Dysmyelination and reduced myelin basic protein gene expression by oligodendrocytes of SHP-1-deficient mice

Mitochondrial protein import clogging as a mechanism of disease

Mitochondrial biogenesis requires the import of >1,000 mitochondrial preproteins from the cytosol. Most studies on mitochondrial protein import are focused on the core import machinery. Whether and how the biophysical properties of substrate preproteins affect overall import efficiency is underexplored. Here, we show that protein traffic into mitochondria can be disrupted by amino acid substitutions in a single substrate preprotein. Pathogenic missense mutations in ADP/ATP translocase 1 (ANT1), and its yeast homolog ADP/ATP carrier 2 (Aac2), cause the protein to accumulate along the protein import pathway, thereby obstructing general protein translocation into mitochondria. This impairs mitochondrial respiration, cytosolic proteostasis, and cell viability independent of ANT1's nucleotide transport activity. The mutations act synergistically, as double mutant Aac2/ANT1 causes severe clogging primarily at the translocase of the outer membrane (TOM) complex. This confers extreme toxicity in yeast. In mice, expression of a super-clogger ANT1 variant led to neurodegeneration and an age-dependent dominant myopathy that phenocopy ANT1-induced human disease, suggesting clogging as a mechanism of disease. More broadly, this work implies the existence of uncharacterized amino acid requirements for mitochondrial carrier proteins to avoid clogging and subsequent disease.

Myelin sheath injury and repairment after subarachnoid hemorrhage

Subarachnoid hemorrhage (SAH) can lead to damage to the myelin sheath in white matter. Through classification and analysis of relevant research results, the discussion in this paper provides a deeper understanding of the spatiotemporal change characteristics, pathophysiological mechanisms and treatment strategies of myelin sheath injury after SAH. The research progress for this condition was also systematically reviewed and compared related to myelin sheath in other fields. Serious deficiencies were identified in the research on myelin sheath injury and treatment after SAH. It is necessary to focus on the overall situation and actively explore different treatment methods based on the spatiotemporal changes in the characteristics of the myelin sheath, as well as the initiation, intersection and common action point of the pathophysiological mechanism, to finally achieve accurate treatment. We hope that this article can help researchers in this field to further clarify the challenges and opportunities in the current research on myelin sheath injury and treatment after SAH.

Regulation of peripheral and central immunity: Understanding the role of Src homology 2 domain-containing tyrosine phosphatases, SHP-1 & SHP-2

Protein tyrosine phosphorylation is a potent post-translational regulatory mechanism necessary for maintaining normal physiological functioning of immune cells and it is under the stringent control of antagonizing actions of Protein tyrosine phosphatases and kinases. Two such important Non-Receptor protein tyrosine phosphatases, SHP-1 and SHP-2, have been found to be expressed in immune cells and reported to be key regulators of immune cell development, functions, and differentiation by modulating the duration and amplitude of the downstream cascade transduced via receptors. They also have been conceded as the immune checkpoints & therapeutic targets and hence, it is important to understand their significance intricately. This review compares the roles of these two important cytoplasmic PTPs, SHP1 & SHP-2 in the regulation of peripheral as well as central immunity.

Regulation of Brain-Derived Neurotrophic Factor and Growth Factor Signaling Pathways by Tyrosine Phosphatase Shp2 in the Retina: A Brief Review

SH2 domain-containing tyrosine phosphatase-2 (PTPN11 or Shp2) is a ubiquitously expressed protein that plays a key regulatory role in cell proliferation, differentiation and growth factor (GF) signaling. This enzyme is well expressed in various retinal neurons and has emerged as an important player in regulating survival signaling networks in the neuronal tissues. The non-receptor phosphatase can translocate to lipid rafts in the membrane and has been implicated to regulate several signaling modules including PI3K/Akt, JAK-STAT and Mitogen Activated Protein Kinase (MAPK) pathways in a wide range of biochemical processes in healthy and diseased states. This review focuses on the roles of Shp2 phosphatase in regulating brain-derived neurotrophic factor (BDNF) neurotrophin signaling pathways and discusses its cross-talk with various GF and downstream signaling pathways in the retina.

