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.

STEP: a family of brain-enriched PTPs. Alternative splicing produces transmembrane, cytosolic and truncated isoforms.

The family of striatal enriched phosphatases (STEPs) consists of protein tyrosine phosphatases (PTPs) that are enriched within the central nervous system. Previous biochemical studies have shown that the STEP family includes transmembrane, as well as soluble, cytosolic proteins. We now extend these findings with the isolation and characterization of a new, truncated member of this family, termed STEP38. The cDNA of STEP38 encodes a protein of 346 amino acids with a predicted mobility of 38 kDa. In contrast to the cytosolic variants, it contains two hydrophobic amino acid sequences at its N-terminus, two sequences enriched in Pro, Glu, Asp, Ser and Thr residues (PEST sequences), and two polyproline domains. We have used differential centrifugation, continuous sucrose gradients, and transfection experiments to clarify the subcellular localization of STEP38 within membrane compartments. These experiments suggest that a pool of STEP38 is targeted to membrane compartments of the endoplasmic reticulum. The STEP38 cDNA contains a stop codon upstream of the catalytic phosphatase domain that is normally present in other STEP variants, and enzymatic assays conform that STEP38 is inactive. Thus, the STEP family consists of cytosolic, transmembrane, and truncated isoforms. These findings are similar to what has been found for some members of the protein tyrosine kinase (PTK) family that uses alternative splicing mechanisms to produce active and inactive variants. By analogy with suggested mechanisms of action for the truncated PTKs, inactive STEP isoforms may participate in signaling events by protecting potential substrates from dephosphorylation by other members of this family.

Antibodies against neural, nuclear, cytoskeletal, and streptococcal epitopes in children and adults with Tourette's syndrome, Sydenham's chorea, and autoimmune disorders.

BACKGROUND: Some cases of Tourette's syndrome (TS) are hypothesized to be caused by autoantibodies that develop in response to a preceding group A beta hemolytic streptococcal infection. METHODS: To test this hypothesis, we looked for the presence ot total and IgG antibodies against neural, nuclear, cytoskeletal and streptococcal epitopes using indirect immunofluorescent assays and Western blot techniques in three patient groups: TS (n = 81), SC (n = 27), and a group of autoimmune disorders (n = 52) and in normal controls (n = 67). Subjects were ranked after titrations of autoantibodies from 0 to 227 according to their level of immunoreactivity. RESULTS: TS patients had a significantly higher mean rank for total antineural and antinuclear antibodies, as well as antistreptolysin O titers. However, among children and adolescents, only the total antinuclear antibodies were increased in TS patients compared to age matched controls. Compared to SC patients, TS patients had a significantly lower mean rank for total and IgG class antineural antibodies, significantly lower IgG class anticytoskeletal antibodies, and a significantly higher rank for total antinuclear antibodies. Compared to a mixed group of autoimmune disorders, the TS patients had a significantly lower mean rank for total and IgG class antineural antibodies, total and IgG class antinuclear antibodies, IgG class anticytoskeletal antibodies, and a significantly higher rank for antistreptococcal antibodies. CONCLUSIONS: TS patients had significantly higher levels of total antineural and antinuclear antibodies than did controls. Their relation to IgG class antineural and antinuclear antibodies, markers for prior streptococcal infection, and other clinical characteristics, especially chronological age, was equivocal.

The psychiatric symptoms of rheumatic fever.

OBJECTIVE: This study examined the frequency and age at onset of psychiatric disorders among children with rheumatic fever, Sydenham's chorea, or both and a comparison group. METHOD: Twenty children with rheumatic fever, 22 with Sydenham's chorea, and 20 comparison children were assessed by means of a semistructured interview and rating scales for tic disorders and obsessive-compulsive disorder. RESULTS: Obsessive-compulsive symptoms were more frequent in both the Sydenham's chorea and rheumatic fever groups than in the comparison group. The Sydenham's chorea group had a higher frequency of major depressive disorder, tic disorders, and attention deficit hyperactivity disorder (ADHD) than both the comparison and rheumatic fever groups. ADHD symptoms were associated with a higher risk of developing Sydenham's chorea. CONCLUSIONS: Both the rheumatic fever and Sydenham's chorea groups were associated with a higher risk of developing neuropsychiatric disorders than the comparison group. ADHD appears to be a risk factor for Sydenham's chorea in children with rheumatic fever.

Exacerbation of Gilles de la Tourette's syndrome associated with thermal stress: a family study.

