Operant Training for Highly Palatable Food Alters Translating Messenger RNA in Nucleus Accumbens D2 Neurons and Reveals a Modulatory Role of Ncdn

BACKGROUND

Highly palatable food triggers behavioral responses including strong motivation. These effects involve the reward system and dopamine neurons, which modulate neurons in the nucleus accumbens (NAc). The molecular mechanisms underlying the long-lasting effects of highly palatable food on feeding behavior are poorly understood.

METHODS

We studied the effects of 2-week operant conditioning of mice with standard or isocaloric highly palatable food. We investigated the behavioral responses and dendritic spine modifications in the NAc. We compared the translating messenger RNA in NAc neurons identified by the type of dopamine receptors they express, depending on the kind of food and training. We tested the consequences of invalidation of an abundant downregulated gene, Ncdn.

RESULTS

Operant conditioning for highly palatable food increased motivation for food even in well-fed mice. In wild-type mice, free choice between regular and highly palatable food increased weight compared with access to regular food only. Highly palatable food increased spine density in the NAc. In animals trained for highly palatable food, translating messenger RNAs were modified in NAc neurons expressing dopamine D2 receptors, mostly corresponding to striatal projection neurons, but not in neurons expressing D1 receptors. Knockout of Ncdn, an abundant downregulated gene, opposed the conditioning-induced changes in satiety-sensitive feeding behavior and apparent motivation for highly palatable food, suggesting that downregulation may be a compensatory mechanism.

CONCLUSIONS

Our results emphasize the importance of messenger RNA alterations in D2 striatal projection neurons in the NAc in the behavioral consequences of highly palatable food conditioning and suggest a modulatory contribution of Ncdn downregulation.

BERNN: Enhancing classification of Liquid Chromatography Mass Spectrometry data with batch effect removal neural networks

Liquid Chromatography Mass Spectrometry (LC-MS) is a powerful method for profiling complex biological samples. However, batch effects typically arise from differences in sample processing protocols, experimental conditions, and data acquisition techniques, significantly impacting the interpretability of results. Correcting batch effects is crucial for the reproducibility of omics research, but current methods are not optimal for the removal of batch effects without compressing the genuine biological variation under study. We propose a suite of Batch Effect Removal Neural Networks (BERNN) to remove batch effects in large LC-MS experiments, with the goal of maximizing sample classification performance between conditions. More importantly, these models must efficiently generalize in batches not seen during training. A comparison of batch effect correction methods across five diverse datasets demonstrated that BERNN models consistently showed the strongest sample classification performance. However, the model producing the greatest classification improvements did not always perform best in terms of batch effect removal. Finally, we show that the overcorrection of batch effects resulted in the loss of some essential biological variability. These findings highlight the importance of balancing batch effect removal while preserving valuable biological diversity in large-scale LC-MS experiments.

Optimal conditions for carrying out trypsin digestions on complex proteomes: From bulk samples to single cells

To identify proteins by the bottom-up mass spectrometry workflow, enzymatic digestion is essential to break down proteins into smaller peptides amenable to both chromatographic separation and mass spectrometric analysis. Trypsin is the most extensively used protease due to its high cleavage specificity and generation of peptides with desirable positively charged N- and C-terminal amino acid residues that are amenable to reverse phase HPLC separation and MS/MS analyses. However, trypsin can yield variable digestion profiles and its protein cleavage activity is interdependent on trypsin source and quality, digestion time and temperature, pH, denaturant, trypsin and substrate concentrations, composition/complexity of the sample matrix, and other factors. There is therefore a need for a more standardized, general-purpose trypsin digestion protocol. Based on a review of the literature we delineate optimal conditions for carrying out trypsin digestions of complex proteomes from bulk samples to limiting amounts of protein extracts. Furthermore, we highlight recent developments and technological advances used in digestion protocols to quantify complex proteomes from single cells. SIGNIFICANCE: Currently, bottom-up MS-based proteomics is the method of choice for global proteome analysis. Since trypsin is the most utilized protease in bottom-up MS proteomics, delineating optimal conditions for carrying out trypsin digestions of complex proteomes in samples ranging from tissues to single cells should positively impact a broad range of biomedical research.

Mass spectrometry in cerebrospinal fluid uncovers association of glycolysis biomarkers with Alzheimer's disease in a large clinical sample

Alzheimer's disease (AD) is a complex and heterogeneous neurodegenerative disorder with contributions from multiple pathophysiological pathways. One of the long-recognized and important features of AD is disrupted cerebral glucose metabolism, but the underlying molecular basis remains unclear. In this study, unbiased mass spectrometry was used to survey CSF from a large clinical cohort, comparing patients who are either cognitively unimpaired (CU; n = 68), suffering from mild-cognitive impairment or dementia from AD (MCI-AD, n = 95; DEM-AD, n = 72), or other causes (MCI-other, n = 77; DEM-other, n = 23), or Normal Pressure Hydrocephalus (NPH, n = 57). The results revealed changes related to altered glucose metabolism. In particular, two glycolytic enzymes, pyruvate kinase (PKM) and aldolase A (ALDOA), were found to be upregulated in CSF from patients with AD compared to those with other neurological conditions. Increases in full-length PKM and ALDOA levels in CSF were confirmed with immunoblotting. Levels of these enzymes furthermore correlated negatively with CSF glucose in matching CSF samples. PKM levels were also found to be increased in AD in publicly available brain-tissue data. These results indicate that ALDOA and PKM may act as technically-robust potential biomarkers of glucose metabolism dysregulation in AD.

Human-specific features and developmental dynamics of the brain N-glycome

Comparative "omics" studies have revealed unique aspects of human neurobiology, yet an evolutionary perspective of the brain N-glycome is lacking. We performed multiregional characterization of rat, macaque, chimpanzee, and human brain N-glycomes using chromatography and mass spectrometry and then integrated these data with complementary glycotranscriptomic data. We found that, in primates, the brain N-glycome has diverged more rapidly than the underlying transcriptomic framework, providing a means for rapidly generating additional interspecies diversity. Our data suggest that brain N-glycome evolution in hominids has been characterized by an overall increase in complexity coupled with a shift toward increased usage of α(2-6)-linked N-acetylneuraminic acid. Moreover, interspecies differences in the cell type expression pattern of key glycogenes were identified, including some human-specific differences, which may underpin this evolutionary divergence. Last, by comparing the prenatal and adult human brain N-glycomes, we uncovered region-specific neurodevelopmental pathways that lead to distinct spatial N-glycosylation profiles in the mature brain.

