Biology subjects

Frei, J. A.

Publications and source records attributed to Frei, J. A..

4 recordsLinked to original sources

bioRxiv2026

Phenotypic screening for small molecules that lower PrP in cultured cells

PrP lowering is a validated therapeutic hypothesis in prion disease. To identify small molecules that reduce PrP levels, we performed phenotypic screening in cultured cells. To prioritize PrP specificity in our primary screen, we generated mouse N2a cells stably expressing GFP and used high content imaging analysis to select compounds that lowered PrP without affecting GFP signal or cell viability. Screening a curated library of 3,492 compounds with annotated mechanisms of action identified two small molecules, EYH (PubChem CID: 71678945) and LCZ (PubChem CID: 24970350), that selectively and dose-dependently lowered PrP. Proteomics on whole cell lysates identified PrP as the #1 or #2 most potently downregulated out of 8,722 proteins detected. Both compounds minimally affected Prnp mRNA, reduced expression of exogenously transfected PrP, and remained potent in non-dividing primary cells, consistent with a post-translational mechanism. Co-treatment with the proteasome inhibitor MG132 yielded accumulation of unglycosylated PrP, demonstrating proteasome clearance of PrP. However, both compounds showed limited or no activity in human cell lines, and failed to reduce PrP in vivo after 14 days of treatment. These findings highlight the challenges associated with mechanism-agnostic phenotypic screening for PrP-lowering compounds and support prioritizing compounds with known mechanisms of action.

neuroscience↗

bioRxiv2020

Altered Expression of Cadherin-8 and Cadherin-11 in Neural Circuit Development: Implications for Autism

Autism spectrum disorder (ASD) is a neurological condition characterized by alterations in social interaction and communication, and restricted and/or repetitive behaviors. The classical type II cadherins cadherin-8 (Cdh8, CDH8) and cadherin-11 (Cdh11, CDH11) have been implicated as autism risk gene candidates. To explore the role of cadherins in the etiology of autism, we investigated their expression patterns during mouse brain development and in autism-specific human tissue. In mice, expression of cadherin-8 and cadherin-11 was developmentally regulated and enriched in the cortex, hippocampus, and thalamus/striatum during the peak of dendrite formation and synaptogenesis. Both cadherins were expressed in synaptic compartments but only cadherin-8 associated with the excitatory synaptic marker neuroligin-1. Induced pluripotent stem cell (iPSC)-derived cortical neural precursor cells (NPCs) and cortical organoids generated from individuals with autism showed upregulated CDH8 expression levels while CDH11 expression levels were downregulated. We used Cdh11 knockout mice of both sexes to analyze the function of cadherin-11, which could help explain phenotypes observed in autism. Cdh11-/- hippocampal neurons exhibited increased dendritic complexity along with altered neuronal and synaptic activity. Similar to the expression profiles in human tissue, levels of cadherin-8 were significantly elevated in Cdh11 knockout brains. Additionally, excitatory synaptic markers neuroligin-1 and PSD-95 were both increased. Together, these results strongly suggest that cadherin-11 is involved in regulating the development of neuronal circuitry and that alterations in the expression levels of cadherin-11 may contribute to the etiology of autism. Significance StatementAutism is a neurodevelopmental condition with high genetic and phenotypic heterogeneity. Multiple genes have been implicated in autism, including the cadherin superfamily of adhesion molecules, cadherin-8 and cadherin-11. This study first characterizes the expression profiles of cadherin-8 and cadherin-11 to understand the potential roles they play in the development of neurons. The study further describes novel contributions of cadherin-11 in neural circuit formation. Loss of cadherin-11 in mice results in altered levels of several synaptic proteins, including PSD-95, neuroligin-1, and cadherin-8, and changes the morphology and activity of excitatory neurons. The levels of cadherin-8 and cadherin-11 in human cells of autistic individuals are both altered, strengthening the hypothesis that these two cadherins may involve in aspects of autism etiology.

neuroscience↗

bioRxiv2019

STXBP5/tomosyn regulates both the small Rho GTPase and the surface expression of AMPA receptors to control the dendritic stability of neurons

Tomosyn, a protein encoded by syntaxin-1-binding protein 5 (STXBP5) gene, has a well-established presynaptic role in the inhibition of neurotransmitter release and the reduction of synaptic transmission by its conical interaction with the soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) machinery. The postsynaptic role of tomosyn in dendritic arborization, spine stability, and trafficking of ionotropic glutamate receptors remains to be elucidated. We used short hairpin RNA (shRNA) to knock down tomosyn in mouse primary neurons to evaluate the postsynaptic cellular function and molecular signaling regulated by tomosyn. Knockdown of tomosyn led to an increase of RhoA GTPase activity accompanied by compromised dendritic arborization, loss of dendritic spines, decreased surface expression of AMPA receptors, and reduced miniature excitatory postsynaptic current (mEPSC) frequency. Inhibiting RhoA signaling was sufficient to rescue the abnormal dendritic morphology and the surface expression of AMPA receptors. The function of tomosyn regulating RhoA is mediated through the N-terminal WD40 motif, where two variants each carrying a single nucleotide mutation in this region, were found in individuals with autism spectrum disorder (ASD). We demonstrated that these variants displayed loss-of-function phenotypes. Unlike the wild-type tomosyn, these two variants failed to restore the reduced dendritic complexity, spine density, as well as decreased surface expression of AMPA receptors in tomosyn knockdown neurons. This study uncovers a critical role of tomosyn, independent of its interaction with the SNARE machinery, in maintaining neuronal function by inhibiting RhoA activity. Further analysis of tomosyn variants also provides a potential mechanism for explaining cellular pathology in ASD.\n\nSignificance StatementThis study unveils a vital role of tomosyn in the maintenance of neuronal morphology, basal synaptic transmission, and AMPA receptor surface expression that is distinct from its presynaptic role. Tomosyn affects dendritic stability and glutamate receptor trafficking via the regulation of the Rho signaling pathway and this interaction is likely independent of the interaction with the dendritic SNARE complex, such as syntaxin-4. The WD40 domain of tomosyn is necessary to conduct the Rho regulation and two autism-associated variants localized at the WD40 domain perturb this function. The current study reveals a novel molecular link between dendritic stability and synaptic function, which could advance a greater understanding of the cellular pathologies involved in neurodevelopmental disorders, such as ASD.

neuroscience↗

bioRxiv2018

Endoglycan plays a role in axon guidance and neuronal migration by negatively regulating cell-cell adhesion

Cell migration and axon guidance are important steps in the formation of neural circuits. Both steps depend on the interactions between cell surface receptors and molecules on cells along the pathway. In addition to cell-cell adhesion, these molecular interactions provide guidance information. The fine-tuning of cell-cell adhesion is an important aspect of cell migration, axon guidance, and synapse formation. Here, we show that Endoglycan, a sialomucin, plays a role in axon guidance and cell migration in the central nervous system. In the absence of Endoglycan, commissural axons failed to properly navigate the midline of the spinal cord. In the developing cerebellum, a lack of Endoglycan prevented migration of Purkinje cells and resulted in a stunted growth of the cerebellar lobes. Taken together, these results support the hypothesis that Endoglycan acts as a lubricant, a negative regulator of cell-cell adhesion, in both commissural axon guidance and Purkinje cell migration.

neuroscience↗