ABCD of IA: A multi-scale agent-based model of T cell activation in inflammatory arthritis

Biomaterial-based agents have been demonstrated to regulate the function of immune cells in models of autoimmunity. However, the complexity of the kinetics of immune cell activation can present a challenge in optimizing the dose and frequency of administration. Here, we report a model of autoreactive T cell activation, which are key drivers in autoimmune inflammatory joint disease. The model is termed a multi-scale Agent-Based, Cell-Driven model of Inflammatory Arthritis (ABCD of IA). Using kinetic rate equations and statistical theory, ABCD of IA simulated the activation and presentation of autoantigens by dendritic cells, interactions with cognate T cells and subsequent T cell proliferation in the lymph node and IA-affected joints. The results, validated with in vivo data from the T cell driven SKG mouse model, showed that T cell proliferation strongly correlated with the T cell receptor (TCR) affinity distribution (TCR-ad), with a clear transition state from homeostasis to an inflammatory state. T cell proliferation was strongly dependent on the amount of antigen in antigenic stimulus event (ASE) at low concentrations. On the other hand, inflammation driven by Th17-inducing cytokine mediated T cell phenotype commitment was influenced by the initial level of Th17-inducing cytokines independent of the amount of arthritogenic antigen. The introduction of inhibitory artificial antigen presenting cells (iaAPCs), which locally suppress T cell activation, reduced T cell proliferation in a dose-dependent manner. The findings in this work set up a framework based on theory and modeling to simulate personalized therapeutic strategies in IA.

Laser capture microscopy (LCM)-RNAseq for topological mapping of synovial pathology during rheumatoid arthritis

OBJECTIVE

Rheumatoid arthritis (RA) is an autoimmune disease in which the joint lining, or synovium, becomes highly inflamed and majorly contributes to disease progression. Understanding pathogenic processes in RA synovium is critical for identifying therapeutic targets. We performed laser capture microscopy (LCM) followed by RNA sequencing (LCM-RNAseq) to study regional transcriptomes throughout RA synovium.

METHODS

Synovial lining, sublining, and vessels were captured by LCM from seven RA and seven osteoarthritis (OA) patients. RNAseq was performed on RNA extracted from captured tissue. Principal component analysis (PCA) was performed on the sample set by disease state. Differential expression analysis was performed between disease states based on log2 fold-change and q-value parameters. Pathway analysis was performed using Reactome Pathway Database on differentially expressed genes (DEGs) between disease states. Significantly enriched pathways in each synovial region were selected based on false discovery rate (FDR).

RESULTS

RA and OA transcriptomes were distinguishable by PCA. Pairwise comparisons of synovial lining, sublining, and vessels between RA and OA revealed substantial differences in transcriptional patterns throughout the synovium. Hierarchical clustering of pathways based on significance revealed a pattern of association between biological function and synovial topology. Analysis of pathways uniquely enriched in each region revealed distinct phenotypic abnormalities. As examples, RA lining was marked by anomalous immune cell signaling, RA sublining by aberrant cell cycle, and RA vessels by alterations in heme scavenging.

CONCLUSION

LCM-RNAseq confirms reported transcriptional differences between RA and OA synovium and provides evidence supporting a relationship between synovial topology and molecular anomalies in RA.

The therapeutic potential of immunoengineering for systemic autoimmunity

Disease-modifying drugs have transformed the treatment options for many systemic autoimmune diseases. However, an evolving understanding of disease mechanisms, which might vary between individuals, is paving the way for the development of novel agents that operate in a patient-tailored manner through immunophenotypic regulation of disease-relevant cells and the microenvironment of affected tissue domains. Immunoengineering is a field that is focused on the application of engineering principles to the modulation of the immune system, and it could enable future personalized and immunoregulatory therapies for rheumatic diseases. An important aspect of immunoengineering is the harnessing of material chemistries to design technologies that span immunologically relevant length scales, to enhance or suppress immune responses by re-balancing effector and regulatory mechanisms in innate or adaptive immunity and rescue abnormalities underlying pathogenic inflammation. These materials are endowed with physicochemical properties that enable features such as localization in immune cells and organs, sustained delivery of immunoregulatory agents, and mimicry of key functions of lymphoid tissue. Immunoengineering applications already exist for disease management, and there is potential for this new discipline to improve disease modification in rheumatology.

Targeting prostate tumor low-molecular weight tyrosine phosphatase for oxidation-sensitizing therapy

Protein tyrosine phosphatases (PTPs) play major roles in cancer and are emerging as therapeutic targets. Recent reports suggest low-molecular weight PTP (LMPTP)-encoded by the ACP1 gene-is overexpressed in prostate tumors. We found ACP1 up-regulated in human prostate tumors and ACP1 expression inversely correlated with overall survival. Using CRISPR-Cas9-generated LMPTP knockout C4-2B and MyC-CaP cells, we identified LMPTP as a critical promoter of prostate cancer (PCa) growth and bone metastasis. Through metabolomics, we found that LMPTP promotes PCa cell glutathione synthesis by dephosphorylating glutathione synthetase on inhibitory Tyr270. PCa cells lacking LMPTP showed reduced glutathione, enhanced activation of eukaryotic initiation factor 2-mediated stress response, and enhanced reactive oxygen species after exposure to taxane drugs. LMPTP inhibition slowed primary and bone metastatic prostate tumor growth in mice. These findings reveal a role for LMPTP as a critical promoter of PCa growth and metastasis and validate LMPTP inhibition as a therapeutic strategy for treating PCa through sensitization to oxidative stress.

Immunomodulatory Nanoparticles for Modulating Arthritis Flares

Disease-modifying drugs have improved the treatment for autoimmune joint disorders, such as rheumatoid arthritis, but inflammatory flares are a common experience. This work reports the development and application of flare-modulating poly(lactic-co-glycolic acid)-poly(ethylene glycol)-maleimide (PLGA-PEG-MAL)-based nanoparticles conjugated with joint-relevant peptide antigens, aggrecan70-84 and type 2 bovine collagen256-270. Peptide-conjugated PLGA-PEG-MAL nanoparticles encapsulated calcitriol, which acted as an immunoregulatory agent, and were termed calcitriol-loaded nanoparticles (CLNP). CLNP had a ∼200 nm hydrodynamic diameter with a low polydispersity index. In vitro, CLNP induced phenotypic changes in bone marrow derived dendritic cells (DC), reducing the expression of costimulatory and major histocompatibility complex class II molecules, and proinflammatory cytokines. Bulk RNA sequencing of DC showed that CLNP enhanced expression of Ctla4, a gene associated with downregulation of immune responses. In vivo, CLNP accumulated in the proximal lymph nodes after intramuscular injection. Administration of CLNP was not associated with changes in peripheral blood cell numbers or cytokine levels. In the collagen-induced arthritis and SKG mouse models of autoimmune joint disorders, CLNP reduced clinical scores, prevented bone erosion, and preserved cartilage proteoglycan, as assessed by high-resolution microcomputed tomography and histomorphometry analysis. The disease protective effects were associated with increased CTLA-4 expression in joint-localized DC and CD4+ T cells but without generalized suppression of T cell-dependent immune response. The results support the potential of CLNP as modulators of disease flares in autoimmune arthropathies.

Revisiting VH1 phosphatase at the time of monkeypox: back to the spotlight

Vaccinia virus is a poxvirus that has been successfully leveraged to develop vaccines for smallpox, which is caused by the closely related Variola virus. Smallpox has been declared as 'eradicated' by the WHO in 1980; however, it still poses a potential bioterrorism threat. More recently, the spreading of monkeypox (MPox) in non-endemic countries has further highlighted the importance of continuing the exploration for druggable targets for poxvirus infections. The vaccinia H1 (VH1) phosphatase is the first reported dual specificity phosphatase (DUSP) able to hydrolyze both phosphotyrosine and phosphoserine/phosphotheonine residues. VH1 is a 20 kDa protein that forms a stable dimer and can dephosphorylate both viral and cellular substrates to regulate the viral replication cycle and host immune response. VH1 dimers adopt a domain swap mechanism with the first 20 amino acids of each monomer involved in dense electrostatic interaction and salt bridge formations while hydrophobic interactions between the N-terminal and C-terminal helices further stabilize the dimer. VH1 appears to be an ideal candidate for discovery of novel anti-poxvirus agents because it is highly conserved within the poxviridae family and is a virulence factor, yet it displays significant divergence in sequence and dimerization mechanism from its human closest ortholog vaccinia H1-related (VHR) phosphatase, encoded by the DUSP3 gene. As the dimeric quaternary structure of VH1 is essential for its phosphatase activity, strategies leading to disruption of the dimer structure might aid in VH1 inhibitor development.

