Biology subjects

Hahn, O.

Publications and source records attributed to Hahn, O..

15 recordsLinked to original sources

bioRxiv2025

Heterochronic myeloid cell replacement reveals the local brain environment as key driver of microglia aging

Aging, the key risk factor for cognitive decline, impacts the brain in a region-specific manner, with microglia among the most affected cell types. However, it remains unclear whether this is intrinsically mediated or driven by age-related changes in neighboring cells. Here, we describe a scalable, genetically modifiable system for in vivo heterochronic myeloid cell replacement. We find reconstituted myeloid cells adopt region-specific transcriptional, morphological and tiling profiles characteristic of resident microglia. Young donor cells in aged brains rapidly acquired aging phenotypes, particularly in the cerebellum, while old cells in young brains adopted youthful profiles. We identified STAT1-mediated signaling as one axis controlling microglia aging, as STAT1-loss prevented aging trajectories in reconstituted cells. Spatial transcriptomics combined with cell ablation models identified rare natural killer cells as necessary drivers of interferon signaling in aged microglia. These findings establish the local environment, rather than cell-autonomous programming, as a primary driver of microglia aging phenotypes.

neuroscience↗

bioRxiv2025

Blockade of VCAM1 or VLA4 preserves cerebrovasculature and prevents cognitive decline late after stroke

Infarct-induced neurodegeneration occurs chronically after stroke, doubling the risk of dementia. Endothelial vascular cell adhesion molecule 1 (VCAM1) facilitates blood-brain barrier opening and immune cell diapedesis by binding very late antigen 4 (VLA4) on immune cells. We hypothesized that vascular dysfunction persists after stroke and contributes to chronic neuroinflammation and cognitive decline via signaling through the VLA4/VCAM1 axis. We used adult (3-5 month old) and middle-aged (10 month old) C57BL/6J male & female mice and a permanent middle cerebral artery occlusion stroke model. Sham surgery consisted of an identical procedure without occlusion of the artery. We quantified vascular integrity using blood vessel length, pericyte coverage of vasculature, tight junctions, and extravascular fibrinogen leakage by immunostaining. Cognitive testing was performed using both Barnes maze and novel object recognition prior to stroke, and 1 and 6 weeks after stroke, and replicated in both male and female mice. We utilized anti-VCAM1, anti-VLA4 or isotype control antibodies to block VCAM1 or VLA4 function, and then to confirm mechanisms we utilized single cell RNA sequencing on immune and endothelial cells, aptamer-based plasma proteomics, and additional immunostaining for vascular integrity. Mouse brains exhibited signs of persistent vascular dysfunction and loss of blood-brain barrier integrity at 8 weeks after stroke, compared to sham animals. We observed reduced ZO-1 tight junction and pericyte coverage of vasculature, and increased extravascular fibrinogen. Mice with stroke also developed a cognitive deficit in both Barnes maze and novel object by 6 weeks. Treatment with anti-VCAM1 or anti-VLA4 resulted in mice with stroke performing as well as sham mice treated with isotype control antibody on both the Barnes maze and novel object recognition tasks. Anti-VCAM1 and anti-VLA4 both increased expression of blood-brain barrier maintenance genes in brain endothelial cells, while only minimally altering immune cell gene expression. Immune cell infiltration was reduced by anti-VCAM1 but not anti-VLA4 in tissue sections. In contrast to this, both antibodies increased blood vessel length and pericyte vascular coverage. Finally, extravascular fibrinogen was reduced by both antibody treatments in multiple brain regions. Together, our findings establish the VLA4/VCAM1 axis as a promising target to preserve vascular integrity and prevent cognitive decline late after stroke. Our data is consistent with a model where blocking either VCAM1 or VLA4 chronically after stroke promotes new blood vessel growth and maturation and restores the blood-brain barrier to prevent infarct-induced neurodegeneration.

neuroscience↗

bioRxiv2025

Cell-surface proteomic profiling identifies CD72 as a regulator of microglial tiling

