Biochemical Effects of Exercise on a Fasciocutaneous Flap in a Rat Model.

Importance: An overwhelming amount of data suggest that cardiovascular exercise has a positive effect on the mind and body, although the precise mechanism is not always clear. Objective: To assess the clinical and biochemical effects of voluntary cardiovascular exercise on pedicled flaps in a rodent model. Design, Setting, and Participants: Eighteen adult Sprague-Dawley male rats were randomized into a resting animal group (RAG) (n=9) and an exercise animal group (EAG) (n=9) for 14 days (July 23, 2013, through July 30, 2013). A pedicled transposition flap was performed on the ventral surface of the rat, and biopsy specimens were taken from the proximal, middle, and distal portions on postoperative days 0, 2, 5, and 9. Flap survival was analyzed planimetrically, and biopsy specimens were analyzed by hematoxylin-eosin-stained microscopy and immunoblotting. The housing, exercise, surgery, and analysis of the rats were conducted at a single basic science research laboratory at the tertiary care center campus of Thomas Jefferson University in Philadelphia, Pennsylvania. Exposures: The rats were caged for 14 days or housed in a cage connected to an exercise wheel and pedometer. Main Outcomes and Measures: Study measures were gross and micrographic necrosis and expression of proteins within cell survival and apoptosis pathways. Results: A total of 18 rats were studied, 9 in the RAG and 9 in the EAG. the mean (SEM) amount of necrosis in flaps was 41.3% (3%) in the RAG rats and 10.5% (3.5%) in the EAG rats (P \u3c .001). Immunoblotting revealed increased Caspase-9 activity resulting in poly-(adenosine diphosphate-ribose) polymerase 1 cleavage in the RAG vs the EAG, as well as lower phosphorylated protein kinase B (also known as Akt), signal transducer and activator of transcription 3, and total B-cell leukemia/lymphoma 2 protein levels. Throughout the postoperative period, the cumulative vascular endothelial growth factor A levels of the EAG flaps were significantly higher than those of the RAG flaps (2.30 vs 1.25 fold induction [FI], P = .002), with differences of 2.76 vs 1.54 FI in the proximal segment, 2.40 vs 1.20 FI in the middle segment, and 1.90 vs 0.79 FI in the distal segment. A similar response was noted when comparing phosphorylated Akt, with cumulative mean (SEM) p-Akt expression levels of 0.62 (0.04) for RAG and 1.98 (0.09) for EAG (P = .002 between the 2 groups). Conclusions and Relevance: Voluntary preoperative exercise improves survival in pedicled fasciocutaneous flaps; the EAG rats had less necrosis, decreased apoptotic markers, and increased amounts of vascular endothelial growth factor A and prosurvival proteins. These results have implications to increase flap survival in other mammal populations, such as humans. Level of Evidence: 3

Systems-level interactions between insulin–EGF networks amplify mitogenic signaling

Crosstalk mechanisms have not been studied as thoroughly as individual signaling pathways. We exploit experimental and computational approaches to reveal how a concordant interplay between the insulin and epidermal growth factor (EGF) signaling networks can potentiate mitogenic signaling. In HEK293 cells, insulin is a poor activator of the Ras/ERK (extracellular signal-regulated kinase) cascade, yet it enhances ERK activation by low EGF doses. We find that major crosstalk mechanisms that amplify ERK signaling are localized upstream of Ras and at the Ras/Raf level. Computational modeling unveils how critical network nodes, the adaptor proteins GAB1 and insulin receptor substrate (IRS), Src kinase, and phosphatase SHP2, convert insulin-induced increase in the phosphatidylinositol-3,4,5-triphosphate (PIP3) concentration into enhanced Ras/ERK activity. The model predicts and experiments confirm that insulin-induced amplification of mitogenic signaling is abolished by disrupting PIP3-mediated positive feedback via GAB1 and IRS. We demonstrate that GAB1 behaves as a non-linear amplifier of mitogenic responses and insulin endows EGF signaling with robustness to GAB1 suppression. Our results show the feasibility of using computational models to identify key target combinations and predict complex cellular responses to a mixture of external cues