Clustering of phosphatase RPTPα promotes Src signaling and the arthritogenic action of synovial fibroblasts

Receptor-type protein phosphatase α (RPTPα) promotes fibroblast-dependent arthritis and fibrosis, in part, by enhancing the activation of the kinase SRC. Synovial fibroblasts lining joint tissue mediate inflammation and tissue damage, and their infiltration into adjacent tissues promotes disease progression. RPTPα includes an ectodomain and two intracellular catalytic domains (D1 and D2) and, in cancer cells, undergoes inhibitory homodimerization, which is dependent on a D1 wedge motif. Through single-molecule localization and labeled molecule interaction microscopy of migrating synovial fibroblasts, we investigated the role of RPTPα dimerization in the activation of SRC, the migration of synovial fibroblasts, and joint damage in a mouse model of arthritis. RPTPα clustered with other RPTPα and with SRC molecules in the context of actin-rich structures. A known dimerization-impairing mutation in the wedge motif (P210L/P211L) and the deletion of the D2 domain reduced RPTPα-RPTPα clustering; however, it also unexpectedly reduced RPTPα-SRC association. The same mutations also reduced recruitment of RPTPα to actin-rich structures and inhibited SRC activation and cellular migration. An antibody against the RPTPα ectodomain that prevented the clustering of RPTPα also inhibited RPTPα-SRC association and SRC activation and attenuated fibroblast migration and joint damage in arthritic mice. A catalytically inactivating RPTPα-C469S mutation protected mice from arthritis and reduced SRC activation in synovial fibroblasts. We conclude that RPTPα clustering retains it to actin-rich structures to promote SRC-mediated fibroblast migration and can be modulated through the extracellular domain.

Short-chain fatty acid-mediated epigenetic modulation of inflammatory T cells in vitro

Short-chain fatty acids (SCFAs) are major metabolic products of indigestible polysaccharides in the gut and mediate the function of immune cells to facilitate homeostasis. The immunomodulatory effect of SCFAs has been attributed, at least in part, to the epigenetic modulation of immune cells through the inhibition the nucleus-resident enzyme histone deacetylase (HDAC). Among the downstream effects, SCFAs enhance regulatory T cells (Treg) over inflammatory T helper (Th) cells, including Th17 cells, which can be pathogenic. Here, we characterize the potential of two common SCFAs-butyrate and pentanoate-in modulating differentiation of T cells in vitro. We show that butyrate but not pentanoate exerts a concentration-dependent effect on Treg and Th17 differentiation. Increasing the concentration of butyrate suppresses the Th17-associated RORγtt and IL-17 and increases the expression of Treg-associated FoxP3. To effectively deliver butyrate, encapsulation of butyrate in a liposomal carrier, termed BLIPs, reduced cytotoxicity while maintaining the immunomodulatory effect on T cells. Consistent with these results, butyrate and BLIPs inhibit HDAC and promote a unique chromatin landscape in T cells under conditions that otherwise promote conversion into a pro-inflammatory phenotype. Motif enrichment analysis revealed that butyrate and BLIP-mediated suppression of Th17-associated chromatin accessibility corresponded with a marked decrease in bZIP family transcription factor binding sites. These results support the utility and further evaluation of BLIPs as an immunomodulatory agent for autoimmune disorders that are characterized by chronic inflammation and pathogenic inflammatory T cells.

Immunomodulatory Microparticles Epigenetically Modulate T Cells and Systemically Ameliorate Autoimmune Arthritis

Disease modifying antirheumatic drugs (DMARDs) have improved the prognosis of autoimmune inflammatory arthritides but a large fraction of patients display partial or nonresponsiveness to front-line DMARDs. Here, an immunoregulatory approach based on sustained joint-localized release of all-trans retinoic acid (ATRA), which modulates local immune activation and enhances disease-protective T cells and leads to systemic disease control is reported. ATRA imprints a unique chromatin landscape in T cells, which is associated with an enhancement in the differentiation of naïve T cells into anti-inflammatory regulatory T cells (Treg ) and suppression of Treg destabilization. Sustained release poly-(lactic-co-glycolic) acid (PLGA)-based biodegradable microparticles encapsulating ATRA (PLGA-ATRA MP) are retained in arthritic mouse joints after intra-articular (IA) injection. IA PLGA-ATRA MP enhance migratory Treg which in turn reduce inflammation and modify disease in injected and uninjected joints, a phenotype that is also reproduced by IA injection of Treg . PLGA-ATRA MP reduce proteoglycan loss and bone erosions in the SKG and collagen-induced arthritis mouse models of autoimmune arthritis. Strikingly, systemic disease modulation by PLGA-ATRA MP is not associated with generalized immune suppression. PLGA-ATRA MP have the potential to be developed as a disease modifying agent for autoimmune arthritis.

T‐helper cell regulation of CD45 phosphatase activity by galectin‐1 and CD43 governs chronic lymphocytic leukaemia proliferation

Chronic lymphocytic leukaemia (CLL) is characterised by malignant mature‐like B cells. Supportive to CLL cell survival is chronic B‐cell receptor (BCR) signalling; however, emerging evidence demonstrates CLL cells proliferate in response to T‐helper (Th) cells in a CD40L‐dependent manner. We showed provision of Th stimulation via CD40L upregulated CD45 phosphatase activity and BCR signalling in non‐malignant B cells. Consequently, we hypothesised Th cell upregulation of CLL cell CD45 activity may be an important regulator of CLL BCR signalling and proliferation. Using patient‐derived CLL cells in a culture system with activated autologous Th cells, results revealed increases in both Th and CLL cell CD45 activity, which correlated with enhanced downstream antigen receptor signalling and proliferation. Concomitantly increased was the surface expression of Galectin‐1, a CD45 ligand, and CD43, a CLL immunophenotypic marker. Galectin‐1/CD43 double expression defined a proliferative CLL cell population with enhanced CD45 activity. Targeting either Galectin‐1 or CD43 using silencing, pharmacology, or monoclonal antibody strategies dampened CD45 activity and CLL cell proliferation. These results highlight a mechanism where activated Th cells drive CLL cell BCR signalling and proliferation via Galectin‐1 and CD43‐mediated regulation of CD45 activity, identifying modulation of CD45 phosphatase activity as a potential therapeutic target in CLL.

Lipid-based regulators of immunity

Lipids constitute a diverse class of molecular regulators with ubiquitous physiological roles in sustaining life. These carbon-rich compounds are primarily sourced from exogenous sources and may be used directly as structural cellular building blocks or as a substrate for generating signaling mediators to regulate cell behavior. In both of these roles, lipids play a key role in both immune activation and suppression, leading to inflammation and resolution, respectively. The simple yet elegant structural properties of lipids encompassing size, hydrophobicity, and molecular weight enable unique biodistribution profiles that facilitate preferential accumulation in target tissues to modulate relevant immune cell subsets. Thus, the structural and functional properties of lipids can be leveraged to generate new materials as pharmacological agents for potently modulating the immune system. Here, we discuss the properties of three classes of lipids: polyunsaturated fatty acids, short-chain fatty acids, and lipid adjuvants. We describe their immunoregulatory functions in modulating disease pathogenesis in preclinical models and in human clinical trials. We conclude with an outlook on harnessing the diverse and potent immune modulating properties of lipids for immunoregulation.

