Reproducing asymmetrical spine shape fluctuations in a model of actin dynamics predicts self-organized criticality

Dendritic spines change their size and shape spontaneously, but the function of this remains unclear. Here, we address this in a biophysical model of spine fluctuations, which reproduces experimentally measured spine fluctuations. For this, we characterize size- and shape fluctuations from confocal microscopy image sequences using autoregressive models and a new set of shape descriptors derived from circular statistics. Using the biophysical model, we extrapolate into longer temporal intervals and find the presence of 1/f noise. When investigating its origins, the model predicts that the actin dynamics underlying shape fluctuations self-organizes into a critical state, which creates a fine balance between static actin filaments and free monomers. In a comparison against a non-critical model, we show that this state facilitates spine enlargement, which happens after LTP induction. Thus, ongoing spine shape fluctuations might be necessary to react quickly to plasticity events.

Abstract 554: Reverse-mode Mitochondrial Na + / Ca2+ Mitochondrial Exchange, Not the Mcu, is the Primary Mode of Ca2+ Import Into the Mitochondria During Ischemia/ Reperfusion in Neonatal Cardiac Myocytes

Ca 2+ entry via the Mitochondrial Calcium Uniporter (MCU) participates in energetic adaption to workload under physiological conditions but is thought to contribute to cell death during ischemia-reperfusion (I/R) injury. We have previously shown that mitochondrial membrane potential (ΔΨm) instability contributes to early-reperfusion arrhythmias and contractile dysfunction; however, the role of mitochondrial Ca 2+ (mCa 2+ ) uptake in triggering ΔΨm oscillation is unclear. Here, by acutely knocking out MCU, we examine whether MCU-mediated mCa 2+ uptake is required to trigger ΔΨm loss or oscillation during early reperfusion in neonatal mouse ventricular myocyte (NMVM) monolayers. We monitored mCa 2+ (with MitoCam) and ΔΨm (with TMRM) in WT(MCU fl/fl ) and MCU-KO (MCU fl/fl +AdCre) NMVMs during in vitro I/R (previously described by Solhjoo et al JMCC, 2015) by confocal microscopy. Image sequences were analyzed for changes in mCa 2+ and ΔΨm by segmenting individual cells in ImageJ. To quantify ΔΨm oscillations in mitochondrial clusters during reperfusion, a new wavelet-transform-based analysis was developed using MATLAB’s wavelet toolbox. Surprisingly, our findings demonstrate that MCU knockout does not significantly alter mCa 2+ import during I/R, nor does it affect ΔΨm recovery during Reperfusion. In fact, MCU-KO moderately shortened the latency to Ischemic ΔΨm depolarization. In contrast, blocking the mitochondrial sodium-calcium exchanger (mNCLX) with CGP-37157 suppressed the mCa 2+ increase during Ischemia. Moreover, blocking mNCLX also did not affect ΔΨm recovery during Reperfusion or the frequency of ΔΨ m oscillations, confirming that mitochondrial ΔΨm instability on reperfusion is not triggered by mCa 2+ . Interestingly, inhibition of mitochondrial electron transport stabilized ΔΨm oscillations during reperfusion. The findings are consistent with mCa 2+ overload being mediated by reverse-mode mNCLX activity and support ROS-induced ROS release as the primary trigger of ΔΨm instability during reperfusion injury.

Lipid-based nanovesicles for nanomedicine

Multifunctional lipid-based nanovesicles (L-NVs) prepared by molecular self-assembly of membrane components together with (bio)-active molecules, by means of compressed CO2-media or other non-conventional methods lead to highly homogeneous, tailor-made nanovesicles that are used for advanced nanomedicine. Confocal microscopy image of siRNA transfection using L-NVs, reprinted with permission from de Jonge,et al.,Gene Therapy, 2006,13, 400–411.