PARP1-mediated PARylation activity is essential for oligodendroglial differentiation and CNS myelination

The function of poly(ADP-ribosyl) polymerase 1 (PARP1) in myelination and remyelination of the central nervous system (CNS) remains enigmatic. Here, we report that PARP1 is an intrinsic driver for oligodendroglial development and myelination. Genetic PARP1 depletion impairs the differentiation of oligodendrocyte progenitor cells (OPCs) into oligodendrocytes and impedes CNS myelination. Mechanistically, PARP1-mediated PARylation activity is not only necessary but also sufficient for OPC differentiation. At the molecular level, we identify the RNA-binding protein Myef2 as a PARylated target, which controls OPC differentiation through the PARylation-modulated derepression of myelin protein expression. Furthermore, PARP1’s enzymatic activity is necessary for oligodendrocyte and myelin regeneration after demyelination. Together, our findings suggest that PARP1-mediated PARylation activity may be a potential therapeutic target for promoting OPC differentiation and remyelination in neurological disorders characterized by arrested OPC differentiation and remyelination failure such as multiple sclerosis.

Wang et al. show that PARP1-mediated PARylation promotes oligodendroglial differentiation and regeneration. They demonstrate that PARP1 PARylates proteins relating to RNA metabolism under physiological conditions and that Myef2 is identified as one of the potential targets that mediates PARP1-regulated myelin gene expression at the posttranscriptional level during oligodendroglial development.

Flavonoids from Rosaroxburghii Tratt prevent reactive oxygen species-mediated DNA damage in thymus cells both combined with and without PARP-1 expression after exposure to radiation in vivo

This study aimed to evaluate the role of FRT in ROS/DNA regulation with or without PARP-1 in radiation-injured thymus cells. The administration of FRT to PARP-1-/- (KO) mice demonstrated that FRT significantly increased the viability of thymus cells and decreased their rate of apoptosis through PARP-1. Radiation increased the levels of ROS, γ-H2AX and 53BP1, and induced DNA double strand breaks. Compared with wild type (WT) mice, levels of ROS, γ-H2AX and 53BP1 in KO mice were much less elevated. The FRT treatment groups also showed little reduction in these indicators in KO mice compared with WT mice. The results of the KO mice study indicated that FRT reduced ROS activation through inhibition of PARP-1. Furthermore, FRT reduced the concentrations of γ-H2AX by decreasing ROS activation. However, we found that FRT did not regulate 53BP1, a marker of DNA damage, because of its elimination of ROS. Levels of apoptosis-inducing factor (AIF), exhibited no significant difference after irradiation in KO mice. To summarize, ROS suppression by PARP-1 knockout in KO mice highlights potential therapeutic target either by PARP-1 inhibition combined with radiation or by treatment with a drug therapy alone. AIF-induced apoptosis could not be activated in KO mice.

XRCC1 mutation is associated with PARP1 hyperactivation and cerebellar ataxia

XRCC1 is a molecular scaffold protein that assembles multi-protein complexes involved in DNA single-strand break repair. Here we show that biallelic mutations in the human XRCC1 gene are associated with ocular motor apraxia, axonal neuropathy, and progressive cerebellar ataxia. Cells from a patient with mutations in XRCC1 exhibited not only reduced rates of single-strand break repair but also elevated levels of protein ADP-ribosylation. This latter phenotype is recapitulated in a related syndrome caused by mutations in the XRCC1 partner protein PNKP and implicates hyperactivation of poly(ADP-ribose) polymerase/s as a cause of cerebellar ataxia. Indeed, remarkably, genetic deletion of Parp1 rescued normal cerebellar ADP-ribose levels and reduced the loss of cerebellar neurons and ataxia in Xrcc1-defective mice, identifying a molecular mechanism by which endogenous single-strand breaks trigger neuropathology. Collectively, these data establish the importance of XRCC1 protein complexes for normal neurological function and identify PARP1 as a therapeutic target in DNA strand break repair-defective disease.

Common and unique genetic interactions of the poly(ADP-ribose) polymerases PARP1 and PARP2 with DNA double-strand break repair pathways

In mammalian cells, chromatin poly(ADP-ribos)ylation (PARylation) at sites of DNA Double-Strand Breaks (DSBs) is mediated by two highly related enzymes, PARP1 and PARP2. However, enzyme-specific genetic interactions with other DSB repair factors remain largely undefined. In this context, it was previously shown that mice lacking PARP1 and H2AX, a histone variant that promotes DSB repair throughout the cell cycle, or the core nonhomologous end-joining (NHEJ) factor Ku80 are not viable, while mice lacking PARP1 and the noncore NHEJ factor DNA-PKcs are severely growth retarded and markedly lymphoma-prone. Here, we have examined the requirement for PARP2 in these backgrounds. We find that, like PARP1, PARP2 is essential for viability in mice lacking H2AX. Moreover, treatment of H2AX-deficient primary fibroblasts or B lymphocytes with PARP inhibitors leads to activation of the G2/M checkpoint and accumulation of chromatid-type breaks in a lineage- and gene-dose dependent manner. In marked contrast to PARP1, loss of PARP2 does not result in additional phenotypes in growth, development or tumorigenesis in mice lacking either Ku80 or DNA-PKcs. Altogether these findings highlight specific nonoverlapping functions of PARP1 and PARP2 at H2AX-deficient chromatin during replicative phases of the cell cycle and uncover a unique requirement for PARP1 in NHEJ-deficient cells.