Emerging proteoglycans and proteoglycan-targeted therapies in rheumatoid arthritis

Rheumatoid arthritis (RA) is a common auto-immune disease-causing inflammation of the joints and damage of the cartilage and bone. The pathogenesis of RA is characterized in many patients by the presence of antibodies against citrullinated proteins. In the joints, proteoglycans are key structural elements of extracellular matrix in the articular cartilage and synovium and are secreted as lubricants in the synovial fluid. Alterations of proteoglycans contribute to mechanism of disease in RA. Proteoglycans such as aggrecan can be citrullinated and become potential targets of the rheumatoid auto-immune response. Proteoglycans are also up-regulated in RA joints and/or undergo alterations of their regulatory functions over cytokines and chemokines, which promotes inflammation and bone damage. Recent studies have aimed to not only clarify these mechanisms but also develop novel proteoglycan-modulating therapeutics. These include agents altering the function and signaling of proteoglycans as well as tolerizing agents based on citrullinated aggrecan. This mini-review summarizes the most recent findings regarding the dysregulation of proteoglycans that contributes to RA pathogenesis and the potential for proteoglycan-modulating agents to improve RA therapy.

Oxidative stress promotes fibrosis in systemic sclerosis through stabilization of a kinase-phosphatase complex

Systemic sclerosis (SSc) is a fibrotic autoimmune disease characterized by pathogenic activation of fibroblasts enhanced by local oxidative stress. The tyrosine phosphatase PTP4A1 was identified as a critical promoter of TGF-β signaling in SSc. Oxidative stress is known to functionally inactivate tyrosine phosphatases. Here, we assessed whether oxidation of PTP4A1 modulates its profibrotic action and found that PTP4A1 forms a complex with the kinase SRC in scleroderma fibroblasts, but surprisingly, oxidative stress enhanced rather than reduced PTP4A1’s association with SRC and its profibrotic action. Through structural assessment of the oxo-PTP4A1-SRC complex, we unraveled an unexpected mechanism whereby oxidation of a tyrosine phosphatase promotes its function through modification of its protein complex. Considering the importance of oxidative stress in the pathogenesis of SSc and fibrosis, our findings suggest routes for leveraging PTP4A1 oxidation as a potential strategy for developing antifibrotic agents.

Integration of T helper and BCR signals governs enhanced plasma cell differentiation of memory B cells by regulation of CD45 phosphatase activity

Humoral immunity relies on the efficient differentiation of memory B cells (MBCs) into antibody-secreting cells (ASCs). T helper (Th) signals upregulate B cell receptor (BCR) signaling by potentiating Src family kinases through increasing CD45 phosphatase activity (CD45 PA). In this study, we show that high CD45 PA in MBCs enhances BCR signaling and is essential for their effective ASC differentiation. Mechanistically, Th signals upregulate CD45 PA through intensifying the surface binding of a CD45 ligand, Galectin-1. CD45 PA works as a sensor of T cell help and defines high-affinity germinal center (GC) plasma cell (PC) precursors characterized by IRF4 expression in vivo. Increasing T cell help in vitro results in an incremental CD45 PA increase and enhances ASC differentiation by facilitating effective induction of the transcription factors IRF4 and BLIMP1. This study connects Th signals with BCR signaling through Galectin-1-dependent regulation of CD45 PA and provides a mechanism for efficient ASC differentiation of MBCs.

Discovery of Orally Bioavailable Purine-Based Inhibitors of the Low-Molecular-Weight Protein Tyrosine Phosphatase

Obesity-associated insulin resistance plays a central role in the pathogenesis of type 2 diabetes. A promising approach to decrease insulin resistance in obesity is to inhibit the protein tyrosine phosphatases that negatively regulate insulin receptor signaling. The low-molecular-weight protein tyrosine phosphatase (LMPTP) acts as a critical promoter of insulin resistance in obesity by inhibiting phosphorylation of the liver insulin receptor activation motif. Here, we report development of a novel purine-based chemical series of LMPTP inhibitors. These compounds inhibit LMPTP with an uncompetitive mechanism and are highly selective for LMPTP over other protein tyrosine phosphatases. We also report the generation of a highly orally bioavailable purine-based analogue that reverses obesity-induced diabetes in mice.

The low molecular weight protein tyrosine phosphatase promotes adipogenesis and subcutaneous adipocyte hypertrophy

Obesity is a major contributing factor to the pathogenesis of Type 2 diabetes. Multiple human genetics studies suggest that high activity of the low molecular weight protein tyrosine phosphatase (LMPTP) promotes metabolic syndrome in obesity. We reported that LMPTP is a critical promoter of insulin resistance in obesity by regulating liver insulin receptor signaling and that inhibition of LMPTP reverses obesity-associated diabetes in mice. Since LMPTP is expressed in adipose tissue but little is known about its function, here we examined the role of LMPTP in adipocyte biology. Using conditional knockout mice, we found that selective deletion of LMPTP in adipocytes impaired obesity-induced subcutaneous adipocyte hypertrophy. We assessed the role of LMPTP in adipogenesis in vitro, and found that LMPTP deletion or knockdown substantially impaired differentiation of primary preadipocytes and 3T3-L1 cells into adipocytes, respectively. Inhibition of LMPTP in 3T3-L1 preadipocytes also reduced adipogenesis and expression of proadipogenic transcription factors peroxisome proliferator activated receptor gamma (PPARγ) and CCAAT/enhancer-binding protein alpha. Inhibition of LMPTP increased basal phosphorylation of platelet-derived growth factor receptor alpha (PDGFRα) on activation motif residue Y849 in 3T3-L1, resulting in increased activation of the mitogen-associated protein kinases p38 and c-Jun N-terminal kinase and increased PPARγ phosphorylation on inhibitory residue S82. Analysis of the metabolome of differentiating 3T3-L1 cells suggested that LMPTP inhibition decreased cell glucose utilization while enhancing mitochondrial respiration and nucleotide synthesis. In summary, we report a novel role for LMPTP as a key driver of adipocyte differentiation via control of PDGFRα signaling.

PTPN2 links colonic and joint inflammation in experimental autoimmune arthritis

Loss-of-function variants of protein tyrosine phosphatase non-receptor type 2 (PTPN2) enhance risk of inflammatory bowel disease and rheumatoid arthritis; however, whether the association between PTPN2 and autoimmune arthritis depends on gut inflammation is unknown. Here we demonstrate that induction of subclinical intestinal inflammation exacerbates development of autoimmune arthritis in SKG mice. Ptpn2-haploinsufficient SKG mice — modeling human carriers of disease-associated variants of PTPN2 — displayed enhanced colitis-induced arthritis and joint accumulation of Tregs expressing RAR-related orphan receptor γT (RORγt) — a gut-enriched Treg subset that can undergo conversion into FoxP3^–IL-17⁺ arthritogenic exTregs. SKG colonic Tregs underwent higher conversion into arthritogenic exTregs when compared with peripheral Tregs, which was exacerbated by haploinsufficiency of Ptpn2. Ptpn2 haploinsufficiency led to selective joint accumulation of RORγt-expressing Tregs expressing the colonic marker G protein–coupled receptor 15 (GPR15) in arthritic mice and selectively enhanced conversion of GPR15⁺ Tregs into exTregs in vitro and in vivo. Inducible Treg-specific haploinsufficiency of Ptpn2 enhanced colitis-induced SKG arthritis and led to specific joint accumulation of GPR15⁺ exTregs. Our data validate the SKG model for studies at the interface between intestinal and joint inflammation and suggest that arthritogenic variants of PTPN2 amplify the link between gut inflammation and arthritis through conversion of colonic Tregs into exTregs.

Loss of protein tyrosine phosphatase non-receptor type 2 amplifies the link between gut and joint inflammation through conversion of colonic Tregs into arthritogenic exTregs.

Synoviocyte-targeted therapy synergizes with TNF inhibition in arthritis reversal

Fibroblast-like synoviocytes (FLS) are joint-lining cells that promote rheumatoid arthritis (RA) pathology. Current disease-modifying antirheumatic agents (DMARDs) operate through systemic immunosuppression. FLS-targeted approaches could potentially be combined with DMARDs to improve control of RA without increasing immunosuppression. Here, we assessed the potential of immunoglobulin-like domains 1 and 2 (Ig1&2), a decoy protein that activates the receptor tyrosine phosphatase sigma (PTPRS) on FLS, for RA therapy. We report that PTPRS expression is enriched in synovial lining RA FLS and that Ig1&2 reduces migration of RA but not osteoarthritis FLS. Administration of an Fc-fusion Ig1&2 attenuated arthritis in mice without affecting innate or adaptive immunity. Furthermore, PTPRS was down-regulated in FLS by tumor necrosis factor (TNF) via a phosphatidylinositol 3-kinase-mediated pathway, and TNF inhibition enhanced PTPRS expression in arthritic joints. Combination of ineffective doses of TNF inhibitor and Fc-Ig1&2 reversed arthritis in mice, providing an example of synergy between FLS-targeted and immunosuppressive DMARD therapies.

