Biology subjects

Ryan, S. K.

Publications and source records attributed to Ryan, S. K..

5 recordsLinked to original sources

bioRxiv2026

CD40 ligand and IFN-γ induce proinflammatory activity and microglia-mediated neurodegeneration in human stem cell models

The cluster of differentiation 40 (CD40)/CD40 ligand (CD40L) co-stimulatory pathway plays a critical role in the activation and regulation of immune networks involving both adaptive and innate immune cells. Dysregulation of this pathway has been implicated in multiple autoimmune diseases, including multiple sclerosis (MS). MS is characterized by progressive neurodegeneration driven by compartmentalized neuroinflammation within the central nervous system (CNS), sustained low-grade T cell infiltration at the blood-brain barrier, and T cell reactivation at CNS border tissues. CD40L-expressing T cells can activate CD40-expressing microglia, which are a critical effector cell that contribute to neurodegeneration in MS. However, the consequence of this functional interaction in the brain remains poorly understood. Here, we demonstrate that the combination of CD40L and interferon-gamma (IFN-{gamma}), a cytokine produced by activated T cells, induces a robust inflammatory response and cell death in human induced pluripotent stem cells (hiPSC)-derived microglia. Stimulation with CD40L elicited microglial clustering, morphological transformation, and robust release of proinflammatory cytokines including interleukin-12 (IL-12), tumor necrosis factor-alpha (TNF-), and IL-6. Anti-CD40L antibody treatment reversed both cell death and inflammatory response and partially normalized the associated transcriptional changes. Furthermore, using an hiPSC-derived tri-culture system comprising neurons, astrocytes, and microglia, we demonstrated that CD40L and IFN-{gamma} trigger microglia-dependent neuronal dysregulation and death. Anti-CD40L treatment substantially attenuated neuronal injury. Finally, transcriptomic enrichment analysis identified CD40L-mediated microglial gene expression signatures that correlated with CD40 expression in primary progressive MS brain tissue but not in the normal-appearing white matter of healthy controls. Collectively, these findings support a role for the microglial CD40/T cell CD40L axis in MS pathology and suggest CD40L blockade as a potential therapeutic strategy warranting further investigation.

neuroscience↗

bioRxiv2024

Glial state changes and neuroinflammatory RIPK1 signaling are a key feature of ALS pathogenesis

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease that causes motor neuron loss in the brain and spinal cord. Neuroinflammation driven by activated microglia and astrocytes is prominent in ALS, but an understanding of cell state dynamics and which pathways contribute to the disease remains unclear. Single nucleus RNA sequencing of ALS spinal cords demonstrated striking changes in glial cell states, including increased expression of inflammatory and glial activation markers. Many of these signals converged on RIPK1 and the necroptotic cell death pathway. Activation of the necroptosis pathway in ALS spinal cords was confirmed in a large bulk RNA sequencing dataset and at the protein level. Blocking RIPK1 kinase activity delayed symptom onset and motor impairment and modulated glial responses in SOD1G93A mice. We used a human iPSC-derived motor neuron, astrocyte, and microglia tri-culture system to identify potential biomarkers secreted upon RIPK1 activation, inhibited pharmacologically in vitro, and modulated in the CSF of people with ALS treated with a RIPK1 inhibitor. These data reveal ALS-enriched glial populations associated with inflammation and suggest a deleterious role for neuroinflammatory signaling in ALS pathogenesis.

neuroscience↗

bioRxiv2021

Microglia ferroptosis is prevalent in neurodegenerative disease and regulated by SEC24B

Iron dysregulation has been implicated in multiple neurodegenerative diseases, including Parkinsons Disease (PD), Amyotrophic Lateral Sclerosis (ALS), and Multiple Sclerosis (MS). One prominent feature of affected brain regions are iron-loaded microglia, but how iron overload influences microglia physiology and disease response is poorly understood. Here we show that microglia are highly susceptible to ferroptosis, an iron-dependent form of cell death. In a tri-culture of human iPSC-derived neurons, astrocytes, and microglia, under ferroptosis-inducing conditions, microglia undergo a drastic shift in cell state, with increased ferritin levels, disrupted glutathione homeostasis, and altered cytokine signaling. Similar ferroptosis-associated signature (FAS) microglia were uncovered in PD, and the signature was also found in a large cohort of PD patient blood samples, raising the possibility that ferroptosis can be identified clinically. We performed a genome-wide CRISPR screen which revealed a novel regulator of ferroptosis, the vesicle trafficking gene SEC24B. A small molecule screen also nominated several candidates which blocked ferroptosis, some of which are already in clinical use. These data suggest that ferroptosis sits at the interface of cell death and inflammation, and inhibition of this process in microglia and other brain cells may provide new ways for treating neurodegenerative disease.

neuroscience↗

bioRxiv2019

Disruption of the blood brain barrier in 22q11.2 deletion syndrome

Neuroimmune dysregulation is implicated in neuropsychiatric disorders including schizophrenia (SZ). As the blood brain barrier (BBB) is the immunological interface between the brain and the periphery, we investigated whether the BBB is intrinsically compromised in the most common genetic risk factor for SZ, the hemizygous deletion of chromosome 22q11.2 (22qDS). BBB-like endothelium (iBBB) differentiated from human 22qDS+SZ-induced pluripotent stem cells exhibited impaired barrier integrity, a phenotype substantiated in a mouse model of 22qDS. The proinflammatory intercellular adhesion molecule-1 (ICAM-1) was upregulated in 22qDS+SZ iBBB and 22qDS mice, indicating compromise of the BBB immune privilege. This immune imbalance resulted in increased migration/activation of leukocytes crossing the 22qDS+SZ iBBB. Finally, we found heightened astrocyte activation in murine and human 22qDS, suggesting that the BBB promotes astrocyte-mediated neuroinflammation. Overall, the barrier-promoting and immune privilege properties of the 22qDS BBB are compromised, and this might increase the risk for neuropsychiatric disease.

neuroscience↗

bioRxiv2019

Neuroinflammation and EIF2 signaling persist in an HiPSC tri-culture model of HIV infection despite antiretroviral treatment

HIV-Associated Neurocognitive Disorders (HAND) affect over half of HIV-infected individuals worldwide, despite antiretroviral therapy (ART). Therapeutically targetable mechanisms underlying HAND remain elusive. We developed a human-induced pluripotent stem cell (HiPSC) based model; whereby, we independently differentiate HiPSCs into neurons, astrocytes, and microglia and systematically combine to generate a tri-culture with or without HIV-infection and ART. scRNAseq analysis on tri-cultures including HIV-infected microglia revealed inflammatory signatures in the microglia and EIF2 signaling in all three cell types. Remarkably, EFZ alone induced a similar response to infection. Treatment with the antiretroviral compound Efavirenz (EFZ) mostly resolved these signatures; However, EFZ increased RhoGDI and CD40 signaling in the HIV-infected microglia. This activation was associated with a persistent increase in TNFa expression. This work establishes a tri-culture that recapitulates key features of HIV infection in the CNS and provides a new model to examine the effects of HIV infection and its treatment with antiretrovirals.

pathology↗