Chronic GCPII (glutamate-carboxypeptidase-II) inhibition reduces pT217Tau levels in the entorhinal and dorsolateral prefrontal cortices of aged macaques

Introduction

Current approaches for treating sporadic Alzheimer's disease (sAD) focus on removal of amyloid beta 1-42 (Aβ1-42) or phosphorylated tau, but additional strategies are needed to reduce neuropathology at earlier stages prior to neuronal damage. Longstanding data show that calcium dysregulation is a key etiological factor in sAD, and the cortical neurons most vulnerable to tau pathology show magnified calcium signaling, for example in dorsolateral prefrontal cortex (dlPFC) and entorhinal cortex (ERC). In primate dlPFC and ERC, type 3 metabotropic glutamate receptors (mGluR3s) are predominately post-synaptic, on spines, where they regulate cAMP-calcium signaling, a process eroded by inflammatory glutamate carboxypeptidase II (GCPII) actions. The current study tested whether enhancing mGluR3 regulation of calcium via chronic inhibition of GCPII would reduce tau hyperphosphorylation in aged macaques with naturally-occurring tau pathology.

Methods

Aged rhesus macaques were treated daily with the GCPII inhibitor, 2-MPPA (2-3-mercaptopropyl-penanedioic acid (2-MPPA)),Aged rhesus macaques were treated daily with the GCPII inhibitor, 2-MPPA (2-3-mercaptopropyl-penanedioic acid (2-MPPA)).

Results

Aged macaques that received 2-MPPA had significantly lower pT217Tau levels in dlPFC and ERC, and had lowered plasma pT217Tau levels from baseline. pT217Tau levels correlated significantly with GCPII activity in dlPFC. Both 2-MPPA- and vehicle-treated monkeys showed cognitive improvement; 2-MPPA had no apparent side effects. Exploratory CSF analyses indicated reduced pS202Tau with 2-MPPA administration, confirmed in dlPFC samples.

Discussion

These data provide proof-of-concept support that GCPII inhibition can reduce tau hyperphosphorylation in the primate cortices most vulnerable in sAD. GCPII inhibition may be particularly helpful in reducing the risk of sAD caused by inflammation. These data in nonhuman primates should encourage future research on this promising mechanism.

Highlights

Inflammation is a key driver of sporadic Alzheimer's disease.GCPII inflammatory signaling in brain decreases mGluR3 regulation of calcium.Chronic inhibition of GCPII inflammatory signaling reduced pT217Tau in aged monkeys.GCPII inhibition is a novel strategy to help prevent tau pathology at early stages.

Peripheral signature of altered synaptic integrity in young onset cannabis use disorder: A proteomic study of circulating extracellular vesicles

BACKGROUND

Rates of Cannabis Use Disorder (CUD) are highest amongst young adults. Paucity of brain tissue samples limits the ability to examine the molecular basis of cannabis related neuropathology. Proteomic studies of neuron-derived extracellular vesicles (NDEs) isolated from the biofluids may reveal markers of neuropathology in CUD.

METHODS

NDEs were extracted using ExoSORT, an immunoaffinity method to enrich NDEs from plasma samples from patients with young onset CUD and matched controls. Differential proteomic profiles were explored with Label Free Quantification (LFQ) mass spectrometry. Selected proteins were validated using orthogonal methods.

RESULTS

A total of 231 (±10) proteins were identified in NDE preparations from CUD and controls of which 28 were differentially abundant between groups. The difference in abundance of properdin (CFP gene) was statistically significant. SHANK1 (SHANK1 gene), an adapter protein at the post-synaptic density, was nominally depleted in the CUD NDE preparations.

CONCLUSION

In this pilot study, we noted a decrease in SHANK1 protein, involved in the structural and functional integrity of glutamatergic post-synapse, a potential peripheral signature of CUD neuropathology. The study shows that LFQ mass spectrometry proteomic analysis of NDEs derived from plasma may yield important insights into the synaptic pathology associated with CUD.

Mass Spectrometry in Cerebrospinal Fluid Uncovers Association of Glycolysis Biomarkers with Alzheimer's Disease in a Large Clinical Sample

Background

Alzheimer's disease (AD) is a complex heterogenous neurodegenerative disorder, characterized by multiple pathophysiologies, including disruptions in brain metabolism. Defining markers for patient stratification across these pathophysiologies is an important step towards personalized treatment of AD. Efficient brain glucose metabolism is essential to sustain neuronal activity, but hypometabolism is consistently observed in AD. The molecular changes underlying these observations remain unclear. Recent studies have indicated dysregulation of several glycolysis markers in AD cerebrospinal fluid and tissue.

Methods

In this study, unbiased mass spectrometry was used to perform a deep proteomic survey of cerebrospinal fluid (CSF) from a large-scale clinically complex cohort to uncover changes related to impaired glucose metabolism.

Results

Two glycolytic enzymes, Pyruvate kinase (PKM) and Aldolase A (ALDOA) were found to be specifically upregulated in AD CSF compared to other non-AD groups. Presence of full-length protein of these enzymes in CSF was confirmed through immunoblotting. Levels of tryptic peptides of these enzymes correlated significantly with CSF glucose and CSF lactate in matching CSF samples.

Conclusions

The results presented here indicate a general dysregulation of glucose metabolism in the brain in AD. We highlight two markers ALDOA and PKM that may act as potential functionally-relevant biomarkers of glucose metabolism dysregulation in AD.

Differential Effects of Cocaine and Morphine on the Diurnal Regulation of the Mouse Nucleus Accumbens Proteome

Substance use disorders are associated with disruptions in sleep and circadian rhythms that persist during abstinence and may contribute to relapse risk. Repeated use of substances such as psychostimulants and opioids may lead to significant alterations in molecular rhythms in the nucleus accumbens (NAc), a brain region central to reward and motivation. Previous studies have identified rhythm alterations in the transcriptome of the NAc and other brain regions following the administration of psychostimulants or opioids. However, little is known about the impact of substance use on the diurnal rhythms of the proteome in the NAc. We used liquid chromatography coupled to tandem mass spectrometry-based quantitative proteomics, along with a data-independent acquisition analysis pipeline, to investigate the effects of cocaine or morphine administration on diurnal rhythms of proteome in the mouse NAc. Overall, our data reveal cocaine and morphine differentially alter diurnal rhythms of the proteome in the NAc, with largely independent differentially expressed proteins dependent on time-of-day. Pathways enriched from cocaine altered protein rhythms were primarily associated with glucocorticoid signaling and metabolism, whereas morphine was associated with neuroinflammation. Collectively, these findings are the first to characterize the diurnal regulation of the NAc proteome and demonstrate a novel relationship between the phase-dependent regulation of protein expression and the differential effects of cocaine and morphine on the NAc proteome. The proteomics data in this study are available via ProteomeXchange with identifier PXD042043.

Uncovering biology by single-cell proteomics

Recent technological advances have opened the door to single-cell proteomics that can answer key biological questions regarding how protein expression, post-translational modifications, and protein interactions dictate cell state in health and disease.

Operant training for highly palatable food alters translating mRNA in nucleus accumbens D2 neurons and reveals a modulatory role of Neurochondrin

BACKGROUND

Highly palatable food triggers behavioral alterations reminiscent of those induced by addictive drugs. These effects involve the reward system and dopamine neurons, which modulate neurons in the nucleus accumbens (NAc). The molecular mechanisms underlying the effects of highly palatable food on feeding behavior are poorly understood.

