Study of hydrogen sulfide biosynthesis in synovial tissue from diabetes-associated osteoarthritis and its influence on macrophage phenotype and abundance

Type 2 diabetes (DB) is an independent risk factor for osteoarthritis (OA). However, the mechanisms underlying the connection between both diseases remain unclear. Synovial macrophages from OA patients with DB present a marked pro-inflammatory phenotype. Since hydrogen sulphide (H₂S) has been previously described to be involved in macrophage polarization, in this study we examined H₂S biosynthesis in synovial tissue from OA patients with DB, observing a reduction of H₂S-synthetizing enzymes in this subset of individuals. To elucidate these findings, we detected that differentiated TPH-1 cells to macrophages exposed to high levels of glucose presented a lower expression of H₂S-synthetizing enzymes and an increased inflammatory response to LPS, showing upregulated expression of markers associated with M1 phenotype (i.e., CD11c, CD86, iNOS, and IL-6) and reduced levels of those related to M2 fate (CD206 and CD163). The co-treatment of the cells with a slow-releasing H₂S donor, GYY-4137, attenuated the expression of M1 markers, but failed to modulate the levels of M2 indicators. GYY-4137 also reduced HIF-1α expression and upregulated the protein levels of HO-1, suggesting their involvement in the anti-inflammatory effects of H₂S induction. In addition, we observed that intraarticular administration of H₂S donor attenuated synovial abundance of CD68⁺ cells, mainly macrophages, in an in vivo model of OA. Taken together, the findings of this study seem to reinforce the key role of H₂S in the M1-like polarization of synovial macrophages associated to OA and specifically its metabolic phenotype, opening new therapeutic perspectives in the management of this pathology.

Dynamics of the canonical RNA degradosome components during glucose stress

The RNA Degradosome (RNAD) is a multi-enzyme complex, which performs important functions in post-transcriptional regulation in Escherichia coli with the assistance of regulatory sRNAs and the RNA chaperone Hfq. Although the interaction of the canonical RNAD components with RNase E has been extensively studied, the dynamic nature of the interactions in vivo remains largely unknown. In this work, we explored the rearrangements upon glucose stress using fluorescence energy transfer (hetero-FRET). Results revealed differences in the proximity of the canonical components with 1% (55.5 mM) glucose concentration, with the helicase RhlB and the glycolytic enzyme Enolase exhibiting the largest changes to the C-terminus of RNase E, followed by PNPase. We quantified ptsG mRNA decay and SgrS sRNA synthesis as they mediate bacterial adaptation to glucose stress conditions. We propose that once the mRNA degradation is completed, the RhlB, Enolase and PNPase decrease their proximity to the C-terminus of RNase E. Based on the results, we present a model where the canonical components of the RNAD coalesce when the bacteria is under glucose-6-phosphate stress and associate it with RNA decay. Our results demonstrate that FRET is a helpful tool to study conformational rearrangements in enzymatic complexes in bacteria in vivo.

Insights into the heparan sulphate-dependent externalisation of transglutaminase-2 (TG2) in glucose-stimulated proximal-like tubular epithelial cells

The extracellular matrix crosslinking enzyme transglutaminase 2 (TG2) is highly implicated in tissue fibrosis that precedes end-stage kidney failure. TG2 is unconventionally secreted through extracellular vesicles in a way that depends on the heparan sulphate (HS) proteoglycan syndecan-4 (Sdc4), the deletion of which reduces experimental kidney fibrosis as a result of lower extracellular TG2 in the tubule-interstitium. Here we establish a model of TG2 externalisation in NRK-52E tubular epithelial cells subjected to glucose stress. HS-binding TG2 mutants had reduced extracellular TG2 in transfected NRK-52E, suggesting that TG2-externalisation depends on an intact TG2 heparin binding site. Inhibition of N-ethylmaleimide sensitive factor (NSF) vesicle-fusing ATPase, which was identified in the recently elucidated TG2 kidney membrane-interactome, led to significantly lower TG2-externalisation, thus validating the involvement of membrane fusion in TG2 secretion. As cyclin-G-associated kinase (GAK) had emerged as a further TG2-partner in the fibrotic kidney, we investigated whether glucose-induced TG2-externalisation was accompanied by TG2 phosphorylation in consensus sequences of cyclin-dependent kinase (CDK). Glucose stress led to intense TG2 phosphorylation in serine/threonine CDK-target. TG2 phosphorylation by tyrosine kinases was also increased by glucose. Although the precise role of glucose-induced TG2 phosphorylation is unknown, these novel data suggest that phosphorylation may be involved in TG2 membrane-trafficking.

