Reinald Shyti

Automatic Registration of Mass Spectrometry Imaging Data Sets to the Allen Brain Atlas

Mass spectrometry imaging holds great potential for understanding the molecular basis of neurological disease. Several key studies have demonstrated its ability to uncover disease-related biomolecular changes in rodent models of disease, even if highly localized or invisible to established histological methods. The high analytical reproducibility necessary for the biomedical application of mass spectrometry imaging means it is widely developed in mass spectrometry laboratories. However, many lack the expertise to correctly annotate the complex anatomy of brain tissue, or have the capacity to analyze the number of animals required in preclinical studies, especially considering the significant variability in sizes of brain regions. To address this issue, we have developed a pipeline to automatically map mass spectrometry imaging data sets of mouse brains to the Allen Brain Reference Atlas, which contains publically available data combining gene expression with brain anatomical locations. Our pipeline enables facile and rapid interanimal comparisons by first testing if each animals tissue section was sampled at a similar location and enabling the extraction of the biomolecular signatures from specific brain regions.

Imaging mass spectrometry to visualize biomolecule distributions in mouse brain tissue following hemispheric cortical spreading depression

MALDI mass spectrometry can simultaneously measure hundreds of biomolecules directly from tissue. Using essentially the same technique but different sample preparation strategies, metabolites, lipids, peptides and proteins can be analyzed. Spatially correlated analysis, imaging MS, enables the distributions of these biomolecular ions to be simultaneously measured in tissues. A key advantage of imaging MS is that it can annotate tissues based on their MS profiles and thereby distinguish biomolecularly distinct regions even if they were unexpected or are not distinct using established histological and histochemical methods e.g. neuropeptide and metabolite changes following transient electrophysiological events such as cortical spreading depression (CSD), which are spreading events of massive neuronal and glial depolarisations that occur in one hemisphere of the brain and do not pass to the other hemisphere , enabling the contralateral hemisphere to act as an internal control. A proof-of-principle imaging MS study, including 2D and 3D datasets, revealed substantial metabolite and neuropeptide changes immediately following CSD events which were absent in the protein imaging datasets. The large high dimensionality 3D datasets make even rudimentary contralateral comparisons difficult to visualize. Instead non-negative matrix factorization (NNMF), a multivariate factorization tool that is adept at highlighting latent features, such as MS signatures associated with CSD events, was applied to the 3D datasets. NNMF confirmed that the protein dataset did not contain substantial contralateral differences, while these were present in the neuropeptide dataset.

Migraine genes and the relation to gender.

(Headache 2011;51:880‐890)

Large-Scale Mass Spectrometry Imaging Investigation of Consequences of Cortical Spreading Depression in a Transgenic Mouse Model of Migraine

AbstractCortical spreading depression (CSD) is the electrophysiological correlate of migraine aura. Transgenic mice carrying the R192Q missense mutation in the Cacna1a gene, which in patients causes familial hemiplegic migraine type 1 (FHM1), exhibit increased propensity to CSD. Herein, mass spectrometry imaging (MSI) was applied for the first time to an animal cohort of transgenic and wild type mice to study the biomolecular changes following CSD in the brain. Ninety-six coronal brain sections from 32 mice were analyzed by MALDI-MSI. All MSI datasets were registered to the Allen Brain Atlas reference atlas of the mouse brain so that the molecular signatures of distinct brain regions could be compared. A number of metabolites and peptides showed substantial changes in the brain associated with CSD. Among those, different mass spectral features showed significant (t-test, P < 0.05) changes in the cortex, 146 and 377 Da, and in the thalamus, 1820 and 1834 Da, of the CSD-affected hemisphere of FHM1 R192Q mice. Our findings reveal CSD- and genotype-specific molecular changes in the brain of FHM1 transgenic mice that may further our understanding about the role of CSD in migraine pathophysiology. The results also demonstrate the utility of aligning MSI datasets to a common reference atlas for large-scale MSI investigations. Graphical Abstractᅟ

Mass spectrometry imaging of amino neurotransmitters: a comparison of derivatization methods and application in mouse brain tissue

The detection of small polar compounds such as amino neurotransmitters by MALDI mass spectrometry imaging has been hindered by low-detection sensitivity and background interferences. Recently, several of on-tissue chemical derivatization strategies have been independently reported that enable their detection. Here, we present a comparison between these methods, and demonstrate the visualization of the distributions of up to 23 amino metabolites in tissue. We applied this methodology to detect alterations of these compounds after inducing an experimental cortical spreading depression in mouse brain, which causes profound transient alterations in key neurotransmitters in one hemisphere and is relevant for migraine and various other neurological disorders.

EHMTI-0262. Dysregulation of inflammatory pathways in a familial hemiplegic migraine 1 mouse model after the induction of cortical spreading depression

Results Our data show that CSD induces differential expression of genes involved in inflammatory pathways in both the FHM1 and wild-type mice. However, we identified a gene set that is up-regulated upon CSD specifically in the FHM1 migraine mouse model. Genes from this gene set are involved in inflammatory and interferon-related signaling, and were often found up-regulated in immunestimulated conditions.

Corticosterone enhances CSD susceptibility via glucocorticoid receptor activation in familial hemiplegic migraine 1 Cacna1a knock-in mice

FHM1 mutant mice carrying the R192Q gain-of-function mutation in CaV2.1 (P/Q-type) calcium channels display enhanced glutamatergic transmission and increased propensity for cortical spreading depression (CSD;1,2). Corticosteroids released after stress also enhance glutamatergic transmission but the relationship between stress and migraine is not well understood.

Monitoring cortical neuronal activity and spreading depression in freely behaving familial hemiplegic migraine Cacna1a R192Q knockin mice

Experimental findings from transgenic migraine mouse models that carry a human FHM1 gain-of-function mutation in CaV2.1 (P/Q-type) calcium channels underscore the role of neuronal hyperexcitability in migraine [1,2]. However, functional data that link the excitability changes to neuronal network activity and the enhanced propensity to cortical spreading depression (CSD), the likely mechanism underlying migraine aura, are largely lacking.