METHODS

We studied the effects of 2-week operant conditioning of mice with standard or isocaloric highly palatable food. We investigated the behavioral effects and dendritic spine modifications in the NAc. We compared the translating mRNA in NAc neurons identified by the type of dopamine receptors they express, depending on the type of food and training. We tested the consequences of invalidation of an abundant downregulated gene, Ncdn (Neurochondrin).

RESULTS

Operant conditioning for highly palatable food increases motivation for food even in well-fed mice. In control mice, free access to regular or highly palatable food results in increased weight as compared to regular food only. Highly palatable food increases spine density in the NAc. In animals trained for highly palatable food, translating mRNAs are modified in NAc dopamine D2-receptor-expressing neurons, mostly corresponding to striatal projection neurons, but not in those expressing D1-receptors. Knock-out of Ncdn, an abundant down-regulated gene, opposes the conditioning-induced changes in satiety-sensitive feeding behavior and apparent motivation for highly palatable food, suggesting down-regulation may be a compensatory mechanism.

CONCLUSIONS

Our results emphasize the importance of mRNA alterations D2 striatal projection neurons in the NAc in the behavioral consequences of highly palatable food conditioning and suggest a modulatory contribution of Ncdn downregulation.

Differential Effects of Cocaine and Morphine on the Diurnal Regulation of the Mouse Nucleus Accumbens Proteome

Substance use disorders (SUDs) are associated with disruptions in sleep and circadian rhythms that persist during abstinence and may contribute to relapse risk. Repeated use of substances such as psychostimulants and opioids may lead to significant alterations in molecular rhythms in the nucleus accumbens (NAc), a brain region central to reward and motivation. Previous studies have identified rhythm alterations in the transcriptome of the NAc and other brain regions following the administration of psychostimulants or opioids. However, little is known about the impact of substance use on the diurnal rhythms of the proteome in the NAc. We used liquid chromatography coupled to tandem mass spectrometry-based (LC-MS/MS) quantitative proteomics, along with a data-independent acquisition (DIA) analysis pipeline, to investigate the effects of cocaine or morphine administration on diurnal rhythms of proteome in the mouse NAc. Overall, our data reveals cocaine and morphine differentially alters diurnal rhythms of the proteome in the NAc, with largely independent differentially expressed proteins dependent on time-of-day. Pathways enriched from cocaine altered protein rhythms were primarily associated with glucocorticoid signaling and metabolism, whereas morphine was associated with neuroinflammation. Collectively, these findings are the first to characterize the diurnal regulation of the NAc proteome and demonstrate a novel relationship between phase-dependent regulation of protein expression and the differential effects of cocaine and morphine on the NAc proteome.

PP1β opposes classic PP1 function, inhibiting spine maturation and promoting LTP

Protein phosphatase 1 (PP1) regulates synaptic plasticity and has been described as a molecular constraint on learning and memory. There are three neuronal isoforms, PP1α, PP1β, and PP1γ, but little is known about their individual functions. PP1α and PP1γ are assumed to mediate the effects of PP1 on learning and memory based on their enrichment at dendritic spines and their preferential binding to neurabin and spinophilin, major PP1 synaptic scaffolding proteins. However, it was recently discovered that human de novo PP1β mutations cause intellectual disability, suggesting an important but ill-defined role for PP1β. In this study, we investigated the functions of each PP1 isoform in hippocampal synaptic physiology using conditional CA1-specific knockout mice. In stark contrast to classic PP1 function, we found that PP1β promotes synaptic plasticity as well as spatial memory. These changes in synaptic plasticity and memory are accompanied by changes in GluA1 phosphorylation, GluN2A levels, and dendritic spine density and morphology, including silent synapse number. These functions of PP1β reveal a previously unidentified signaling pathway regulating spine maturation and plasticity, broadening our understanding of the complex role of PP1 in synaptic physiology.

Adult-specific Reelin expression alters striatal neuronal organization: implications for neuropsychiatric disorders

In addition to neuronal migration, brain development, and adult plasticity, the extracellular matrix protein Reelin has been extensively implicated in human psychiatric disorders such as schizophrenia, bipolar disorder, and autism spectrum disorder. Moreover, heterozygous reeler mice exhibit features reminiscent of these disorders, while overexpression of Reelin protects against its manifestation. However, how Reelin influences the structure and circuits of the striatal complex, a key region for the above-mentioned disorders, is far from being understood, especially when altered Reelin expression levels are found at adult stages. In the present study, we took advantage of complementary conditional gain- and loss-of-function mouse models to investigate how Reelin levels may modify adult brain striatal structure and neuronal composition. Using immunohistochemical techniques, we determined that Reelin does not seem to influence the striatal patch and matrix organization (studied by μ-opioid receptor immunohistochemistry) nor the density of medium spiny neurons (MSNs, studied with DARPP-32). We show that overexpression of Reelin leads to increased numbers of striatal parvalbumin- and cholinergic-interneurons, and to a slight increase in tyrosine hydroxylase-positive projections. We conclude that increased Reelin levels might modulate the numbers of striatal interneurons and the density of the nigrostriatal dopaminergic projections, suggesting that these changes may be involved in the protection of Reelin against neuropsychiatric disorders.

DARPP-32/protein phosphatase 1 regulates Rasgrp2 as a novel component of dopamine D1 receptor signaling in striatum

Dopamine regulates psychomotor function by D1 receptor/PKA-dependent phosphorylation of DARPP-32. DARPP-32, phosphorylated at Thr34 by PKA, inhibits protein phosphatase 1 (PP1), and amplifies the phosphorylation of other PKA/PP1 substrates following D1 receptor activation. In addition to the D1 receptor/PKA/DARPP-32 signaling pathway, D1 receptor stimulation is known to activate Rap1/ERK signaling. Rap1 activation is mediated through the phosphorylation of Rasgrp2 (guanine nucleotide exchange factor; activation) and Rap1gap (GTPase-activating protein; inhibition) by PKA. In this study, we investigated the role of PP1 inhibition by phospho-Thr34 DARPP-32 in the D1 receptor-induced phosphorylation of Rasgrp2 and Rap1gap at PKA sites. The analyses in striatal and NAc slices from wild-type and DARPP-32 knockout mice revealed that the phosphorylation of Rasgrp2 at Ser116/Ser117 and Ser586, but not of Rasgrp2 at Ser554 or Rap1gap at Ser441 or Ser499 induced by a D1 receptor agonist, is under the control of the DARPP-32/PP1. The results were supported by pharmacological analyses using a selective PP1 inhibitor, tautomycetin. In addition, analyses using a PP1 and PP2A inhibitor, okadaic acid, revealed that all sites of Rasgrp2 and Rap1gap were regulated by PP2A. Thus, the interactive machinery of DARPP-32/PP1 may contribute to efficient D1 receptor signaling via Rasgrp2/Rap1 in the striatum.