The control of oligodendrocyte bioenergetics by interferon-gamma (IFN-γ) and Src homology region 2 domain-containing phosphatase-1 (SHP-1)

Glycolysis and mitochondrial respiration are essential for oligodendrocyte metabolism in both the developing and adult CNS. Based on recent reports on the effects of the proinflammatory cytokine IFN-γ on metabolism and on oligodendrocytes, we addressed whether IFN-γ may affect oligodendrocyte bioenergetics in ways relevant to CNS disease. Oligodendrocytes of mice treated with IFN-γ showed significant reductions in aerobic glycolysis and mitochondrial respiration. As expected, IFN-γ treatment led to the induction of STAT1 in oligodendrocytes indicating active signaling into these cells. To determine the direct effects of IFN-γ on oligodendrocyte metabolism, cultured oligodendrocytes were treated with IFN-γ in vitro, which resulted in suppression of glycolysis similar to oligodendrocytes of animals treated with IFN-γ in vivo. Mice lacking SHP-1, a key regulator of IFN-γ and STAT1 signaling in CNS glia, had high constitutive levels of STAT1 and decreased aerobic glycolysis and mitochondrial respiration rates relative to wild type mouse oligodendrocytes. Together, these data show that IFN-γ and SHP-1 control oligodendrocyte bioenergetics in ways that may relate to the role of this cytokine in CNS disease.

Hippocalcin Promotes Neuronal Differentiation and Inhibits Astrocytic Differentiation in Neural Stem Cells

Hippocalcin (HPCA) is a calcium-binding protein that is restricted to nervous tissue and contributes to neuronal activity. Here we report that, in addition to inducing neurogenesis, HPCA inhibits astrocytic differentiation of neural stem cells. It promotes neurogenesis by regulating protein kinase Cα (PKCα) activation by translocating to the membrane and binding to phosphoinositide-dependent protein kinase 1 (PDK1), which induces PKCα phosphorylation. We also found that phospholipase D1 (PLD1) is implicated in the HPCA-mediated neurogenesis pathway; this enzyme promotes dephosphorylation of signal transducer and activator of transcription 3 (STAT3[Y705]), which is necessary for astrocytic differentiation. Moreover, we found that the SH2-domain-containing tyrosine phosphatase 1 (SHP-1) acts upstream of STAT3. Importantly, this SHP-1-dependent STAT3-inhibitory mechanism is closely involved in neurogenesis and suppression of gliogenesis by HPCA. Taken together, these observations suggest that HPCA promotes neuronal differentiation through activation of the PKCα/PLD1 cascade followed by activation of SHP-1, which dephosphorylates STAT3(Y705), leading to inhibition of astrocytic differentiation.

•

Hippocalcin is required for neuronal differentiation in neural stem cells

•

PKCα/PLD1 activation is required for hippocalcin-mediated neuronal differentiation

•

Blocking of STAT3(Y705) activity by hippocalcin decreases astrocytic differentiation

•

Hippocalcin promotes neurogenesis by inhibiting gliogenesis in neural stem cells

Developmental expression and function analysis of protein tyrosine phosphatase receptor type D in oligodendrocyte myelination

Receptor protein tyrosine phosphatases (RPTPs) are extensively expressed in the central nervous system (CNS), and have distinct spatial and temporal patterns in different cell types during development. Previous studies have demonstrated possible roles for RPTPs in axon outgrowth, guidance, and synaptogenesis. In the present study, our results revealed that protein tyrosine phosphatase, receptor type D (PTPRD) was initially expressed in mature neurons in embryonic CNS, and later in oligodendroglial cells at postnatal stages when oligodendrocytes undergo active axonal myelination process. In PTPRD mutants, oligodendrocyte differentiation was normal and a transient myelination delay occurred at early postnatal stages, indicating the contribution of PTPRD to the initiation of axonal myelination. Our results also showed that the remyelination process was not affected in the absence of PTPRD function after a cuprizone-induced demyelination in adult animals.

The control of reactive oxygen species production by SHP-1 in oligodendrocytes

We have previously described reduced myelination and corresponding myelin basic protein (MBP) expression in the central nervous system of Src homology 2 domain-containing protein tyrosine phosphatase 1 (SHP-1) deficient motheaten (me/me) mice compared with normal littermate controls. Deficiency in myelin and MBP expression in both brains and spinal cords of motheaten mice correlated with reduced MBP mRNA expression levels in vivo and in purified oligodendrocytes in vitro. Therefore, SHP-1 activity seems to be a critical regulator of oligodendrocyte gene expression and function. Consistent with this role, this study demonstrates that oligodendrocytes of motheaten mice and SHP-1-depleted N20.1 cells produce higher levels of reactive oxygen species (ROS) and exhibit corresponding markers of increased oxidative stress. In agreement with these findings, we demonstrate that increased production of ROS coincides with ROS-induced signaling pathways known to affect myelin gene expression in oligodendrocytes. Antioxidant treatment of SHP-1-deficient oligodendrocytes reversed the pathological changes in these cells, with increased myelin protein gene expression and decreased expression of nuclear factor (erythroid-2)-related factor 2 (Nrf2) responsive gene, heme oxygenase-1 (HO-1). Furthermore, we demonstrate that SHP-1 is expressed in human white matter oligodendrocytes, and there is a subset of multiple sclerosis subjects that demonstrate a deficiency of SHP-1 in normal-appearing white matter. These studies reveal critical pathways controlled by SHP-1 in oligodendrocytes that relate to susceptibility of SHP-1-deficient mice to both developmental defects in myelination and to inflammatory demyelinating diseases.

