Future work is needed to evaluate whether a combination of different biochemical and structural outcomes using these imaging techniques can provide complementary information regarding the utilization of specific metabolic pathways. Antioxid. Redox Signal. 00, 000-000.

Stem cells reside in specialized niches that are critical for their function. Upon activation hair follicle stem cells (HFSCs) exit their niche to generate the outer root sheath (ORS), but a subset of ORS progeny returns to the niche to resume a SC state. Mechanisms of this fate reversibility are unclear. We show that the ability of ORS cells to return to the SC state requires suppression of a metabolic switch from glycolysis to oxidative phosphorylation and glutamine metabolism that occurs during early HFSC lineage progression. HFSC fate reversibility and glutamine metabolism are regulated by the mammalian target of rapamycin complex 2 (mTORC2)-Akt signaling axis within the niche. Deletion of mTORC2 results in a failure to re-establish the HFSC niche, defective hair follicle regeneration, and compromised long-term maintenance of HFSCs. These findings highlight the importance of spatiotemporal control of SC metabolic states in organ homeostasis.

Calcific aortic valve disease (CAVD) is the most common form of valve disease where the only available treatment strategy is surgical valve replacement. Technologies for the early detection of CAVD would benefit the development of prevention, mitigation and alternate therapeutic strategies. Two-photon excited fluorescence (TPEF) microscopy is a label-free, non-destructive imaging technique that has been shown to correlate with multiple markers for cellular differentiation and phenotypic changes in cancer and wound healing. Here we show how specific TPEF markers, namely, the optical redox ratio and mitochondrial fractal dimension, correlate with structural, functional and phenotypic changes occurring in the aortic valve interstitial cells (VICs) during osteogenic differentiation. The optical redox ratio, and fractal dimension of mitochondria were assessed and correlated with gene expression and nuclear morphology of VICs. The optical redox ratio decreased for VICs during early osteogenic differentiation and correlated with biological markers for CAVD progression. Fractal dimension correlated with structural and osteogenic markers as well as measures of nuclear morphology. Our study suggests that TPEF imaging markers, specifically the optical redox ratio and mitochondrial fractal dimension, can be potentially used as a tool for assessing early CAVD progression in vitro. Calcific aortic stenosis or calcific aortic valve disease (CAVD) is a progressive disease involving multiple signaling pathways, endothelial dysfunction, cytokine infiltration, collagen remodeling, as well as lipid and calcium deposition 1-4. The symptoms and markers for CAVD manifest via both degenerative (apoptotic) and active (osteogenic) mechanisms 5,6. Aortic valve endothelial and interstitial cells differentiate into an osteoblast-like phenotype, the extracellular matrix becomes thicker and stiffer and calcium mineralization occurs throughout the tissue 7,8. Aortic stenosis and sclerosis have an increased prevalence in the elderly and contribute to a 50% elevated risk of infarction and other potentially fatal cardiovascular pathologies 2,9,10. Currently, valve replacement is the preferred treatment method, as other strategies, such as the retardation of calcific progression, prevention and early diagnosis, are non-existent 11. Diagnostic techniques like echocardiography, cardiac MRI and cardiac CT are widely used, but are only sensitive during later stages of the disease once there is tissue mineralization, and hemodynamic and geometric impairment 12,13. Aortic valve interstitial cells (VICs) are the primary cells in the heart valves and are involved in tissue maintenance, repair and remodeling 14. VICs exist in a quiescent state under healthy conditions and are activated due to injury or disease 15 , potentially differentiating into an osteogenic-like phenotype to potentiate calcification 2. Current in vitro biochemical techniques to assess CAVD are typically destructive as they involve cell lysis or fixation and do not facilitate the longitu...

An improved technique for fractal characterization called the modified blanket method is introduced that can quantify surrounding fractal structures on a pixel by pixel basis without artifacts associated with scale-dependent image features such as object size. The method interprets images as topographical maps, obtaining information regarding the local surface area as a function of image resolution. Local fractal dimension (FD) can be quantified from the power law exponent derived from the surface area and image resolution relationship. We apply this technique on simulated cell images of known FD and compared the obtained values to power spectral density (PSD) analysis. Our method is sensitive to a wider FD range (2.0-4.5), having a mean error of 1.4% compared to 6% for PSD analysis. This increased sensitivity and an ability to compute regional FD properties enabled the discrimination of the differences in radiation resistant cancer cell responses that could not be detected using PSD analysis.

Biexponential fitting of autofluorescence lifetime decay curves is susceptible to significant error. Binning data from all pixels within whole cells and performing non-linear curvefitting in MATLAB can greatly improve measurement accuracy.