Biology subjects

Krasemann, S.

Publications and source records attributed to Krasemann, S..

8 recordsLinked to original sources

bioRxiv2026

Mechanisms of resilience to autosomal dominant Alzheimer's disease via oligogenic modulation of rare variants in the entorhinal cortex

Two PSEN1 E280A carriers have presented extreme protection against autosomal dominant Alzheimers disease (ADAD), with over two decades of delay for dementia onset. One of them, a male heterozygous for the RELN-COLBOS protective variant showed increased neuronal density in the entorhinal cortex 1. We conducted a deep phenotyping and genotyping study of the entorhinal cortex in protected and unprotected PSEN1 E280A cases, sporadic AD, and non-demented controls. We used single nuclei and spatial transcriptomics, whole genome sequencing, and candidate genotype-associated expression changes (GAEC) analysis. Our results showed unique neuronal and oligodendrocytic populations in the male RELN-COLBOS patient. Unique RELN positive inhibitory interneurons were enriched in cortical Layer I, while unique abundant ADAMTSL1 positive excitatory neurons were distributed in Layers II/III and Layer Va. These neurons and mature myelinated oligodendrocytes benefitted from increased expression of LRP6 receptor, functioning as a non-canonical receptor for the mutated Reelin protein encoded by RELN-COLBOS. Finally, GAEC and pathway enrichment analyses suggested that other mutations enhanced RELN-COLBOS effects in oligodendrocytes in the male RELN-COLBOS patient, explaining the phenotypic differences with his sister, a RELN-COLBOS carrier with no evident protection from ADAD. Our findings suggest that extreme deviations of the PSEN1 E280A phenotype are more likely attributed to oligogenic effects, including simultaneous mutations occurring in genes including ITGA2, involved in single molecular pathways, such as the Integrins / Focal Adhesion pathway, as potential disease modifiers for Alzheimers disease (AD).

neuroscience↗

bioRxiv2026

Astrocyte-driven small vessel disease is an early, amyloid-independent feature of PSEN1 E280A familial Alzheimer's disease

Cerebral Small vessel disease (cSVD) is a prevalent feature of Alzheimers disease (AD) pathology. Whether this pathology is a late consequence of amyloid and tau accumulation or an early, direct effect of PSEN1 dysfunction has remained unresolved. We found that it is more severe in familial AD (FAD) caused by E280A mutation in presenilin 1 (PSEN1). These cases present with a distinctive proteomic signature, associated with pathological features, more dysregulated in the occipital cortex (OC) compared to the frontal cortex (FC), and characterized by multiple dysregulated proteins involved in extracellular matrix (ECM) and RNA-associated processes. This proteomic fingerprint was associated with abnormal collagen build up, ECM disorganization, and signatures of aberrant angiogenesis. Six months old transgenic knock-in mice homozygous for Psen1 E280A mutation (PSEN1Ki) also showed a similar phenotype with microvascular tortuosity and proteomic changes. Critically, these mice develop neither A{beta} plaques nor tau tangles, indicating that the shared microvascular and RNA-associated changes are direct consequences of PSEN1 dysfunction rather than downstream effects of amyloid pathology. Remarkably, dysregulated RNA-associated protein networks overlapped between FAD and PSEN1Ki mice. Cerebral microvessels microstructure in PSEN1Ki mice at two months and six months showed abnormal astrocytic end-feet with lamellar deposits implicating blood-brain barrier damage. Finally, single nuclei transcriptomic analysis of AD patients and controls showed similar abnormal astrocytes in both sporadic and familial variants, but FAD astrocytes expressed dysregulated genes identified in the proteomic analyses, such as GLUL, APOE, and CLU. Our findings suggest that cSVD is an early pathological event in PSEN1 FAD and that is driven by abnormal RNA-associated processes and astrocytic dysfunction.

neuroscience↗

bioRxiv2026

HIV-1 promotes cell-to-cell interactions enabling spread from CD4+ T cells to microglia

