Analysis of grayscale characteristics in images of labeled microtubules from cultured cardiac myocytes

Male histone deacetylase 6 (HDAC6) knockout mice have enhanced ventilatory responses to hypoxic challenge

Histone deacetylase 6 (HDAC6) is a class II histone deacetylase that is predominantly localized in the cytoplasm of cells. HDAC6 associates with microtubules and regulates acetylation of tubulin and other proteins. The possibility that HDAC6 participates in hypoxic signaling is supported by evidence that 1) hypoxic gas challenges cause microtubule depolymerization, 2) expression of hypoxia inducible factor alpha (HIF-1α) is regulated by microtubule alterations in response to hypoxia, and 3) inhibition of HDAC6 prevents HIF-1α expression and protects tissue from hypoxic/ischemic insults. The aim of this study was to address whether the absence of HDAC6 alters ventilatory responses during and/or after hypoxic gas challenge (10% O2, 90% N2 for 15 min) in adult male wildtype (WT) C57BL/6 mice and HDAC6 knock-out (KO) mice. Key findings were that 1) baseline values for frequency of breathing, tidal volume, inspiratory and expiratory times, and end expiratory pause were different between knock-out mice and wildtype mice, 2) ventilatory responses during hypoxic challenge were more robust in KO mice than WT mice for recorded parameters including, frequency of breathing, minute ventilation, inspiratory and expiratory durations, peak inspiratory and expiratory flows, and inspiratory and expiratory drives, and 3) responses upon return to room-air were markedly different in KO compared to WT mice for frequency of breathing, minute ventilation, inspiratory and expiratory durations, end expiratory pause (but not end inspiratory pause), peak inspiratory and expiratory flows, and inspiratory and expiratory drives. These data suggest that HDAC6 may have a fundamentally important role in regulating the hypoxic ventilatory response in mice.

Male histone deacetylase 6 (HDAC6) knockout mice have enhanced ventilatory responses to hypoxic challenge

Histone deacetylase 6 (HDAC6) is a class II histone deacetylase that is predominantly localized in the cytoplasm of cells. HDAC6 associates with microtubules, regulating acetylation of tubulin and other proteins. The possibility that HDAC6 participates in hypoxic signaling is supported by evidence that (1) hypoxic gas challenges cause microtubule depolymerization, (2) expression of hypoxia inducible factor alpha (HIF)-1α is regulated by microtubule alterations in response to hypoxia, and (3) inhibition of HDAC6 prevents HIF-1α expression and protects tissue from hypoxic/ischemic insults. The aim of this study was to address whether the absence of HDAC6 alters ventilatory responses during and/or after hypoxic gas challenges (10% O2, 90% N2 for 15 min) in adult male wild-type (WT) C57BL/6 mice and HDAC6 knockout (KO) mice. Key findings were that (1) baseline values for frequency of breathing, tidal volume, inspiratory and expiratory times and end expiratory pause were different between KO mice and WT mice, (2) ventilatory responses during hypoxic challenge were more robust in KO mice than WT mice for parameters including frequency of breathing, minute ventilation, inspiratory and expiratory durations, peak inspiratory and expiratory flows, inspiratory and expiratory drives, and (3) responses upon return to room-air were markedly different in KO mice than WT mice for frequency of breathing, minute ventilation, inspiratory and expiratory durations, end expiratory (but not end inspiratory) pauses, peak inspiratory and expiratory flows, and inspiratory or expiratory drives. These data suggest that HDAC6 may have a fundamentally important role in regulating the neural responses to hypoxia.

Evaluation of intratumoral heterogeneity by using diffusion kurtosis imaging and stretched exponential diffusion-weighted imaging in an orthotopic hepatocellular carcinoma xenograft model

Background

To investigate the value of diffusion kurtosis imaging (DKI) and diffusion-weighted imaging (DWI) with a stretched exponential model (SEM) in the evaluation of tumor heterogeneity in an orthotopic hepatocellular carcinoma (HCC) xenograft model.