PTPN22 phosphorylation acts as a molecular rheostat for the inhibition of TCR signaling

The hematopoietic-specific protein tyrosine phosphatase nonreceptor type 22 (PTPN22) is encoded by a major autoimmunity risk gene. PTPN22 inhibits T cell activation by dephosphorylating substrates involved in proximal T cell receptor (TCR) signaling. Here, we found by mass spectrometry that PTPN22 was phosphorylated at Ser⁷⁵¹ by PKCα in Jurkat and primary human T cells activated with phorbol ester/ionomycin or antibodies against CD3/CD28. The phosphorylation of PTPN22 at Ser⁷⁵¹ prolonged its half-life by inhibiting K48-linked ubiquitination and impairing recruitment of the phosphatase to the plasma membrane, which is necessary to inhibit proximal TCR signaling. Additionally, the phosphorylation of PTPN22 at Ser⁷⁵¹ enhanced the interaction of PTPN22 with the carboxyl-terminal Src kinase (CSK), an interaction that is impaired by the PTPN22 R620W variant associated with autoimmune disease. The phosphorylation of Ser⁷⁵¹ did not affect the recruitment of PTPN22 R620W to the plasma membrane but protected this mutant from degradation. Together, out data indicate that phosphorylation at Ser⁷⁵¹ mediates a reciprocal regulation of PTPN22 stability versus translocation to TCR signaling complexes by CSK-dependent and CSK-independent mechanisms.

RPTPα phosphatase activity is allosterically regulated by the membrane-distal catalytic domain

Receptor-type protein tyrosine phosphatase α (RPTPα) is an important positive regulator of SRC kinase activation and a known promoter of cancer growth, fibrosis, and arthritis. The domain structure of RPTPs comprises an extracellular region, a transmembrane helix, and two tandem intracellular catalytic domains referred to as D1 and D2. The D2 domain of RPTPs is believed to mostly play a regulatory function; however, no regulatory model has been established for RPTPα-D2 or other RPTP-D2 domains. Here, we solved the 1.8 Å resolution crystal structure of the cytoplasmic region of RPTPα, encompassing D1 and D2, trapped in a conformation that revealed a possible mechanism through which D2 can allosterically inhibit D1 activity. Using a D2-truncation RPTPα variant and mutational analysis of the D1/D2 interfaces, we show that D2 inhibits RPTPα phosphatase activity and identified a ⁴⁰⁵PFTP⁴⁰⁸ motif in D1 that mediates the inhibitory effect of D2. Expression of the gain-of-function F406A/T407A RPTPα variant in HEK293T cells enhanced SRC activation, supporting the relevance of our proposed D2-mediated regulation mechanism in cell signaling. There is emerging interest in the development of allosteric inhibitors of RPTPs but a scarcity of validated allosteric sites for RPTPs. The results of our study not only shed light on the regulatory role of RPTP-D2 domains, but also provide a potentially useful tool for the discovery of chemical probes targeting RPTPα and other RPTPs.

Secreted Protein Acidic and Rich in Cysteine Mediated Biomimetic Delivery of Methotrexate by Albumin-Based Nanomedicines for Rheumatoid Arthritis Therapy

Rheumatoid arthritis (RA) is one of the most common chronic autoimmune diseases. Despite considerable advances in clinical treatment of RA, suboptimal response to therapy and treatment discontinuation are still unresolved challenges due to systemic toxicity. It is of crucial importance to actively target and deliver therapeutic agents to inflamed joints in order to promote in situ activity and decrease systemic toxicity. In this study, we found that SPARC (secreted protein acidic and rich in cysteine) was overexpressed in the synovial fluid and synovium of RA patients as well as mice with collagen-induced arthritis (CIA), which has been scarcely reported. Building upon the SPARC signature of RA joint microenvironment and the intrinsic high affinity of SPARC for albumin, we fabricated methotrexate-loaded human serum albumin nanomedicines (MTX@HSA NMs) and explored them as biomimetic drug delivery systems for RA therapy. Upon intravenous injection of chlorin e6-labeled MTX@HSA NMs into CIA mice, the fluorescence/magnetic resonance dual-modal imaging revealed higher accumulations and longer retention of MTX@HSA NMs in inflamed joints with respect to free MTX molecules. In vivo therapeutic evaluations suggested that the MTX@HSA NMs were able to attenuate the progression of RA with better efficacy and fewer side effects even at half  dose of administrated MTX in comparison with free MTX. By unraveling the mechanism driving the efficient accumulation of MTX@HSA NMs in RA joints and showing their ability to improve the safety and therapeutic efficacy of MTX, our work sheds light on the development of innovative anti-RA nanomedicines with a strong potential for clinical translation.

The Contribution of PTPN22 to Rheumatic Disease

One of the unresolved questions in modern medicine is why certain individuals develop a disorder such as rheumatoid arthritis (RA) or lupus, while others do not. Contemporary science indicates that genetics is partly responsible for disease development, while environmental and stochastic factors also play a role. Among the many genes that increase the risk of autoimmune conditions, the risk allele encoding the W620 variant of protein tyrosine phosphatase N22 (PTPN22) is shared between multiple rheumatic diseases, suggesting that it plays a fundamental role in the development of immune dysfunction. Herein, we discuss how the presence of the PTPN22 risk allele may shape the signs and symptoms of these diseases. Besides the emerging clarity regarding how PTPN22 tunes T and B cell antigen receptor signaling, we discuss recent discoveries of important functions of PTPN22 in myeloid cell lineages. Taken together, these new insights reveal important clues to the molecular mechanisms of prevalent diseases like RA and lupus and may open new avenues for the development of personalized therapies that spare the normal function of the immune system.

PTPN14 phosphatase and YAP promote TGFβ signalling in rheumatoid synoviocytes

OBJECTIVE

We aimed to understand the role of the tyrosine phosphatase PTPN14-which in cancer cells modulates the Hippo pathway by retaining YAP in the cytosol-in fibroblast-like synoviocytes (FLS) from patients with rheumatoid arthritis (RA).

METHODS

Gene/protein expression levels were measured by quantitative PCR and/or Western blotting. Gene knockdown in RA FLS was achieved using antisense oligonucleotides. The interaction between PTPN14 and YAP was assessed by immunoprecipitation. The cellular localisation of YAP and SMAD3 was examined via immunofluorescence. SMAD reporter studies were carried out in HEK293T cells. The RA FLS/cartilage coimplantation and passive K/BxN models were used to examine the role of YAP in arthritis.

RESULTS

RA FLS displayed overexpression of PTPN14 when compared with FLS from patients with osteoarthritis (OA). PTPN14 knockdown in RA FLS impaired TGFβ-dependent expression of MMP13 and potentiation of TNF signalling. In RA FLS, PTPN14 formed a complex with YAP. Expression of PTPN14 or nuclear YAP-but not of a non-YAP-interacting PTPN14 mutant-enhanced SMAD reporter activity. YAP promoted TGFβ-dependent SMAD3 nuclear localisation in RA FLS. Differences in epigenetic marks within Hippo pathway genes, including YAP, were found between RA FLS and OA FLS. Inhibition of YAP reduced RA FLS pathogenic behaviour and ameliorated arthritis severity.

CONCLUSION

In RA FLS, PTPN14 and YAP promote nuclear localisation of SMAD3. YAP enhances a range of RA FLS pathogenic behaviours which, together with epigenetic evidence, points to the Hippo pathway as an important regulator of RA FLS behaviour.