Gilles de la Tourette's syndrome (TS) is a familial disorder that is often exacerbated by stress or fatigue. Here we present a family of a TS proband that has several members with obsessive-compulsive symptoms, a bleeding disorder, and an unusual sensitivity to heat. The proband, who is affected by all of these traits, was challenged with heat or exercise in climate-controlled conditions and showed a marked increase in the frequency of tics.

Protein tyrosine phosphatases in the nervous system.

Protein tyrosine phosphatases (PTPs) act to oppose the action of tyrosine kinases and serve important roles in regulating levels of phosphotyrosine in cells. Accumulating evidence points to the roles of PTPs in neuronal development and function, as well as neurotransmitter and growth factor receptor signaling cascades. By analogy to the family of tyrosine kinases, there are both receptor-like and intracellular tyrosine phosphatases. A number of these have been identified in the brain and found to be nervous system-enriched. This article describes brain-enriched PTPs, their localization patterns in brain, and speculations regarding their functional roles.

Identification of two alternatively spliced transcripts of STEP: a subfamily of brain-enriched protein tyrosine phosphatases.

A brain-enriched protein tyrosine phosphatase termed STEP46 (striatal enriched phosphatase) was previously isolated and characterized. Immunological studies with a STEP monoclonal antibody recognized several STEP-immunoreactive proteins, and suggested that additional STEP-related polypeptides existed. This study reports the isolation of two alternatively spliced transcripts of the STEP gene. One of these, STEP20 (with a predicted molecular mass of 20 kDa) was further characterized and found to lack the conserved tyrosine phosphatase domain. Northern analysis detected a 2.8 kb STEP20 message in mouse brain. The second alternatively spliced transcript, STEP61, has a 5'-extended open reading frame that encodes a protein with a predicted molecular mass of 61 kDa and contains a single tyrosine phosphatase domain. The exon-intron organization responsible for the novel STEP20 and STEP61 sequences was determined in the mouse STEP genomic DNA. We propose that the original STEP46, along with STEP20 and STEP61, are members of a brain-enriched subfamily of protein tyrosine phosphatases, and that STEP isoforms may have distinct functions within the central nervous system.

The localization of an antibody to STEP in embryonic striatal tissue grafts.

We used immunohistochemical staining with antibodies against the novel protein striatal enriched phosphatase (STEP) to investigate the internal organization of grafts of embryonic striatal tissues implanted in the ibotenic acid-lesioned neostriatum of adult rats. STEP immunoreactivity was found in discrete patches within the grafts, which colocalized with areas designated as 'patch' zones when stained for the enzyme acetylcholinesterase and with antibodies against tyrosine hydroxylase and DARPP-32. As previously hypothesized, the pattern of STEP immuno-reactivity in embryonic striatal tissue grafts provides further indication that the patch zones are indeed comprised of striatal like cell populations. The novel protein STEP provides a sensitive and precise marker for this compartment within the grafts.

Genetic mechanisms in childhood psychiatric disorders.

OBJECTIVE: This review summarizes research findings on the genetics of several childhood psychiatric disorders. METHOD: One hundred fifty papers were reviewed from the past several decades and were selected because they have suggested that genetic factors may play a role in the etiology of certain childhood disorders. This review is not meant to be exhaustive but rather has emphasized those disorders for which a genetic etiology has been proposed by different research groups. RESULTS: The more classical approaches to genetic research are reviewed and critiqued. The status of research for a number of childhood disorders is summarized. The molecular basis for several developmental disorders is presented and the prospects for arriving at a similar molecular understanding for other childhood psychiatric illnesses are discussed. CONCLUSIONS: Genetic factors play a determining role for certain developmental disorders. However, the molecular basis for other psychiatric disorders has yet to be elucidated and there are complicating factors that bear on genetic research of complex behavioral disorders.

The genetics of childhood psychiatric disorders: a decade of progress.

OBJECTIVE: To review the literature over the past decade on the genetics of childhood neuropsychiatric disorders. METHOD: A computerized search was performed for articles published in the past decade, and selected papers were highlighted. RESULTS: The past decade of research has illuminated the complex genetics of early-onset mental disorders. Advances in statistical methodologies and laboratory-based gene-hunting techniques are laying the foundation for a deeper understanding of both the biological and environmental factors that contribute to mental illness. Researchers are on the verge of identifying and characterizing genetic vulnerabilities involved in common childhood psychiatric syndromes. CONCLUSIONS: Although the study of the genetics of childhood psychiatric disorders has advanced significantly over the past decade, considerable work remains. The identification of genes conferring vulnerability to psychiatric illnesses will have the potential to transform the field by providing insight into both biological and environmental determinants that contribute to serious developmental and psychiatric disorders in children and adolescents. These advances promise new understanding and new avenues for prevention and treatment. They will also present physicians and families with significant clinical and ethical challenges.