NF-κB signaling regulates myelination in the CNS

Besides myelination of neuronal axons by oligodendrocytes to facilitate propagation of action potentials, oligodendrocytes also support axon survival and function. A key transcription factor involved in these processes is nuclear factor-κB (NF-κB), a hetero or homodimer of the Rel family of proteins, including p65, c-Rel, RelB, p50, and p52. Under unstimulated, NF-κB remains inactive in the cytoplasm through interaction with NF-κB inhibitors (IκBs). Upon activation of NF-κB the cytoplasmic IκBs gets degradated, allowing the translocation of NF-κB into the nucleus where the dimer binds to the κB consensus DNA sequence and regulates gene transcription. In this review we describe how oligodendrocytes are, directly or indirectly via neighboring cells, regulated by NF-κB signaling with consequences for innate and adaptive immunity and for regulation of cell apoptosis and survival.

Signaling mechanisms regulating myelination in the central nervous system

The precise and coordinated production of myelin is essential for proper development and function of the nervous system. Diseases that disrupt myelin, including multiple sclerosis, cause significant functional disability. Current treatment aims to reduce the inflammatory component of the disease, thereby preventing damage resulting from demyelination. However, therapies are not yet available to improve natural repair processes after damage has already occurred. A thorough understanding of the signaling mechanisms that regulate myelin generation will improve our ability to enhance repair. in this review, we summarize the positive and negative regulators of myelination, focusing primarily on central nervous system myelination. Axon-derived signals, extracellular signals from both diffusible factors and the extracellular matrix, and intracellular signaling pathways within myelinating oligodendrocytes are discussed. Much is known about the positive regulators that drive myelination, while less is known about the negative regulators that shift active myelination to myelin maintenance at the appropriate time. Therefore, we also provide new data on potential negative regulators of CNS myelination.

Protein tyrosine phosphatase receptor type z negatively regulates oligodendrocyte differentiation and myelination

Background

Fyn tyrosine kinase-mediated down-regulation of Rho activity through activation of p190RhoGAP is crucial for oligodendrocyte differentiation and myelination. Therefore, the loss of function of its counterpart protein tyrosine phosphatase (PTP) may enhance myelination during development and remyelination in demyelinating diseases. To test this hypothesis, we investigated whether Ptprz, a receptor-like PTP (RPTP) expressed abuntantly in oligodendrocyte lineage cells, is involved in this process, because we recently revealed that p190RhoGAP is a physiological substrate for Ptprz.

Methodology/Principal Findings

We found an early onset of the expression of myelin basic protein (MBP), a major protein of the myelin sheath, and early initiation of myelination in vivo during development of the Ptprz-deficient mouse, as compared with the wild-type. In addition, oligodendrocytes appeared earlier in primary cultures from Ptprz-deficient mice than wild-type mice. Furthermore, adult Ptprz-deficient mice were less susceptible to experimental autoimmune encephalomyelitis (EAE) induced by active immunization with myelin/oligodendrocyte glycoprotein (MOG) peptide than were wild-type mice. After EAE was induced, the tyrosine phosphorylation of p190RhoGAP increased significantly, and the EAE-induced loss of MBP was markedly suppressed in the white matter of the spinal cord in Ptprz-deficient mice. Here, the number of T-cells and macrophages/microglia infiltrating into the spinal cord did not differ between the two genotypes after MOG immunization. All these findings strongly support the validity of our hypothesis.

Conclusions/Significance

Ptprz plays a negative role in oligodendrocyte differentiation in early central nervous system (CNS) development and remyelination in demyelinating CNS diseases, through the dephosphorylation of substrates such as p190RhoGAP.

Longitudinal in vivo developmental changes of metabolites in the hippocampus of Fmr1 knockout mice

Fragile X syndrome (FXS) is the most common form of inherited mental retardation and is studied in the Fmr1 knockout (KO) mouse, which models both the anatomical and behavioral changes observed in FXS patients. In vitro studies have shown many alterations in synaptic plasticity and increased density of immature dendritic spines in the hippocampus, a region involved in learning and memory. In this study, magnetic resonance imaging (MRI) and (1) H magnetic resonance spectroscopy (MRS) were used to determine in vivo longitudinal changes in volume and metabolites in the hippocampus during the critical period of early myelination and synaptogenesis at post-natal days (PND) 18, 21, and 30 in Fmr1 KO mice compared with wild-type (WT) controls. MRI demonstrated an increase in volume of the hippocampus in the Fmr1 KO mouse compared with controls. MRS revealed significant developmental changes in the ratios of hippocampal metabolites N-acetylaspartate (NAA), myo-inositol (Ins), and taurine to total creatine (tCr) in Fmr1 KO mice compared with WT controls. Ins was decreased at PND 30, and taurine was increased at all ages studied in Fmr1 KO mice compared with controls. An imbalance of brain metabolites in the hippocampus of Fmr1 KO mice during the critical developmental period of synaptogenesis and early myelination could have long-lasting effects that adversely affect brain development and contribute to ongoing alterations in brain function.

