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SummaryShort-term fasting is beneficial for the regeneration of multiple tissue types. However, the effects of fasting on muscle regeneration are largely unknown. Here we report that fasting slows muscle repair both immediately after the conclusion of fasting as well as after multiple days of refeeding. We show that ketosis, either endogenously produced during fasting or a ketogenic diet, or exogenously administered, promotes a deep quiescent state in muscle stem cells (MuSCs). Although deep quiescent MuSCs are less poised to activate, slowing muscle regeneration, they have markedly improved survival when facing sources of cellular stress. Further, we show that ketone bodies, specifically β-hydroxybutyrate, directly promote MuSC deep quiescence via a non-metabolic mechanism. We show that β-hydroxybutyrate functions as an HDAC inhibitor within MuSCs leading to acetylation and activation of an HDAC1 target protein p53. Finally, we demonstrate that p53 activation contributes to the deep quiescence and enhanced resilience observed during fasting.

Inorganic lead halide perovskite nanostructures show promise as the active layers in photovoltaics, light emitting diodes, and other optoelectronic devices. They are robust in the presence of oxygen and water, and the electronic structure and dynamics of these nanostructures can be tuned through quantum confinement. Here we create aligned bundles of CsPbBr3 nanowires with widths resulting in quantum confinement of the electronic wave functions and subject them to ultrafast microscopy. We directly image rapid one-dimensional exciton diffusion along the nanowires, and we measure an exciton trap density of roughly one per nanowire. Using transient absorption microscopy, we observe a polarization-dependent splitting of the band edge exciton line, and from the polarized fluorescence of nanowires in solution, we determine that the exciton transition dipole moments are anisotropic in strength. Our observations are consistent with a model in which splitting is driven by shape anisotropy in conjunction with long-range exchange.

Chronic or excess glucocorticoid exposure causes lipid disorders such as hypertriglyceridemia and hepatic steatosis. Angptl4 (angiopoietin-like 4), a primary target gene of the glucocorticoid receptor in hepatocytes and adipocytes, is required for hypertriglyceridemia and hepatic steatosis induced by the synthetic glucocorticoid dexamethasone. Angptl4 has also been shown to be required for dexamethasone-induced hepatic ceramide production. Here, we further examined the role of ceramide-mediated signaling in hepatic dyslipidemia caused by chronic glucocorticoid exposure. Using a stable isotope-labeling technique, we found that dexamethasone treatment induced the rate of hepatic de novo lipogenesis and triglyceride synthesis. These dexamethasone responses were compromised in Angptl4-null mice (Angptl4(−/−)). Treating mice with myriocin, an inhibitor of the rate-controlling enzyme of de novo ceramide synthesis, serine palmitoyltransferase long-chain base subunit 1 (SPTLC1)/SPTLC2, decreased dexamethasone-induced plasma and liver triglyceride levels in WT but not Angptl4(−/−) mice. We noted similar results in mice infected with adeno-associated virus–expressing small hairpin RNAs targeting Sptlc2. Protein phosphatase 2 phosphatase activator (PP2A) and protein kinase Cζ (PKCζ) are two known downstream effectors of ceramides. We found here that mice treated with an inhibitor of PKCζ, 2-acetyl-1,3-cyclopentanedione (ACPD), had lower levels of dexamethasone-induced triglyceride accumulation in plasma and liver. However, small hairpin RNA–mediated targeting of the catalytic PP2A subunit (Ppp2ca) had no effect on dexamethasone responses on plasma and liver triglyceride levels. Overall, our results indicate that chronic dexamethasone treatment induces an ANGPTL4–ceramide–PKCζ axis that activates hepatic de novo lipogenesis and triglyceride synthesis, resulting in lipid disorders.

TEMPO (2, 2, 6, 6-tetramethylphiperidine-1-oxyl) and its derivatives are stable free radical nitroxides widely used in the field of chemistry, biology, and pharmacology. TEMPO was previously found to be mutagenic and to induce micronuclei in mammalian cells. In this study, we investigated and quantified the genotoxicity of 4 structurally similar nitroxides, TEMPO and 3 of its derivatives (4-hydroxy-TEMPO, 4-oxo-TEMPO, and 4-methoxy-TEMPO), using the mouse lymphoma assay (MLA) and Comet assay in L5178Y Tk(+/−) cells. The results showed that all tested nitroxides were cytotoxic and mutagenic in the MLA, both in the presence and absence of S9, with metabolic activation significantly enhancing the cytotoxicity and/or utagenicity. In addition, the 4 nitroxides caused DNA-strand breakage. The mutagenicity and DNA damaging dose-responses of the test articles were compared using the PROAST benchmark dose software package. The potency ranking of the 4 nitroxides for mutagenicity was different from the ranking of the DNA damaging effects. The mode of action analysis by a multi-endpoint DNA damage pathway assay classified all 4 nitroxides as clastogens. In addition, the majority of the induced Tk mutants showed loss of heterozygosity at the Tk and D11Mit42 loci (ie, chromosome damage

