bims-nadaut 2023-08-20 papers

Issue of 2023–08–20
seven papers selected by
Niall Wilson, Newcastle University

bioRxiv. 2023 Aug 02. pii: 2023.07.31.551317. [Epub ahead of print]

DePARylation is critical for S phase progression and cell survival.

Litong Nie, Chao Wang, Xiaoguang Liu, Min Huang, Xu Feng, Mengfan Tang, Siting Li, Qinglei Hang, Hongqi Teng, Xi Shen, Li Ma, Boyi Gan, Junjie Chen.

Poly(ADP-ribose)ylation or PARylation by PAR polymerase 1 (PARP1) and dePARylation by poly(ADP-ribose) glycohydrolase (PARG) are equally important for the dynamic regulation of DNA damage response. PARG, the most active dePARylation enzyme, is recruited to sites of DNA damage via pADPr-dependent and PCNA-dependent mechanisms. Targeting dePARylation is considered an alternative strategy to overcome PARP inhibitor resistance. However, precisely how dePARylation functions in normal unperturbed cells remains elusive. To address this challenge, we conducted multiple CRISPR screens and revealed that dePARylation of S phase pADPr by PARG is essential for cell viability. Loss of dePARylation activity initially induced S phase-specific pADPr signaling, which resulted from unligated Okazaki fragments and eventually led to uncontrolled pADPr accumulation and PARP1/2-dependent cytotoxicity. Moreover, we demonstrated that proteins involved in Okazaki fragment ligation and/or base excision repair regulate pADPr signaling and cell death induced by PARG inhibition. In addition, we determined that PARG expression is critical for cellular sensitivity to PARG inhibition. Additionally, we revealed that PARG is essential for cell survival by suppressing pADPr. Collectively, our data not only identify an essential role for PARG in normal proliferating cells but also provide a potential biomarker for the further development of PARG inhibitors in cancer therapy.
Significance statement: Poly(ADP-ribosyl)ation is a reversible post-translational modification. Although PARG may have a protective effect against excessive PARP1 engagement, detailed knowledge of PARG's mechanism of action remains elusive. Here, we showed that PARG participates in DNA replication, especially in Okazaki fragment maturation. Moreover, PARG level is critically important for cellular sensitivity to PARG inhibition, which is a valuable biomarker for PARGi-based therapy.

DOI: https://doi.org/10.1101/2023.07.31.551317

Cell Death Dis. 2023 08 15. 14(8): 524

PARP1-catalyzed PARylation of YY1 mediates endoplasmic reticulum stress in granulosa cells to determine primordial follicle activation.

Wei Chen, Qiukai E, Bo Sun, Pengxue Zhang, Nan Li, Shujia Fei, Yingnan Wang, Shuting Liu, Xiaoqiu Liu, Xuesen Zhang.

Although only a small number of primordial follicles are known to be selectively activated during female reproductive cycles, the mechanisms that trigger this recruitment remain largely uncharacterized. Misregulated activation of primordial follicles may lead to the exhaustion of the non-renewable pool of primordial follicles, resulting in premature ovarian insufficiency. Here, we found that poly(ADP-ribose) polymerase 1 (PARP1) enzymatic activity in the surrounding granulosa cells (GCs) in follicles determines the subpopulation of the dormant primordial follicles to be awakened. Conversely, specifically inhibiting PARP1 in oocytes in an in vitro mouse follicle reconstitution model does not affect primordial follicle activation. Further analysis revealed that PARP1-catalyzed transcription factor YY1 PARylation at Y185 residue facilitates YY1 occupancy at Grp78 promoter, a key molecular chaperone of endoplasmic reticulum stress (ERS), and promotes Grp78 transcription in GCs, which is required for GCs maintaining proper ERS during primordial follicle activation. Inhibiting PARP1 prevents the loss of primordial follicle pool by attenuating the excessive ERS in GCs under fetal bisphenol A exposure. Together, we demonstrate that PARP1 in GCs acts as a pivotal modulator to determine the fate of the primordial follicles and may represent a novel therapeutic target for the retention of primordial follicle pool in females.

DOI: https://doi.org/10.1038/s41419-023-05984-w

Phytother Res. 2023 Aug 14.