SHP-2 promotes the maturation of oligodendrocyte precursor cells through Akt and ERK1/2 signaling in vitro

Background

Oligodendrocyte precursor cells (OPCs) differentiate into oligodendrocytes (OLs), which are responsible for myelination. Myelin is essential for saltatory nerve conduction in the vertebrate nervous system. However, the molecular mechanisms of maturation and myelination by oligodendrocytes remain elusive.

Methods and Findings

In the present study, we showed that maturation of oligodendrocytes was attenuated by sodium orthovanadate (a comprehensive inhibitor of tyrosine phosphatases) and PTPi IV (a specific inhibitor of SHP-2). It is also found that SHP-2 was persistently expressed during maturation process of OPCs. Down-regulation of endogenous SHP-2 led to impairment of oligodendrocytes maturation and this effect was triiodo-L-thyronine (T3) dependent. Furthermore, over-expression of SHP-2 was shown to promote maturation of oligodendrocytes. Finally, it has been identified that SHP-2 was involved in activation of Akt and extracellular-regulated kinases 1 and 2 (ERK1/2) induced by T3 in oligodendrocytes.

Conclusions

SHP-2 promotes oligodendrocytes maturation via Akt and ERK1/2 signaling in vitro.

Promoter-specific induction of the phosphatase SHP-1 by viral infection and cytokines in CNS glia

We have previously shown that the protein tyrosine phosphatase SHP-1 is highly expressed in CNS glia and is an important modulator of cytokine signaling. As such, mice genetically lacking SHP-1 display constitutive myelin abnormalities, severe virus-induced demyelinating disease, and defects in innate anti-viral responses in the CNS. In this study, we show the differential distribution of the SHP-1 promoter-specific transcripts and demonstrate that several cytokines significantly induce SHP-1 expression in CNS glia. Consistent with these cytokine effects, infection with a neurotropic virus both in vitro and in vivo up-regulates SHP-1 transcripts and protein in CNS cells. Using CNS glial cultures of gene knockout mice, we show that interferons-beta and interferons-gamma act through STAT-1 and interferon regulatory factor-1 to induce the SHP-1 promoter I transcripts. Conversely, interferons-beta and IL-6 act through STAT-3 to induce SHP-1 promoter II transcripts. This study demonstrates that interferons and other cytokines associated with virus infections in the CNS can significantly induce the expression of SHP-1 through STAT-1/3 activity and provides a better understanding of the molecular mechanisms regulating cytokine-induced expression important for multiple homeostatic functions of SHP-1 in the CNS.

Tyrosine phosphatases Shp1 and Shp2 have unique and opposing roles in oligodendrocyte development

Oligodendrocyte progenitor cells first proliferate to generate sufficient cell numbers and then differentiate into myelin-producing oligodendrocytes. The signal transduction mediators that underlie these events, however, remain poorly understood. The tyrosine phosphatase Shp1 has been linked to oligodendrocyte differentiation as Shp1-deficient mice show hypomyelination. The Shp1 homolog, Shp2, has recently been shown to regulate astrogliogenesis, but its role in oligodendrocyte development remains unknown. Here, we report that Shp2 protein levels were developmentally regulated in oligodendrocytes, with Shp2 phosphorylation being promoted by oligodendroglial mitogens but suppressed by laminin, an extracellular matrix protein that promotes oligodendroglial differentiation. In contrast, oligodendrocyte progenitors were found to be unresponsive to mitogens following Shp2, but not Shp1, depletion. In agreement with previous studies, Shp1 depletion led to decreased levels of myelin basic protein in differentiating oligodendrocytes, as well as reduced outgrowth of myelin membrane sheets. Shp2 depletion in contrast did not prevent oligodendrocyte differentiation but promoted expanded myelin membrane outgrowth. Taken together these data suggest that Shp1 and Shp2 have distinct functions in oligodendrocyte development: Shp2 regulates oligodendrocyte progenitor proliferation and Shp1 regulates oligodendrocyte differentiation. Adhesion to laminin may additionally provide extrinsic regulation of Shp2 activity and thus promote the transition from progenitor to differentiating oligodendrocyte.

