Biology subjects

Celikkaya, H.

Publications and source records attributed to Celikkaya, H..

3 recordsLinked to original sources

bioRxiv2025

APOE-ϵ4-induced Fibronectin at the blood-brain barrier is a conserved pathological mediator of disrupted astrocyte-endothelia interaction in Alzheimer's disease

Blood-brain barrier (BBB) dysfunction is a key feature of Alzheimers disease (AD), particularly in individuals carrying the APOE-{varepsilon}4 allele. This dysfunction worsens neuroinflammation and hinders the removal of toxic proteins, such as amyloid-beta (A{beta}42), from the brain. In post-mortem brain tissues and in animal models, we previously reported that fibronectin accumulates at the BBB predominantly in APOE-{varepsilon}4 carriers. Furthermore, we found a loss-of-function variant in the fibronectin 1 (FN1) gene significantly reduces aggregated fibronectin levels and decreases AD risk among APOE-{varepsilon}4 carriers. Yet, the molecular mechanisms downstream of fibronectin at the BBB remain unclear. The extracellular matrix (ECM) plays a crucial role in maintaining BBB homeostasis and orchestrating the interactions between BBB cell types, including endothelia and astrocytes. Understanding the mechanisms affecting the ECM and BBB cell types will be critical for developing effective therapies against AD, especially among APOE-{varepsilon}4 carriers. Here, we demonstrate that APOE-{varepsilon}4, A{beta}42, and inflammation drive the induction of FN1 expression in several models including zebrafish, mice, iPSC-derived human 3D astrocyte and 3D cerebrovascular cell cultures, and in human brains. Fibronectin accumulation disrupts astroglial-endothelial interactions and the signalling cascade between vascular endothelial growth factor (VEGF), heparin-binding epidermal growth factor (HBEGF) and Insulin-like growth factor 1 (IGF1). This accumulation of fibronectin in APOE-{varepsilon}4- associated AD potentiates BBB dysfunction, which strongly implicates reducing fibronectin deposition as a potential therapeutic target for AD. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=197 SRC="FIGDIR/small/634732v1_ufig1.gif" ALT="Figure 1"> View larger version (70K): org.highwire.dtl.DTLVardef@1efff03org.highwire.dtl.DTLVardef@14f40cdorg.highwire.dtl.DTLVardef@27743aorg.highwire.dtl.DTLVardef@3fa9a9_HPS_FORMAT_FIGEXP M_FIG C_FIG Accessibility textThis image illustrates the effects of different APOE isoforms (ApoE-{varepsilon}3 and ApoE-{varepsilon}4) on blood-brain barrier (BBB) integrity, focusing on the molecular interactions between astrocytes and endothelial cells. This figure emphasizes the detrimental effects of ApoE-{varepsilon}4 on BBB integrity via fibronectin accumulation and altered signaling pathways. The top section provides a schematic overview of the blood-brain barrier, highlighting astrocytes, endothelial cells, and their interface. The left panel represents the ApoE-{varepsilon}3 condition: Normal fibronectin (FN1) levels support healthy interactions between astrocytes and endothelial cells. Growth factors, including VEGFA, HBEGF, and IGF1, maintain BBB integrity through their respective receptors (VEGFR and EGFR). Green arrows indicate activation of these signaling pathways. The right panel depicts the ApoE-{varepsilon}4 condition: Elevated fibronectin (FN1) disrupts astrocyte-endothelium interactions. FN1 binds integrins and activates focal adhesion kinase (FAK), inhibiting VEGFA, which is required for endothelial HBEGF that in turn activates IGF1 signaling. Red symbols indicate inhibition of HBEGF, VEGFA, and IGF1 pathways, leading to BBB dysfunction. HighlightsAPOE-{varepsilon}4 drives fibronectin deposition in Alzheimers, disrupting astrocyte-endothelia interactions. APOE-{varepsilon}4 and fibronectin co-localize, forming aggregates at blood-brain barrier (BBB). Fibronectin alters the signaling between VEGF, IGF1, and HBEGF impairing BBB function. Reducing fibronectin restores BBB integrity and offsets APOE-{varepsilon}4 pathology.