Microglial tiling--the phenomenon of consistent cell-to-cell distances and non-overlapping processes--is regarded as a qualitative indicator of homeostasis, but mechanisms of microglial tiling are unknown. We used cell-surface proximity labeling and mass spectrometry to profile the microglial cell-surface proteome in an in vitro model of homeostatic glial physiology and used single-cell RNA sequencing and public databases to identify candidate cell-surface proteins that might modulate tiling. We designed an image-based functional assay which measures six morphological/spatial readouts to screen these proteins for modulation of tiling. CD72, a coreceptor to the B cell receptor that is expressed by microglia, disrupted tiling; we validated its effects in vitro and in situ in organotypic hippocampal brain slices. Phosphoproteomic studies revealed that CD72 modulates pathways associated with cell adhesion, repulsive receptors, microglial activation, and cytoskeletal organization. These results lay the groundwork for further investigation of the functional roles of tiling in homeostasis and disease.

neuroscience↗

bioRxiv2025

A spatio-temporal brain miRNA expression atlas identifies sex-independent age-related microglial driven miR-155-5p increase

An in-depth understanding of the molecular processes composing aging is crucial to develop therapeutic approaches that decrease aging as a key risk factor for cognitive decline. Herein, we present a spatio-temporal brain atlas (15 different regions) of microRNA (miRNA) expression across the mouse lifespan (7 time points) and two aging interventions composed of 1009 samples. MiRNAs are promising therapeutic targets, as they silence genes by complementary base-pair binding of messenger RNAs and are known to mediate aging speed. We first established sex- and brain-region-specific miRNA expression patterns in young adult samples. Then we focused on sex-dependent and independent brain-region-specific miRNA expression changes during aging. The corpus callosum in males and the choroid plexus in females exhibited strong sex-specific age-related signatures. In this work, we identified three sex-independent brain aging miRNAs (miR-146a-5p, miR-155-5p and miR-5100). We showed for miR-155-5p that these expression changes are driven by aging microglia. MiR-155-5p targets mTOR signaling pathway components and other cellular communication pathways and is hence a promising therapeutic target.

molecular biology↗

bioRxiv2024

Spatiotemporal transcriptomic niches of complement pathway and serine protease inhibitor activation in aging and infection

Aging is a multifactorial and complex physiological process, affecting every organ with characteristic manifestations. Understanding the molecular mechanisms that drive aging processes is crucial to targeting age-related disorders. Recent reports suggest that severe post-infection syndromes can partially accelerate aging. However, the underlying gene-encoded regulatory interplay, whether being shared or distinct between aging and infection biology are poorly understood. Here, we employed spatial transcriptomics to establish a multi-organ atlas (brain, heart, kidney, liver, lung, and spleen) across the mouse lifespan (4, 17, and 26 months). Dissecting high-quality fresh-frozen tissue samples at unbiased molecular resolution, we found both organ-specific and cross-organ gene dysregulation upon aging. We identified age-related trajectories in gene expression and cell state, some only detectable within their spatial context, and provide validation at subcellular resolution. The most prominent effect was organ-wide immune system activation with spatially variable severity. We therefore evaluated how aging mimics the expression signatures observed in systemic infection, using spatial transcriptomics slices from young mice infected with Plasmodium berghei ANKA. While on the gene level the effect sizes caused by the infection outweighed those of aging, we reveal a shared activation of the early complement pathway (C4b) and serine protease inhibitors (Serpin gene family) within by phenotype distinct spatial niches. We show that this common RNA signature is driven by tissue-specific cell types and eventually affects protein levels in the aged brain, rendering them a target for future mechanistic and drug discovery studies. Taken together, our study provides a coherent in-depth and cross-organ transcriptomics atlas to systematically study aging and infection in the mouse at spatiotemporal resolution. Key highlightsO_LILarge-scale and high-resolution atlas of spatial transcriptomics from six organs to study aging and systemic infection across two mouse cohorts. C_LIO_LIStrong transcriptional alterations found in distinct organ-specific niches for aging and acute malaria, with organ- and cell type-associated immune responses. C_LIO_LIDysregulation of early complement proteases (C4b) and serine protease inhibitors (Serpina3n) as common theme across central nervous system and peripheral organs. C_LI