Reduced expression of phosphatase PTPN2 promotes pathogenic conversion of Tregs in autoimmunity

Genetic variants at the PTPN2 locus, which encodes the tyrosine phosphatase PTPN2, cause reduced gene expression and are linked to rheumatoid arthritis (RA) and other autoimmune diseases. PTPN2 inhibits signaling through the T cell and cytokine receptors, and loss of PTPN2 promotes T cell expansion and CD4- and CD8-driven autoimmunity. However, it remains unknown whether loss of PTPN2 in FoxP3+ regulatory T cells (Tregs) plays a role in autoimmunity. Here we aimed to model human autoimmune-predisposing PTPN2 variants, the presence of which results in a partial loss of PTPN2 expression, in mouse models of RA. We identified that reduced expression of Ptpn2 enhanced the severity of autoimmune arthritis in the T cell-dependent SKG mouse model and demonstrated that this phenotype was mediated through a Treg-intrinsic mechanism. Mechanistically, we found that through dephosphorylation of STAT3, PTPN2 inhibits IL-6-driven pathogenic loss of FoxP3 after Tregs have acquired RORγt expression, at a stage when chromatin accessibility for STAT3-targeted IL-17-associated transcription factors is maximized. We conclude that PTPN2 promotes FoxP3 stability in mouse RORγt+ Tregs and that loss of function of PTPN2 in Tregs contributes to the association between PTPN2 and autoimmunity.

Nitric Oxide Dependent Degradation of Polyethylene Glycol-Modified Single-Walled Carbon Nanotubes: Implications for Intra-Articular Delivery

Polyethylene glycol (PEG)-modified carbon nanotubes have been successfully employed for intra-articular delivery in mice without systemic or local toxicity. However, the fate of the delivery system itself remains to be understood. In this study 2 kDa PEG-modified single-walled carbon nanotubes (PNTs) are synthesized, and trafficking and degradation following intra-articular injection into the knee-joint of healthy mice are studied. Using confocal Raman microspectroscopy, PNTs can be imaged in the knee-joint and are found to either egress from the synovial cavity or undergo biodegradation over a period of 3 weeks. Raman analysis discloses that PNTs are oxidatively degraded mainly in the chondrocyte-rich cartilage and meniscus regions while PNTs can also be detected in the synovial membrane regions, where macrophages can be found. Furthermore, using murine chondrocyte (ATDC-5) and macrophage (RAW264.7) cell lines, biodegradation of PNTs in activated, nitric oxide (NO)-producing chondrocytes, which is blocked upon pharmacological inhibition of inducible nitric oxide synthase (iNOS), can be shown. Biodegradation of PNTs in macrophages is also noted, but after a longer period of incubation. Finally, cell-free degradation of PNTs upon incubation with the peroxynitrite-generating compound, SIN-1 is demonstrated. The present study paves the way for the use of PNTs as delivery systems in the treatment of diseases of the joint.

Protein Tyrosine Phosphatases in Systemic Sclerosis: Potential Pathogenic Players and Therapeutic Targets

PURPOSE OF REVIEW

The pathogenesis of systemic sclerosis depends on a complex interplay between autoimmunity, vasculopathy, and fibrosis. Reversible phosphorylation on tyrosine residues, in response to growth factors and other stimuli, critically regulates each one of these three key pathogenic processes. Protein tyrosine kinases, the enzymes that catalyze addition of phosphate to tyrosine residues, are known players in systemic sclerosis, and tyrosine kinase inhibitors are undergoing clinical trials for treatment of this disease. Until recently, the role of tyrosine phosphatases-the enzymes that counteract the action of tyrosine kinases by removing phosphate from tyrosine residues-in systemic sclerosis has remained largely unknown. Here, we review the function of tyrosine phosphatases in pathways relevant to the pathogenesis of systemic sclerosis and their potential promise as therapeutic targets to halt progression of this debilitating rheumatic disease.

RECENT FINDINGS

Protein tyrosine phosphatases are emerging as important regulators of a multitude of signaling pathways and undergoing validation as molecular targets for cancer and other common diseases. Recent advances in drug discovery are paving the ways to develop new classes of tyrosine phosphatase modulators to treat human diseases. Although so far only few reports have focused on tyrosine phosphatases in systemic sclerosis, these enzymes play a role in multiple pathways relevant to disease pathogenesis. Further studies in this field are warranted to explore the potential of tyrosine phosphatases as drug targets for systemic sclerosis.

Targeting Tyrosine Phosphatases: Time to End the Stigma

Protein tyrosine phosphatases (PTPs) are a family of enzymes essential for numerous cellular processes, and several PTPs have been validated as therapeutic targets for human diseases. Historically, the development of drugs targeting PTPs has been highly challenging, leading to stigmatization of these enzymes as undruggable targets. Despite these difficulties, efforts to drug PTPs have persisted, and recent years have seen an influx of new probes providing opportunities for biological examination of old and new PTP targets. Here we discuss progress towards drugging PTPs with special emphasis on the development of selective probes with biological activity. We describe the development of new small-molecule orthosteric, allosteric, and oligomerization-inhibiting PTP inhibitors and discuss new studies targeting the receptor PTP (RPTP) subfamily with biologics.

Diabetes reversal by inhibition of the low-molecular-weight tyrosine phosphatase

Obesity-associated insulin resistance plays a central role in type 2 diabetes. As such, tyrosine phosphatases that dephosphorylate the insulin receptor (IR) are potential therapeutic targets. The low-molecular-weight protein tyrosine phosphatase (LMPTP) is a proposed IR phosphatase, yet its role in insulin signaling in vivo has not been defined. Here we show that global and liver-specific LMPTP deletion protects mice from high-fat diet-induced diabetes without affecting body weight. To examine the role of the catalytic activity of LMPTP, we developed a small-molecule inhibitor with a novel uncompetitive mechanism, a unique binding site at the opening of the catalytic pocket, and an exquisite selectivity over other phosphatases. This inhibitor is orally bioavailable, and it increases liver IR phosphorylation in vivo and reverses high-fat diet-induced diabetes. Our findings suggest that LMPTP is a key promoter of insulin resistance and that LMPTP inhibitors would be beneficial for treating type 2 diabetes.

Epigenetic alterations in rheumatoid arthritis fibroblast-like synoviocytes

Rheumatoid arthritis is an immune-mediated disease that primarily affects diarthrodial joints. Susceptibility and severity of this disease are influenced by nongenetic factors, such as environmental stress, suggesting an important role of epigenetic changes. In this review, we summarize the epigenetic changes (DNA methylation, histone modification and miRNA expression) in fibroblast-like synoviocytes, which are the joint-lining mesenchymal cells that play an important role in joint inflammation and damage. We also review the effects of these epigenetic changes on rheumatoid arthritis pathogenesis and discuss their therapeutic potential.

Receptor Protein Tyrosine Phosphatase α-Mediated Enhancement of Rheumatoid Synovial Fibroblast Signaling and Promotion of Arthritis in Mice

OBJECTIVE

During rheumatoid arthritis (RA), fibroblast-like synoviocytes (FLS) critically promote disease pathogenesis by aggressively invading the extracellular matrix of the joint. The focal adhesion kinase (FAK) signaling pathway is emerging as a contributor to the anomalous behavior of RA FLS. The receptor protein tyrosine phosphatase α (RPTPα), which is encoded by the PTPRA gene, is a key promoter of FAK signaling. The aim of this study was to investigate whether RPTPα mediates FLS aggressiveness and RA pathogenesis.

METHODS

Through RPTPα knockdown, we assessed FLS gene expression by quantitative polymerase chain reaction analysis and enzyme-linked immunosorbent assay, invasion and migration by Transwell assays, survival by annexin V and propidium iodide staining, adhesion and spreading by immunofluorescence microscopy, and activation of signaling pathways by Western blotting of FLS lysates. Arthritis development was examined in RPTPα-knockout (KO) mice using the K/BxN serum-transfer model. The contribution of radiosensitive and radioresistant cells to disease was evaluated by reciprocal bone marrow transplantation.

RESULTS

RPTPα was enriched in the RA synovial lining. RPTPα knockdown impaired RA FLS survival, spreading, migration, invasiveness, and responsiveness to platelet-derived growth factor, tumor necrosis factor, and interleukin-1 stimulation. These phenotypes correlated with increased phosphorylation of Src on inhibitory Y(527) and decreased phosphorylation of FAK on stimulatory Y(397) . Treatment of RA FLS with an inhibitor of FAK phenocopied the knockdown of RPTPα. RPTPα-KO mice were protected from arthritis development, which was due to radioresistant cells.

CONCLUSION

By regulating the phosphorylation of Src and FAK, RPTPα mediates proinflammatory and proinvasive signaling in RA FLS, correlating with the promotion of disease in an FLS-dependent model of RA.