Protein phosphatase-1 inhibitor-2 promotes PP1γ positive regulation of synaptic transmission

Inhibitor-2 (I-2) is a prototypic inhibitor of protein phosphatase-1 (PP1), a major serine-threonine phosphatase that regulates synaptic plasticity and learning and memory. Although I-2 is a potent inhibitor of PP1 in vitro, our previous work has elucidated that, in vivo, I-2 may act as a positive regulator of PP1. Here we show that I-2 and PP1γ, but not PP1α, positively regulate synaptic transmission in hippocampal neurons. Moreover, we demonstrated that I-2 enhanced PP1γ interaction with its major synaptic scaffold, neurabin, by Förster resonance energy transfer (FRET)/Fluorescence lifetime imaging microscopy (FLIM) studies, while having a limited effect on PP1 auto-inhibitory phosphorylation. Furthermore, our study indicates that the effect of I-2 on PP1 activity in vivo is dictated by I-2 threonine-72 phosphorylation. Our work thus demonstrates a molecular mechanism by which I-2 positively regulates PP1 function in synaptic transmission.

Translational profiling of mouse dopaminoceptive neurons reveals region-specific gene expression, exon usage, and striatal prostaglandin E2 modulatory effects

Forebrain dopamine-sensitive (dopaminoceptive) neurons play a key role in movement, action selection, motivation, and working memory. Their activity is altered in Parkinson's disease, addiction, schizophrenia, and other conditions, and drugs that stimulate or antagonize dopamine receptors have major therapeutic applications. Yet, similarities and differences between the various neuronal populations sensitive to dopamine have not been systematically explored. To characterize them, we compared translating mRNAs in the dorsal striatum and nucleus accumbens neurons expressing D1 or D2 dopamine receptor and prefrontal cortex neurons expressing D1 receptor. We identified genome-wide cortico-striatal, striatal D1/D2 and dorso/ventral differences in the translating mRNA and isoform landscapes, which characterize dopaminoceptive neuronal populations. Expression patterns and network analyses identified novel transcription factors with presumptive roles in these differences. Prostaglandin E2 (PGE2) was a candidate upstream regulator in the dorsal striatum. We pharmacologically explored this hypothesis and showed that misoprostol, a PGE2 receptor agonist, decreased the excitability of D2 striatal projection neurons in slices, and diminished their activity in vivo during novel environment exploration. We found that misoprostol also modulates mouse behavior including by facilitating reversal learning. Our study provides powerful resources for characterizing dopamine target neurons, new information about striatal gene expression patterns and regulation. It also reveals the unforeseen role of PGE2 in the striatum as a potential neuromodulator and an attractive therapeutic target.

Glutamate Carboxypeptidase II in Aging Rat Prefrontal Cortex Impairs Working Memory Performance

Glutamate carboxypeptidase II (GCPII) expression in brain is increased by inflammation, and reduces NAAG (N-acetyl aspartyl glutamate) stimulation of mGluR3 signaling. Genetic insults in this signaling cascade are increasingly linked to cognitive disorders in humans, where increased GCPII and or decreased NAAG-mGluR3 are associated with impaired prefrontal cortical (PFC) activation and cognitive impairment. As aging is associated with increased inflammation and PFC cognitive deficits, the current study examined GCPII and mGluR3 expression in the aging rat medial PFC, and tested whether GCPII inhibition with 2-(3-mercaptopropyl) pentanedioic acid (2-MPPA) would improve working memory performance. We found that GCPII protein was expressed on astrocytes and some microglia as expected from previous studies, but was also prominently expressed on neurons, and showed increased levels with advancing age. Systemic administration of the GCPII inhibitor, 2-MPPA, improved working memory performance in young and aged rats, and also improved performance after local infusion into the medial PFC. As GCPII inhibitors are well-tolerated, they may provide an important new direction for treatment of cognitive disorders associated with aging and/or inflammation.

Simple, Single-Shot Phosphoproteomic Analysis of Heat-Stable Tau Identifies Age-Related Changes in pS235- and pS396-Tau Levels in Non-human Primates

Age is the most significant risk factor for Alzheimer's disease (AD), and understanding its role in specific aspects of AD pathology will be critical for therapeutic development. Neurofibrillary tangles composed of hyperphosphorylated tau are a quintessential hallmark of AD. To study age-related changes in tau phosphorylation, we developed a simple, antibody-free approach for single shot analysis of tau phosphorylation across the entire protein by liquid-chromatography tandem mass spectrometry. This methodology is species independent; thus, while initially developed in a rodent model, we utilized this technique to analyze 36 phosphorylation sites on rhesus monkey tau from the prefrontal cortex (PFC), a region vulnerable to AD-linked degeneration. Data are available via ProteomeXchange with identifier PXD027971. We identified novel, age-related changes in tau phosphorylation in the rhesus monkey PFC and analyzed patterns of phosphorylation change across domains of the protein. We confirmed a significant increase and positive correlation with age of phosphorylated serine 235 tau and phosphorylated serine 396 tau levels in an expanded cohort of 14 monkeys. Histology showed robust labeling for tau phosphorylated at these sites in vulnerable layer III pyramidal cells in the PFC. The results presented in this study suggest an important role of the natural aging process in tau phosphorylation in rhesus monkey.

Synaptic proteins associated with cognitive performance and neuropathology in older humans revealed by multiplexed fractionated proteomics

Alzheimer's disease (AD) is defined by the presence of abundant amyloid-β (Aβ) and tau neuropathology. While this neuropathology is necessary for AD diagnosis, it is not sufficient for causing cognitive impairment. Up to one third of community dwelling older adults harbor intermediate to high levels of AD neuropathology at death yet demonstrate no significant cognitive impairment. Conversely, there are individuals who exhibit dementia with no gross explanatory neuropathology. In prior studies, synapse loss correlated with cognitive impairment. To understand how synaptic composition changes in relation to neuropathology and cognition, multiplexed liquid chromatography mass-spectrometry was used to quantify enriched synaptic proteins from the parietal association cortex of 100 subjects with contrasting levels of AD pathology and cognitive performance. 123 unique proteins were significantly associated with diagnostic category. Functional analysis showed enrichment of serotonin release and oxidative phosphorylation categories in normal (cognitively unimpaired, low neuropathology) and "resilient" (unimpaired despite AD pathology) individuals. In contrast, frail individuals, (low pathology, impaired cognition) showed a metabolic shift towards glycolysis and increased presence of proteasome subunits.