Low glucose stress decreases cellular NADH and mitochondrial ATP in colonic epithelial cancer cells: Influence of mitochondrial substrates

In this study, we investigated how colonic epithelial cells maintained pyridine nucleotide (NADH/NAD⁺) redox homeostasis upon acute metabolic variation imposed by glucose deprivation or supplementation with mitochondrial substrates, succinate and malate/glutamate (M/G). Our results showed that low glucose caused cellular NADH/NAD⁺ redox imbalance that diminished lactate dehydrogenase (LDH) activity and resulted in lower lactate contents. The concurrent activation of malic enzyme (ME) suggested a role for malate in preserving cellular pyruvate that remained unchanged at low glucose. Mitochondrial substrates restored cellular NADH/NAD⁺ redox homeostasis at low glucose in association with specific compartmental catabolism of mitochondrial substrates. As compared with normal glucose, M/G and low glucose promoted glycolytic ATP production but inhibited mitochondrial-derived ATP generation in association with decreased glucose availability for mitochondrial respiration. At normal glucose, succinate and M/G enhanced mitochondrial respiratory activity, but had minimal impact on mitochondrial-derived ATP production. Collectively, these results are consistent with low glucose-induced NADH/NAD⁺ redox imbalance in association with decreased aerobic glycolysis that is reversed by supplementation with M/G but not succinate.

Synthesis and Characterization of Sygyzium cumini Nanoparticles for Its Protective Potential in High Glucose-Induced Cardiac Stress: a Green Approach

There exists a complex and multifactorial relationship between diabetes and cardiovascular disease. Hyperglycemia is an important factor imposing damage (glucose toxicity) on cardiac cell leading to diabetic cardiomyopathy. There are substantial clinical evidences on the adverse effects of conventional therapies in the prevention/treatment of diabetic cardiovascular complications. Currently, green-synthesized nanoparticles have emerged as a safe, efficient, and inexpensive alternative for therapeutic uses. The present study discloses the silver nanoparticle biosynthesizing capability and cardioprotective potential of Syzygium cumini seeds already reported to have antidiabetic properties. Newly generated silver nanoparticles S. cumini MSE silver nanoparticles (SmSNPs) were characterized by UV-visible spectroscopy, scanning electron microscopy (SEM), zeta sizer, X-ray diffraction (XRD), and Fourier transform infrared (FTIR) spectroscopy. Using methanolic extract of S. cumini seeds, an average size of 40-100-nm nanoparticles with 43.02 nm and -19.6 mV zeta potential were synthesized. The crystalline nature of SmSNPs was identified by using XRD. 2,2-Diphenyl-1-picrylhydrazyl (DPPH) and 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid (ABTS) assays revealed the antioxidative potential to be 66.87 (±0.7) % and 86.07 (±0.92) % compared to 60.29 (±0.02) % and 85.67 (±1.27) % for S. cumini MSE. In vitro study on glucose-stressed H9C2 cardiac cells showed restoration in cell size, nuclear morphology, and lipid peroxide formation upon treatment of SmSNPs. Our findings concluded that S. cumini MSE SmSNPs significantly suppress the glucose-induced cardiac stress in vitro by maintaining the cellular integrity and reducing the oxidative damages therefore establishing its therapeutic potential in diabetic cardiomyopathy.

Elevated oxygen consumption rate in response to acute low-glucose stress: Metformin restores rate to normal level

Cardiovascular disease (CVD) continues to be the leading cause of mortality among all age demographics in the United States, with the highest occurrence in populations aged 65 and older. Glucose levels, particularly hyperglycemia, are associated with the premature onset of age-related diseases including CVD. A major challenge in the treatment of elderly patients with chronically elevated blood glucose is the frequency of hypoglycemic episodes. Molecular mechanisms of hypoglycemia remain unclear, but are associated with premature onset of age-related-diseases. Here we report a mitochondrial metabolic profile assessing short-term (up to six hours) and longer-term (12-24h) durations of low-glucose stress. We observed that the anti-diabetic biguanide and mitochondrial complex I inhibitor, metformin, can lower and restore the elevated oxygen consumption rate during shorter-term glucose stress to levels similar to that of cells cultured in normal glucose. This effect appears, in part, to involve activation of the 5' AMP-activated protein kinase (AMPK).