cell biology↗

bioRxiv2017

Interleukin-4 restores neurogenic plasticity of the primary human neural stem cells through suppression of Kynurenic acid production upon Amyloid-β42 toxicity

The immune response is an important determinant of the plasticity and neurogenic capacity of neural stem cells (NSCs) upon amyloid-beta42 (A{beta}42) toxicity in Alzheimers disease (AD). However, the direct effects of individual immuno-modulatory effectors on NSC plasticity remain to be elucidated and are the motivation for reductionist tissue-mimetic culture experiments. Using starPEG-Heparin hydrogel system that provides a defined 3D cell-instructive neuro-microenvironment culture system, sustains high levels of proliferative and neurogenic activity of human NSCs, and recapitulates the fundamental pathological consequences of Amyloid toxicity upon A{beta}42 administration, we found that the anti-inflammatory cytokine interleukin-4 (IL4) restores the plasticity and neurogenic capacity of NSCs by suppressing the A{beta}42-induced kynurenic acid-producing enzyme kynurenine aminotransferase 2 (KAT2), which we also found to be upregulated in the brains of the AD model, APP/PS1dE9 mouse. Our transcriptome analyses showed that IL4 treatment restores the expression levels of NSC and cortical subtype markers. Thus, our dissective neuro-microenvironment culture revealed IL4-mediated neuroinflammatory crosstalk for human NSC plasticity and predicted a new mechanistic target for therapeutic intervention in AD.

neuroscience↗

bioRxiv2017

Instructive starPEG-Heparin biohybrid 3D cultures for modeling human neural stem cell plasticity, neurogenesis, and neurodegeneration

Three-dimensional models of human neural development and neurodegeneration are crucial when exploring stem-cell-based regenerative therapies in a tissue-mimetic manner. However, existing 3D culture systems are not sufficient to model the inherent plasticity of NSCs due to their ill-defined composition and lack of controllability of the physical properties. Adapting a glycosaminoglycan-based, cell-responsive hydrogel platform, we stimulated primary and induced human neural stem cells (NSCs) to manifest neurogenic plasticity and form extensive neuronal networks in vitro. The 3D cultures exhibited neurotransmitter responsiveness, electrophysiological activity, and tissue-specific extracellular matrix (ECM) deposition. By whole transcriptome sequencing, we identified that 3D cultures express mature neuronal markers, and reflect the in vivo make-up of mature cortical neurons compared to 2D cultures. Thus, our data suggest that our established 3D hydrogel culture supports the tissue-mimetic maturation of human neurons. We also exemplarily modeled neurodegenerative conditions by treating the cultures with A{beta}42 peptide and observed the known human pathological effects of Alzheimers disease including reduced NSC proliferation, impaired neuronal network formation, synaptic loss and failure in ECM deposition as well as elevated Tau hyperphosphorylation and formation of neurofibrillary tangles. We determined the changes in transcriptomes of primary and induced NSC-derived neurons after A{beta}42, providing a useful resource for further studies. Thus, our hydrogel-based human cortical 3D cell culture is a powerful platform for studying various aspects of neural development and neurodegeneration, as exemplified for A{beta}42 toxicity and neurogenic stem cell plasticity.\n\nSignificanceNeural stem cells (NSC) are reservoir for new neurons in human brains, yet they fail to form neurons after neurodegeneration. Therefore, understanding the potential use of NSCs for stem cell-based regenerative therapies requires tissue-mimetic humanized experimental systems. We report the adaptation of a 3D bio-instructive hydrogel culture system where human NSCs form neurons that later form networks in a controlled microenvironment. We also modeled neurodegenerative toxicity by using Amyloid-beta4 peptide, a hallmark of Alzheimers disease, observed phenotypes reminiscent of human brains, and determined the global gene expression changes during development and degeneration of neurons. Thus, our reductionist humanized culture model will be an important tool to address NSC plasticity, neurogenicity, and network formation in health and disease.

neuroscience↗