molecular biology↗

bioRxiv2024

Circulatory proteins shape microglia state and boost phagocytosis

Microglia, the brains immune cells, are highly responsive to their local environment. Given that circulatory proteins can enter the brain, we asked whether microglia are responsive to such proteins. Here, we identify a stable population of microglia specialized to take up circulatory proteins in a region-specific manner under physiological conditions; human hematopoietic stem cell-derived microglia replacing endogenous microglia in chimeric mice show similar regional specialization. Plasma-positive microglia are characterized by prominent expression of genes related to innate immunity and antigen presentation and exhibit high metabolic and phagocytic activity. This activity is dependent, in part, on microglial uptake and accumulation of circulatory Apolipoprotein AI (ApoA-I). Our findings thus identify a new model of communication between brain and periphery through specialized microglia.

neuroscience↗

bioRxiv2024

Gpr37 modulates the severity of inflammation-induced GI dysmotility by regulating enteric reactive gliosis.

The enteric nervous system (ENS) is contained within two layers of the gut wall and is made up of neurons, immune cells, and enteric glia cells (EGCs) that regulate gastrointestinal (GI) function. EGCs in both inflammatory bowel disease (IBD) and irritable bowel syndrome (IBS) change in response to inflammation, referred to as reactive gliosis. Whether EGCs restricted to a specific layer or region within the GI tract alone can influence intestinal immune response is unknown. Using bulk RNA-sequencing and in situ hybridization, we identify G-protein coupled receptor Gpr37, as a gene expressed only in EGCs of the myenteric plexus, one of the two layers of the ENS. We show that Gpr37 contributes to key components of LPS-induced reactive gliosis including activation of NF-kB and IFN-y signaling and response genes, lymphocyte recruitment, and inflammation-induced GI dysmotility. Targeting Gpr37 in EGCs presents a potential avenue for modifying inflammatory processes in the ENS.

neuroscience↗

bioRxiv2023

Augmentation of a neuroprotective myeloid state by hematopoietic cell transplantation

Multiple sclerosis (MS) is an autoimmune disease associated with inflammatory demyelination in the central nervous system (CNS). Autologous hematopoietic cell transplantation (HCT) is under investigation as a promising therapy for treatment-refractory MS. Here we identify a reactive myeloid state in chronic experimental autoimmune encephalitis (EAE) mice and MS patients that is surprisingly associated with neuroprotection and immune suppression. HCT in EAE mice leads to an enhancement of this myeloid state, as well as clinical improvement, reduction of demyelinated lesions, suppression of cytotoxic T cells, and amelioration of reactive astrogliosis reflected in reduced expression of EAE- associated gene signatures in oligodendrocytes and astrocytes. Further enhancement of myeloid cell incorporation into the CNS following a modified HCT protocol results in an even more consistent therapeutic effect corroborated by additional amplification of HCT-induced transcriptional changes, underlining myeloid-derived beneficial effects in the chronic phase of EAE. Replacement or manipulation of CNS myeloid cells thus represents an intriguing therapeutic direction for inflammatory demyelinating disease.

neuroscience↗

bioRxiv2022

Genetic Variants of Phospholipase C-γ 2 Confer Altered Microglial Phenotypes and Differential Risk for Alzheimers Disease