HIV-1 infection of the brain occurs early in acute infection and results in neuroinflammation and - when untreated - in cognitive impairment, yet the mechanisms by which microglia become infected remain poorly defined. Evidence from simian immunodeficiency virus (SIV) studies supports a model in which infected CD4+ T cells disseminate HIV-1 to tissue macrophages, but this has not yet been confirmed for human microglia. Here, we used human monocyte-derived microglia (MDMi) and autologous HIV-1-infected primary CD4+ T cells to investigate viral transmission and immune cell interactions. Transcriptional profiling of MDMi confirmed microglia signature genes such as CX3CR1, P2RY12 and C1QB, and surface staining showed expression of CD4 and the HIV-1 coreceptor CCR5. Compared to cell-free infection, direct cell-to-cell contact between MDMi and HIV-1-infected CD4+ T cells markedly enhanced productive infection of MDMi. HIV-1 infection downmodulated the "dont-eat-me" signal CD47 and increased phosphatidylserine on the surface of primary CD4+ T cells. Consequently, HIV-1 infection of primary CD4+ T cells increased microglia-CD4+ T cell interactions and resulted in enhanced phagocytosis by MDMi. Together, this supports a mechanism where HIV-1 facilitates cell-to-cell spread from primary CD4+ T cells to microglia, which has important implications for therapeutic targeting of HIV-1 brain reservoir seeding.

immunology↗

bioRxiv2025

Merkel cell polyomavirus infection and persistence modelled in skin organoids

Merkel cell polyomavirus (MCPyV) causes most Merkel cell carcinomas (MCC). The virus is one of the few known human tumor viruses, and due to its direct role in this skin cancer development, it is a bona fide model for viral tumorigenesis and tumorigenesis in general. Chronic viruses in humans such as MCPyV are highly adapted to their host and current models to study infection, persistence and pathogenesis are highly limited. We here use an induced pluripotent stem cell (iPSC)-derived hair-bearing skin organoid (SkO) system to demonstrate efficient viral infection, progression and spread of MCPyV. Using bulk-, single cell - and spatial-transcriptomics, combined with immunostaining and nucleic acid hybridization technologies, we show that MCPyV ensures persistence due to a quasi-latency state within the majority of dermal fibroblasts carry the viral genome. Further, we identify the cell type of productive infection with papillary fibroblasts and dermal sheath fibroblasts supporting viral replication and progeny production. Our high-resolution methods demonstrate that the virus in these cells evades the innate immune response, as evidenced by the efficacy of interferon-beta treatment or ruxolitinib, a JAK/STAT inhibitor, in suppressing or stimulating viral replication. We show that iPSC-derived SkOs are able to support infection and long-term persistence of the virus under conditions very similar to those found in humans. Thus, this infection model provides a robust platform for understanding and characterizing the interaction of this virus with the immune system in infection, testing treatment strategies to control reactivation and map processes involved in tumor development.

molecular biology↗

bioRxiv2025

Complex Human Hair Bearing Skin Organoids as Model for Herpes Simplex Virus 1 Infection in the Skin

Epithelial surfaces are the initial site of Herpes Simplex Virus 1 (HSV-1) infection. After latency establishment in the peripheral nervous system, reactivation can lead to skin pathologies. To reflect the complexity of skin we used complex human hair bearing skin organoids as a new model system for HSV-1 infection. We analyzed spread of the infection through the three-dimensional tissue and the cell type specific host response in a spatial temporal manner. Single-cell-resolution spatial transcriptomics and imaging shows a restricted viral infection in keratinocytes of the epidermis and hair follicles. The host factor IER3 is upregulated in papillary fibroblasts of the dermis as the infection progresses through the tissue. In keratinocytes of the stratum basale, we find IRF3 upregulated in infected but also virus negative cells, suggesting a signaling mechanism to initiate antiviral responses. Furthermore, we find a cell type specific inflammatory response with an upregulation of TNFSF9 in dermal fibroblasts and TNF in keratinocytes. TNF target genes are induced in neighboring uninfected cells suggesting the induction of a localized inflammatory reaction to suppress viral infection. In summary, our findings position human hair-bearing skin organoids as a highly physiological model system for studying HSV-1 pathogenesis and reveal spatially organized host responses.

