STAT1- and NFAT-independent amplification of purinoceptor function integrates cellular senescence with interleukin-6 production in preadipocytes.

BACKGROUND AND PURPOSE: Senescent preadipocytes promote adipose tissue dysfunction by secreting pro-inflammatory factors, although little is known about the mechanisms regulating their production. We investigated if up-regulated purinoceptor function sensitizes senescent preadipocytes to cognate agonists and how such sensitization regulates inflammation. EXPERIMENTAL APPROACH: Etoposide was used to trigger senescence in 3T3-L1 preadipocytes. CRISPR/Cas9 technology or pharmacology allowed studies of transcription factor function. Fura-2 imaging was used for calcium measurements. Interleukin-6 levels were quantified using quantitative PCR and ELISA. Specific agonists and antagonists supported studies of purinoceptor coupling to interleukin-6 production. Experiments in MS1 VEGF angiosarcoma cells and adipose tissue samples from obese mice complemented preadipocyte experiments. KEY RESULTS: DNA damage-induced senescence up-regulated purinoceptor expression levels in preadipocytes and MS1 VEGF angiosarcoma cells. ATP-evoked Ca2+ release was potentiated in senescent preadipocytes. ATP enhanced interleukin-6 production, an effect mimicked by ADP but not UTP, in a calcium-independent manner. Senescence-associated up-regulation and activation of the adenosine A3 receptor also enhanced interleukin-6 production. However, nucleotide hydrolysis was not essential because exposure to ATPγS also enhanced interleukin-6 secretion. Pharmacological experiments suggested coupling of P2X ion channels and P2Y12 -P2Y13 receptors to downstream interleukin-6 production. Interleukin-6 signalling exacerbated inflammation during senescence and compromised adipogenesis. CONCLUSIONS AND IMPLICATIONS: We report a previously uncharacterized link between cellular senescence and purinergic signalling in preadipocytes and endothelial cancer cells, raising the possibility that up-regulated purinoceptors play key modulatory roles in senescence-associated conditions like obesity and cancer. There is potential for exploitation of specific purinoceptor antagonists as therapeutics in inflammatory disorders.

Angiogenic content of microparticles in patients with diabetes and coronary artery disease predicts networks of endothelial dysfunction.

BACKGROUND: Elevated endothelial microparticles (EMPs) levels are surrogate markers of vascular dysfunction. We analyzed EMPs with apoptotic characteristics and assessed the angiogenic contents of microparticles in the blood of patients with type 2 diabetes (T2D) according to the presence of coronary artery disease (CAD). METHODS: A total of 80 participants were recruited and equally classified as (1) healthy without T2D, (2) T2D without cardiovascular complications, (3) T2D and chronic coronary artery disease (CAD), and (4) T2D and acute coronary syndrome (ACS). MPs were isolated from the peripheral circulation, and EMPs were characterized using flow cytometry of CD42 and CD31. CD62E was used to determine EMPs' apoptotic/activation state. MPs content was extracted and profiled using an angiogenesis array. RESULTS: Levels of CD42- CD31 + EMPs were significantly increased in T2D with ACS (257.5 ± 35.58) when compared to healthy subjects (105.7 ± 12.96, p < 0.01). There was no significant difference when comparing T2D with and without chronic CAD. The ratio of CD42-CD62 +/CD42-CD31 + EMPs was reduced in all T2D patients, with further reduction in ACS when compared to chronic CAD, reflecting a release by apoptotic endothelial cells. The angiogenic content of the full population of MPs was analyzed. It revealed a significant differential expression of 5 factors in patients with ACS and diabetes, including TGF-ß1, PD-ECGF, platelet factor 4, serpin E1, and thrombospondin 1. Ingenuity Pathway Analysis revealed that those five differentially expressed molecules, mainly TGF-ß1, inhibit key pathways involved in normal endothelial function. Further comparison of the three diabetes groups to healthy controls and diabetes without cardiovascular disease to diabetes with CAD identified networks that inhibit normal endothelial cell function. Interestingly, DDP-IV was the only differentially expressed protein between chronic CAD and ACS in patients with diabetes. CONCLUSION: Our data showed that the release of apoptosis-induced EMPs is increased in diabetes, irrespective of CAD, ACS patients having the highest levels. The protein contents of MPs interact in networks that indicate vascular dysfunction.

SIRT1 promotes lipid metabolism and mitochondrial biogenesis in adipocytes and coordinates adipogenesis by targeting key enzymatic pathways.