Risperidone treatment of children and adolescents with chronic tic disorders: a preliminary report.

OBJECTIVE: The purpose of this trial was to investigate the short-term safety and efficacy of risperidone in the treatment of chronic tic disorders in children and adolescents. METHOD: This was an 11-week open-label trial and included seven subjects (five boys and two girls) with a mean age of 12.9 +/- 1.9 years. The sample included five patients with Tourette's syndrome and two with chronic motor tic disorder. The children were seen at baseline and for two follow-up visits. Three children had a comorbid diagnosis of obsessive-compulsive disorder (OCD). RESULTS: Clinical response, as measured by the Yale Global Tic Severity Scale and the Children's version of the Yale-Brown Obsessive Compulsive Scale, revealed a statistically significant reduction in tic scores ranging from 26% [corrected] to 66%. One of three children with comorbid OCD showed substantial improvement; the other two subjects showed no change. The most frequent side effect was weight gain, which ranged from 8 to 14 lb. CONCLUSIONS: Risperidone, a neuroleptic with both serotonin- and dopamine-blocking properties, appears to be effective in reducing tic frequency and intensity in children and adolescents with chronic tic disorders.

Transient compartmental expression of a family of protein tyrosine phosphatases in the developing striatum.

The expression of a family of intracellular protein tyrosine phosphatases (STEP) was studied in the striatum of rats during ontogeny. Links between the formation of dopamine islands and STEP immunoreactive patches in the striatum were examined since previous work had suggested that STEP isoforms were selectively expressed in dopaminoceptive brain regions. STEP protein and mRNAs were distributed in a patchy manner during the first postnatal week. By 2 weeks, STEP immunoreactivity was homogeneous, indicating that both patch and matrix neurons express STEP by maturity. Two-color immunofluorescent staining was also performed to compare STEP with specific markers for patch and matrix. Tyrosine hydroxylase immunoreactive fibers from the substantia nigra form distinctive dopamine islands in the striatum during late embryonic development, and occupy the sites of future patches [23,37,38,54]. These fiber islands align with STEP immunoreactive neuronal patches during the first two postnatal weeks, suggesting that STEP is a marker for patch neurons in early postnatal development. When STEP's distribution was compared with other markers for patch (substance P) or matrix (calbindin), STEP co-localized with substance P in most striatal neurons on postnatal days 1 through 7. However, STEP was also expressed within a subset of calbindin-positive neurons in the lateral striatum, but not with these neurons elsewhere in the striatum. By adulthood, STEP colocalized with both markers. These results suggest that STEP is expressed first within patch neurons but not matrix, and subsequently within both. The expression of STEP may be triggered by the arrival of striatal afferents or other regulatory factors.

Genetics of central nervous system developmental disorders.

The construction of the nervous system is regulated by genetic and environmental factors. In this article, we have highlighted some of the important molecules and genes that contribute to early stages of CNS development. Future research in the neurosciences will address how genetic and environmental factors interact with each other during brain development and in the mature nervous system.

Thermal sensitivity in Tourette syndrome: preliminary report.

The effects of heat on tic symptoms were studied in a sample of 78 adults with Tourette syndrome. 62 men and 16 women completed a survey concerning the type, onset, and course of their tics. 10 adult male subjects also participated in a thermal challenge during which ambient temperature was raised from 22 degrees C to 35 degrees C following a control period. Of the 78, 24% or 19 reported increased tics upon exposure to heat. Compared to the remaining 59 subjects, there were no differences in sex distribution, current age, or overall course of illness. In the thermal challenge, there was general increase in tics that was correlated with sweat rate (r = .55, p = .001). This effect was prominent in 5 of 10 subjects (rs = .29 to .63). There were no mean differences in current age, age of onset, or current severity of symptoms between the five subjects of each group. Tic symptoms in a subgroup of patients with Tourette syndrome may be sensitive to heat. Abnormal heat regulation is not a likely explanation for the observed increase in tics. The increase may be due to normal heat-loss mechanisms through dopaminergic pathways.

Genetic manipulation of STEP reverses behavioral abnormalities in a fragile X syndrome mouse model.