GSAP regulates lipid homeostasis and mitochondrial function associated with Alzheimer's disease

Biochemical, pathogenic, and human genetic data confirm that GSAP (γ-secretase activating protein), a selective γ-secretase modulatory protein, plays important roles in Alzheimer's disease (AD) and Down's syndrome. However, the molecular mechanism(s) underlying GSAP-dependent pathogenesis remains largely elusive. Here, through unbiased proteomics and single-nuclei RNAseq, we identified that GSAP regulates multiple biological pathways, including protein phosphorylation, trafficking, lipid metabolism, and mitochondrial function. We demonstrated that GSAP physically interacts with the Fe65-APP complex to regulate APP trafficking/partitioning. GSAP is enriched in the mitochondria-associated membrane (MAM) and regulates lipid homeostasis through the amyloidogenic processing of APP. GSAP deletion generates a lipid environment unfavorable for AD pathogenesis, leading to improved mitochondrial function and the rescue of cognitive deficits in an AD mouse model. Finally, we identified a novel GSAP single-nucleotide polymorphism that regulates its brain transcript level and is associated with an increased AD risk. Together, our findings indicate that GSAP impairs mitochondrial function through its MAM localization and that lowering GSAP expression reduces pathological effects associated with AD.

Sex Differences in the Ventral Tegmental Area and Nucleus Accumbens Proteome at Baseline and Following Nicotine Exposure

Sex differences in behaviors relevant to nicotine addiction have been observed in rodent models and human subjects. Behavioral, imaging, and epidemiological studies also suggest underlying sex differences in mesolimbic dopamine signaling pathways. In this study we evaluated the proteome in the ventral tegmental area (VTA) and nucleus accumbens (NAc) shell in male and female mice. Experimental groups included two mouse strains (C3H/HeJ and C57BL/6J) at baseline, a sub-chronic, rewarding regimen of nicotine in C3H/HeJ mice, and chronic nicotine administration and withdrawal in C57BL/6J mice. Isobaric labeling with a TMT 10-plex system, sample fractionation, and tandem mass spectrometry were used to quantify changes in protein abundance. In C3H/HeJ mice, similar numbers of proteins were differentially regulated between sexes at baseline compared with within each sex after sub-chronic nicotine administration. In C57BL/6J mice, there were significantly greater numbers of proteins differentially regulated between sexes at baseline compared with within each sex after chronic nicotine administration and withdrawal. Despite differences by sex, strain, and nicotine exposure parameters, glial fibrillary acidic protein (GFAP) and dopamine and cAMP-regulated phosphoprotein of 32 kDa (DARPP-32, Ppp1r1b) were repeatedly identified as significantly altered proteins, especially in the VTA. Further, network analyses showed sex- and nicotine-dependent regulation of a number of signaling pathways, including dopaminergic signaling. Sub-chronic nicotine exposure in female mice increased proteins related to dopaminergic signaling in the NAc shell but decreased them in the VTA, whereas the opposite pattern was observed in male mice. In contrast, dopaminergic signaling pathways were similarly upregulated in both male and female VTA after chronic nicotine and withdrawal. Overall, this study identifies significant sex differences in the proteome of the mesolimbic system, at baseline and after nicotine reward or withdrawal, which may help explain differential trajectories and susceptibility to nicotine addiction in males and females.

Pathogenic MAST3 Variants in the STK Domain Are Associated with Epilepsy

OBJECTIVE

The MAST family of microtubule-associated serine-threonine kinases (STKs) have distinct expression patterns in the developing and mature human and mouse brain. To date, only MAST1 has been conclusively associated with neurological disease, with de novo variants in individuals with a neurodevelopmental disorder, including a mega corpus callosum.

METHODS

Using exome sequencing, we identify MAST3 missense variants in individuals with epilepsy. We also assess the effect of these variants on the ability of MAST3 to phosphorylate the target gene product ARPP-16 in HEK293T cells.

RESULTS

We identify de novo missense variants in the STK domain in 11 individuals, including 2 recurrent variants p.G510S (n = 5) and p.G515S (n = 3). All 11 individuals had developmental and epileptic encephalopathy, with 8 having normal development prior to seizure onset at <2 years of age. All patients developed multiple seizure types, 9 of 11 patients had seizures triggered by fever and 9 of 11 patients had drug-resistant seizures. In vitro analysis of HEK293T cells transfected with MAST3 cDNA carrying a subset of these patient-specific missense variants demonstrated variable but generally lower expression, with concomitant increased phosphorylation of the MAST3 target, ARPP-16, compared to wild-type. These findings suggest the patient-specific variants may confer MAST3 gain-of-function. Moreover, single-nuclei RNA sequencing and immunohistochemistry shows that MAST3 expression is restricted to excitatory neurons in the cortex late in prenatal development and postnatally.

INTERPRETATION

In summary, we describe MAST3 as a novel epilepsy-associated gene with a potential gain-of-function pathogenic mechanism that may be primarily restricted to excitatory neurons in the cortex. ANN NEUROL 2021;90:274-284.

Longitudinal CSF proteomics identifies NPTX2 as a prognostic biomarker of Alzheimer's disease

Introduction: Biomarkers that reflect pathologic processes affecting neuronal function during preclinical and early stages of Alzheimer's disease (AD) are needed to aid drug development.

Methods: A targeted, stable isotope, quantitative mass spectrometry‐based investigation of longitudinal changes in concentrations of previously identified candidate biomarkers was performed in cerebrospinal fluid (CSF) of Alzheimer's Disease Neuroimaging Initiative participants who were classified as cognitively normal (CN; n = 76) or with mild cognitive impairment (MCI; n = 111) at baseline.

Results: Of the candidate biomarkers, the CSF concentration of neuronal pentraxin 2 (NPTX2), a protein involved in synaptic function, exhibited rates of change that were significantly different between three comparison groups (i.e., CN vs. MCI participants; AD pathology positive vs. negative defined by phosphorylated tau181/amyloid beta1‐42 ratio; and clinical progressors vs. non‐progressors). The rate of change of NPTX2 also significantly correlated with declining cognition.

Discussion: CSF NPTX2 concentration is a strong prognostic biomarker candidate of accelerated cognitive decline with potential use as a therapeutic target.

Age-related calcium dysregulation linked with tau pathology and impaired cognition in non-human primates

Introduction

The etiology of sporadic Alzheimer's disease (AD) requires non‐genetically modified animal models.

Methods

The relationship of tau phosphorylation to calcium‐cyclic adenosine monophosphate (cAMP)‐protein kinase A (PKA) dysregulation was analyzed in aging rhesus macaque dorsolateral prefrontal cortex (dlPFC) and rat primary cortical neurons using biochemistry and immuno‐electron microscopy. The influence of calcium leak from ryanodine receptors (RyRs) on neuronal firing and cognitive performance was examined in aged macaques.

Results

Aged monkeys naturally develop hyperphosphorylated tau, including AD biomarkers (AT8 (pS202/pT205) and pT217) and early tau pathology markers (pS214 and pS356) that correlated with evidence of increased calcium leak (pS2808‐RyR2). Calcium also regulated early tau phosphorylation in vitro. Age‐related reductions in the calcium‐binding protein, calbindin, and in phosphodiesterase PDE4D were seen within dlPFC pyramidal cell dendrites. Blocking RyRs with S107 improved neuronal firing and cognitive performance in aged macaques.

Discussion

Dysregulated calcium signaling confers risk for tau pathology and provides a potential therapeutic target.