Genetic association studies have demonstrated the critical involvement of the microglial immune response in Alzheimers disease (AD) pathogenesis. Phospholipase C-gamma-2 (PLCG2) is selectively expressed by microglia and acts in many immune receptor signaling pathways. In AD, PLCG2 is induced uniquely in plaque-associated microglia. A genetic variant of PLCG2, PLCG2P522R, is a mild hypermorph that attenuates AD risk. We report the identification of a PLCG2 variant, PLCG2M28L, associated with loss-of-function and confers increased AD risk. PLCG2P522R attenuates disease in an amyloidogenic murine AD model, whereas PLCG2M28L exacerbates the plaque burden associated with altered phagocytosis and A{beta} clearance. The variants bidirectionally modulate disease pathology by inducing distinct transcriptional programs that identify microglial subpopulations associated with protective or detrimental phenotypes. In summary, these findings identify PLCG2M28L as a new AD risk variant and demonstrate that PLCG2 variants can differentially orchestrate microglial responses in AD pathogenesis that can be therapeutically targeted. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=122 SRC="FIGDIR/small/519685v1_ufig1.gif" ALT="Figure 1"> View larger version (48K): org.highwire.dtl.DTLVardef@19f0aa6org.highwire.dtl.DTLVardef@74191eorg.highwire.dtl.DTLVardef@1d3a3forg.highwire.dtl.DTLVardef@db2a44_HPS_FORMAT_FIGEXP M_FIG C_FIG HighlightsO_LIA genetic variant of PLCG2, M28L, is associated with an increased risk for Alzheimers disease (AD) C_LIO_LIIn an amyloidogenic AD mouse model, PLCG2M28L exacerbates disease pathogenesis C_LIO_LIConversely, PLCG2P522R, a protective PLCG2 variant, attenuates AD pathogenesis C_LIO_LIThe PLCG2 variants uniquely alter the microglial transcriptome and phenotypes C_LI

neuroscience↗

bioRxiv2022

A spatiotemporal map of the aging mouse brain reveals white matter tracts as vulnerable foci

Aging is the key risk factor for cognitive decline, yet the molecular changes underlying brain aging remain poorly understood. Here, we conducted spatiotemporal RNA-seq of the mouse brain, profiling 1,076 samples from 15 regions across 7 ages and 2 rejuvenation interventions. Our analysis identified a brain-wide gene signature of aging in glial cells, which exhibited spatially defined changes in magnitude. By integrating spatial and single-nucleus transcriptomics, we found that glia aging was particularly accelerated in white matter compared to cortical regions, while specialized neuronal populations showed region-specific expression changes. Rejuvenation interventions, including young plasma injection and dietary restriction, exhibited distinct effects on gene expression in specific brain regions. Furthermore, we discovered differential gene expression patterns associated with three human neurodegenerative diseases, highlighting the importance of regional aging as a potential modulator of disease. Our findings identify molecular foci of brain aging, providing a foundation to target age-related cognitive decline.

neuroscience↗

bioRxiv2021

Vesicle-bound regulatory RNAs are associated with tissue aging

Previous work on murine models and human demonstrated global as well as tissue-specific molecular aging trajectories in solid tissues and body fluids1-8. Extracellular vesicles like exosomes play a crucial role in communication and information exchange in between such systemic factors and solid tissues9,10. We sequenced freely circulating and vesicle-bound small regulatory RNAs in mice at five time points across the average life span from 2 to 18 months. Intriguingly, each small RNA class exhibits unique aging patterns, which showed differential signatures between vesicle-bound and freely circulating molecules. In particular, tRNA fragments showed overall highest correlation with aging which also matched well between sample types, facilitating age prediction with non-negative matrix factorization (86% accuracy). Interestingly, rRNAs exhibited inverse correlation trajectories between vesicles and plasma while vesicle-bound microRNAs (miRNAs) were exceptionally strong associated with aging. Affected miRNAs regulate the inflammatory response and transcriptional processes, and adipose tissues show considerable effects in associated gene regulatory modules. Finally, nanoparticle tracking and electron microscopy suggest a shift from overall many small to fewer but larger vesicles in aged plasma, potentially contributing to systemic aging trajectories and affecting the molecular aging of organs.

molecular biology↗

bioRxiv2019

A nutritional memory impairs survival, transcriptional and metabolic response to dietary restriction in old mice

Dietary restriction (DR) during adulthood can greatly extend lifespan and improve metabolic health in diverse species. However, whether DR in mammals is still effective when applied for the first time at old age remains elusive. Here, we conducted a late-life DR switch experiment employing 800 mice, by switching old animals from ad libitum (AL) to DR and vice versa. Strikingly, the switch from DR-to-AL acutely increased mortality, while the switch from AL-to-DR caused only a weak and gradual increase in survival, highlighting a memory of earlier nutrition. A significant association between fat preservation and survival response pointed to the white adipose tissue (WAT) as a potential memory source. Consistently, post-switch RNA-seq profiling in liver and WAT demonstrated that the transcriptional and metabolic program of chronic DR remained largely refractory to the AL-to-DR switch specifically in adipose tissue. Integration of lipidomics confirmed impaired membrane lipogenesis and limited mitochondrial copy number increase under late-life DR as functional consequences of this memory effect. Together, our results provide evidence for a nutritional memory as a limiting factor for DR-induced longevity and metabolic remodeling of WAT in mammals.

physiology↗

bioRxiv2019

Aging-associated changes in transcriptional elongation influence metazoan longevity.

