atrophy are proposed to be the characteristic brain MRI features of AM. The previously reported decreased T₂ signal intensity in basal ganglia and thalami was not detected in this quantitative study. Rather, this relative MR appearance seems to be related to the diffuse high T₂ signal in the adjacent white matter and not the gray matter iron deposition that has been hypothesized.

Global CNS correction in a large brain model of human alpha-mannosidosis by intravascular gene therapy

Intravascular injection of certain adeno-associated virus vector serotypes can cross the blood-brain barrier to deliver a gene into the CNS. However, gene distribution has been much more limited within the brains of large animals compared to rodents, rendering this approach suboptimal for treatment of the global brain lesions present in most human neurogenetic diseases. The most commonly used serotype in animal and human studies is 9, which also has the property of being transported via axonal pathways to distal neurons. A small number of other serotypes share this property, three of which were tested intravenously in mice compared to 9. Serotype hu.11 transduced fewer cells in the brain than 9, rh8 was similar to 9, but hu.32 mediated substantially greater transduction than the others throughout the mouse brain. To evaluate the potential for therapeutic application of the hu.32 serotype in a gyrencephalic brain of larger mammals, a hu.32 vector expressing the green fluorescent protein reporter gene was evaluated in the cat. Transduction was widely distributed in the cat brain, including in the cerebral cortex, an important target since mental retardation is an important component of many of the human neurogenetic diseases. The therapeutic potential of a hu.32 serotype vector was evaluated in the cat homologue of the human lysosomal storage disease alpha-mannosidosis, which has globally distributed lysosomal storage lesions in the brain. Treated alpha-mannosidosis cats had reduced severity of neurological signs and extended life spans compared to untreated cats. The extent of therapy was dose dependent and intra-arterial injection was more effective than intravenous delivery. Pre-mortem, non-invasive magnetic resonance spectroscopy and diffusion tensor imaging detected differences between the low and high doses, and showed normalization of grey and white matter imaging parameters at the higher dose. The imaging analysis was corroborated by post-mortem histological analysis, which showed reversal of histopathology throughout the brain with the high dose, intra-arterial treatment. The hu.32 serotype would appear to provide a significant advantage for effective treatment of the gyrencephalic brain by systemic adeno-associated virus delivery in human neurological diseases with widespread brain lesions.

Large animal models contribute to the development of therapies for central and peripheral nervous system dysfunction in patients with lysosomal storage diseases

Lysosomal storage diseases (LSDs) are a group of 70 monogenic disorders characterized by the lysosomal accumulation of a substrate. As a group, LSDs affect ~1 in 5000 live births; however, each individual storage disease is rare, limiting the ability to perform natural history studies or to perform clinical trials. Perhaps in no other biomedical field have naturally occurring large animal (canine, feline, ovine, caprine, and bovine) models been so essential for understanding the fundamentals of disease pathogenesis and for developing safe and effective therapies. These models were critical for the development of hematopoietic stem cell transplantation in α- and β- mannosidosis, fucosidosis, and the mucopolysaccharidoses; enzyme replacement therapy for fucosidosis, the mucopolysaccharidoses, and neuronal ceroid lipofuscinosis; and small molecule therapy in Niemann-Pick type C disease. However, their most notable contributions to the biomedical field are in the development of gene therapy for LSDs. Adeno-associated viral vectors to treat nervous system disease have been evaluated in the large animal models of α-mannosidosis, globoid cell leukodystrophy, GM1 and GM2 gangliosidosis, the mucopolysaccharidoses, and neuronal ceroid lipofuscinosis. This review article will summarize the large animal models available for study as well as their contributions to the development of central and peripheral nervous system dysfunction in LSDs.

Stereotaxic Diffusion Tensor Imaging White Matter Atlas for the in vivo Domestic Feline Brain

The cat brain is a useful model for neuroscientific research and with the increasing use of advanced neuroimaging techniques there is a need for an open-source stereotaxic white matter brain atlas to accompany the cortical gray matter atlas, currently available. A stereotaxic white matter atlas would facilitate anatomic registration and segmentation of the white matter to aid in lesion localization or standardized regional analysis of specific regions of the white matter. In this article, we document the creation of a stereotaxic feline white matter atlas from diffusion tensor imaging (DTI) data obtained from a population of eight mesaticephalic felines. Deterministic tractography reconstructions were performed to create tract priors for the major white matter projections of Corpus callosum (CC), fornix, cingulum, uncinate, Corona Radiata (CR), Corticospinal tract (CST), inferior longitudinal fasciculus (ILF), Superior Longitudinal Fasciculus (SLF), and the cerebellar tracts. T1-weighted, fractional anisotropy (FA), mean diffusivity (MD), radial diffusivity (RD) and axial diffusivity (AD) population maps were generated. The volume, mean tract length and mean FA, MD, AD and RD values for each tract prior were documented. A structural connectome was then created using previously published cortical priors and the connectivity metrics for all cortical regions documented. The provided white matter atlas, diffusivity maps, tract priors and connectome will be a valuable resource for anatomical, pathological and translational neuroimaging research in the feline model. Multi-atlas population maps and segmentation priors are available at Cornell’s digital repository: https://ecommons.cornell.edu/handle/1813/58775.2.

