ARTD1 deletion causes increased hepatic lipid accumulation in mice fed a high-fat diet and impairs adipocyte function and differentiation.

ADP-ribosyltransferase Diphtheria toxin-like 1 [ARTD1; formerly called poly-ADP-ribose polymerase 1 (PARP1)] is a chromatin-associated enzyme involved in regulating metabolic homeostasis. The liver is at the core of glucose and lipid metabolism and is significantly affected by obesity and the metabolic syndrome. Here, we show that when fed a high-fat diet (HFD), mice lacking ARTD1 developed exacerbated hepatic steatosis. ARTD1(-/-) mice had a 19% higher liver weight than wild-type (WT) animals and exhibited a significantly increased serum concentration of cholesterol (38%) and impaired glucose tolerance. In addition, adipocyte function and size were significantly reduced in ARTD1(-/-) mice fed an HFD (7794 µm(2) for WT and 5579 µm(2) for ARTD1(-/-) mice). The significantly reduced adipogenic differentiation of adipose-derived stromal cells (ASCs) isolated from ARTD1(-/-) mice (28 vs. 11% Oil red O-positive cells in WT and ARTD1(-/-) ASCs, respectively) suggested that impaired adipogenesis as the underlying cause for this adipose tissue malfunction. This function of ARTD1 was specific for adipogenesis, since osteogenic differentiation was not affected by the ARTD1 deletion. In summary, we show that ARTD1(-/-) mice fed an HFD display impaired adipogenesis and show exacerbated hepatic steatosis, which can have important implications for nonalcoholic fatty liver disease.

PARP inhibitor with selectivity toward ADP-ribosyltransferase ARTD3/PARP3.

Inhibiting ADP-ribosyl transferases with PARP-inhibitors is considered a promising strategy for the treatment of many cancers and ischemia, but most of the cellular targets are poorly characterized. Here, we describe an inhibitor of ADP-ribosyltransferase-3/poly(ADP-ribose) polymerase-3 (ARTD3), a regulator of DNA repair and mitotic progression. In vitro profiling against 12 members of the enzyme family suggests selectivity for ARTD3, and crystal structures illustrate the molecular basis for inhibitor selectivity. The compound is active in cells, where it elicits ARTD3-specific effects at submicromolar concentration. Our results show that by targeting the nicotinamide binding site, selective inhibition can be achieved among the closest relatives of the validated clinical target, ADP-ribosyltransferase-1/poly(ADP-ribose) polymerase-1.

Poly(ADP-ribose)polymerase-1 (PARP1) controls adipogenic gene expression and adipocyte function.

Poly(ADP-ribose)polymerase-1 (PARP1) is a chromatin-associated enzyme that was described to affect chromatin compaction. Previous reports suggested a dynamic modulation of the chromatin landscape during adipocyte differentiation. We thus hypothesized that PARP1 plays an important transcriptional role in adipogenesis and metabolism and therefore used adipocyte development and function as a model to elucidate the molecular action of PARP1 in obesity-related diseases. Our results show that PARP1-dependent ADP-ribose polymer (PAR) formation increases during adipocyte development and, at late time points of adipogenesis, is involved in the sustained expression of PPARγ2 and of PPARγ2 target genes. During adipogenesis, PARP1 was recruited to PPARγ2 target genes such as CD36 or aP2 in a PAR-dependent manner. Our results also reveal a PAR-dependent decrease in repressory histone marks (e.g. H3K9me3) and an increase in stimulatory marks (e.g. H3K4me3) at the PPARγ2 promoter, suggesting that PARP1 may exert its regulatory function during adipogenesis by altering histone marks. Interestingly, activation of PARP1 enzymatic activity was prevented with a topoisomerase II inhibitor. These data hint at topoisomerase II-dependent, transient, site-specific double-strand DNA breaks as the cause for poly(ADP)-ribose formation, adipogenic gene expression, and adipocyte function. Together, our study identifies PARP1 as a critical regulator of PPARγ2-dependent gene expression with implications in adipocyte function and obesity-related disease models.

Hyperoxia modulates TGF-beta/BMP signaling in a mouse model of bronchopulmonary dysplasia.

Prematurely born infants who require oxygen therapy often develop bronchopulmonary dysplasia (BPD), a debilitating disorder characterized by pronounced alveolar hypoplasia. Hyperoxic injury is believed to disrupt critical signaling pathways that direct lung development, causing BPD. We investigated the effects of normobaric hyperoxia on transforming growth factor (TGF)-beta and bone morphogenetic protein (BMP) signaling in neonatal C57BL/6J mice exposed to 21% or 85% O(2) between postnatal days P1 and P28. Growth and respiratory compliance were significantly impaired in pups exposed to 85% O(2), and these pups also exhibited a pronounced arrest of alveolarization, accompanied by dysregulated expression and localization of both receptor (ALK-1, ALK-3, ALK-6, and the TGF-beta type II receptor) and Smad (Smads 1, 3, and 4) proteins. TGF-beta signaling was potentiated, whereas BMP signaling was impaired both in the lungs of pups exposed to 85% O(2) as well as in MLE-12 mouse lung epithelial cells and NIH/3T3 and primary lung fibroblasts cultured in 85% O(2). After exposure to 85% O(2), primary alveolar type II cells were more susceptible to TGF-beta-induced apoptosis, whereas primary pulmonary artery smooth muscle cells were unaffected. Exposure of primary lung fibroblasts to 85% O(2) significantly enhanced the TGF-beta-stimulated production of the alpha(1) subunit of type I collagen (Ialpha(1)), tissue inhibitor of metalloproteinase-1, tropoelastin, and tenascin-C. These data demonstrated that hyperoxia significantly affects TGF-beta/BMP signaling in the lung, including processes central to septation and, hence, alveolarization. The amenability of these pathways to genetic and pharmacological manipulation may provide alternative avenues for the management of BPD.