Biology subjects

Bamji, S. X.

Publications and source records attributed to Bamji, S. X..

8 recordsLinked to original sources

bioRxiv2025

Loss of brain insulin production impairs learning and memory in female mice

Diabetes is characterized by dysfunctional insulin release and action, and it is a risk factor for Alzheimers disease, the most common form of dementia. Alterations in brain insulin signalling and metabolism have been linked with Alzheimers disease. The ancestral insulin gene, Ins2, is transcribed locally within the brain. Here we demonstrate that hippocampal Ins2 mRNA is higher in females than males, and modulated by diet. To specifically determine how locally-produced insulin influences hippocampal function, we used mice with germline Ins2 knockout (Ins2-/-) and the normal complement of wildtype Ins1 alleles. Compensation from the Ins1 gene ensured normal glucose tolerance, normal insulin sensitivity, normal fasting insulin, and normal body weight under these conditions. Using the Morris water maze, we found that visuo-spatial learning and memory performance of female Ins2-/- mice was significantly impaired relative to wild-type mice, whereas the performance of male Ins2-/- and wild-type mice did not differ. We profiled isolated hippocampi from female Ins2-/- and littermate control mice using RNA sequencing to provide an unbiased analysis of gene expression differences that underlie these behavioural changes. Cyclin D1 (Ccnd1) was significantly reduced in Ins2-/- mice, prompting us to examine adult neurogenesis using exogenous mitotic marker EdU and the immature neuronal marker doublecortin (DCX). Our data demonstrate female-specific roles for brain-derived Ins2 on learning and memory function in mice. Research in contextO_ST_ABSWhat is already known about this subject?C_ST_ABSO_LIAlzheimers disease and type 2 diabetes share common risk factors and metabolic dysfunction. C_LIO_LIInsulin and insulin signalling are known to have positive effects on neuronal health and cognition. C_LIO_LILocal insulin production has been reported in the brain, including the hippocampus, which plays critical roles in learning and memory, as well as Alzheimers pathophysiology. C_LI What is the key question?O_LIWhat are the consequences of deleting the Ins2 gene, which selectively prevents local brain insulin production, on learning and memory in mice? C_LI What are the new findings?O_LIHippocampal insulin production via the Ins2 gene is sexually dimorphic and modulated by diet. C_LIO_LIKnocking out brain insulin production in Ins2-/- mice does not have significant effects on glucose homeostasis in these diet and housing conditions. C_LIO_LIKnocking out brain insulin production in Ins2-/- mice results in learning and memory impairments in female but not male mice. C_LI How might this impact on clinical practice in the foreseeable future?O_LIThese pre-clinical observations demonstrate a causal role for insulin in learning and memory, but will require additional human studies before they can impact clinical practice. C_LI

physiology↗

bioRxiv2023

Micro-Scale Control of Oligodendrocyte Morphology and Myelination by the Intellectual Disability-Linked Protein Acyltransferase ZDHHC9

Mutations in the X-linked ZDHHC9 gene cause cognitive deficits in humans, with a subset of patients suffering from epilepsy. X-linked intellectual disability (XLID) is often ascribed to neuronal deficits, but here we report that expression of human and mouse ZDHHC9 orthologs is far higher in myelinating oligodendrocytes (OLs) than in other CNS cell types. ZDHHC9 codes for a protein acyltransferase (PAT), and we found that ZDHHC9 is the most highly expressed PAT in OLs. Wild type ZDHHC9 localizes to Golgi outposts in OL processes, but other PATs and XLID mutant forms of ZDHHC9 are restricted to OL cell bodies. Using genetic tools for OL progenitor fate tracing and sparse cell labeling, we show that mice lacking Zdhhc9 have grossly normal OL development but display extensive morphological and structural myelin abnormalities. Consistent with the hypothesis that these deficits are OL-autonomous, they are broadly phenocopied by acute Zdhhc9 knockdown in cultured conditions. Finally, we found that ZDHHC9 palmitoylates Myelin Basic Protein (MBP) in heterologous cells, and that palmitoylation of MBP is impaired in the Zdhhc9 knockout brain. Our findings provide critical insights into the mechanisms of ZDHHC9-associated XLID and shed new light on the palmitoylation-dependent control of myelination.

neuroscience↗

bioRxiv2023

The X-Linked Intellectual Disability gene, ZDHHC9, is important for oligodendrocyte maturation and myelin formation

Two percent of patients with X-linked intellectual disability (XLID) exhibit loss-of-function mutations in the enzyme, ZDHHC9. One of the main anatomical deficits observed in these patients is a decrease in corpus callosum volume and a concurrent disruption in white matter integrity. In this study, we demonstrate that deletion of Zdhhc9 in mice disrupts the balance of mature oligodendrocyte subtypes within the corpus callosum. While overall mature oligodendrocyte numbers are unchanged, there is a marked increase in MOL5/6 cells that are enriched in genes associated with cell adhesion and synapses, and a concomitant decrease in MOL2/3 cells that are enriched in genes associated with myelination. In line with this, we observed a decrease in the density of myelinated axons and disruptions in myelin compaction in the corpus callosum of Zdhhc9 knockout mice. RNA sequencing and proteomic analysis further unveiled a reduction in genes and proteins essential for lipid metabolism, cholesterol synthesis, and myelin compaction. These findings reveal a previously under-appreciated and fundamental role for ZDHHC9 and protein palmitoylation in regulating oligodendrocyte subtype determination and myelinogenesis, offering mechanistic insights into the deficits observed in white matter volume in patients with mutations in ZDHHC9.

neuroscience↗

bioRxiv2022

Activity-dependent post-translational regulation of palmitoylating and de-palmitoylating enzymes in the hippocampus