Lentiviral vector-mediated gene transfer and RNA silencing technology in neuronal dysfunctions

Lentiviral-mediated gene transfer in vivo or in cultured mammalian neurons can be used to address a wide variety of biological questions, to design animal models for specific neurodegenerative pathologies, or to test potential therapeutic approaches in a variety of brain disorders. Lentiviruses can infect nondividing cells, thereby allowing stable gene transfer in postmitotic cells such as mature neurons. An important contribution has been the use of inducible vectors: the same animal can thus be used repeatedly in the doxycycline-on or -off state, providing a powerful mean for assessing the function of a gene candidate in a disorder within a specific neuronal circuit. Furthermore, lentivirus vectors provide a unique tool to integrate siRNA expression constructs with the aim to locally knockdown expression of a specific gene, enabling to assess the function of a gene in a very specific neuronal pathway. Lentiviral vector-mediated delivery of short hairpin RNA results in persistent knockdown of gene expression in the brain. Therefore, the use of lentiviruses for stable expression of siRNA in brain is a powerful aid to probe gene functions in vivo and for gene therapy of diseases of the central nervous system. In this chapter, I review the applications of lentivirus-mediated gene transfer in the investigation of specific gene candidates involved in major brain disorders and neurodegenerative processes. Major applications have been in polyglutamine disorders, such as synucleinopathies and Parkinson's disease, or in investigating gene function in Huntington's disease, dystonia, or muscular dystrophy. Recently, lentivirus gene transfer has been an invaluable tool for evaluation of gene function in behavioral disorders such as drug addiction and attention-deficit hyperactivity disorder or in learning and cognition.

Protein-tyrosine phosphatase alpha acts as an upstream regulator of Fyn signaling to promote oligodendrocyte differentiation and myelination

The tyrosine kinase Fyn plays a key role in oligodendrocyte differentiation and myelination in the central nervous system, but the molecules responsible for regulating Fyn activation in these processes remain poorly defined. Here we show that receptor-like protein-tyrosine phosphatase alpha (PTPalpha) is an important positive regulator of Fyn activation and signaling that is required for the differentiation of oligodendrocyte progenitor cells (OPCs). PTPalpha is expressed in OPCs and is up-regulated during differentiation. We used two model systems to investigate the role of PTPalpha in OPC differentiation: the rat CG4 cell line where PTPalpha expression was silenced by small interfering RNA, and oligosphere-derived primary OPCs isolated from wild-type and PTPalpha-null mouse embryos. In both cell systems, the ablation of PTPalpha inhibited differentiation and morphological changes that accompany this process. Although Fyn was activated upon induction of differentiation, the level of activation was severely reduced in cells lacking PTPalpha, as was the activation of Fyn effector molecules focal adhesion kinase, Rac1, and Cdc42, and inactivation of Rho. Interestingly, another downstream effector of Fyn, p190RhoGAP, which is responsible for Rho inactivation during differentiation, was not affected by PTPalpha ablation. In vivo studies revealed defective myelination in the PTPalpha(-/-) mouse brain. Together, our findings demonstrate that PTPalpha is a critical regulator of Fyn activation and of specific Fyn signaling events during differentiation, and is essential for promoting OPC differentiation and central nervous system myelination.

Protein tyrosine phosphatases expression during development of mouse superior colliculus

Protein tyrosine phosphatases (PTPs) are key regulators of different processes during development of the central nervous system. However, expression patterns and potential roles of PTPs in the developing superior colliculus remain poorly investigated. In this study, a degenerate primer-based reverse transcription-polymerase chain reaction (RT-PCR) approach was used to isolate seven different intracellular PTPs and nine different receptor-type PTPs (RPTPs) from embryonic E15 mouse superior colliculus. Subsequently, the expression patterns of 11 PTPs (TC-PTP, PTP1C, PTP1D, PTP-MEG2, PTP-PEST, RPTPJ, RPTPε, RPTPRR, RPTPσ, RPTPκ and RPTPγ) were further analyzed in detail in superior colliculus from embryonic E13 to postnatal P20 stages by quantitative real-time RT-PCR, Western blotting and immunohistochemistry. Each of the 11 PTPs exhibits distinct spatiotemporal regulation of mRNAs and proteins in the developing superior colliculus suggesting their versatile roles in genesis of neuronal and glial cells and retinocollicular topographic mapping. At E13, additional double-immunohistochemical analysis revealed the expression of PTPs in collicular nestin-positive neural progenitor cells and RC-2-immunoreactive radial glia cells, indicating the potential functional importance of PTPs in neurogenesis and gliogenesis.