Methods

Thirty orthotopic HCC xenograft nude mice models were established and randomly divided into two groups, the sorafenib induction group (n=15) and control group (n=15). Every mouse in each group underwent MRI with DKI and SEM on a 1.5T MR scanner at 7, 14, and 21 days after sorafenib intervention. DKI and SEM parameters including mean kurtosis (MK), mean diffusivity (MD), α, and distributed diffusion coefficient (DDC) were measured, calculated, and compared between the two groups and among different time points. Sequential correlations between histopathological results including necrotic fraction (NF), micro-vessel density (MVD), Ki-67 index, standard deviation (SD), and kurtosis from hematoxylin-eosin staining, and DKI and SEM parameters were analyzed.

Results

MK, MD, and DDC of HCC in the sorafenib induction group were significantly higher than those in the control group at each time point (P<0.05), while α was significantly lower (P<0.05). Significantly positive correlations were found between MK and NF (r=0.693, P=0.010), SD (r =0.785, P=0.003), kurtosis (r=0.779, P=0.003), between MD and NF (r=0.794, P=0.003), SD (r=0.629, P=0.020), kurtosis (r=0.645, P=0.018), and between DDC and NF (r=0.800, P=0.003), SD (r=0.636, P=0.020), kurtosis (r=0.664, P=0.016), and significantly negative correlations were observed between α and NF (r=-0.704, P=0.009), SD (r=-0.754, P=0.003), and kurtosis (r=-0.792, P=0.003) in the sorafenib induction group.

Conclusions

DKI and SEM parameters may be potentially useful for evaluating intratumoral heterogeneity in HCC.

Dynamic microtubule association of Doublecortin X (DCX) is regulated by its C-terminus

Doublecortin X (DCX), known to be essential for neuronal migration and cortical layering in the developing brain, is a 40 kDa microtubule (MT)-associated protein. DCX directly interacts with MTs via its two structured doublecortin (DC) domains, but the dynamics of this association and the possible regulatory roles played by the flanking unstructured regions remain poorly defined. Here, we employ quantitative fluorescence recovery after photobleaching (FRAP) protocols in living cells to reveal that DCX shows remarkably rapid and complete exchange within the MT network but that the removal of the C-terminal region significantly slows this exchange. We further probed how MT organization or external stimuli could additionally modulate DCX exchange dynamics. MT depolymerisation (nocodazole treatment) or stabilization (taxol treatment) further enhanced DCX exchange rates, however the exchange rates for the C-terminal truncated DCX protein were resistant to the impact of taxol-induced stabilization. Furthermore, in response to a hyperosmotic stress stimulus, DCX exchange dynamics were slowed, and again the C-terminal truncated DCX protein was resistant to the stimulus. Thus, the DCX dynamically associates with MTs in living cells and its C-terminal region plays important roles in the MT-DCX association.

A Quantitative Method for Microtubule Analysis in Fluorescence Images

Microtubule analysis is of significant value for a better understanding of normal and pathological cellular processes. Although immunofluorescence microscopic techniques have proven useful in the study of microtubules, comparative results commonly rely on a descriptive and subjective visual analysis. We developed an objective and quantitative method based on image processing and analysis of fluorescently labeled microtubular patterns in cultured cells. We used a multi-parameter approach by analyzing four quantifiable characteristics to compose our quantitative feature set. Then we interpreted specific changes in the parameters and revealed the contribution of each feature set using principal component analysis. In addition, we verified that different treatment groups could be clearly discriminated using principal components of the multi-parameter model. High predictive accuracy of four commonly used multi-classification methods confirmed our method. These results demonstrated the effectiveness and efficiency of our method in the analysis of microtubules in fluorescence images. Application of the analytical methods presented here provides information concerning the organization and modification of microtubules, and could aid in the further understanding of structural and functional aspects of microtubules under normal and pathological conditions.