PI3K/Akt-sensitive MEK-independent compensatory circuit of ERK activation in ER-positive PI3K-mutant T47D breast cancer cells

ERCDeposited by bulk impor

Emergence of bimodal cell population responses from the interplay between analog single-cell signaling and protein expression noise

Background: Cell-to-cell variability in protein expression can be large, and its propagation through signaling networks affects biological outcomes. Here, we apply deterministic and probabilistic models and biochemical measurements to study how network topologies and cell-to-cell protein abundance variations interact to shape signaling responses. Results: We observe bimodal distributions of extracellular signal-regulated kinase (ERK) responses to epidermal growth factor (EGF) stimulation, which are generally thought to indicate bistable or ultrasensitive signaling behavior in single cells. Surprisingly, we find that a simple MAPK/ERK-cascade model with negative feedback that displays graded, analog ERK responses at a single cell level can explain the experimentally observed bimodality at the cell population level. Model analysis suggests that a conversion of graded input–output responses in single cells to digital responses at the population level is caused by a broad distribution of ERK pathway activation thesholds brought about by cell-to-cell variability in protein expression. Conclusions: Our results show that bimodal signaling response distributions do not necessarily imply digital (ultrasensitive or bistable) single cell signaling, and the interplay between protein expression noise and network topologies can bring about digital population responses from analog single cell dose responses. Thus, cells can retain the benefits of robustness arising from negative feedback, while simultaneously generating population-level on/off responses that are thought to be critical for regulating cell fate decisions.SFIDeposited by bulk impor

Aging effects on pedicled fasciocutaneous flap survival in rats

Sudeep Roy is a third year resident in the Department of Otolaryngology. He received his medical degree from New York Medical College. Objectives: To characterize the effects of aging on the vascular proliferation, cell survival pathways, and viability of pedicled flaps in an inherently ischemic environment in rats. Presentation: 12 minute

In vivo label-free optical signatures of chemotherapy response in human pancreatic ductal adenocarcinoma patient-derived xenografts

Abstract Pancreatic cancer is a devastating disease often detected at later stages, necessitating swift and effective chemotherapy treatment. However, chemoresistance is common and its mechanisms are poorly understood. Here, label-free multi-modal nonlinear optical microscopy was applied to study microstructural and functional features of pancreatic tumors in vivo to monitor inter- and intra-tumor heterogeneity and treatment response. Patient-derived xenografts with human pancreatic ductal adenocarcinoma were implanted into mice and characterized over five weeks of intraperitoneal chemotherapy (FIRINOX or Gem/NabP) with known responsiveness/resistance. Resistant and responsive tumors exhibited a similar initial metabolic response, but by week 5 the resistant tumor deviated significantly from the responsive tumor, indicating that a representative response may take up to five weeks to appear. This biphasic metabolic response in a chemoresistant tumor reveals the possibility of intra-tumor spatiotemporal heterogeneity of drug responsiveness. These results, though limited by small sample size, suggest the possibility for further work characterizing chemoresistance mechanisms using nonlinear optical microscopy

Cross-talk between mitogenic Ras/MAPK and survival PI3K/Akt pathways: a fine balance

In the present paper, we describe multiple levels of cross-talk between the PI3K (phosphoinositide 3-kinase)/Akt and Ras/MAPK (mitogen-activated protein kinase) signalling pathways. Experimental data and computer simulations demonstrate that cross-talk is context-dependent and that both pathways can activate or inhibit each other. Positive influence of the PI3K pathway on the MAPK pathway is most effective at sufficiently low doses of growth factors, whereas negative influence of the MAPK pathway on the PI3K pathway is mostly pronounced at high doses of growth factors. Pathway cross-talk endows a cell with emerging capabilities for processing and decoding signals from multiple receptors activated by different combinations of extracellular cues.Deposited by bulk impor