circRNA-PTPN4 mediated regulation of FOXO3 and ZO-1 expression: implications for blood-brain barrier integrity and cognitive function in uremic encephalopathy

Uremic encephalopathy (UE) poses a significant challenge in neurology, leading to the need to investigate the involvement of non-coding RNA (ncRNA) in its development. This study employed ncRNA-seq and RNA-seq approaches to identify fundamental ncRNAs, specifically circRNA and miRNA, in the pathogenesis of UE using a mouse model. In vitro and in vivo experiments were conducted to explore the circRNA-PTPN4/miR-301a-3p/FOXO3 axis and its effects on blood-brain barrier (BBB) function and cognitive abilities. The research revealed that circRNA-PTPN4 binds to and inhibits miR-301a-3p, leading to an increase in FOXO3 expression. This upregulation results in alterations in the transcriptional regulation of ZO-1, affecting the permeability of human brain microvascular endothelial cells (HBMECs). The axis also influences the growth, proliferation, and migration of HBMECs. Mice with UE exhibited cognitive deficits, which were reversed by overexpression of circRNA-PTPN4, whereas silencing FOXO3 exacerbated these deficits. Furthermore, the uremic mice showed neuronal loss, inflammation, and dysfunction in the BBB, with the expression of circRNA-PTPN4 demonstrating therapeutic effects. In conclusion, circRNA-PTPN4 plays a role in promoting FOXO3 expression by sequestering miR-301a-3p, ultimately leading to the upregulation of ZO-1 expression and restoration of BBB function in mice with UE. This process contributes to the restoration of cognitive abilities.

CircDLGAP4 induces autophagy and improves endothelial cell dysfunction in atherosclerosis by targeting PTPN4 with miR-134-5p

OBJECTIVE

Circular RNAs (circRNAs), a new subgroup of non-coding RNAs in the human transcriptome, are crucial in atherosclerosis (AS). Here, a newly identified circRNA circDLGAP4 was demonstrated to be downregulated in oxidized forms of low-density lipoprotein (ox-LDL)-induced HUVECs.

METHODS

This research adopted ox-LDL to stimulate human umbilical vein endothelial cells (HUVECs) to mimic AS in vitro. To further validate the protective action of circDLGAP4 in AS, a mouse model of AS was constructed with a high-fat diet. Functional assays evaluated circDLGAP4 role in AS in vitro and in vivo. Moreover, mechanism assays evaluated association of circDLGAP4/miR-134-5p/PTPN4.

RESULTS

CircDLGAP4 was induced to promote cell proliferative behavior and autophagy, inhibit apoptotic and inflammatory activities in ox-LDL-treated HUVECs, and attenuated endothelial barrier function. CircDLGAP4 regulated PTPN4 by directly targeting miR-134-5p. Meanwhile, inhibiting miR-134-5p reduced ox-LDL-induced cell dysfunction. Knockout of PTPN4 reversed circDLGAP4 overexpression or miR-134-5p downregulation in vitro. In addition, reducing circDLGAP4 or overexpressing miR-134-5p increased the red atherosclerotic plaque and lesion area of AS mice, reduced autophagy level, and promoted the release of inflammatory cytokines.

CONCLUSION

This study extends the role of circRNA in AS by inducing autophagy and improving endothelial dysfunction in AS via the circDLGAP4/miR-134-5p/PTPN4 axis.

The protein-tyrosine phosphatase PTPMEG interacts with glutamate receptor delta 2 and epsilon subunits

Glutamate receptor (GluR) delta2 is selectively expressed in cerebellar Purkinje cells and plays a crucial role in cerebellum-dependent motor learning. Although GluRdelta2 belongs to an ionotropic GluR family, little is known about its pharmacological features and downstream signaling cascade. To study molecular mechanisms underlying GluRdelta2-dependent motor learning, we employed yeast two-hybrid screening to isolate GluRdelta2-interacting molecules and identified protein-tyrosine phosphatase PTPMEG. PTPMEG is a family member of band 4.1 domain-containing protein-tyrosine phosphatases and is expressed prominently in brain. Here, we showed by in situ hybridization analysis that the PTPMEG mRNA was enriched in mouse thalamus and Purkinje cells. We also showed that PTPMEG interacted with GluRdelta2 as well as with N-methyl-d-aspartate receptor GluRepsilon1 in cultured cells and in brain. PTPMEG bound to the putative C-terminal PDZ target sequence of GluRdelta2 and GluRepsilon1 via its PDZ domain. Examination of the effect of PTPMEG on tyrosine phosphorylation of GluRepsilon1 unexpectedly revealed that PTPMEG enhanced Fyn-mediated tyrosine phosphorylation of GluRepsilon1 in its PTPase activity-dependent manner. Thus, we conclude that PTPMEG associates directly with GluRdelta2 and GluRepsilon1. Moreover, our data suggest that PTPMEG plays a role in signaling downstream of the GluRs and/or in regulation of their activities through tyrosine dephosphorylation.

