GATM and GAMT synthesize creatine locally throughout the mammalian body and within oligodendrocytes of the brain.
The enzymes glycine amidinotransferase, mitochondrial (GATM also known as AGAT) and guanidinoacetate N-methyltransferase (GAMT) function together to synthesize creatine from arginine, glycine, and S-Adenosyl methionine. Deficiency in either enzyme or the creatine transporter, CT1, results in a devastating neurological disorder, Cerebral Creatine Deficiency Syndrome (CCDS). To better understand the pathophysiology of CCDS, we mapped the distribution of GATM and GAMT at single cell resolution, leveraging RNA sequencing analysis combined with in vivo immunofluorescence (IF). Using the mouse as a model system, we find that GATM and GAMT are coexpressed in several tissues with distinct and overlapping cellular sources, implicating local synthesis as an important mechanism of creatine metabolism in numerous organs. Extending previous findings at the RNA level, our analysis demonstrates that oligodendrocytes express the highest level of Gatm and Gamt of any cell type in the body. We confirm this finding in the mouse brain by IF, where GATM localizes to the mitochondria of oligodendrocytes, whereas both oligodendrocytes and cerebral cortical neurons express GAMT. Interestingly, the latter is devoid of GATM. Single nucleus assay for transposase-accessible chromatin sequencing (snATAC-seq) analysis of 4 brain regions highlights a similar primacy of oligodendrocytes in the expression of GATM and GAMT in the human central nervous system. Importantly, an active putative regulatory element within intron 2 of human GATM is detected in oligodendrocytes but not neurons.
View details for DOI 10.1016/j.brainres.2021.147627
View details for PubMedID 34418357
Enantiomers of 2-methylglutamate and 2-methylglutamine selectively impact mouse brain metabolism and behavior.
2021; 11 (1): 8138
Imbalance of excitatory and inhibitory neurotransmission is implicated in a wide range of psychiatric and neurologic disorders. Here we tested the hypothesis that insertion of a methyl group on the stereogenic alpha carbon of L-Glu or L-Gln would impact the gamma-aminobutyric acid (GABA) shunt and the glutamate-glutamine cycle. (S)-2-methylglutamate, or (S)-2MeGlu, was efficiently transported into brain and synaptosomes where it was released by membrane depolarization in a manner equivalent to endogenous L-Glu. (R)-2MeGlu was transported less efficiently into brain and synaptosomes but was not released by membrane depolarization. Each enantiomer of 2MeGlu had limited activity across a panel of over 30 glutamate and GABA receptors. While neither enantiomer of 2MeGlu was metabolized along the GABA shunt, (S)-2MeGlu was selectively converted to (S)-2-methylglutamine, or (S)-2MeGln, which was subsequently slowly hydrolyzed back to (S)-2MeGlu in brain. rac-2MeGln was also transported into brain, with similar efficiency as (S)-2MeGlu. A battery of behavioral tests in young adult wild type mice showed safety with up to single 900mg/kg dose of (R)-2MeGlu, (S)-2MeGlu, or rac-2MeGln, suppressed locomotor activity with single≥100mg/kg dose of (R)-2MeGlu or (S)-2MeGlu. No effect on anxiety or hippocampus-dependent learning was evident. Enantiomers of 2MeGlu and 2MeGln show promise as potential pharmacologic agents and imaging probes for cells that produce or transport L-Gln.
View details for DOI 10.1038/s41598-021-87569-1
View details for PubMedID 33854131
Mass-tag barcoding for multiplexed analysis of human synaptosomes and other anuclear events.
Cytometry. Part A : the journal of the International Society for Analytical Cytology
Mass-tag cell barcoding has increased the throughput, multiplexing, and robustness of multiple cytometry approaches. Previously, we adapted mass cytometry for cells to analyze synaptosome preparations (mass synaptometry or SynTOF), extending mass cytometry to these smaller, anuclear particles. To improve throughput and individual event resolution, we report here the application of palladium-based barcoding in human synaptosomes. Up to 20 individual samples, each with a unique combinatorial barcode, were pooled for labeling with an antibody cocktail. Our synaptosome protocol used six palladium-based barcoding reagents, and in combination with sequential gating increased the identification of presynaptic events approximately fourfold. These same parameters also efficiently resolved two other anuclear particles: human red blood cells and platelets. The addition of palladium-based mass-tag barcoding to our approach improves mass cytometry of synaptic particles.
View details for DOI 10.1002/cyto.a.24340
View details for PubMedID 33818911
Creatine transport and pathological changes in creatine transporter deficient mice.