Companion animal models of neurological disease

Clinical translation of novel therapeutics that improve the survival and quality of life of patients with neurological disease remains a challenge, with many investigational drug and device candidates failing in advanced stage clinical trials. Naturally occurring inherited and acquired neurological diseases, such as epilepsy, inborn errors of metabolism, brain tumors, spinal cord injury, and stroke occur frequently in companion animals, and many of these share epidemiologic, pathophysiologic and clinical features with their human counterparts. As companion animals have a relatively abbreviated lifespan and genetic background, are immunocompetent, share their environment with human caregivers, and can be clinically managed using techniques and tools similar to those used in humans, they have tremendous potential for increasing the predictive value of preclinical drug and device studies. Here, we review comparative features of spontaneous neurological diseases in companion animals with an emphasis on neuroimaging methods and features, illustrate their historical use in translational studies, and discuss inherent limitations associated with each disease model. Integration of companion animals with naturally occurring disease into preclinical studies can complement and expand the knowledge gained from studies in other animal models, accelerate or improve the manner in which research is translated to the human clinic, and ultimately generate discoveries that will benefit the health of humans and animals.

Impact of fixation, coil, and number of excitations on diffusion tensor imaging of rat brains at 7.0 T

BACKGROUND

We sought to compare diffusion tensor imaging (DTI) parameters in vivo and ex vivo in the brain and to explore the effects of radiofrequency coil and number of excitations on ex vivo DTI parameters.

METHODS

Six Sprague-Dawley rat brains were used to obtain in vivo and ex vivo DTI maps with different coils and number of excitations. DTI parameters of white matter and grey matter including diffusivities, fractional anisotropy, and other dimensionless ratios (λ2/λ1, λ3/λ1, and λ2/λ3) were obtained from reconstruction maps. Comparisons of ex vivo signal-to-noise ratio with different coils and number of excitations were conducted.

RESULTS

Diffusivities decreased significantly after fixation in all the selected white matter and grey matter regions of interest (all at p < 0.001). The diffusivities in white matter integrity decreased more than in grey matter integrity after fixation (all at p < 0.001). The ratio of λ2/λ3 in the major brain structures changed after fixation (most at p < 0.05). There were differences in major ex vivo brain structures in DTI parameters and signal-to-noise ratio between surface coil and volume coil, and between one and four excitations (most at p < 0.05).

CONCLUSION

The impact of fixation, coil, and number of excitations on DTI parameters should be taken into consideration in clinical and experimental studies at 7.0 T.

Early detection of whole body radiation induced microstructural and neuroinflammatory changes in hippocampus: A diffusion tensor imaging and gene expression study

Ionizing radiation is known to a cause systemic inflammatory response within hours of exposure that may affect the central nervous system (CNS). The present study was carried out to look upon the influence of radiation induced systemic inflammatory response in hippocampus within 24 hr of whole body radiation exposure. A Diffusion Tensor Imaging (DTI) study was conducted in mice exposed to a 5-Gy radiation dose through a ⁶⁰ Co source operating at 2.496 Gy/min at 3 hr and 24 hr post irradiation and in sham-irradiated controls using 7 T animal MRI system. The results showed a significant decrease in Mean Diffusivity (MD), Radial Diffusivity (RD), and Axial Diffusivity (AD) in hippocampus at 24 hr compared with controls. Additionally, marked change in RD was observed at 3 hr. Increased serum C-Reactive Protein (CRP) level depicted an increased systemic/peripheral inflammation. The neuroinflammatory response in hippocampus was characterized by increased mRNA expression of IL-1β, IL-6, and Cox-2 at the 24 hr time point. Additionally, in the irradiated group, reactive astrogliosis was illustrated, with noticeable changes in GFAP expression at 24 hr. Altered diffusivity and enhanced neuroinflammatory expression in the hippocampal region showed peripheral inflammation induced changes in brain. Moreover, a negative correlation between gene expression and DTI parameters depicted a neuroinflammation induced altered microenvironment that might affect water diffusivity. The study showed that there was an influence of whole body radiation exposure on hippocampus even during the early acute phase that could be reflected in terms of neuroinflammatory response as well as microstructural changes. © 2016 Wiley Periodicals, Inc.