Physiological homeostasis becomes compromised during aging, as a result of impairment of cellular processes, including transcription and RNA splicing. However, the molecular mechanisms leading to the loss of transcriptional fidelity are so far elusive, as are ways of preventing it. Here, we profiled and analyzed genome-wide, aging-related changes in transcriptional processes across different organisms: nematode worms, fruit flies, mice, rats and humans. The average transcriptional elongation speed (Pol-II speed) increased with age in all five species. Along with these changes in elongation speed we observed changes in splicing, including a reduction of unspliced transcripts and the formation of more circular RNAs. Two lifespan-extending interventions, dietary restriction and lowered insulin/Igf signaling, both reversed most of these aging-related changes. Genetic variants in Pol-II that reduced its speed in worms and flies increased their lifespan. Similarly, reducing Pol-II speed by overexpressing histone components, to counter age-associated changes in nucleosome positioning, also extended lifespan in flies and the division potential of human cells. Our findings uncover fundamental molecular mechanisms underlying animal aging and lifespan-extending interventions, and point to possible preventative measures.

genomics↗

bioRxiv2019

Lipid droplet accumulating microglia represent a dysfunctional and pro-inflammatory state in the aging brain

Microglia become progressively activated and seemingly dysfunctional with age, and genetic studies have linked these cells to the pathogenesis of a growing number of neurodegenerative diseases. Here we report a striking buildup of lipid droplets in microglia with aging in mouse and human brains. These cells, which we call lipid droplet-accumulating microglia (LAM), are defective in phagocytosis, produce high levels of reactive oxygen species, and secrete pro-inflammatory cytokines. RNA sequencing analysis of LAM revealed a transcriptional profile driven by innate inflammation distinct from previously reported microglial states. An unbiased CRISPR-Cas9 screen identified genetic modifiers of lipid droplet formation; surprisingly, variants of several of these genes, including progranulin, are causes of autosomal dominant forms of human neurodegenerative diseases. We thus propose that LAM contribute to age-related and genetic forms of neurodegeneration.

neuroscience↗

bioRxiv2019

The murine transcriptome reveals global aging nodes with organ-specific phase and amplitude

Aging is the single greatest cause of disease and death worldwide, and so understanding the associated processes could vastly improve quality of life. While the field has identified major categories of aging damage such as altered intercellular communication, loss of proteostasis, and eroded mitochondrial function1, these deleterious processes interact with extraordinary complexity within and between organs. Yet, a comprehensive analysis of aging dynamics organism-wide is lacking. Here we performed RNA-sequencing of 17 organs and plasma proteomics at 10 ages across the mouse lifespan. We uncover previously unknown linear and non-linear expression shifts during aging, which cluster in strikingly consistent trajectory groups with coherent biological functions, including extracellular matrix regulation, unfolded protein binding, mitochondrial function, and inflammatory and immune response. Remarkably, these gene sets are expressed similarly across tissues, differing merely in age of onset and amplitude. Especially pronounced is widespread immune cell activation, detectable first in white adipose depots in middle age. Single-cell RNA-sequencing confirms the accumulation of adipose T and B cells, including immunoglobulin J-expressing plasma cells, which also accrue concurrently across diverse organs. Finally, we show how expression shifts in distinct tissues are highly correlated with corresponding protein levels in plasma, thus potentially contributing to aging of the systemic circulation. Together, these data demonstrate a similar yet asynchronous inter- and intra-organ progression of aging, thereby providing a foundation to track systemic sources of declining health at old age.

genomics↗