Fragile X syndrome (FXS), the most common inherited form of intellectual disability and prevailing known genetic basis of autism, is caused by an expansion in the Fmr1 gene that prevents transcription and translation of fragile X mental retardation protein (FMRP). FMRP binds to and controls translation of mRNAs downstream of metabotropic glutamate receptor (mGluR) activation. Recent work shows that FMRP interacts with the transcript encoding striatal-enriched protein tyrosine phosphatase (STEP; Ptpn5). STEP opposes synaptic strengthening and promotes synaptic weakening by dephosphorylating its substrates, including ERK1/2, p38, Fyn and Pyk2, and subunits of N-methyl-d-aspartate (NMDA) and AMPA receptors. Here, we show that basal levels of STEP are elevated and mGluR-dependent STEP synthesis is absent in Fmr1(KO) mice. We hypothesized that the weakened synaptic strength and behavioral abnormalities reported in FXS may be linked to excess levels of STEP. To test this hypothesis, we reduced or eliminated STEP genetically in Fmr1(KO) mice and assessed mice in a battery of behavioral tests. In addition to attenuating audiogenic seizures and seizure-induced c-Fos activation in the periaqueductal gray, genetically reducing STEP in Fmr1(KO) mice reversed characteristic social abnormalities, including approach, investigation and anxiety. Loss of STEP also corrected select nonsocial anxiety-related behaviors in Fmr1(KO) mice, such as light-side exploration in the light/dark box. Our findings indicate that genetically reducing STEP significantly diminishes seizures and restores select social and nonsocial anxiety-related behaviors in Fmr1(KO) mice, suggesting that strategies to inhibit STEP activity may be effective for treating patients with FXS.

The tyrosine phosphatase STEP constrains amygdala-dependent memory formation and neuroplasticity.

STriatal-Enriched protein tyrosine Phosphatase (STEP; PTPN5) is expressed in brain regions displaying adult neuroplasticity. STEP modulates neurotransmission by dephosphorylating regulatory tyrosine residues on its substrates. In this way, STEP inactivates extracellular-signal-regulated kinase 1/2 (ERK1/2), limiting the duration and spatial distribution of ERK signaling. Two additional substrates, the tyrosine kinase Fyn and the NR2B subunit of the N-methyl-d-aspartic acid receptor, link STEP to glutamate receptor internalization in the synapse. Thus, STEP may act through parallel pathways to oppose the development of experience-dependent synaptic plasticity. We examined the hypothesis that the absence of STEP facilitates amygdala-dependent behavioral and synaptic plasticity (i.e., fear conditioning and long-term potentiation) using STEP-deficient mice (STEP KO). These mice show no detectable expression of STEP in the brain along with increases in Tyr phosphorylation of STEP substrates. Here we demonstrate that STEP KO mice also display augmented fear conditioning as measured by an enhancement in conditioned suppression of instrumental response when a fear-associated conditioned stimulus was presented. Deletion of STEP also increases long-term potentiation and ERK phosphorylation in the lateral amygdala. The current experiments demonstrate that deletion of STEP can enhance experience-induced neuroplasticity and memory formation and identifies STEP as a target for pharmacological treatment aimed at improving the formation of long-term memories.

The tyrosine phosphatase STEP: implications in schizophrenia and the molecular mechanism underlying antipsychotic medications.

Glutamatergic signaling through N-methyl-D-aspartate receptors (NMDARs) is required for synaptic plasticity. Disruptions in glutamatergic signaling are proposed to contribute to the behavioral and cognitive deficits observed in schizophrenia (SZ). One possible source of compromised glutamatergic function in SZ is decreased surface expression of GluN2B-containing NMDARs. STEP(61) is a brain-enriched protein tyrosine phosphatase that dephosphorylates a regulatory tyrosine on GluN2B, thereby promoting its internalization. Here, we report that STEP(61) levels are significantly higher in the postmortem anterior cingulate cortex and dorsolateral prefrontal cortex of SZ patients, as well as in mice treated with the psychotomimetics MK-801 and phencyclidine (PCP). Accumulation of STEP(61) after MK-801 treatment is due to a disruption in the ubiquitin proteasome system that normally degrades STEP(61). STEP knockout mice are less sensitive to both the locomotor and cognitive effects of acute and chronic administration of PCP, supporting the functional relevance of increased STEP(61) levels in SZ. In addition, chronic treatment of mice with both typical and atypical antipsychotic medications results in a protein kinase A-mediated phosphorylation and inactivation of STEP(61) and, consequently, increased surface expression of GluN1/GluN2B receptors. Taken together, our findings suggest that STEP(61) accumulation may contribute to the pathophysiology of SZ. Moreover, we show a mechanistic link between neuroleptic treatment, STEP(61) inactivation and increased surface expression of NMDARs, consistent with the glutamate hypothesis of SZ.