Cytoskeletal protein tyrosine phosphatase PTPH1 reduces T cell antigen receptor signaling

The subgroup of protein tyrosine phosphatases that contain an N-terminal ezrin-, radixin- and moesin homology (ERM) domain and a C-terminal catalytic domain is represented by three enzymes in Jurkat T cells, PTPH1, PTP-MEG1 and PTP36. These enzymes are located at the cytoplasmic face of the plasma membrane and may be involved in regulation of the membrane cytoskeleton, signal transduction, or both. Here we report that expression of PTPH1 in Jurkat T cells reduced the TCR-induced activation of reporter genes encompassing parts of the IL-2 gene promoter and driven by nuclear factor of activated T cells plus activator protein-1. PTP-MEG1 had a weaker inhibitory effect, while PTP36 had none. The catalytically inactive mutants PTPH1-CS and PTP-MEG1-CS lacked effects on gene transcription. Expression of active PTPH1 also reduced receptor-induced activation of Erk2 MAP kinase, its upstream activator, Mek, and the Jnk kinases. The effect of PTPH1 was reduced by deletion of its N-terminal ERM domain. We suggest that PTPH1 inhibits T cell activation by dephosphorylating membrane-associated targets involved in TCR signaling.

Alendronate inhibition of protein-tyrosine-phosphatase-meg1

Alendronate (4-amino-1-hydroxybutylidene-1,1-bisphosphonate) is a potent bisphosphonate that inhibits osteoclastic bone resorption and has proven effective for the treatment of osteoporosis. Its molecular mechanism of action, however, has not been defined precisely. Here we report that alendronate is a potent inhibitor of the protein-tyrosine-phosphatase-meg1 (PTPmeg1). Two substrates were employed in this study: fluorescein diphosphate and the phosphotyrosyl peptide src-pY527. With either substrate, alendronate was a slow binding inhibitor of PTPmeg1. Among the other bisphosphonates studied, alendronate was more potent and selective for PTPmeg1. The hydrolysis of fluorescein diphosphate by PTP epsilon and PTPmeg1 was sensitive to alendronate, with IC50 values of less than 1 microM; PTPsigma, however, under the same conditions, was inhibited by only 50% with 141 microM alendronate. Similarly, with the src-pY527 substrate, alendronate inhibition was also PTP dependent. Alendronate inhibited PTPmeg1 with an IC50 value of 23 microM, PTPsigma with an IC50 value of 2 microM, and did not inhibit PTP epsilon at concentrations up to 1 mM. The alendronate inhibition of these three PTPs and two substrates is consistent with the formation of a ternary complex comprised of enzyme, substrate, and inhibitor. PTP inhibition by hisphosphonates or vanadate was diminished by the metal chelating agent EDTA, or by the reducing agent dithiothreitol, suggesting that a metal ion and the oxidation of a cysteine residue are required for full inhibition. These observations show substrate- and enzyme-specific PTP inhibition by alendronate and support the possibility that a certain PTP(s) may be the molecular target for alendronate action.

Identification, cloning, and expression of a cytosolic megakaryocyte protein-tyrosine-phosphatase with sequence homology to cytoskeletal protein 4.1

We have isolated a cDNA encoding a third type of protein-tyrosine-phosphatase. We screened human megakaryoblastic cell line (MEG-01) an umbilical vein endothelial cell cDNA libraries to obtain a 3.7-kilobase cDNA designated PTPase MEG. Northern blot analysis of MEG-01 RNA detected a 3.7-kilobase transcript, suggesting that a full-length cDNA has been identified. PTPase MEG cDNA contains an open reading frame of 926 amino acids. The cDNA has a G+C-rich 5' untranslated region of 771 nucleotides that has the potential to form stable stem-loop structures and has two upstream ATG codons. The predicted protein (Mr = 105,910) has no apparent membrane-spanning region and contains a single protein-tyrosine-phosphatase domain (amino acids 659-909) that is 35-40% identical to previously described tyrosine-phosphatase domains. The recombinant phosphatase domain possesses protein-tyrosine-phosphatase activity when expressed in Escherichia coli. The amino-terminal region (amino acids 31-367) is 45% identical to the amino terminus of human erythrocyte protein 4.1, a cytoskeletal protein. The identification of a protein-tyrosine-phosphatase that is related to cytoskeletal proteins implies that cell signaling activities reside not only in transmembrane receptors but in cytoskeletal elements as well.