Loss of Ftsj1 perturbs codon-specific translation efficiency in the brain and is associated with X-linked intellectual disability

FtsJ RNA 2'-O-methyltransferase 1 (FTSJ1) gene has been implicated in X-linked intellectual disability (XLID), but the molecular pathogenesis is unknown. We show that Ftsj1 is responsible for 2'-O-methylation of 11 species of cytosolic transfer RNAs (tRNAs) at the anticodon region, and these modifications are abolished in Ftsj1 knockout (KO) mice and XLID patient-derived cells. Loss of 2'-O-methylation in Ftsj1 KO mouse selectively reduced the steady-state level of tRNA^Phe in the brain, resulting in a slow decoding at Phe codons. Ribosome profiling showed that translation efficiency is significantly reduced in a subset of genes that need to be efficiently translated to support synaptic organization and functions. Ftsj1 KO mice display immature synaptic morphology and aberrant synaptic plasticity, which are associated with anxiety-like and memory deficits. The data illuminate a fundamental role of tRNA modification in the brain through regulation of translation efficiency and provide mechanistic insights into FTSJ1-related XLID.

Phosphodiesterase PDE4D Is Decreased in Frontal Cortex of Aged Rats and Positively Correlated With Working Memory Performance and Inversely Correlated With PKA Phosphorylation of Tau

Age is the largest risk factor for Alzheimer’s disease (AD) and contributes to cognitive impairment in otherwise healthy individuals. Thus, it is critical that we better understand the risk aging presents to vulnerable regions of the brain and carefully design therapeutics to address those effects. In this study we examined age-related changes in cAMP-regulatory protein, phosphodiesterase 4D (PDE4D). Inhibition of PDE4D is currently under investigation as a therapeutic target for AD based on memory-enhancing effects in rodent hippocampus. Therefore, it is important to understand the role of PDE4D in brain regions particularly vulnerable to disease such as the frontal association cortex (FC), where cAMP signaling can impair working memory via opening of potassium channels. We found that PDE4D protein level was decreased in the FC of both moderately and extremely aged rats, and that PDE4D level was correlated with performance on a FC-dependent working memory task. In extremely aged rats, PDE4D was also inversely correlated with levels of phosphorylated tau at serine 214 (S214), a site phosphorylated by protein kinase A. In vitro studies of the PDE4D inhibitor, GEBR-7b, further illustrated that inhibition of PDE4D activity enhanced phosphorylation of tau. pS214-tau phosphorylation is associated with early AD tau pathology, promotes tau dissociation from microtubules and primes subsequent tau hyperphosphorylation at other critical AD-related sites. Age-related loss of PDE4D may thus contribute to the specific vulnerability of the FC to degeneration in AD, and play a critical role in normal cAMP regulation, cautioning against the use of pan-PDE4D inhibitors as therapeutics.

cAMP-regulated phosphoproteins DARPP-32, ARPP16/19, and RCS modulate striatal signal transduction through protein kinases and phosphatases

Decades of research led by Paul Greengard identified protein phosphorylation as a ubiquitous and vital post-translational modification involved in many neuronal signaling pathways. In particular, his discovery that second messenger-regulated protein phosphorylation plays a central role in the propagation and transduction of signals in the nervous system has been essential in understanding the molecular mechanisms of neuronal communication. The establishment of dopamine (DA) as an essential neurotransmitter in the central nervous system, combined with observations that DA activates G-protein-coupled receptors to control the production of cyclic adenosine monophosphate (cAMP) in postsynaptic neurons, has provided fundamental insight into the regulation of neurotransmission. Notably, DA signaling in the striatum is involved in many neurological functions such as control of locomotion, reward, addiction, and learning, among others. This review focuses on the history, characterization, and function of cAMP-mediated regulation of serine/threonine protein phosphatases and their role in DA-mediated signaling in striatal neurons. Several small, heat- and acid-stable proteins, including DARPP-32, RCS, and ARPP-16/19, were discovered by the Greengard laboratory to be regulated by DA- and cAMP signaling, and found to undergo a complex but coordinated sequence of phosphorylation and dephosphorylation events. These studies have contributed significantly to the establishment of protein phosphorylation as a ubiquitous and vital process in signal propagation in neurons, paradigm shifting discoveries at the time. Understanding DA-mediated signaling in the context of signal propagation has led to numerous insights into human conditions and the development of treatments and therapies.

Classical complement cascade initiating C1q protein within neurons in the aged rhesus macaque dorsolateral prefrontal cortex

BACKGROUND

Cognitive impairment in schizophrenia, aging, and Alzheimer's disease is associated with spine and synapse loss from the dorsolateral prefrontal cortex (dlPFC) layer III. Complement cascade signaling is critical in driving spine loss and disease pathogenesis. Complement signaling is initiated by C1q, which tags synapses for elimination. C1q is thought to be expressed predominately by microglia, but its expression in primate dlPFC has never been examined. The current study assayed C1q levels in aging primate dlPFC and rat medial PFC (mPFC) and used immunoelectron microscopy (immunoEM), immunoblotting, and co-immunoprecipitation (co-IP) to reveal the precise anatomical distribution and interactions of C1q.

METHODS

Age-related changes in C1q levels in rhesus macaque dlPFC and rat mPFC were examined using immunoblotting. High-spatial resolution immunoEM was used to interrogate the subcellular localization of C1q in aged macaque layer III dlPFC and aged rat layer III mPFC. co-IP techniques quantified protein-protein interactions for C1q and proteins associated with excitatory and inhibitory synapses in macaque dlPFC.

RESULTS

C1q levels were markedly increased in the aged macaque dlPFC. Ultrastructural localization found the expected C1q localization in glia, including those ensheathing synapses, but also revealed extensive localization within neurons. C1q was found near synapses, within terminals and in spines, but was also observed in dendrites, often near abnormal mitochondria. Similar analyses in aging rat mPFC corroborated the findings in rhesus macaques. C1q protein increasingly associated with PSD95 with age in macaque, consistent with its synaptic localization as evidenced by EM.

CONCLUSIONS

These findings reveal novel, intra-neuronal distribution patterns for C1q in the aging primate cortex, including evidence of C1q in dendrites. They suggest that age-related changes in the dlPFC may increase C1q expression and synaptic tagging for glial phagocytosis, a possible mechanism for age-related degeneration.

Alzheimer's-like pathology in aging rhesus macaques: Unique opportunity to study the etiology and treatment of Alzheimer's disease

Although mouse models of Alzheimer's disease (AD) have provided tremendous breakthroughs, the etiology of later onset AD remains unknown. In particular, tau pathology in the association cortex is poorly replicated in mouse models. Aging rhesus monkeys naturally develop cognitive deficits, amyloid plaques, and the same qualitative pattern and sequence of tau pathology as humans, with tangles in the oldest animals. Thus, aging rhesus monkeys can play a key role in AD research. For example, aging monkeys can help reveal how synapses in the prefrontal association cortex are uniquely regulated compared to the primary sensory cortex in ways that render them vulnerable to calcium dysregulation and tau phosphorylation, resulting in the selective localization of tau pathology observed in AD. The ability to assay early tau phosphorylation states and perform high-quality immunoelectron microscopy in monkeys is a great advantage, as one can capture early-stage degeneration as it naturally occurs in situ. Our immunoelectron microscopy studies show that phosphorylated tau can induce an "endosomal traffic jam" that drives amyloid precursor protein cleavage to amyloid-β in endosomes. As amyloid-β increases tau phosphorylation, this creates a vicious cycle where varied precipitating factors all lead to a similar phenotype. These data may help explain why circuits with aggressive tau pathology (e.g., entorhinal cortex) may degenerate prior to producing significant amyloid pathology. Aging monkeys therefore can play an important role in identifying and testing potential therapeutics to protect the association cortex, including preventive therapies that are challenging to test in humans.