Abnormal PTPN11 enhancer methylation promotes rheumatoid arthritis fibroblast-like synoviocyte aggressiveness and joint inflammation

The PTPN11 gene, encoding the tyrosine phosphatase SHP-2, is overexpressed in rheumatoid arthritis (RA) fibroblast-like synoviocytes (FLS) compared with osteoarthritis (OA) FLS and promotes RA FLS invasiveness. Here, we explored the molecular basis for PTPN11 overexpression in RA FLS and the role of SHP-2 in RA pathogenesis. Using computational methods, we identified a putative enhancer in PTPN11 intron 1, which contained a glucocorticoid receptor- binding (GR-binding) motif. This region displayed enhancer function in RA FLS and contained 2 hypermethylation sites in RA compared with OA FLS. RA FLS stimulation with the glucocorticoid dexamethasone induced GR binding to the enhancer and PTPN11 expression. Glucocorticoid responsiveness of PTPN11 was significantly higher in RA FLS than OA FLS and required the differentially methylated CpGs for full enhancer function. SHP-2 expression was enriched in the RA synovial lining, and heterozygous Ptpn11 deletion in radioresistant or innate immune cells attenuated K/BxN serum transfer arthritis in mice. Treatment with SHP-2 inhibitor 11a-1 reduced RA FLS migration and responsiveness to TNF and IL-1β stimulation and reduced arthritis severity in mice. Our findings demonstrate how abnormal epigenetic regulation of a pathogenic gene determines FLS behavior and demonstrate that targeting SHP-2 or the SHP-2 pathway could be a therapeutic strategy for RA.

Targeting phosphatase-dependent proteoglycan switch for rheumatoid arthritis therapy

Despite the availability of several therapies for rheumatoid arthritis (RA) that target the immune system, a large number of RA patients fail to achieve remission. Joint-lining cells, called fibroblast-like synoviocytes (FLS), become activated during RA and mediate joint inflammation and destruction of cartilage and bone. We identify RPTPσ, a transmembrane tyrosine phosphatase, as a therapeutic target for FLS-directed therapy. RPTPσ is reciprocally regulated by interactions with chondroitin sulfate or heparan sulfate containing extracellular proteoglycans in a mechanism called the proteoglycan switch. We show that the proteoglycan switch regulates FLS function. Incubation of FLS with a proteoglycan-binding RPTPσ decoy protein inhibited cell invasiveness and attachment to cartilage by disrupting a constitutive interaction between RPTPσ and the heparan sulfate proteoglycan syndecan-4. RPTPσ mediated the effect of proteoglycans on FLS signaling by regulating the phosphorylation and cytoskeletal localization of ezrin. Furthermore, administration of the RPTPσ decoy protein ameliorated in vivo human FLS invasiveness and arthritis severity in the K/BxN serum transfer model of RA. Our data demonstrate that FLS are regulated by an RPTPσ-dependent proteoglycan switch in vivo, which can be targeted for RA therapy. We envision that therapies targeting the proteoglycan switch or its intracellular pathway in FLS could be effective as a monotherapy or in combination with currently available immune-targeted agents to improve control of disease activity in RA patients.

Chondrocyte clocks make cartilage time-sensitive material

Circadian rhythms mediated by both central and tissue-specific peripheral clocks allow for the synchronization of biological processes with diurnal cycles such as activity and rest. Disruption of these rhythms can be caused by altered sleep-awake patterns or by pathological conditions and can initiate or exacerbate human disease through mechanisms that are only partially understood. In this issue, Dudek et al. identify a chondrocyte-autonomous cartilage clock and demonstrate that expression of an important circadian pacemaker, BMAL1, decreases during osteoarthritis progression. They show that chondrocyte-specific deletion of BMAL1 leads to cartilage degradation and disruption of key pathways, shifting cartilage homeostasis toward a catabolic state. These findings provide insight into the interplay between circadian rhythm and cartilage in osteoarthritis.

Ptpn22 and Cd2 Variations Are Associated with Altered Protein Expression and Susceptibility to Type 1 Diabetes in Nonobese Diabetic Mice

By congenic strain mapping using autoimmune NOD.C57BL/6J congenic mice, we demonstrated previously that the type 1 diabetes (T1D) protection associated with the insulin-dependent diabetes (Idd)10 locus on chromosome 3, originally identified by linkage analysis, was in fact due to three closely linked Idd loci: Idd10, Idd18.1, and Idd18.3. In this study, we define two additional Idd loci—Idd18.2 and Idd18.4—within the boundaries of this cluster of disease-associated genes. Idd18.2 is 1.31 Mb and contains 18 genes, including Ptpn22, which encodes a phosphatase that negatively regulates T and B cell signaling. The human ortholog of Ptpn22, PTPN22, is associated with numerous autoimmune diseases, including T1D. We, therefore, assessed Ptpn22 as a candidate for Idd18.2; resequencing of the NOD Ptpn22 allele revealed 183 single nucleotide polymorphisms with the C57BL/6J (B6) allele—6 exonic and 177 intronic. Functional studies showed higher expression of full-length Ptpn22 RNA and protein, and decreased TCR signaling in congenic strains with B6-derived Idd18.2 susceptibility alleles. The 953-kb Idd18.4 locus contains eight genes, including the candidate Cd2. The CD2 pathway is associated with the human autoimmune disease, multiple sclerosis, and mice with NOD-derived susceptibility alleles at Idd18.4 have lower CD2 expression on B cells. Furthermore, we observed that susceptibility alleles at Idd18.2 can mask the protection provided by Idd10/Cd101 or Idd18.1/Vav3 and Idd18.3. In summary, we describe two new T1D loci, Idd18.2 and Idd18.4, candidate genes within each region, and demonstrate the complex nature of genetic interactions underlying the development of T1D in the NOD mouse model.

Deletion of low molecular weight protein tyrosine phosphatase (Acp1) protects against stress-induced cardiomyopathy

The low molecular weight protein tyrosine phosphatase (LMPTP), encoded by the ACP1 gene, is a ubiquitously expressed phosphatase whose in vivo function in the heart and in cardiac diseases remains unknown. To investigate the in vivo role of LMPTP in cardiac function, we generated mice with genetic inactivation of the Acp1 locus and studied their response to long‐term pressure overload. Acp1^−/− mice develop normally and ageing mice do not show pathology in major tissues under basal conditions. However, Acp1^−/− mice are strikingly resistant to pressure overload hypertrophy and heart failure. Lmptp expression is high in the embryonic mouse heart, decreased in the postnatal stage, and increased in the adult mouse failing heart. We also show that LMPTP expression increases in end‐stage heart failure in humans. Consistent with their protected phenotype, Acp1^−/− mice subjected to pressure overload hypertrophy have attenuated fibrosis and decreased expression of fibrotic genes. Transcriptional profiling and analysis of molecular signalling show that the resistance of Acp1^−/− mice to pathological cardiac stress correlates with marginal re‐expression of fetal cardiac genes, increased insulin receptor beta phosphorylation, as well as PKA and ephrin receptor expression, and inactivation of the CaMKIIδ pathway. Our data show that ablation of Lmptp inhibits pathological cardiac remodelling and suggest that inhibition of LMPTP may be of therapeutic relevance for the treatment of human heart failure. © 2015 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Phosphatase Inhibitors Function as Novel, Broad Spectrum Botulinum Neurotoxin Antagonists in Mouse and Human Embryonic Stem Cell-Derived Motor Neuron-Based Assays

There is an urgent need to develop novel treatments to counter Botulinum neurotoxin (BoNT) poisoning. Currently, the majority of BoNT drug development efforts focus on directly inhibiting the proteolytic components of BoNT, i.e. light chains (LC). Although this is a rational approach, previous research has shown that LCs are extremely difficult drug targets and that inhibiting multi-serotype BoNTs with a single LC inhibitor may not be feasible. An alternative approach would target neuronal pathways involved in intoxication/recovery, rather than the LC itself. Phosphorylation-related mechanisms have been implicated in the intoxication pathway(s) of BoNTs. However, the effects of phosphatase inhibitors upon BoNT activity in the physiological target of BoNTs, i.e. motor neurons, have not been investigated. In this study, a small library of phosphatase inhibitors was screened for BoNT antagonism in the context of mouse embryonic stem cell-derived motor neurons (ES-MNs). Four inhibitors were found to function as BoNT/A antagonists. Subsequently, we confirmed that these inhibitors protect against BoNT/A in a dose-dependent manner in human ES-MNs. Additionally, these compounds provide protection when administered in post-intoxication scenario. Importantly, the inhibitors were also effective against BoNT serotypes B and E. To the best of our knowledge, this is the first study showing phosphatase inhibitors as broad-spectrum BoNT antagonists.