Journal of inherited metabolic disease
The severe impact on brain function and lack of effective therapy for patients with creatine (Cr) transporter deficiency motivated the generation of three ubiquitous Slc6a8 deficient mice (-/y). While each mouse knock-out line has similar behavioral effects at 2 to 3 months of age, other features critical to the efficient use of these mice in drug discovery are unclear or lacking: the concentration of Cr in brain and heart differ widely between mouse lines, there are limited data on histopathologic changes, and no data on Cr uptake. Here, we determined survival, measured endogenous Cr and uptake of its deuterium-labeled analogue Cr-d3 using a liquid chromatography coupled with tandem mass spectrometry assay, and performed comprehensive histopathologic examination on the Slc6a8-/y mouse developed by Skelton et. al. Our results show that Slc6a8-/y mice have widely varying organ-specific uptake of Cr-d3, significantly diminished growth with the exception of brain, progressive vacuolar myopathy, and markedly shortened lifespan. This article is protected by copyright. All rights reserved.
View details for DOI 10.1002/jimd.12358
View details for PubMedID 33389772
Enantiomers of 4-aminopentanoic acid act as false GABAergic neurotransmitters and impact mouse behavior.
Journal of neurochemistry
Imbalance in the metabolic pathway linking excitatory and inhibitory neurotransmission has been implicated in multiple psychiatric and neurologic disorders. Recently, we described enantiomer-specific effects of 2-methylglutamate, which is not decarboxylated to the corresponding methyl analogue of gamma-aminobutyric acid (GABA): 4-aminopentanoic acid (4APA). Here we tested the hypothesis that 4APA also has enantiomer-specific actions in brain. Mouse cerebral synaptosome uptake (nmol/mg protein over 30 min) of (R)-4APA or (S)-4APA was time- and temperature dependent; however, the R enantiomer had greater uptake, reduction of endogenous GABA concentration, and release following membrane depolarization than did the S enantiomer. (S)-4APA exhibited some weak agonist (GABAA α4β3δ, GABAA α5β2γ2, and GABAB B1/B2) and antagonist (GABAA α6β2γ2) activity while (R)-4APA showed weak agonist activity only with GABAA α5β2γ2. Both 4APA enantiomers (100 mg/kg IP) were detected in mouse brain 10 min after injection, and by one hour had reached concentrations that were stable over six hours; both enantiomers were cleared rapidly from mouse serum over six hours. Two-month old mice had no mortality following 100 to 900 mg/kg IP of each 4APA enantiomer but ded have similar dose-dependent reduction in distance moved in a novel cage. Neither enantiomer at 30 or 100 mg/kg impacted outcomes in twenty-three measures of well-being, activity chamber, or withdrawal from hotplate. Our results suggest that enantiomers of 4APA are active in mouse brain, and that (R)-4APA may act as a novel false neurotransmitter of GABA. Future work will focus on disease models and on possible applications as neuroimaging agents.
View details for DOI 10.1111/jnc.15474
View details for PubMedID 34273193
Single-cell peripheral immunoprofiling of Alzheimer's and Parkinson's diseases.
2020; 6 (48)
Peripheral blood mononuclear cells (PBMCs) may provide insight into the pathogenesis of Alzheimer's disease (AD) or Parkinson's disease (PD). We investigated PBMC samples from 132 well-characterized research participants using seven canonical immune stimulants, mass cytometric identification of 35 PBMC subsets, and single-cell quantification of 15 intracellular signaling markers, followed by machine learning model development to increase predictive power. From these, three main intracellular signaling pathways were identified specifically in PBMC subsets from people with AD versus controls: reduced activation of PLCgamma2 across many cell types and stimulations and selectively variable activation of STAT1 and STAT5, depending on stimulant and cell type. Our findings functionally buttress the now multiply-validated observation that a rare coding variant in PLCG2 is associated with a decreased risk of AD. Together, these data suggest enhanced PLCgamma2 activity as a potential new therapeutic target for AD with a readily accessible pharmacodynamic biomarker.
View details for DOI 10.1126/sciadv.abd5575
View details for PubMedID 33239300
- Mass synaptometry: High-dimensional multi parametric assay for single synapses JOURNAL OF NEUROSCIENCE METHODS 2019; 312: 73–83
An Activity Switch in Human Telomerase Based on RNA Conformation and Shaped by TCAB1.
Ribonucleoprotein enzymes require dynamic conformations of their RNA constituents for regulated catalysis. Human telomerase employs a non-coding RNA (hTR) with a bipartite arrangement of domains-a template-containing core and a distal three-way junction (CR4/5) that stimulates catalysis through unknown means. Here, we show that telomerase activity unexpectedly depends upon the holoenzyme protein TCAB1, which in turn controls conformation of CR4/5. Cells lacking TCAB1 exhibit a marked reduction in telomerase catalysis without affecting enzyme assembly. Instead, TCAB1 inactivation causes unfolding of CR4/5 helices that are required for catalysis and for association with the telomerase reverse-transcriptase (TERT). CR4/5 mutations derived from patients with telomere biology disorders provoke defects in catalysis and TERT binding similar to TCAB1 inactivation. These findings reveal a conformational "activity switch" in human telomerase RNA controlling catalysis and TERT engagement. The identification of two discrete catalytic states for telomerase suggests an intramolecular means for controlling telomerase in cancers and progenitor cells.