Honokiol attenuates high glucose-induced peripheral neuropathy via inhibiting ferroptosis and activating AMPK/SIRT1/PGC-1ɑ pathway in Schwann cells.

Man Hu, Wen Jiang, Chen Ye, Ting Hu, Qingqing Yu, Moran Meng, Lijuan Sun, Jichao Liang, Yong Chen.

Schwann cells injury induced by high glucose (HG) contributes to the development of diabetic peripheral neuropathy (DPN). Honokiol has been reported to regulate glucose metabolism, however, its effect on DPN and the precise molecular mechanisms remain unclear. This study aimed to investigate the role of AMPK/SIRT1/PGC-1α axis in the protective effects of honokiol on DPN. The biochemical assay and JC-1 staining results demonstrated that honokiol reduced HG-induced oxidative stress and ferroptosis as well as mitochondrial dysfunction in Schwann cells. RT-qPCR and western blotting were utilized to investigate the mechanism of action of honokiol, and the results showed that HG-induced inhibition of AMPK/SIRT1/PGC-1α axis and changes of downstream gene expression profile were restored by honokiol. Moreover, silencing of Sirt1 by siRNA delivery markedly diminished the changes of gene expression profile induced by honokiol in HG-induced Schwann cells. More importantly, we found that administration of honokiol remarkably attenuated DPN via improving sciatic nerve conduction velocity and increasing thermal and mechanical sensitivity in streptozotocin-induced diabetic rats. Collectively, these results demonstrate that honokiol can attenuate HG-induced Schwann cells injury and peripheral nerve dysfunction, suggesting a novel potential strategy for treatment of DPN.

Keywords: SIRT1; Schwann cells; ferroptosis; honokiol; mitochondrial dysfunction; oxidative stress

DOI: https://doi.org/10.1002/ptr.7984

Front Oncol. 2023 ;13 1225220

Ability of metformin to deplete NAD+ contributes to cancer cell susceptibility to metformin cytotoxicity and is dependent on NAMPT expression.

Yongxian Zhuang, Allison B Haugrud, Meg A Schaefer, Shanta M Messerli, W Keith Miskimins.

Background: Nicotinamide adenine dinucleotide (NAD+) is vital for not only energy metabolism but also signaling pathways. A major source of NAD+ depletion is the activation of poly (ADP-ribose) polymerase (PARP) in response to DNA damage. We have previously demonstrated that metformin can cause both caspase-dependent cell death and PARP-dependent cell death in the MCF7 breast cancer cells but not in the MDA-MB-231 (231) breast cancer cells while in high-glucose media. We hypothesize that depletion of NAD+ in MCF7 cells via activation of PARP contributes to the cell death caused by metformin. Nicotinamide phosphoribosyltransferase (NAMPT), a key rate-limiting step in converting nicotinamide (vitamin B3) into NAD+, is essential for regenerating NAD+ for normal cellular processes. Evidence shows that overexpression of NAMPT is associated with tumorigenesis. We hypothesize that NAMPT expression may determine the extent to which cancer cells are sensitive to metformin.
Results: In this study, we found that metformin significantly decreases NAD+ levels over time, and that this could be delayed by PARP inhibitors. Pretreatment with NAD+ in MCF7 cells also prevents cell death and the enlargement of mitochondria and protects mitochondria from losing membrane potential caused by metformin. This leads to MCF7 cell resistance to metformin cytotoxicity in a manner similar to 231 cells. By studying the differences in NAD+ regulation in these two breast cancer cell lines, we demonstrate that NAMPT is expressed at higher levels in 231 cells than in MCF7 cells. When NAMPT is genetically repressed in 231 cells, they become much more sensitive to metformin-induced cell death. Conversely, overexpressing NAMPT in HEK-293 (293) cells causes the cells to be more resistant to metformin's growth inhibitory effects. The addition of a NAMPT activator also decreased the sensitivity of MCF7 cells to metformin, while the NAMPT activator, P7C3, protects against metformin-induced cytotoxicity.
Conclusions: Depletion of cellular NAD+ is a key aspect of sensitivity of cancer cells to the cytotoxic effects of metformin. NAMPT plays a key role in maintaining sufficient levels of NAD+, and cells that express elevated levels of NAMPT are resistant to killing by metformin.

