Biology subjects

Huitinga, I.

Publications and source records attributed to Huitinga, I..

8 recordsLinked to original sources

bioRxiv2025

Spatially resolved mapping of monoacylglycerol lipase activity in the brain

Visualizing signaling systems in the brain with high spatial resolution is critical to understand brain function and to develop therapeutics. Especially enzymes are often regulated on the post-translational level, resulting in a disconnect between protein levels and activity. Conventional antibody-based methods have limitations, including potential cross reactivity and the inability of antibodies to discriminate between active and inactive enzyme states. Monoacylglycerol lipase (MAGL), an enzyme degrading the neuroprotective endocannabinoid 2-arachidonoylglycerol, is the target of inhibitors currently in clinical trials for the treatment of several neurological disorders. To support translational and (pre)clinical studies and fully realize the therapeutic opportunities of MAGL inhibitors, it is essential to map the spatial distribution of MAGL activity throughout the brain in both health and disease. Here, we introduce selective fluorescent activity-based probes for MAGL enabling direct visualization of its enzymatic activity in lysates, cultured cells and tissue sections. We show that oxidative stress, which inactivates MAGL through the oxidation of regulatory cysteines, reduces probe labeling, thereby validating the probes activity-dependence. Extending this approach, we developed an activity-based histology protocol to visualize MAGL activity in fresh-frozen mouse and human brain tissues. This approach revealed robust MAGL activity in astrocytes and presynaptic terminals within the mouse hippocampus, and further allows detection of MAGL activity in the human cerebral cortex. Collectively, these findings establish selective activity-based probes as powerful tools mapping MAGL activity with high spatial resolution across mammalian brain tissue.

neuroscience↗

bioRxiv2025

Reduced triacylglycerols and lipid droplets are associated with resilience to Alzheimers disease

IntroductionWhile it has become clear that alterations in lipid metabolism are associated with AD, it is unclear how they contribute to both cognitive decline and the pathophysiology of AD. MethodsWe performed lipidomics and activity-based protein profiling in the frontal cortex of control, AD and resilient donors, i.e. individuals with AD pathology without cognitive decline. Subsequently we integrated these data using multi-omics factor analysis and correlated the multi-omics profiles to disease and clinical parameters. ResultsThe most pronounced alterations in lipids were in the {omega}6-derived oxylipins, which were particularly increased in the AD patients. Both triacylglycerols (TAGs) and lipid droplets were more abundant in the AD donors compared to the resilient donors. Enzyme activities showed a similar direction in the AD and resilient donors, including decreased activity of ABHD6. Multi-omics factor analysis showed that increased oxylipins, loss of inhibitory cells, synaptic genes and genes related to the inflammatory response were associated with A{beta} plaque load in both AD and resilient donors. ConclusionOur multi-omics data show a response associated with A{beta} load shared among AD and resilient donors and, for the first time, reduced lipid droplets in resilient donors.

neuroscience↗

bioRxiv2024

Microglial states determine lesion dynamics in multiple sclerosis

Summary paragraphMultiple sclerosis (MS) is a neuroinflammatory disease of the central nervous system, characterized by demyelinating lesions 1. Lesion expansion contributes to progression and increased disability, while remyelination can recover neurological deficits. However, mechanisms driving lesion dynamics are largely unclear, hindering the development of effective therapeutics. We propose that distinct states of microglia are involved in lesion expansion and remyelination 2,3. Using Stereo-seq, an RNA capture based high-resolution spatial transcriptomics technology with single-cell resolution, on post-mortem human brain tissue, we compared mixed active/inactive lesions with lipid-laden foamy microglia with lesions containing ramified microglia. We identified distinct cellular and molecular mechanisms underlying lesion activity and remyelination, linked to microglia phenotypes and states. Lesions with foamy microglia were characterized by elevated immune activation, increased lymphocyte densities, upregulated immunoglobulin production (IGHG1, IGHG3), increased complement system activity, indication of iron dysregulation (FTL, FTH1), and increased demyelination. In contrast, lesions with ramified microglia exhibited gene expression profiles indicative of myelin stability (ABCA2, QKI) and neuro-axonal protection, fostering an environment conducive to repair and remyelination. Our findings highlight the role of microglial states in lesion expansion and repair in MS and offer promising avenues for the development of therapeutic approaches aimed at preventing MS disability progression.

neuroscience↗

bioRxiv2024

Foamy microglia link oxylipins to disease progression in multiple sclerosis

Multiple sclerosis (MS) is a neuroinflammatory disease characterized by expanding demyelinating lesions, leading to severe and irreversible disability. The mechanisms driving lesion expansion, however, remain poorly understood. Here, using a multi-omics approach, we identified foamy microglia as primary contributors to the molecular profile of lesions and disease progression in secondary progressive MS. Lesions with foamy microglia are marked by the accumulation of cholesterol esters, bismonoacylglycerolphosphates (BMP), and oxylipins, along with high B-cell infiltration, increased levels of immunoglobulin G1, and elevated expression of Fc{gamma}- and complement receptors. Lesions with foamy GPNMB+-microglia display markers of enhanced phagocytosis, lipid metabolism, lysosomal dysfunction, and antigen presentation, but lack classical pro-inflammatory markers. Our data suggest that sustained phagocytosis of myelin overwhelms microglial endo-lysosomal capacity, leading to lipid droplet and oxylipin formation. This microglial phenotype may induce further recruitment of adaptive immune cells, axonal damage, drive lesion expansion and prevent remyelination. Monoacylglycerol lipase, involved in producing oxylipin precursors, was identified as a potential therapeutic target to disrupt this cycle and prevent chronic lesion expansion.