In Memoriam: David C. Gadsby, PhD

Andersen et al. commemorate the life of the eminent physiologist, David Gadsby.

ProteomicsBrowser: MS/proteomics data visualization and investigation

SUMMARY

Large-scale, quantitative proteomics data are being generated at ever increasing rates by high-throughput, mass spectrometry technologies. However, due to the complexity of these large datasets as well as the increasing numbers of post-translational modifications (PTMs) that are being identified, developing effective methods for proteomic visualization has been challenging. ProteomicsBrowser was designed to meet this need for comprehensive data visualization. Using peptide information files exported from mass spectrometry search engines or quantitative tools as input, the peptide sequences are aligned to an internal protein database such as UniProtKB. Each identified peptide ion including those with PTMs is then visualized along the parent protein in the Browser. A unique property of ProteomicsBrowser is the ability to combine overlapping peptides in different ways to focus analysis of sequence coverage, charge state or PTMs. ProteomicsBrowser includes other useful functions, such as a data filtering tool and basic statistical analyses to qualify quantitative data.

AVAILABILITY AND IMPLEMENTATION

ProteomicsBrowser is implemented in Java8 and is available at https://medicine.yale.edu/keck/nida/proteomicsbrowser.aspx and https://github.com/peng-gang/ProteomicsBrowser.

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

Development of Targeted Mass Spectrometry-Based Approaches for Quantitation of Proteins Enriched in the Postsynaptic Density (PSD)

The postsynaptic density (PSD) is a structural, electron-dense region of excitatory glutamatergic synapses, which is involved in a variety of cellular and signaling processes in neurons. The PSD is comprised of a large network of proteins, many of which have been implicated in a wide variety of neuropsychiatric disorders. Biochemical fractionation combined with mass spectrometry analyses have enabled an in-depth understanding of the protein composition of the PSD. However, the PSD composition may change rapidly in response to stimuli, and robust and reproducible methods to thoroughly quantify changes in protein abundance are warranted. Here, we report on the development of two types of targeted mass spectrometry-based assays for quantitation of PSD-enriched proteins. In total, we quantified 50 PSD proteins in a targeted, parallel reaction monitoring (PRM) assay using heavy-labeled, synthetic internal peptide standards and identified and quantified over 2100 proteins through a pre-determined spectral library using a data-independent acquisition (DIA) approach in PSD fractions isolated from mouse cortical brain tissue.

Cell-Type-Specific Proteomics: A Neuroscience Perspective

Cell-type-specific analysis has become a major focus for many investigators in the field of neuroscience, particularly because of the large number of different cell populations found in brain tissue that play roles in a variety of developmental and behavioral disorders. However, isolation of these specific cell types can be challenging due to their nonuniformity and complex projections to different brain regions. Moreover, many analytical techniques used for protein detection and quantitation remain insensitive to the low amounts of protein extracted from specific cell populations. Despite these challenges, methods to improve proteomic yield and increase resolution continue to develop at a rapid rate. In this review, we highlight the importance of cell-type-specific proteomics in neuroscience and the technical difficulties associated. Furthermore, current progress and technological advancements in cell-type-specific proteomics research are discussed with an emphasis in neuroscience.

Striatal Signaling Regulated by the H3R Histamine Receptor in a Mouse Model of tic Pathophysiology

Histamine dysregulation has been identified as a rare genetic cause of tic disorders; mice with a knockout of the histidine decarboxylase (Hdc) gene represent a promising model of this pathophysiology. How alterations in the histamine system lead to neuropsychiatric disease, however, remains unclear. The H3R histamine receptor is elevated in the striatum of Hdc KO mice, and H3R agonists, acting in the dorsal striatum, trigger tic-like movements in the model. In wild-type mice, H3R in the dorsal striatum differentially regulates mitogen-activated protein kinase (MAPK) and protein kinase B (Akt) signaling in D1R dopamine receptor-expressing striatonigral medium spiny neurons (dMSNs) and D2R dopamine receptor-expressing striatopallidal MSNs (iMSNs), respectively. We examined the effects of H3R agonist treatment on MSN signaling in the Hdc-KO model. In dMSNs, MAPK signaling was elevated at baseline in the Hdc-KO model, resembling what is seen after H3R activation in WT animals. Similarly, in iMSNs, Akt phosphorylation was reduced at baseline in the KO model, resembling what is seen after H3R activation in WT animals. H3R activation in Hdc-KO mice further enhanced the baseline effect on Akt phosphorylation in iMSNs but attenuated the abnormality in MAPK signaling in dMSNs. These observations support the hypothesis that constitutive activity of upregulated H3R receptors in the Hdc-KO model mediates the observed alterations in baseline MSN signaling; but further activation of H3R, which produces tic-like repetitive movements in the model, has more complex effects.

Isoform-Level Interpretation of High-Throughput Proteomics Data Enabled by Deep Integration with RNA-seq

Cellular control of gene expression is a complex process that is subject to multiple levels of regulation, but ultimately it is the protein produced that determines the biosynthetic state of the cell. One way that a cell can regulate the protein output from each gene is by expressing alternate isoforms with distinct amino acid sequences. These isoforms may exhibit differences in localization and binding interactions that can have profound functional implications. High-throughput liquid chromatography tandem mass spectrometry proteomics (LC-MS/MS) relies on enzymatic digestion and has lower coverage and sensitivity than transcriptomic profiling methods such as RNA-seq. Digestion results in predictable fragmentation of a protein, which can limit the generation of peptides capable of distinguishing between isoforms. Here we exploit transcript-level expression from RNA-seq to set prior likelihoods and enable protein isoform abundances to be directly estimated from LC-MS/MS, an approach derived from the principle that most genes appear to be expressed as a single dominant isoform in a given cell type or tissue. Through this deep integration of RNA-seq and LC-MS/MS data from the same sample, we show that a principal isoform can be identified in >80% of gene products in homogeneous HEK293 cell culture and >70% of proteins detected in complex human brain tissue. We demonstrate that the incorporation of translatome data from ribosome profiling further refines this process. Defining isoforms in experiments with matched RNA-seq/translatome and proteomic data increases the functional relevance of such data sets and will further broaden our understanding of multilevel control of gene expression.

