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Serine/Threonine phosphatase PP2A is essential for optimal B cell function

ABSTRACT: Protein phosphatase 2A (PP2A), a serine/threonine phosphatase, has been shown to control T cell function. We found that in vitro activated B cells and B cells from various lupus-prone mice and patients with systemic lupus erythematosus display increased PP2A activity. To understand the contribution of PP2A to B cell function, we generated a Cd19CrePpp2r1aflox/flox (flox/flox) mouse which lacks functional PP2A only in B cells. Flox/flox mice displayed reduced spontaneous germinal center formation and decreased responses to T-dependent and T-independent antigens while their B cells responded poorly in vitro to stimulation with an anti-CD40 antibody or CpG in the presence of IL-4. Transcriptome and metabolome studies revealed altered NAD and purine/pyrimidine metabolism and increased expression of purine nucleoside phosphorylase in PP2A-deficient B cells. Our results demonstrate that PP2A is required for optimal B cell function and may contribute to increased B cell activity in systemic autoimmunity.

ORGANISM(S): Mus musculus

PROVIDER: GSE144700 | GEO | 2020/02/04

REPOSITORIES: GEO

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Project description:Protein phosphatase 2A (PP2A) is one of the most common serine/threonine phosphatases in mammalian cells and primarily functions to regulate cell signaling, glycolipid metabolism, and apoptosis. Its PP2A catalytic subunit (PP2Ac) plays an important role in its function. Nonetheless, at present, there are only a few reports on the regulatory role of PP2Ac in pancreatic β-cells under lipotoxicity. Mouse pancreatic insulinoma (MIN6) cells were transfected by lentiviruses to generate PP2Ac knockdown cells and incubated with palmitate (PA) to establish the lipotoxicity model. Serine/Threonine Phosphatase Assay System kit, Cell Counting Kit-8 (CCK-8), flow cytometry, enzyme-linked immunosorbent assay (ELISA), Western Blotting (WB) and other techniques were used to measure PP2A activity, cell viability, apoptosis, oxidative stress, and insulin secretion. An animal model of lipotoxicity with knockdown of PP2Ac was established by a high-fat diet (HFD) after using adeno-associated viruses (AAV) to interfere with PP2Ac expression in mouse pancreatic tissues. Serine/Threonine Phosphatase Assay System kit, ELISA, pancreatic tissue immunofluorescence and other techniques were used to measure PP2A activity in pancreatic tissue, serum insulin level and the proliferation of mouse pancreatic β-cells. We found that PP2Ac knockdown inhibited lipotoxicity-induced PP2A hyperactivation, increased the resistance of pancreatic β-cells to lipotoxicity, decreased PA-induced apoptosis in MIN6 cells, protected the function of both the endoplasmic reticulum (ER) and mitochondria, and improved insulin secretion. By mRNA sequencing and Western blotting analysis, we hypothesized that the protective effects of PP2Ac knockdown in MIN6 cells may be mediated by the MAPK pathway. Moreover, the results obtained from animal experiments suggest that the specific knockdown of pancreatic PP2Ac could effectively attenuate HFD-induced insulin resistance and reduce the compensatory proliferation of pancreatic β-cells in mice. The present study revealed the effects and mechanisms of interfering with PP2Ac gene expression on pancreatic β-cells in vivo and in vitro, which might provide insights for the treatment of type 2 diabetes in the clinic.

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Serine/Threonine phosphatase PP2A is essential for optimal B cell function

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