Summary SIRT1 is a NAD+-dependent enzyme that affects metabolism by deacetylating key transcriptional regulators of energy expenditure. Here we tested whether deletion of PARP-2, an alternative NAD+ consuming enzyme, impacts on NAD+ bioavailability and SIRT1 activity. Our results indicate that PARP-2 deficiency increases SIRT1 activity in cultured myotubes. However, this increase was not due to changes in NAD+ levels, but to an increase in SIRT1 expression, as PARP-2 acts as a direct negative regulator of the SIRT1 promoter. PARP-2 deletion in mice increases SIRT1 levels, promotes energy expenditure, and increases mitochondrial content. Furthermore, PARP-2−/− mice were protected against diet-induced obesity. Despite being insulin sensitized, PARP-2−/− mice were glucose intolerant due to a defective pancreatic function. Hence, while inhibition of PARP activity promotes oxidative metabolism through SIRT1 activation, the use of PARP inhibitors for metabolic purposes will require further understanding of the specific functions of different PARP family members.

The existence of a gut-skin axis is supported by increasing evidence, but its translational potential is not widely recognized. Studies linked inflammatory skin diseases to an imbalanced gut microbiome; hence, the modulation of the gut microbiota to improve skin condition seems to be a feasible approach. Today, there is a growing interest in natural products as alternatives to synthetic drugs. In this respect, oral probiotics could be a simple, safe and cheap modality in the therapeutic management of skin inflammation. Unfortunately, very few studies have looked into how probiotic supplementation influences inflammatory skin disorders. The result, though promising, are difficult to implement in clinical practice due to the heterogeneity of the applied supplemental regimen in the different studies. In this Viewpoint, we aim to encourage the conduction of more research in that direction to explore unambiguously the therapeutic potential of oral probiotics in dermatology. We focus on the most common inflammatory skin diseases (atopic dermatitis, psoriasis, rosacea, acne vulgaris) with an associated gut dysbiosis, but we also discuss some less common, but very serious skin pathologies (eg erythema nodosum, pyoderma gangrenosum, hidradenitis suppurativa) that are possibly linked to a disturbed gut flora composition. We dissect the possible mechanisms along the gut-skin axis and highlight novel points where probiotics could interfere in this communication in the diseased state.

Our data identify PARP-2 as a mediator of DOX toxicity by regulating vascular SIRT1 activity and mitochondrial biogenesis. Moreover, to the best of our knowledge, this is the first report of SIRT1 as a protective factor in the vasculature upon oxidative stress.

Cancer cells are characterized by metabolic alterations, namely, depressed mitochondrial oxidation, enhanced glycolysis and pentose phosphate shunt flux to support rapid cell growth, which is called the Warburg effect. In our study we assessed the metabolic consequences of a joint treatment of MCF-7 breast cancer cells with AICAR, an inducer of AMP-activated kinase (AMPK) jointly with methotrexate (MTX), a folate-analog antimetabolite that blunts de novo nucleotide synthesis. MCF7 cells, a model of breast cancer cells, were resistant to the individual application of AICAR or MTX, however combined treatment of AICAR and MTX reduced cell proliferation. Prolonged joint application of AICAR and MTX induced AMPK and consequently enhanced mitochondrial oxidation and reduced the rate of glycolysis. These metabolic changes suggest an anti-Warburg rearrangement of metabolism that led to the block of the G1/S and the G2/M transition slowing down cell cycle. The slowdown of cell proliferation was abolished when mitotropic transcription factors, PGC-1α, PGC-1β or FOXO1 were silenced. In human breast cancers higher expression of AMPKα and FOXO1 extended survival. AICAR and MTX exerts similar additive antiproliferative effect on other breast cancer cell lines, such as SKBR and 4T1 cells, too. Our data not only underline the importance of Warburg metabolism in breast cancer cells but nominate the AICAR+MTX combination as a potential cytostatic regime blunting Warburg metabolism. Furthermore, we suggest the targeting of AMPK and FOXO1 to combat breast cancer.

Abstract:Poly(ADP-ribose) polymerase (PARP)-2 is a nuclear enzyme that belongs to the PARP family and PARP-2 is responsible for 5-15% of total cellular PARP activity. PARP-2 was originally described in connection to DNA repair and in physiological and pathophysiological processes associated with genome maintenance (e.g. centromere and telomere protection, spermiogenesis, thymopoesis, azoospermia and tumorigenesis). Recent reports identified important rearrangements in gene expression upon the knockout of PARP-2. Such rearrangements heavily impact on inflammation and metabolism. Metabolic effects are mediated through modifying PPARg and SIRT1 function. Altered gene expression gives rise to a complex phenotype characterized primarily by enhanced mitochondrial activity that results both in beneficial (loss of fat, enhanced insulin sensitivity) and in disadvantageous (pancreatic beta cell hypofunction upon high fat feeding) consequences. Enhanced mitochondrial biogenesis provides protection in oxidative stress related diseases. Hereby, we review the recent developments in PARP-2 research with special attention to the involvement of PARP-2 in transcriptional and metabolic regulation. We would like to thank the referee for his/her efforts to further improve our manuscript.1. Page 2 -the modifications here are fairly minimalistic and the abbreviations ARTD2 and ARTD1 are not even defined. Powered by Editorial Manager® and Preprint Manager® from Aries Systems Corporationand ARTD1 are not even defined.In the corresponding section we incorporated the basic information on the newly proposed nomenclature in our previous version upon the suggestion of the Reviewer. We agree with the Reviewer that the appearance of the new nomenclature in our manuscript is important. Moreover, in the current version we added ARTD-2 as a keyword to help those future readers that follow the new nomenclature. The fact that ARTD1 is the equivalent of PARP-1 is defined in the chapter "PARP superfamily" second paragraph, first row. We added the abbreviation of ARDT-2 in the last sentence in the first paragraph of the chapter "The PARP superfamily". We think that these are sufficient for the understanding of the position of PARP-2 in the PARP/ARTD superfamily.We would like to note here, that the proposed new nomenclature did not gain ground in the scientific community yet. There are only 3 relevant papers on Medline for the keyword ARTD1, ARTD2 or ARTD (since 2010, the publication of the paper by In summary, we are confident that our review sufficiently takes the new nomenclature into consideration despite of the fact that it is not yet accepted by the scientific community. Sequence homology modeling was carried out by Ame and co-workers (Ame et al. Bioessays. 26:882-893. 2004). They classified sequences as PARPs on the basis of sequence homology, therefore sequence homology does exist. However, mutation(s) in a sequence does not necessarily mean that sequence homology is lost. In the incriminated text, mutations mean rather point mutations that aff...