The aggregation and photodegradation of rhodamine derivatives adsorbed to TiO2 are investigated using diffuse reflectance spectroscopy, steady-state fluorescence, and time-correlated single-photon-counting (TCSPC) measurements. Rhodamine dyes containing substituted amines (i.e., 5-ROX, R101, RB) exhibit an ∼50 nm hypsochromic shift in λmax upon adsorption to TiO2 relative to solution. By examining a rhodamine derivative with primary amines (i.e., R560) as well as control experiments on insulating ZrO2 substrates, we demonstrate that photocatalyzed N-dealkylation is largely responsible for the spectral changes observed upon surface adsorption to TiO2. For R560, which does not undergo N-dealkylation, diffuse reflectance spectra show that mainly monomers and J-aggregates are present on TiO2. Comparative lifetime measurements for R560 on TiO2 and ZrO2 show that the injection yield for R560/TiO2 is increased with dye-loading concentration (i.e., from 0.63 for monomers to ∼0.80 for heavily doped films), indicat...

It is well established that chronic and/or excess glucocorticoid (GC) exposure causes glucose and lipid homeostasis disorders. Previous studies have shown that chronic glucocorticoid exposure elevates hepatic ceramide production to inhibit insulin action and increase triglyceride accumulation in the liver. Glucocorticoid treatment not only increases the levels of hepatic ceramides, but also the levels of sphingosine-1-phosphate (S1P). This is because glucocorticoids not only promote the ceramide synthetic pathway, but also increase the expression of sphingosine kinase 1 (Sphk1). Ceramides can be converted to sphingosine, which is further converted to S1P through Sphk1. Here, we reduced the expression of Sphk1 in liver to evaluate its role in chronic glucocorticoid exposure-induced glucose and lipid disorders. We found that mice with reduced hepatic Sphk1 expression had improved glucose and pyruvate tolerance, while no significant difference in insulin tolerance was found upon glucocorticoid treatment. In contrast, glucocorticoid treatment-induced hepatic steatosis and hypertriglyceridemia were exacerbated in these mice with reduced hepatic Sphk1 expression. These results are surprising, as insulin resistance is frequently associated with the development of hepatic dyslipidemia. In this case, while Sphk1 is involved in the insulin resistance induced by glucocorticoids, it plays a negative role in chronic glucocorticoid treatment-induced hepatic dyslipidemia. Here, we will report our recent analysis on the mechanism underlying the role of Sphk1, ceramides, and S1P, in chronic glucocorticoid exposure-induced metabolic disorders. Disclosure R.A. Lee: None. A. Tsay: None. M. Chang: None. N. Yiv: None. J.H. Tan: None. J. Wang: None. Funding National Institutes of Health (R01DK113019)

The blinking and photobleaching dynamics of alizarin (1,2-dihydroxyanthraquinone) and purpurin (1,2,4-trihydroxyanthraquinone) are investigated using single-molecule spectroscopy. The time-dependent emission of alizarin and purpurin on glass under N2 is analyzed using the change point detection (CPD) method to compile on- and off-event distributions. The number of distinct emissive events per molecule is about four times higher for alizarin relative to purpurin, consistent with an excited-state intramolecular proton transfer (ESIPT) process to populate an emissive tautomer state. To elucidate the mechanism for blinking (i.e., switching between on and off events), maximum likelihood estimation (MLE), goodness-of-fit tests based on the Kolmogorov–Smirnov (KS) statistic, and the log-likelihood ratio (LLR) tests are used to establish the best fits to the on- and off-interval probability distributions. For both alizarin and purpurin the on intervals are log-normally distributed, and off intervals are Weibull d...

The effects of dye structure, driving force of photoinduced electron transfer, and adsorption affinity on the dispersive electron-transfer dynamics of rhodamines on TiO2 films are investigated using single-molecule microscopy. The time-dependent emission (i.e., blinking dynamics) of rhodamine-sensitized TiO2 films are quantified using maximum likelihood estimation (MLE) and quantitative goodness-of-fit tests based on the Kolmogorov–Smirnov (KS) statistic to determine the best fit to the photophysical data. Although the observation of significant p-values (i.e., ranging from 0.16 to 0.53) seems to support the power-law model for the on-time distributions, only a minor subset of the data are actually represented by power laws (i.e., ∼15–20% of events). Instead, the MLE/KS analysis reveals that log-normal distributions, not power laws, most closely represent the entire on-time and off-time distributions for RB, R6G, R123, and 5-ROX on TiO2. Monte Carlo simulations based on the Albery model for dispersive ele...

We demonstrate the first biosensing strategy that relies on quantum dot (QD) fluorescence blinking to report the presence of a target molecule. Unlike other biosensors that utilize QDs, our method does not require the analyte to induce any fluorescence intensity or color changes, making it readily applicable to a wide range of target species. Instead, our approach relies on the understanding that blinking, a single particle phenomenon, is obscured when several QDs lie within the detection volume of a confocal microscope. If QDs are engineered to aggregate when they encounter a particular target molecule, the observation of quasi-continuous emission should indicate its presence. As proof of concept, we programmed DNAs to drive rapid isothermal assembly of QDs in the presence of a target strand (oncogene K-ras). The assemblies, confirmed by various gel techniques, contained multiple QDs and were readily distinguished from free QDs by the absence of blinking.