Macrophages of multiple sclerosis patients display deficient SHP-1 expression and enhanced inflammatory phenotype

Recent studies in mice have demonstrated that the protein tyrosine phosphatase SHP-1 is a crucial negative regulator of proinflammatory cytokine signaling, TLR signaling, and inflammatory gene expression. Furthermore, mice genetically lacking SHP-1 (me/me) display a profound susceptibility to inflammatory CNS demyelination relative to wild-type mice. In particular, SHP-1 deficiency may act predominantly in inflammatory macrophages to increase CNS demyelination as SHP-1-deficient macrophages display coexpression of inflammatory effector molecules and increased demyelinating activity in me/me mice. Recently, we reported that PBMCs of multiple sclerosis (MS) patients have a deficiency in SHP-1 expression relative to normal control subjects indicating that SHP-1 deficiency may play a similar role in MS as to that seen in mice. Therefore, it became essential to examine the specific expression and function of SHP-1 in macrophages from MS patients. Herein, we document that macrophages of MS patients have deficient SHP-1 protein and mRNA expression relative to those of normal control subjects. To examine functional consequences of the lower SHP-1, the activation of STAT6, STAT1, and NF-kappaB was quantified and macrophages of MS patients showed increased activation of these transcription factors. In accordance with this observation, several STAT6-, STAT1-, and NF-kappaB-responsive genes that mediate inflammatory demyelination were increased in macrophages of MS patients following cytokine and TLR agonist stimulation. Supporting a direct role of SHP-1 deficiency in altered macrophage function, experimental depletion of SHP-1 in normal subject macrophages resulted in an increased STAT/NF-kappaB activation and increased inflammatory gene expression to levels seen in macrophages of MS patients. In conclusion, macrophages of MS patients display a deficiency of SHP-1 expression, heightened activation of STAT6, STAT1, and NF-kappaB and a corresponding inflammatory profile that may be important in controlling macrophage-mediated demyelination in MS.

Interferon-beta treatment in multiple sclerosis attenuates inflammatory gene expression through inducible activity of the phosphatase SHP-1

Interferon-beta is a current treatment for multiple sclerosis (MS). Interferon-beta is thought to exert its therapeutic effects on MS by down-modulating the immune response by multiple potential pathways. Here, we document that treatment of MS patients with interferon beta-1a (Rebif) results in a significant increase in the levels and function of the protein tyrosine phosphatase SHP-1 in PBMCs. SHP-1 is a crucial negative regulator of cytokine signaling, inflammatory gene expression, and CNS demyelination as evidenced in mice deficient in SHP-1. In order to examine the functional significance of SHP-1 induction in MS PBMCs, we analyzed the activity of proinflammatory signaling molecules STAT1, STAT6, and NF-kappaB, which are known SHP-1 targets. Interferon-beta treatment in vivo resulted in decreased NF-kappaB and STAT6 activation and increased STAT1 activation. Further analysis in vitro showed that cultured PBMCs of MS patients and normal subjects had a significant SHP-1 induction following interferon-beta treatment that correlated with decreased NF-kappaB and STAT6 activation. Most importantly, experimental depletion of SHP-1 in cultured PBMCs abolished the anti-inflammatory effects of interferon-beta treatment, indicating that SHP-1 is a predominant mediator of interferon-beta activity. In conclusion, interferon-beta treatment upregulates SHP-1 expression resulting in decreased transcription factor activation and inflammatory gene expression important in MS pathogenesis.

Modulation of macrophage infiltration and inflammatory activity by the phosphatase SHP-1 in virus-induced demyelinating disease

The protein tyrosine phosphatase SHP-1 is a crucial negative regulator of cytokine signaling and inflammatory gene expression, both in the immune system and in the central nervous system (CNS). Mice genetically lacking SHP-1 (me/me) display severe inflammatory demyelinating disease following inoculation with the Theiler's murine encephalomyelitis virus (TMEV) compared to infected wild-type mice. Therefore, it became essential to investigate the mechanisms of TMEV-induced inflammation in the CNS of SHP-1-deficient mice. Herein, we show that the expression of several genes relevant to inflammatory demyelination in the CNS of infected me/me mice is elevated compared to that in wild-type mice. Furthermore, SHP-1 deficiency led to an abundant and exclusive increase in the infiltration of high-level-CD45-expressing (CD45(hi)) CD11b(+) Ly-6C(hi) macrophages into the CNS of me/me mice, in concert with the development of paralysis. Histological analyses of spinal cords revealed the localization of these macrophages to extensive inflammatory demyelinating lesions in infected SHP-1-deficient mice. Sorted populations of CNS-infiltrating macrophages from infected me/me mice showed increased amounts of viral RNA and an enhanced inflammatory profile compared to wild-type macrophages. Importantly, the application of clodronate liposomes effectively depleted splenic and CNS-infiltrating macrophages and significantly delayed the onset of TMEV-induced paralysis. Furthermore, macrophage depletion resulted in lower viral loads and lower levels of inflammatory gene expression and demyelination in the spinal cords of me/me mice. Finally, me/me macrophages were more responsive than wild-type macrophages to chemoattractive stimuli secreted by me/me glial cells, indicating a mechanism for the increased numbers of infiltrating macrophages seen in the CNS of me/me mice. Taken together, these findings demonstrate that infiltrating macrophages in SHP-1-deficient mice play a crucial role in promoting viral replication by providing abundant viral targets and contribute to increased proinflammatory gene expression relevant to the effector mechanisms of macrophage-mediated demyelination.