microbiology↗

bioRxiv2023

Cleavage site-directed antibodies reveal the prion protein in humans is shed by ADAM10 at Y226 and associates with misfolded protein deposits in neurodegenerative diseases

Proteolytic cell surface release ( shedding) of the prion protein (PrP), a broadly expressed GPI-anchored glycoprotein, by the metalloprotease ADAM10 impacts on neurodegenerative and other diseases in animal and in vitro models. Recent studies employing the latter also suggest shed PrP (sPrP) to be a ligand in intercellular communication and critically involved in PrP-associated physiological tasks. Although expectedly an evolutionary conserved event, and while soluble forms of PrP are present in human tissues and body fluids, neither proteolytic PrP shedding and its cleavage site nor involvement of ADAM10 or the biological relevance of this process have been demonstrated for the human body thus far. In this study, cleavage site prediction and generation (plus detailed characterization) of sPrP-specific antibodies enabled us to identify PrP cleaved at tyrosin 226 as the physiological and strictly ADAM10-dependent shed form in humans. Using cell lines, neural stem cells and brain organoids, we show that shedding of human PrP can be stimulated by PrP-binding ligands without targeting the protease, which may open novel therapeutic perspectives. Site-specific antibodies directed against human sPrP also detect the shed form in brains of cattle, sheep and deer, hence in all most relevant species naturally affected by fatal and transmissible prion diseases. In human and animal prion diseases, but also in patients with Alzheimers disease, sPrP relocalizes from a physiological diffuse tissue pattern to intimately associate with extracellular aggregates of misfolded proteins characteristic for the respective pathological condition. Findings and research tools presented here will accelerate novel insight into the roles of PrP shedding (as a process) and sPrP (as a released factor) in neurodegeneration and beyond.

neuroscience↗

bioRxiv2023

APOE3 Christchurch modulates tau phosphorylation and regulates β-catenin/Wnt/Cadherin signaling in induced pluripotent stem cell-derived cerebral organoids from Alzheimer's cases

Alzheimers disease (AD) is the most common cause of dementia among older adults. APOE3 Christchurch (R136S, APOE3Ch) variant homozygosity was reported in an individual with extreme resistance to autosomal dominant AD due to the PSEN1 E280A mutation. This subject had a delayed clinical age at onset and resistance to tauopathy and neurodegeneration despite extremely high amyloid plaque burden. We established induced pluripotent stem (iPS) cell-derived cerebral organoids from this resistant case and from a non-protected kindred control (with PSEN1 E280A and APOE3/3). We used CRISPR/Cas9 gene editing to successfully remove the APOE3Ch to wild type in iPS cells from the protected case and to introduce the APOE3Ch as homozygote in iPS cells from the non-protected case to examine causality. We found significant reduction of tau phosphorylation (pTau 202/205 and pTau396) in cerebral organoids with the APOE3Ch variant, consistent with the strikingly reduced tau pathology found in the resistant case. We identified Cadherin and Wnt pathways as signaling mechanisms regulated by the APOE3Ch variant through single cell RNA sequencing in cerebral organoids. We also identified elevated {beta}-catenin protein, a regulator of tau phosphorylation, as a candidate mediator of APOE3Ch resistance to tauopathy. Our findings show that APOE3Ch is necessary and sufficient to confer resistance to tauopathy in an experimental ex-vivo model establishing a foundation for the development of novel, protected case-inspired therapeutics for tauopathies, including Alzheimers.

neuroscience↗

bioRxiv2020

SARS-CoV-2 infects carotid arteries: implications for vascular disease and organ injury in COVID-19

Stroke and central nervous system dysfunction are cardinal symptoms in critically ill corona virus disease 19 (COVID-19) patients. In an autopsy series of 32 COVID-19 patients, we investigated whether carotid arteries were infected with SARS-CoV-2 by employing genomic, virologic, histochemical and transcriptomic analyses. We show that SARS-CoV-2 productively infects and modulates vascular responses in carotid arteries. This finding has far reaching implications for the understanding and clinical treatment of COVID-19.

microbiology↗