cAMP regulation of protein phosphatases PP1 and PP2A in brain

Normal functioning of the brain is dependent upon a complex web of communication between numerous cell types. Within neuronal networks, the faithful transmission of information between neurons relies on an equally complex organization of inter- and intra-cellular signaling systems that act to modulate protein activity. In particular, post-translational modifications (PTMs) are responsible for regulating protein activity in response to neurochemical signaling. The key second messenger, cyclic adenosine 3',5'-monophosphate (cAMP), regulates one of the most ubiquitous and influential PTMs, phosphorylation. While cAMP is canonically viewed as regulating the addition of phosphate groups through its activation of cAMP-dependent protein kinases, it plays an equally critical role in regulating removal of phosphate through indirect control of protein phosphatase activity. This dichotomy of regulation by cAMP places it as one of the key regulators of protein activity in response to neuronal signal transduction throughout the brain. In this review we focus on the role of cAMP in regulation of the serine/threonine phosphatases protein phosphatase 1 (PP1) and protein phosphatase 2A (PP2A) and the relevance of control of PP1 and PP2A to regulation of brain function and behavior.

The dominant protein phosphatase PP1c isoform in smooth muscle cells, PP1cβ, is essential for smooth muscle contraction

Contractile force development of smooth muscle is controlled by balanced kinase and phosphatase activities toward the myosin regulatory light chain (RLC). Numerous biochemical and pharmacological studies have investigated the specificity and regulatory activity of smooth muscle myosin light-chain phosphatase (MLCP) bound to myosin filaments and comprised of the regulatory myosin phosphatase target subunit 1 (MYPT1) and catalytic protein phosphatase 1cβ (PP1cβ) subunits. Recent physiological and biochemical evidence obtained with smooth muscle tissues from a conditional MYPT1 knockout suggests that a soluble, MYPT1-unbound form of PP1cβ may additionally contribute to myosin RLC dephosphorylation and relaxation of smooth muscle. Using a combination of isoelectric focusing and isoform-specific immunoblotting, we found here that more than 90% of the total PP1c in mouse smooth muscles is the β isoform. Moreover, conditional knockout of PP1cα or PP1cγ in adult smooth muscles did not result in an apparent phenotype in mice up to 6 months of age and did not affect smooth muscle contractions ex vivo In contrast, smooth muscle-specific conditional PP1cβ knockout decreased contractile force development in bladder, ileal, and aortic tissues and reduced mouse survival. Bladder smooth muscle tissue from WT mice was selectively permeabilized to remove soluble PP1cβ to measure contributions of total (α-toxin treatment) and myosin-bound (Triton X-100 treatment) phosphatase activities toward phosphorylated RLC in myofilaments. Triton X-100 reduced PP1cβ content by 60% and the rate of RLC dephosphorylation by 2-fold. These results are consistent with the selective dephosphorylation of RLC by both MYPT1-bound and -unbound PP1cβ forms in smooth muscle.

Striatin-1 is a B subunit of protein phosphatase PP2A that regulates dendritic arborization and spine development in striatal neurons

Striatin-1, a subunit of the serine/threonine phosphatase PP2A, is preferentially expressed in neurons in the striatum. As a member of the striatin family of B subunits, striatin-1 is a core component together with PP2A of a multiprotein complex called STRIPAK, the striatin-interacting phosphatase and kinase complex. Little is known about the function of striatin-1 or the STRIPAK complex in the mammalian striatum. Here, we identify a selective role for striatin-1 in striatal neuron maturation. Using a small hairpin RNA (shRNA) knockdown approach in primary striatal neuronal cultures, we determined that reduced expression of striatin-1 results in increased dendritic complexity and an increased density of dendritic spines, classified as stubby spines. The dendritic phenotype was rescued by co-expression of a striatin-1 mutant construct insensitive to the knockdown shRNA but was not rescued by co-expression of PP2A- or Mob3-binding deficient striatin-1 constructs. Reduction of striatin-1 did not result in deficits in neuronal connectivity in this knockdown model, as we observed no abnormalities in synapse formation or in spontaneous excitatory postsynaptic currents. Thus, this study suggests that striatin-1 is a regulator of neuronal development in striatal neurons.

The Tyrosine Phosphatase STEP Is Involved in Age-Related Memory Decline

Cognitive disabilities that occur with age represent a growing and expensive health problem. Age-associated memory deficits are observed across many species, but the underlying molecular mechanisms remain to be fully identified. Here, we report elevations in the levels and activity of the striatal-enriched phosphatase (STEP) in the hippocampus of aged memory-impaired mice and rats, in aged rhesus monkeys, and in people diagnosed with amnestic mild cognitive impairment (aMCI). The accumulation of STEP with aging is related to dysfunction of the ubiquitin-proteasome system that normally leads to the degradation of STEP. Higher level of active STEP is linked to enhanced dephosphorylation of its substrates GluN2B and ERK1/2, CREB inactivation, and a decrease in total levels of GluN2B and brain-derived neurotrophic factor (BDNF). These molecular events are reversed in aged STEP knockout and heterozygous mice, which perform similarly to young control mice in the Morris water maze (MWM) and Y-maze tasks. In addition, administration of the STEP inhibitor TC-2153 to old rats significantly improved performance in a delayed alternation T-maze memory task. In contrast, viral-mediated STEP overexpression in the hippocampus is sufficient to induce memory impairment in the MWM and Y-maze tests, and these cognitive deficits are reversed by STEP inhibition. In old LOU/C/Jall rats, a model of healthy aging with preserved memory capacities, levels of STEP and GluN2B are stable, and phosphorylation of GluN2B and ERK1/2 is unaltered. Altogether, these data suggest that elevated levels of STEP that appear with advancing age in several species contribute to the cognitive declines associated with aging.

Inhibition of STEP61 ameliorates deficits in mouse and hiPSC-based schizophrenia models

The brain-specific tyrosine phosphatase, STEP (STriatal-Enriched protein tyrosine Phosphatase) is an important regulator of synaptic function. STEP normally opposes synaptic strengthening by increasing N-methyl D-aspartate glutamate receptor (NMDAR) internalization through dephosphorylation of GluN2B and inactivation of the kinases extracellular signal-regulated kinase 1/2 and Fyn. Here we show that STEP₆₁ is elevated in the cortex in the Nrg1^+/- knockout mouse model of schizophrenia (SZ). Genetic reduction or pharmacological inhibition of STEP prevents the loss of NMDARs from synaptic membranes and reverses behavioral deficits in Nrg1^+/- mice. STEP₆₁ protein is also increased in cortical lysates from the central nervous system-specific ErbB2/4 mouse model of SZ, as well as in human induced pluripotent stem cell (hiPSC)-derived forebrain neurons and Ngn2-induced excitatory neurons, from two independent SZ patient cohorts. In these selected SZ models, increased STEP₆₁ protein levels likely reflect reduced ubiquitination and degradation. These convergent findings from mouse and hiPSC SZ models provide evidence for STEP₆₁ dysfunction in SZ.