SHP-1 deficiency and increased inflammatory gene expression in PBMCs of multiple sclerosis patients

Recent studies in mice have demonstrated that the protein tyrosine phosphatase SHP-1 is a crucial negative regulator of cytokine signaling, inflammatory gene expression, and demyelination in central nervous system. The present study investigates a possible similar role for SHP-1 in the human disease multiple sclerosis (MS). The levels of SHP-1 protein and mRNA in PBMCs of MS patients were significantly lower compared to normal subjects. Moreover, promoter II transcripts, expressed from one of two known promoters, were selectively deficient in MS patients. To examine functional consequences of the lower SHP-1 in PBMCs of MS patients, we measured the intracellular levels of phosphorylated STAT6 (pSTAT6). As expected, MS patients had significantly higher levels of pSTAT6. Accordingly, siRNA to SHP-1 effectively increased the levels of pSTAT6 in PBMCs of controls to levels equal to MS patients. Additionally, transduction of PBMCs with a lentiviral vector expressing SHP-1 lowered pSTAT6 levels. Finally, multiple STAT6-responsive inflammatory genes were increased in PBMCs of MS patients relative to PBMCs of normal subjects. Thus, PBMCs of MS patients display a stable deficiency of SHP-1 expression, heightened STAT6 phosphorylation, and an enhanced state of activation relevant to the mechanisms of inflammatory demyelination.

The Src homology 2 domain tyrosine phosphatases SHP-1 and SHP-2: diversified control of cell growth, inflammation, and injury

Interest in the diverse biology of protein tyrosine phosphatases that are encoded by more than 100 genes in the human genome continues to grow at an accelerated pace. In particular, two cytoplasmic protein tyrosine phosphatases composed of two Src homology 2 (SH2) NH2-terminal domains and a C-terminal protein-tyrosine phosphatase domain referred to as SHP-1 and SHP-2 are known to govern a host of cellular functions. SHP-1 and SHP-2 modulate progenitor cell development, cellular growth, tissue inflammation, and cellular chemotaxis, but more recently the role of SHP-1 and SHP-2 to directly control cell survival involving oxidative stress pathways has come to light. SHP-1 and SHP-2 are fundamental for the function of several growth factor and metabolic pathways yielding far reaching implications for disease pathways and disorders such as diabetes, neurodegeneration, and cancer. Although SHP-1 and SHP-2 can employ similar or parallel cellular pathways, these proteins also clearly exert opposing effects upon downstream cellular cascades that affect early and late apoptotic programs. SHP-1 and SHP-2 modulate cellular signals that involve phosphatidylinositol 3-kinase, Akt, Janus kinase 2, signal transducer and activator of transcription proteins, mitogen-activating protein kinases, extracellular signal-related kinases, c-Jun-amino terminal kinases, and nuclear factor-kappaB. Our progressive understanding of the impact of SHP-1 and SHP-2 upon multiple cellular environments and organ systems should continue to facilitate the targeted development of treatments for a variety of disease entities.

Tyrosine phosphatases epsilon and alpha perform specific and overlapping functions in regulation of voltage-gated potassium channels in Schwann cells

Tyrosine phosphatases (PTPs) epsilon and alpha are closely related and share several molecular functions, such as regulation of Src family kinases and voltage-gated potassium (Kv) channels. Functional interrelationships between PTPepsilon and PTPalpha and the mechanisms by which they regulate K+ channels and Src were analyzed in vivo in mice lacking either or both PTPs. Lack of either PTP increases Kv channel activity and phosphorylation in Schwann cells, indicating these PTPs inhibit Kv current amplitude in vivo. Open probability and unitary conductance of Kv channels are unchanged, suggesting an effect on channel number or organization. PTPalpha inhibits Kv channels more strongly than PTPepsilon; this correlates with constitutive association of PTPalpha with Kv2.1, driven by membranal localization of PTPalpha. PTPalpha, but not PTPepsilon, activates Src in sciatic nerve extracts, suggesting Src deregulation is not responsible exclusively for the observed phenotypes and highlighting an unexpected difference between both PTPs. Developmentally, sciatic nerve myelination is reduced transiently in mice lacking either PTP and more so in mice lacking both PTPs, suggesting both PTPs support myelination but are not fully redundant. We conclude that PTPepsilon and PTPalpha differ significantly in their regulation of Kv channels and Src in the system examined and that similarity between PTPs does not necessarily result in full functional redundancy in vivo.