View details for PubMedID 29804836
Distributed hepatocytes expressing telomerase repopulate the liver in homeostasis and injury.
Hepatocytes are replenished gradually during homeostasis and robustly after liver injury1, 2. In adults, new hepatocytes originate from the existing hepatocyte pool3-8, but the cellular source of renewing hepatocytes remains unclear. Telomerase is expressed in many stem cell populations, and mutations in telomerase pathway genes have been linked to liver diseases9-11. Here we identify a subset of hepatocytes that expresses high levels of telomerase and show that this hepatocyte subset repopulates the liver during homeostasis and injury. Using lineage tracing from the telomerase reverse transcriptase (Tert) locus in mice, we demonstrate that rare hepatocytes with high telomerase expression (TERTHighhepatocytes) are distributed throughout the liver lobule. During homeostasis, these cells regenerate hepatocytes in all lobular zones, and both self-renew and differentiate to yield expanding hepatocyte clones that eventually dominate the liver. In response to injury, the repopulating activity of TERTHighhepatocytes is accelerated and their progeny cross zonal boundaries. RNA sequencing shows that metabolic genes are downregulated in TERTHighhepatocytes, indicating that metabolic activity and repopulating activity may be segregated within the hepatocyte lineage. Genetic ablation of TERTHighhepatocytes combined with chemical injury causes a marked increase in stellate cell activation and fibrosis. These results provide support for a 'distributed model' of hepatocyte renewal in which a subset of hepatocytes dispersed throughout the lobule clonally expands to maintain liver mass.
View details for PubMedID 29618815
- LRP2 in SHH-dependent adult neurogenesis ELSEVIER SCIENCE BV. 2017: S116
Loss of Lrp2 in Zebrafish Disrupts Pronephric Tubular Clearance But Not Forebrain Development
2011; 240 (6): 1567-1577
Low-density lipoprotein receptor-related protein 2 (LRP2) is a multifunctional cell surface receptor conserved from nematodes to humans. In mammals, it acts as regulator of sonic hedgehog and bone morphogenetic protein pathways in patterning of the embryonic forebrain and as a clearance receptor in the adult kidney. Little is known about activities of this LRP in other phyla. Here, we extend the functional elucidation of LRP2 to zebrafish as a model organism of receptor (dys)function. We demonstrate that expression of Lrp2 in embryonic and larval fish recapitulates the patterns seen in mammalian brain and kidney. Furthermore, we studied the consequence of receptor deficiencies in lrp2 and in lrp2b, a homologue unique to fish, using ENU mutagenesis or morpholino knockdown. While receptor-deficient zebrafish suffer from overt renal resorption deficiency, their brain development proceeds normally, suggesting evolutionary conservation of receptor functions in pronephric duct clearance but not in patterning of the teleost forebrain.
View details for DOI 10.1002/dvdy.22624
View details for Web of Science ID 000291560300025
View details for PubMedID 21455927
View details for PubMedCentralID PMC3278082
LRP2 in ependymal cells regulates BMP signaling in the adult neurogenic niche
JOURNAL OF CELL SCIENCE
2010; 123 (11): 1922–30
The microenvironment of growth factors in the subependymal zone (SEZ) of the adult brain provides the instructive milieu for neurogenesis to proceed in this germinal niche. In particular, tight regulation of bone morphogenetic protein (BMP) signaling is essential to balance proliferative and non-proliferative cell fate specification. However, the regulatory pathways that control BMP signaling in the SEZ are still poorly defined. We demonstrate that LRP2, a clearance receptor for BMP4 is specifically expressed in ependymal cells of the lateral ventricles in the adult brain. Intriguingly, expression is restricted to the ependyma that faces the stem cell niche. Expression is not seen in ependyma elsewhere in the lateral ventricles or in the dentate gyrus, the second major neurogenic zone of the adult brain. We further show that lack of LRP2 expression in adult mice results in impaired proliferation of neural precursor cells in the SEZ resulting in decreased numbers of neuroblasts reaching the olfactory bulb. Reduced neurogenesis coincides with increased BMP4 expression and enhanced activation of downstream mediators phospho-SMAD1/5/8 and ID3 in the stem cell niche. Our findings suggest a novel mechanism whereby LRP2-mediated catabolism of BMP4 in the ependyma modulates the microenvironment of the SEZ and enables adult neurogenesis to proceed.
View details for DOI 10.1242/jcs.065912
View details for Web of Science ID 000277862000011
View details for PubMedID 20460439