Keywords: breast cancer; metformin; nicotinamide adenine dinucleotide (NAD+); nicotinamide phosphoribosyltransferase (NAMPT); tumorigenesis

DOI: https://doi.org/10.3389/fonc.2023.1225220

Poult Sci. 2023 Aug 05. pii: S0032-5791(23)00511-4. [Epub ahead of print]102(10): 102992

Modified rougan decoction attenuates hepatocyte apoptosis through ameliorating mitochondrial dysfunction by upregulated SIRT1/PGC-1α signaling pathway.

Wenjia Wang, Desheng Wu, Jinxue Ding, Jinli Wang, Jinwu Meng, Ke Ming, Siya Li, Tianxin Qiu, Jiaguo Liu, Danchen Aaron Yang.

The modified rougan decoction (MRGD) compound formula has been proven a certain ability to relieve lipopolysaccharide-enrofloxacin (LPS-ENR)-induced liver oxidant injury in chickens. Recent advances have shown that mitochondrial dysfunction affects the development of many diseases, leading to increased interest in exploring its effects. Using LPS-ENR-injured in vivo and in vitro to further evaluate the effects of MRGD on mitochondrial structure and function, and emphasized further investigation of its molecular mechanism. After LPS-ENR treatment, the levels of inflammation and apoptosis markers were increased, along with higher mitochondrial injury. Results showed that MRGD reduced inflammatory factors expression and inhibited the nuclear translocation of NF-κB P65, reducing the inflammatory response in vivo and in vitro. Additionally, MRGD pretreatment inhibited mitochondrial dysfunction, mitochondrial oxidative stress, and mitochondrial pathway apoptosis by maintaining mitochondrial structure and function. Moreover, treatment with the inhibitor EX527 showed that MRGD promoted mitochondrial biogenesis ability through the SIRT1/PGC-1α pathway and interfered with mitochondrial dynamics, and activate Nrf2. In summary, MRGD played a key role in promoting mitochondrial function and thus alleviating hepatocyte apoptosis in vivo and in vitro at least in part.

Keywords: SIRT1/PGC-1α; apoptosis; chicken liver; inflammation; mitochondrial dysfunction

DOI: https://doi.org/10.1016/j.psj.2023.102992

Nucleic Acids Res. 2023 Aug 17. pii: gkad659. [Epub ahead of print]

Absence of mitochondrial SLC25A51 enhances PARP1-dependent DNA repair by increasing nuclear NAD+ levels.

Anka Güldenpfennig, Ann-Katrin Hopp, Lukas Muskalla, Patrick Manetsch, Fabio Raith, Lars Hellweg, Cyril Dördelmann, Deena M Leslie Pedrioli, Kai Johnsson, Giulio Superti-Furga, Michael O Hottiger.

Though the effect of the recently identified mitochondrial NAD+ transporter SLC25A51 on glucose metabolism has been described, its contribution to other NAD+-dependent processes throughout the cell such as ADP-ribosylation remains elusive. Here, we report that absence of SLC25A51 leads to increased NAD+ concentration not only in the cytoplasm and but also in the nucleus. The increase is not associated with upregulation of the salvage pathway, implying an accumulation of constitutively synthesized NAD+ in the cytoplasm and nucleus. This results in an increase of PARP1-mediated nuclear ADP-ribosylation, as well as faster repair of DNA lesions induced by different single-strand DNA damaging agents. Lastly, absence of SLC25A51 reduces both MMS/Olaparib induced PARP1 chromatin retention and the sensitivity of different breast cancer cells to PARP1 inhibition. Together these results provide evidence that SLC25A51 might be a novel target to improve PARP1 inhibitor based therapies by changing subcellular NAD+ redistribution.

DOI: https://doi.org/10.1093/nar/gkad659

Am J Respir Cell Mol Biol. 2023 Aug 16.

Boosting the Exhausted Vasculature - SIRT3 (to the) Rescue.

Senka Ljubojevic-Holzer, Slaven Crnkovic.

Keywords: SIRT3; adventitial fibroblasts; mitochondrial dysfunction; pulmonary hypertension

DOI: https://doi.org/10.1165/rcmb.2023-0199ED