Angiotensin II Type-2 Receptor Stimulation Prevents Neural Damage by Transcriptional Activation of Methyl Methanesulfonate Sensitive 2

The molecular mechanisms of the contribution of angiotensin II type-1 receptor blockers to neuronal protection are still unclear. Here, we investigated the effect of angiotensin II type-2 (AT2) receptor stimulation on neurons and cognitive function involving a new neuroprotective factor, methyl methanesulfonate sensitive 2 (MMS2). Angiotensin II treatment of neurospheres enhanced their differentiation and increased MMS2 expression. Knockdown of the MMS2 gene by small interference RNA (siRNA) significantly reduced the number of neurospheres, with loss of sphere formation. An angiotensin II type-1 receptor blocker, valsartan, enhanced such neurosphere differentiation and MMS2 induction, whereas an AT2 receptor antagonist, PD123319, inhibited them. After mice underwent permanent middle cerebral artery occlusion, AT2 receptor mRNA expression was significantly increased in the ischemic side of the brain. Passive avoidance rate to evaluate cognitive function was significantly impaired in AT2 receptor null (Agtr2-) mice compared with wild-type mice. Treatment with valsartan prevented the cognitive decline in wild-type mice, but this effect was weaker in Agtr2- mice. In ischemic brain regions, MMS2 was increased in wild-type mice, but not in Agtr2- mice. Valsartan also enhanced MMS2 expression to a greater degree in wild-type mice. Finally, intracerebroventricular administration of MMS2 siRNA showed more impaired avoidance rate after middle cerebral artery occlusion compared with that in control siRNA-transfected mice. These findings experimentally support the clinical evidence and indicate a unique mechanism of the AT2 receptor in brain protection.

Expression profiling reveals multiple myelin alterations in murine succinate semialdehyde dehydrogenase deficiency

Succinic semialdehyde dehydrogenase (SSADH) deficiency, a rare genetic defect of GABA degradation recently modelled in mice (SSADH(-/-) mice), manifests early absence seizures that evolve into generalized convulsive seizures and lethal status epilepticus in gene-ablated mice. Disrupted GABA homeostasis, in conjunction with the epileptic phenotype and increased gamma-hydroxybutyric acid (GHB), suggested that expression profiling with the U74Av2 Affymetrix system would reveal dysregulation of receptor genes associated with GABAergic and glutamatergic neurotransmission. Unexpectedly, we found significant downregulation for genes associated with myelin biogenesis and compaction, predominantly in hippocampus and cortex. These results were confirmed by: (1) myelin basic protein (MBP) immunohistochemistry; (2) western blotting of myelin-associated glycoprotein (MAG) and MBP; (3) qRT-PCR analyses of myelin-associated oligodendrocytic basic protein (MOBP), MAG, MBP and proteolipid protein (PLP) in hippocampus, cortex and spinal cord; (4) quantitation of ethanolamine and choline plasmalogens, all core myelin components; (5) evaluation of myelin content in brain sections employing toluidine blue staining; and (6) ultrastructural evaluation of myelin sheath thickness via electron microscopy. We speculate that increased GABA/GHB, acting through GABAergic systems, results in decreased levels of the neurosteroids progesterone and allopregnanolone [Gupta et al (2003) Ann Neurol 54(Supplement 6): S81-S90] and phosphorylation of mitogen-activated protein (MAP) kinase, with resulting myelin protein abnormalities primarily in the cortex of SSADH(-/-) mice.

Controlling cytokine signaling by constitutive inhibitors

Cytokines are secreted proteins that regulate diverse biological functions by binding to receptors at the cell surface to activate complex signal transduction pathways including the Janus kinase-signal transducer and activator of transcription (JAK-STAT) pathway. Stringent mechanisms of signal attenuation are essential for ensuring an appropriate, controlled cellular response. Three families of proteins, the SH2-containing phosphatases (SHP), the protein inhibitors of activated STATs (PIAS), and the suppressors of cytokine signaling (SOCS), inhibit specific and distinct aspects of cytokine signal transduction. The analysis of mice lacking genes for members of the SHP has shed much light on the roles of these proteins in vivo. In recent in vitro studies, the protein modifiers ubiquitin and small ubiquitin-like modifier (SUMO) have emerged as key players in the strategies employed by SOCS and PIAS to repress signaling. This review throws light on the mechanisms of action of these regulators as being evolved by the latest researches.