Activity-induced changes in protein palmitoylation can regulate the plasticity of synaptic connections, critically impacting learning and memory. Palmitoylation is a reversible post-translational modification regulated by both palmitoyl-acyl transferases that mediate palmitoylation and palmitoyl thioesterases that depalmitoylate proteins. However, it is not clear how fluctuations in synaptic activity can mediate the dynamic palmitoylation of neuronal proteins. Using primary hippocampal cultures, we demonstrate that synaptic activity does not impact the transcription of palmitoylating / depalmitoylating enzymes, changes in thioesterase activity, nor post-translational modification of the depalmitoylating enzymes, ABHD17 and APT2. In contrast, synaptic activity does mediate post-translational modification of the palmitoylating enzymes ZDHHC2, ZDHHC5, and ZDHHC9 (but not ZDHHC8) to influence protein-protein interaction, enzyme stability and enzyme function. Post-translational modifications of ZDHHC enzymes were also observed in the hippocampus following fear conditioning. Together, our findings demonstrate that signaling events activated by synaptic activity largely impact activity of the ZDHHC family of palmitoyl-acyl transferases with less influence on the activity of palmitoyl thioesterases.

neuroscience↗

bioRxiv2021

Synaptic Activity-Dependent Changes in the Hippocampal Palmitoylome

Dynamic protein S-palmitoylation is critical for neuronal function, development, and synaptic plasticity. Activity-dependent changes in palmitoylation have been observed for several neuronal substrates, however a full characterization of the activity-regulated palmitoylome is lacking. Here, we use an unbiased approach to identify differentially palmitoylated proteins in the mouse hippocampus following context-dependent fear conditioning. Of the 121 differentially palmitoylated proteins identified 63 were synaptic proteins, while others were associated with metabolic functions, cytoskeletal organization, and signal transduction. The vast majority of synaptic proteins exhibited increased palmitoylation following fear conditioning, whereas proteins that exhibited decreased palmitoylation were predominantly associated with metabolic processes. We show a link between dynamic palmitoylation and synapse plasticity by demonstrating that the palmitoylation of one of our identified proteins, PRG-1/LPPR4, is essential for activity-induced insertion of AMPA receptors into the postsynaptic membrane. Together, this study identifies networks of synaptic proteins whose dynamic palmitoylation may play a central role in learning and memory. SUMMARYThis study identifies networks of proteins that undergo dynamic post-translational palmitoylation in response to fear conditioning and demonstrates that palmitoylation of one of these proteins is essential for synapse plasticity. Together, this illustrates the importance of palmitoylation in learning/memory and synapse plasticity.

neuroscience↗

bioRxiv2021

BrainPalmSeq: A curated RNA-seq database of palmitoylating and de-palmitoylating enzyme expression in the mouse brain

Protein S-palmitoylation is a reversible post-translational lipid modification that plays a critical role in neuronal development and plasticity, while dysregulated S-palmitoylation underlies a number of severe neurological disorders. Dynamic S-palmitoylation is regulated by a large family of ZDHHC palmitoylating enzymes, their accessory proteins, and a small number of known de-palmitoylating enzymes. Here, we curated and analyzed expression data for the proteins that mediate S-palmitoylation from publicly available RNAseq datasets, providing a comprehensive overview of their distribution in the mouse nervous system. We developed a web-tool that enables interactive visualization of the expression patterns for these proteins in the nervous system (http://brainpalmseq.med.ubc.ca/), and explored this resource to find region and cell-type specific expression patterns that give insight into the function of palmitoylating and de-palmitoylating enzymes in the brain and neurological disorders. We found coordinated expression of ZDHHC enzymes with their accessory proteins, de-palmitoylating enzymes and other brain-expressed genes that included an enrichment of S-palmitoylation substrates. Finally, we utilized ZDHHC expression patterns to predict and validate palmitoylating enzyme-substrate interactions.

neuroscience↗

bioRxiv2020

Regulation of Hippocampal Excitatory Synapses by the Zdhhc5 Palmitoyl Acyl Transferase

Palmitoylation is the most common post-translational lipid modification in the brain; however, the role of palmitoylation and palmitoylating enzymes in the nervous system remains elusive. One of these enzymes, Zdhhc5, has previously been shown to regulate synapse plasticity. Here, we report that Zdhhc5 is also essential for the formation of excitatory, but not inhibitory synapses both in vitro and in vivo. We demonstrate in vitro that this is dependent on Zdhhc5s enzymatic activity, its localization at the plasma membrane, and its C-terminal domain which has been shown to be truncated in a patient with schizophrenia. Loss of Zdhhc5 in mice results in a decrease in the density of excitatory hippocampal synapses accompanied by alterations in membrane capacitance and synaptic currents, consistent with an overall decrease in spine number and silent synapses. These findings reveal an important role for Zdhhc5 in the formation and/or maintenance of excitatory synapses.

neuroscience↗

bioRxiv2019

Multi-model functionalization of disease-associated PTEN missense mutations identifies multiple molecular mechanisms underlying protein dysfunction

Functional variomics provides the foundation for personalized medicine by linking genetic variation to disease expression, outcome and treatment, yet its utility is dependent on appropriate assays to evaluate mutation impact on protein function. To fully assess the effects of 106 missense and nonsense variants of PTEN associated with autism spectrum disorder, somatic cancer and PHTS, we take a deep phenotypic profiling approach using 18 assays in 5 model systems spanning diverse cellular environments ranging from molecular function to neuronal morphogenesis and behavior. Variants inducing instability occurred across the protein, resulting in partial to complete loss of function (LoF), which was well correlated across models. However, assays were selectively sensitive to variants located in substrate binding and catalytic domains, which exhibited complete LoF or dominant negativity independent of effects on stability. Our results indicate that full characterization of variant impact requires assays sensitive to instability and a range of protein functions.

genetics↗