neuroscience↗

bioRxiv2023

Profiling of microglia nodules in multiple sclerosis reveals propensity for lesion formation

Clusters of ramified HLA-DR+ cells, known as microglia nodules, are associated with brain pathology. Here we investigated if microglia nodules in the normal-appearing white matter (NAWM) of multiple sclerosis (MS) are different from microglia nodules in white matter (WM) in stroke and whether they may relate to the start of demyelinating MS lesions. We studied the relation between microglia nodules and pathological severity in an MS autopsy cohort (n=167), and we compared frequency, size, and gene expression of microglia nodules in MS (n=7) and stroke (n=7). MS donors with microglia nodules (64%) had a higher lesion load and a higher proportion of active lesions compared to donors without microglia nodules (36%). We found altered expression of genes in microglia nodules in MS compared to stroke, including genes previously shown to be upregulated in MS lesions. Genes associated with lipid metabolism, presence and proliferation of T and B cells, production of and response to immunoglobulins and cytokines (specifically TNF and IFN), activation of the complement cascade, and metabolic stress were upregulated. Using immunohistochemistry, we confirmed that in MS, more than in stroke, microglia nodules are associated with membrane attack complexes, have phagocytosed oxidized phospholipids, and have a tubular mitochondrial network reflecting increased metabolic activity. Furthermore, in MS, some nodules encapsulated partially demyelinated axons. Taken together, we propose that activation of some microglia nodules in MS by pro-inflammatory cytokines and immunoglobulins in combination with phagocytosis of oxidized phospholipids may lead to a volatile phenotype prone to form MS lesions.

neuroscience↗

bioRxiv2022

Conservation and divergence of myelin proteome and oligodendrocyte transcriptome profiles between humans and mice

Human myelin disorders are commonly studied in mouse models. Since both clades evolutionarily diverged approximately 85 million years ago, it is critical to know to what extent the myelin protein composition has remained similar. Here we use quantitative proteomics to analyze myelin purified from human white matter and find that the relative abundance of the structural myelin proteins PLP, MBP, CNP and SEPTIN8 correlates well with that in C57Bl/6N- mice. Conversely, multiple other proteins were identified exclusively or predominantly in human or mouse myelin. This is exemplified by peripheral myelin protein-2 (PMP2), which was specific to human CNS myelin, while tetraspanin-2 (TSPAN2) and connexin-29 (CX29/GJC3) were confined to mouse myelin. Assessing published scRNA-seq-datasets, human and mouse oligodendrocytes display well-correlating transcriptome profiles but divergent expression of distinct genes including Pmp2, Tspan2 and Gjc3. Species-dependent diversity of oligodendroglial mRNA-expression and myelin protein composition can be informative when translating from mouse models to humans.

neuroscience↗

bioRxiv2021

Common micro- and macroscale principles of connectivity in the human brain

The brain requires efficient information transfer between neurons and between large-scale brain regions. Brain connectivity follows predictable organizational principles: at the cellular level, larger supragranular pyramidal neurons have larger dendritic trees, more synapses, more complex branching and perform more complex neuronal computations; at the macro-scale, region-to-region connections are suggested to display a diverse architecture with highly connected hub-areas facilitating complex information integration and computation. Here, we explore the hypothesis that the branching structure of large-scale region-to-region connectivity follows similar organizational principles as known for the neuronal scale. We examine microscale connectivity of basal dendritic trees of supragranular pyramidal neurons (300+) across ten cortical areas in five human donor brains (1M/4F). Dendritic complexity was quantified as the number of branch points, tree length, spine count, spine density and overall branching complexity. High-resolution diffusion-weighted MRI was used to construct white matter trees of cortico-cortical wiring. Examining the complexity of the resulting white matter trees using the same measures as for dendritic trees shows multimodal association areas to have larger, more complexly branched white matter trees than primary areas (all p<0.0001) and regional macroscale complexity to run in parallel with microscale measures, in terms of number of inputs (r=0.677, p=0.032), branch points (r=0.790, p=0.006), total tree length (r=0.664, p=0.036) and branching complexity (r=0.724, p=0.018). Our findings support the integrative theory that brain connectivity is structured following similar principles of connectivity at the neuronal and macroscale level, and provide a framework to study connectivity changes in brain conditions at multiple levels of brain organization.

neuroscience↗

bioRxiv2021

Complement-associated loss of CA2 inhibitory synapses in the demyelinated hippocampus impairs memory

The complement system is implicated in synapse loss in the MS hippocampus, but the functional consequences of synapse loss remain poorly understood. Here, in post-mortem MS hippocampi with demyelination we find that deposits of the complement component C1q are enriched in the CA2 subfield, are linked to loss of inhibitory synapses and are significantly higher in MS patients with cognitive impairments compared to those with preserved cognitive functions. Using the cuprizone mouse model of demyelination, we corroborated that C1q deposits are highest within the demyelinated dorsal hippocampal CA2 pyramidal layer, and co-localized with inhibitory synapses engulfed by microglia/macrophages. In agreement with the loss of inhibitory perisomatic synapses, we further found that Schaffer collateral feedforward inhibition but not excitation was impaired in CA2 pyramidal neurons and accompanied by a reduced spike output. Ultimately, we show that these electrophysiological changes were associated with an impaired encoding of social memories. Together, our findings identify CA2 as a critical circuit in demyelinated intrahippocampal lesions and memory dysfunctions in MS.

neuroscience↗