The NAD+-dependent deacetylase SIRT1 controls key metabolic functions by deacetylating target proteins and strategies that promote SIRT1 function such as SIRT1 overexpression or NAD+ boosters alleviate metabolic complications. We previously reported that SIRT1-depletion in 3T3-L1 preadipocytes led to C-Myc activation, adipocyte hyperplasia, and dysregulated adipocyte metabolism. Here, we characterized SIRT1-depleted adipocytes by quantitative mass spectrometry-based proteomics, gene-expression and biochemical analyses, and mitochondrial studies. We found that SIRT1 promoted mitochondrial biogenesis and respiration in adipocytes and expression of molecules like leptin, adiponectin, matrix metalloproteinases, lipocalin 2, and thyroid responsive protein was SIRT1-dependent. Independent validation of the proteomics dataset uncovered SIRT1-dependence of SREBF1c and PPARα signaling in adipocytes. SIRT1 promoted nicotinamide mononucleotide acetyltransferase 2 (NMNAT2) expression during 3T3-L1 differentiation and constitutively repressed NMNAT1 and 3 levels. Supplementing preadipocytes with the NAD+ booster nicotinamide mononucleotide (NMN) during differentiation increased expression levels of leptin, SIRT1, and PGC-1α and its transcriptional targets, and reduced levels of pro-fibrotic collagens (Col6A1 and Col6A3) in a SIRT1-dependent manner. Investigating the metabolic impact of the functional interaction of SIRT1 with SREBF1c and PPARα and insights into how NAD+ metabolism modulates adipocyte function could potentially lead to new avenues in developing therapeutics for obesity complications.

Signal Transducer and Activator of Transcription 3 (STAT3) Suppresses STAT1/Interferon Signaling Pathway and Inflammation in Senescent Preadipocytes.

Obesity promotes premature aging and dysfunction of white adipose tissue (WAT) through the accumulation of cellular senescence. The senescent cells burden in WAT has been linked to inflammation, insulin-resistance (IR), and type 2 diabetes (T2D). There is limited knowledge about molecular mechanisms that sustain inflammation in obese states. Here, we describe a robust and physiologically relevant in vitro system to trigger senescence in mouse 3T3-L1 preadipocytes. By employing transcriptomics analyses, we discovered up-regulation of key pro-inflammatory molecules and activation of interferon/signal transducer and activator of transcription (STAT)1/3 signaling in senescent preadipocytes, and expression of downstream targets was induced in epididymal WAT of obese mice, and obese human adipose tissue. To test the relevance of STAT1/3 signaling to preadipocyte senescence, we used Clustered Regularly Interspaced Short Palindromic Repeats/CRISPR associated protein 9 (CRISPR/Cas9) technology to delete STAT1/3 and discovered that STAT1 promoted growth arrest and cooperated with cyclic Guanosine Monophosphate-Adenosine Monophosphate (GMP-AMP) synthase-stimulator of interferon genes (cGAS-STING) to drive the expression of interferon ß (IFNß), C-X-C motif chemokine ligand 10 (CXCL10), and interferon signaling-related genes. In contrast, we discovered that STAT3 was a negative regulator of STAT1/cGAS-STING signaling-it suppressed senescence and inflammation. These data provide insights into how STAT1/STAT3 signaling coordinates senescence and inflammation through functional interactions with the cGAS/STING pathway.

Non-enzymatic conversion of primary oxidation products of Docosahexaenoic acid into less toxic acid molecules.

Docosahexaenoic acid (DHA) is long chain omega-3 fatty acid with known health benefits and clinical significance. However, 4-hydroxy hexenal (HHE), an enzymatic oxidation product of DHA has recently been reported to have health-damaging effects. This conflict raises major concern on the long-term clinical use of these fatty acids. Even though the enzymatic and non-enzymatic conversion of HHE to nontoxic acid molecules is possible by the aldehyde detoxification systems, it has not yet studied. To address this, primary oxidation products of DHA in lipoxidase system were subjected to non-enzymatic conversion at physiological temperature over a period of 1 week. The reaction was monitored using HPLC, IR spectroscopy and biochemical assays (based on the loss of conjugated dienes, lipid peroxides aldehydes). Short term and long term cytotoxicity of the compounds generated at various time points were analyzed. IR and HPLC spectra revealed that the level of aldehydes in the primary oxidation products reduced over time, generating acids and acid derivatives within a week period. In short term and long term cytotoxicity analysis, initial decomposition products were found more toxic than the 1-week decomposition products. Further, when primary oxidation products were subjected to aldehyde dehydrogenase mediated oxidation, it generated products that are also less toxic. The study suggests the possible non-enzymatic conversion of primary oxidation products of DHA to less cytotoxic acid molecules. Exploration of the physiological roles of these acid molecules may explain the biological potential of omega-3 fatty acids.