PARP1 In Regulation Research Articles

8729 Role of PARP1 in Macrophage-dependent Regulation of Adipose Tissue Inflammation, Adipogenesis, and Diet-induced Obesity

Abstract Disclosure: J. Zhu: None. R. Gupte: None. T.S. Nandu: None. W.L. Kraus: None. D. Huang: None. Adipose tissue macrophages play a significant role in maintaining adipose tissue homeostasis, as well as promoting chronic low-grade inflammation during the development of obesity and metabolic dysfunction. However, the crosstalk between macrophages and adipocytes, especially how macrophages affect adipogenesis in obese adipose tissue, are still poorly understood. We have investigated the function of PARP1 in the control of adipogenesis by using an adipocyte precursor-specific Parp1 knockout mouse model. Here, to investigate the role of macrophage PARP1 in regulating adipogenesis, we deleted Parp1 in the myeloid lineage by crossing Parp1loxp/loxp mice with LysMCre mice (Parp1 cKOLysMCre). Macrophages-specific knockout of Parp1 dramatically reduced LPS-induced pro-inflammatory gene expression in bone marrow-derived macrophages (BMDMs). To explore whether macrophage-specific Parp1 knockout affects adipocyte differentiation, we treated the primary preadipocytes from stromal vascular fraction (SVF) of white adipose tissue with the conditioned medium from LPS-stimulated control or Parp1 cKOLysMCre BMDMs throughout a 6-day period of differentiation. We observed that exposure of preadipocytes to the conditioned medium of Parp1 cKOLysMCre macrophages promoted adipogenesis by Oil Red O staining, as well as by monitoring the expression of key proadipogenic marker genes (e.g., Adipoq and Fabp4) by RT-qPCR. To further investigate the role of macrophage-specific deletion of Parp1 in metabolic outcomes, we fed the Parp1 cKOLysMCre mice with a high fat diet for 12 weeks. The knockout mice exhibited a significant increase in body weight compared to the control mice. Interestingly, we observed a reduction of the total number of macrophages resident in the adipose tissue from macrophage-specific Parp1 knockout mice. To explore the underlying mechanism, we performed single cell RNA-seq for adipose tissue macrophages using sorted SVF cells collected from HFD-fed mice. The results demonstrated dramatic reductions in macrophage M1 marker genes and pro-inflammatory transcription factors in Parp1 cKOLysMCre mice. Taken together, our study suggests that Parp1 knockout in macrophages selectively affects the recruitment and pro-inflammatory activation of macrophages, as well as adipocyte differentiation in adipose tissue. Importantly, despite the decreased adipose tissue inflammation, macrophage-specific Parp1 knockout enhanced adipogenesis, which leads to obesity in mice.This work was supported by a grant from the NIH/NIDDK (R01 DK069710) and funds from the Cecil H. and Ida Green Center for Reproductive Biology Sciences Endowment, to W.L.K., and a grant from NSFC (82270929) to D.H. Presentation: 6/1/2024

The Role of PARP1 in Monocyte and Macrophage Commitment and Specification: Future Perspectives and Limitations for the Treatment of Monocyte and Macrophage Relevant Diseases with PARP Inhibitors.

Modulation of PARP1 expression, changes in its enzymatic activity, post-translational modifications, and inflammasome-dependent cleavage play an important role in the development of monocytes and numerous subtypes of highly specialized macrophages. Transcription of PARP1 is governed by the proliferation status of cells at each step of their development. Higher abundance of PARP1 in embryonic stem cells and in hematopoietic precursors supports their self-renewal and pluri-/multipotency, whereas a low level of the enzyme in monocytes determines the pattern of surface receptors and signal transducers that are functionally linked to the NFκB pathway. In macrophages, the involvement of PARP1 in regulation of transcription, signaling, inflammasome activity, metabolism, and redox balance supports macrophage polarization towards the pro-inflammatory phenotype (M1), which drives host defense against pathogens. On the other hand, it seems to limit the development of a variety of subsets of anti-inflammatory myeloid effectors (M2), which help to remove tissue debris and achieve healing. PARP inhibitors, which prevent protein ADP-ribosylation, and PARP1‒DNA traps, which capture the enzyme on chromatin, may allow us to modulate immune responses and the development of particular cell types. They can be also effective in the treatment of monocytic leukemia and other cancers by reverting the anti- to the proinflammatory phenotype in tumor-associated macrophages.

Opposing roles of mitochondrial and nuclear PARP1 in the regulation of mitochondrial and nuclear DNA integrity: implications for the regulation of mitochondrial function.

The positive role of PARP1 in regulation of various nuclear DNA transactions is well established. Although a mitochondrial localization of PARP1 has been suggested, its role in the maintenance of the mitochondrial DNA is currently unknown. Here we investigated the role of PARP1 in the repair of the mitochondrial DNA in the baseline and oxidative stress conditions. We used wild-type A549 cells or cells depleted of PARP1. Our data show that intra-mitochondrial PARP1 interacts with a key mitochondrial-specific DNA base excision repair (BER) enzymes, namely EXOG and DNA polymerase gamma (Polγ), which under oxidative stress become poly(ADP-ribose)lated (PARylated). Interaction between mitochondrial BER enzymes was significantly affected in the presence of PARP1. Moreover, the repair of the oxidative-induced damage to the mitochondrial DNA in PARP1-depleted cells was found to be more robust compared to control counterpart. In addition, mitochondrial biogenesis was enhanced in PARP1-depleted cells, including mitochondrial DNA copy number and mitochondrial membrane potential. This observation was further confirmed by analysis of lung tissue isolated from WT and PARP1 KO mice. In summary, we conclude that mitochondrial PARP1, in opposite to nuclear PARP1, exerts a negative effect on several mitochondrial-specific transactions including the repair of the mitochondrial DNA.