Generation of NOD mice carrying R619W mutation in PTPN22 gene by CRISPR/Cas9-mediated genome engineering (BA4P.134)

An allelic variant of protein tyrosine phosphatase nonreceptor 22 (PTPN22), PTPN22R620W, is strongly associated with type 1 diabetes (T1D) and several other autoimmune diseases in human, and increases the risk of developing T1D by 2-4 fold. Non-obese diabetic (NOD) mouse is an ideal spontaneous T1D model that shares with human many genetic pathways contributing to T1D; however, it has not previously been possible to introduce targeted mutations into NOD mice due to a lack of germline competent NOD embryonic stem cells. To overcome this technological hindrance, we used CRISPR/Cas9 technology to precisely mutate PTPN22 gene in its endogenous locus in NOD zygotes, and successfully produced 2 independent lines of NOD mice expressing PTPN22R619W variant, a murine ortholog of the human autoimmune-associated allele. We have also obtained a line carrying PTPN22 null allele. We have demonstrated the mutated PTPN22 genes in all lines have successfully germline transmitted. We have found a significant increase of T1D incidence in the heterozygous NOD PTPN22R619W mice, suggesting its strong effect in heterozygosity, which is very relevant to human T1D since PTPN22R620W is most commonly carried in heterozygosity. This is the first time the autoimmune-associated PTPN22 allele has been introduced into a spontaneous model of T1D and, to the best of our knowledge, the first time CRISPR/Cas9 technology has been used to genetically modify NOD mice.

Polyethylene-glycol-modified single-walled carbon nanotubes for intra-articular delivery to chondrocytes

Osteoarthritis (OA) is a common and debilitating degenerative disease of articular joints for which no disease-modifying medical therapy is currently available. Inefficient delivery of pharmacologic agents into cartilage-resident chondrocytes after systemic administration has been a limitation to the development of anti-OA medications. Direct intra-articular injection enables delivery of high concentrations of agents in close proximity to chondrocytes; however, the efficacy of this approach is limited by the fast clearance of small molecules and biomacromolecules after injection into the synovial cavity. Coupling of pharmacologic agents with drug delivery systems able to enhance their residence time and cartilage penetration can enhance the effectiveness of intra-articularly injected anti-OA medications. Herein we describe an efficient intra-articular delivery nanosystem based on single-walled carbon nanotubes (SWCNTs) modified with polyethylene glycol (PEG) chains (PEG-SWCNTs). We show that PEG-SWCNTs are capable to persist in the joint cavity for a prolonged time, enter the cartilage matrix, and deliver gene inhibitors into chondrocytes of both healthy and OA mice. PEG-SWCNT nanoparticles did not elicit systemic or local side effects. Our data suggest that PEG-SWCNTs represent a biocompatible and effective nanocarrier for intra-articular delivery of agents to chondrocytes.

The protein tyrosine phosphatase PTPN22 controls forkhead box protein 3 T regulatory cell induction but is dispensable for T helper type 1 cell polarization

Protein tyrosine phosphatases (PTPs) regulate T cell receptor (TCR) signalling and thus have a role in T cell differentiation. Here we tested whether the autoimmune predisposing gene PTPN22 encoding for a PTP that inhibits TCR signalling affects the generation of forkhead box protein 3 (FoxP3)(+) T regulatory (Treg ) cells and T helper type 1 (Th1) cells. Murine CD4(+) T cells isolated from Ptpn22 knock-out (Ptpn22(KO) ) mice cultured in Treg cell polarizing conditions showed increased sensitivity to TCR activation compared to wild-type (WT) cells, and subsequently reduced FoxP3 expression at optimal-to-high levels of activation. However, at lower levels of TCR activation, Ptpn22(KO) CD4(+) T cells showed enhanced expression of FoxP3. Similar experiments in humans revealed that at optimal levels of TCR activation PTPN22 knock-down by specific oligonucleotides compromises the differentiation of naive CD4(+) T cells into Treg cells. Notably, in vivo Treg cell conversion experiments in mice showed delayed kinetic but overall increased frequency and number of Treg cells in the absence of Ptpn22. In contrast, the in vitro and in vivo generation of Th1 cells was comparable between WT and Ptpn22(KO) mice, thus suggesting PTPN22 as a FoxP3-specific regulating factor. Together, these results propose PTPN22 as a key factor in setting the proper threshold for FoxP3(+) Treg cell differentiation.

TGFβ responsive tyrosine phosphatase promotes rheumatoid synovial fibroblast invasiveness

OBJECTIVE

In rheumatoid arthritis (RA), fibroblast-like synoviocytes (FLS) that line joint synovial membranes aggressively invade the extracellular matrix, destroying cartilage and bone. As signal transduction in FLS is mediated through multiple pathways involving protein tyrosine phosphorylation, we sought to identify protein tyrosine phosphatases (PTPs) regulating the invasiveness of RA FLS. We describe that the transmembrane receptor PTPκ (RPTPκ), encoded by the transforming growth factor (TGF) β-target gene, PTPRK, promotes RA FLS invasiveness.

METHODS

Gene expression was quantified by quantitative PCR. PTP knockdown was achieved using antisense oligonucleotides. FLS invasion and migration were assessed in transwell or spot assays. FLS spreading was assessed by immunofluorescence microscopy. Activation of signalling pathways was analysed by Western blotting of FLS lysates using phosphospecific antibodies. In vivo FLS invasiveness was assessed by intradermal implantation of FLS into nude mice. The RPTPκ substrate was identified by pull-down assays.

RESULTS

PTPRK expression was higher in FLS from patients with RA versus patients with osteoarthritis, resulting from increased TGFB1 expression in RA FLS. RPTPκ knockdown impaired RA FLS spreading, migration, invasiveness and responsiveness to platelet-derived growth factor, tumour necrosis factor and interleukin 1 stimulation. Furthermore, RPTPκ deficiency impaired the in vivo invasiveness of RA FLS. Molecular analysis revealed that RPTPκ promoted RA FLS migration by dephosphorylation of the inhibitory residue Y527 of SRC.

CONCLUSIONS

By regulating phosphorylation of SRC, RPTPκ promotes the pathogenic action of RA FLS, mediating cross-activation of growth factor and inflammatory cytokine signalling by TGFβ in RA FLS.

"PEST control": regulation of molecular barcodes by tyrosine phosphatases

The emerging concept of "molecular barcodes" refers to the dynamic combination of post-translational modifications, often of different nature (e.g., phosphorylation and ubiquitination) that gives rise to multiple forms of a protein which can relay distinct signals throughout a cell. In a recent Cell Research paper by Wang et al., the authors report that a PEST domain-containing tyrosine phosphatase, PTPN18, is able to regulate both phosphorylation and ubiquitination of the HER2 oncogene, barcoding HER2 for increased proteasomal degradation rather than for intracellular trafficking.

Ion channel TRPV1-dependent activation of PTP1B suppresses EGFR-associated intestinal tumorigenesis

The intestinal epithelium has a high rate of turnover, and dysregulation of pathways that regulate regeneration can lead to tumor development; however, the negative regulators of oncogenic events in the intestinal epithelium are not fully understood. Here we identified a feedback loop between the epidermal growth factor receptor (EGFR), a known mediator of proliferation, and the transient receptor potential cation channel, subfamily V, member 1 (TRPV1), in intestinal epithelial cells (IECs). We found that TRPV1 was expressed by IECs and was intrinsically activated upon EGFR stimulation. Subsequently, TRPV1 activation inhibited EGFR-induced epithelial cell proliferation via activation of Ca2+/calpain and resulting activation of protein tyrosine phosphatase 1B (PTP1B). In a murine model of multiple intestinal neoplasia (Apc(Min/+) mice), TRPV1 deficiency increased adenoma formation, and treatment of these animals with an EGFR kinase inhibitor reversed protumorigenic phenotypes, supporting a functional association between TRPV1 and EGFR signaling in IECs. Administration of a TRPV1 agonist suppressed intestinal tumorigenesis in Apc(Min/+) mice, similar to--as well as in conjunction with--a cyclooxygenase-2 (COX-2) inhibitor, which suggests that targeting both TRPV1 and COX-2 has potential as a therapeutic approach for tumor prevention. Our findings implicate TRPV1 as a regulator of growth factor signaling in the intestinal epithelium through activation of PTP1B and subsequent suppression of intestinal tumorigenesis.

Cellular biochemistry methods for investigating protein tyrosine phosphatases

SIGNIFICANCE

The protein tyrosine phosphatases (PTPs) are a family of proteins that play critical roles in cellular signaling and influence many aspects of human health and disease. Although a wealth of information has been collected about PTPs since their discovery, many questions regarding their regulation and function still remain.

CRITICAL ISSUES

Of particular importance are the elucidation of the biological substrates of individual PTPs and understanding of the chemical and biological basis for temporal and spatial resolution of PTP activity within a cell.

RECENT ADVANCES

Drawing from recent advances in both biology and chemistry, innovative approaches have been developed to study the intracellular biochemistry and physiology of PTPs. We provide a summary of PTP-tailored techniques and approaches, emphasizing methodologies to study PTP activity within a cellular context. We first provide a discussion of methods for identifying PTP substrates, including substrate-trapping mutants and synthetic peptide libraries for substrate selectivity profiling. We next provide an overview of approaches for monitoring intracellular PTP activity, including a discussion of mechanistic-based probes, gel-based assays, substrates that can be used intracellularly, and assays tied to cell growth. Finally, we review approaches used for monitoring PTP oxidation, a key regulatory pathway for these enzymes, discussing the biotin switch method and variants of this approach, along with affinity trapping techniques and probes designed to detect PTP oxidation.

FUTURE DIRECTIONS

Further development of approaches to investigate the intracellular PTP activity and functions will provide specific insight into their mechanisms of action and control of diverse signaling pathways.

Autoimmunity-associated LYP-W620 does not impair thymic negative selection of autoreactive T cells

A C1858T (R620W) variation in the PTPN22 gene encoding the tyrosine phosphatase LYP is a major risk factor for human autoimmunity. LYP is a known negative regulator of signaling through the T cell receptor (TCR), and murine Ptpn22 plays a role in thymic selection. However, the mechanism of action of the R620W variant in autoimmunity remains unclear. One model holds that LYP-W620 is a gain-of-function phosphatase that causes alterations in thymic negative selection and/or thymic output of regulatory T cells (Treg) through inhibition of thymic TCR signaling. To test this model, we generated mice in which the human LYP-W620 variant or its phosphatase-inactive mutant are expressed in developing thymocytes under control of the proximal Lck promoter. We found that LYP-W620 expression results in diminished thymocyte TCR signaling, thus modeling a "gain-of-function" of LYP at the signaling level. However, LYP-W620 transgenic mice display no alterations of thymic negative selection and no anomalies in thymic output of CD4(+)Foxp3(+) Treg were detected in these mice. Lck promoter-directed expression of the human transgene also causes no alteration in thymic repertoire or increase in disease severity in a model of rheumatoid arthritis, which depends on skewed thymic selection of CD4(+) T cells. Our data suggest that a gain-of-function of LYP is unlikely to increase risk of autoimmunity through alterations of thymic selection and that LYP likely acts in the periphery perhaps selectively in regulatory T cells or in another cell type to increase risk of autoimmunity.

Covalent inhibition of the lymphoid tyrosine phosphatase

Covalent inhibitors of lymphoid tyrosine phosphatase (LYP) were identified from a screen of the NIH Molecular Libraries Small Molecules Repository (MLSMR). Both of the two lead compounds identified have phosphotyrosine-mimetic benzoic acid moieties as well as electrophilic acrylonitrile groups. Inhibition kinetics of both compounds are consistent with covalent modification of the enzyme, with nanomolar KI and reciprocal millisecond kinact values, representing the best efficiency ratios (kinact /KI ) among currently reported covalent LYP inhibitors. Covalent inhibitors can provide longer efficacy and better selectivity than more conventional noncovalent inhibitors, and these lead compounds are an important step toward the development of protein tyrosine phosphatase (PTP)-targeted covalent therapeutic compounds.

Targeted nanodrugs for cancer therapy: prospects and challenges

The recent advent of nanomedicine holds potential to revolutionize cancer therapy. This innovative discipline has paved the way for the emergence of a new class of drugs based on nanoengineered particles. These "nanodrugs" are designed to greatly enhance drug therapeutic indices. First-generation nanodrugs consisted of conventional anti-cancer drugs loaded into/onto nanoengineered particles (nanocarriers) devoid of targeting features (non-targeted nanodrugs). Non-targeted nanodrugs have provided the opportunity to carry large amounts of drugs, including poorly water-soluble and/or permeable drugs, to several types of tumors, improving the therapeutic index with respect to comparable free drugs. Although effective, the primary delivery mechanism of non-targeted nanodrugs was through passive tissue accumulation, due to pathophysiological differences between tumor-associated and healthy vessels, and through non-specific targeting of cell subsets, posing the danger of off-target binding and effects. Recently, the therapeutic indices of certain anti-cancer drugs were further improved by attaching targeting ligands to nanodrugs (targeted-nanodrugs). Targeted-nanodrugs selectively bind to cognate receptors expressed on target cells and enter cells more efficiently than non-targeted formulations. Although these advancements have been sufficiently beneficial to place targeted-nanodrugs into clinical development for use in cancer therapy, they also come at a price. The addition of ligands to drug-loaded nanocarriers often leads to additional synthesis steps and costs, and more complex biological performance relative to ligand-devoid nanodrugs. Here, we will discuss the benefits and challenges facing the addition of targeting features to nanodrugs for cancer therapy.

Tyrosine phosphatase PTPN22: multifunctional regulator of immune signaling, development, and disease

Inheritance of a coding variant of the protein tyrosine phosphatase nonreceptor type 22 (PTPN22) gene is associated with increased susceptibility to autoimmunity and infection. Efforts to elucidate the mechanisms by which the PTPN22-C1858T variant modulates disease risk revealed that PTPN22 performs a signaling function in multiple biochemical pathways and cell types. Capable of both enzymatic activity and adaptor functions, PTPN22 modulates signaling through antigen and innate immune receptors. PTPN22 plays roles in lymphocyte development and activation, establishment of tolerance, and innate immune cell-mediated host defense and immunoregulation. The disease-associated PTPN22-R620W variant protein is likely involved in multiple stages of the pathogenesis of autoimmunity. Establishment of a tolerant B cell repertoire is disrupted by PTPN22-R620W action during immature B cell selection, and PTPN22-R620W alters mature T cell responsiveness. However, after autoimmune attack has initiated tissue injury, PTPN22-R620W may foster inflammation through modulating the balance of myeloid cell-produced cytokines.

Substrate selection influences molecular recognition in a screen for lymphoid tyrosine phosphatase inhibitors

Assay design is an important variable that influences the outcome of an inhibitor screen. Here, we have investigated the hypothesis that protein tyrosine phosphatase inhibitors with improved biological activity could be identified from a screen by using a biologically relevant peptide substrate, rather than traditional phosphotyrosine mimetic substrates. A 2000-member library of drugs and drug-like compounds was screened for inhibitors of lymphoid tyrosine phosphatase (LYP) by using both a peptide substrate (Ac-ARLIEDNE-pCAP-TAREG-NH₂, peptide 1) and a small-molecule phosphotyrosine mimetic substrate (difluoromethyl umbelliferyl phosphate, DiFMUP). The results demonstrate that compounds that inhibited enzyme activity on the peptide substrate had greater biological activity than compounds that only inhibited enzyme activity on DiFMUP. Finally, epigallocatechin-3,5-digallate was identified as the most potent inhibitor of lymphoid tyrosine phosphatase activity to date, with an IC₅₀ of 50 nM and significant activity in T-cells. Molecular docking simulations provided a first model for binding of this potent inhibitor to LYP; this will constitute the platform for ongoing lead optimization efforts.