Hartzell, H. C. | Search bioRxiv

bioRxiv2019

Myosoft: an automated muscle histology analysis tool using machine learning algorithm utilizing FIJI/ImageJ software.

BackgroundSkeletal muscle is comprised of a heterogeneous population of muscle fibers which can be classified by their metabolic and contractile properties (fiber \"types\"). Fiber type is a primary determinant of muscle function along with fiber size (cross-sectional area). The fiber type composition of a muscle responds to physiological changes like exercise and aging and is often altered in disease states. Thus, analysis of fiber size and type in histological muscle preparations is a useful method for quantifying key indicators of muscle function and for measuring responses to a variety of stimuli or stressors. These analyses are near-ubiquitous in the fields of muscle physiology and myopathy, but are most commonly performed manually, which is highly labor- and time-intensive. To offset this obstacle, we developed Myosoft, a novel method to automate morphometric and fiber type analysis in muscle sections stained with fluorescent antibodies.\n\nMethodsMuscle sections were stained for cell membrane (laminin) and myofiber type (myosin heavy chain isoforms). Myosoft, running in the open access software platform FIJI (ImageJ), was used to analyze myofiber size and type in transverse sections of entire gastrocnemius/soleus muscles.\n\nResultsMyosoft provides accurate analysis of muscle histology >50-times faster than manual analysis. We demonstrate that Myosoft is capable of handling high-content images even when image or staining quality is suboptimal, which is a marked improvement over currently available, comparable programs.\n\nConclusionsMyosoft is a reliable, accurate, high-throughput, and convenient tool to analyze high-content muscle histology. Myosoft is freely available to download from Github at https://github.com/Hyojung-Choo/Myosoft/tree/Myosoft-hub.

physiology↗

bioRxiv2019

A Network of Phosphatidylinositol 4,5-bisphosphate Binding Sites Regulate Gating of the Ca2+-activated Cl- Channel ANO1 (TMEM16A)

ANO1 (TMEM16A) is a Ca2+-activated Cl- channel that regulates diverse cellular functions including fluid secretion, neuronal excitability, and smooth muscle contraction. ANO1 is activated by elevation of cytosolic Ca2+ and modulated by phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2). Here we describe a closely concerted experimental and computational study, including electrophysiology, mutagenesis, functional assays, and extended sampling of lipid-protein interactions with molecular dynamics (MD) to characterize PI(4,5)P2 binding modes and sites on ANO1. ANO1 currents in excised inside-out patches activated by 270 nM Ca2+ at +100 mV are increased by exogenous PI(4,5)P2 with an EC50 = 1.24 {micro}M. The effect of PI(4,5)P2 is dependent on membrane voltage and Ca2+ and is explained by a stabilization of the ANO1 Ca2+-bound open state. Unbiased atomistic MD simulations with 1.4 mol% PI(4,5)P2 in a phosphatidylcholine bilayer identified 8 binding sites with significant probability of binding PI(4,5)P2. Three of these sites captured 85% of all ANO1 - PI(4,5)P2 interactions. Mutagenesis of basic amino acids near the membrane-cytosol interface found three regions of ANO1 critical for PI(4,5)P2 regulation that correspond to the same three sites identified by MD. PI(4,5)P2 is stabilized by hydrogen bonding between amino acid sidechains and phosphate/hydroxyl groups on PI(4,5)P2. Binding of PI(4,5)P2 alters the position of the cytoplasmic extension of TM6, which plays a crucial role in ANO1 channel gating, and increases the accessibility of the inner vestibule to Cl-ions. We propose a model consisting of a network of three PI(4,5)P2 binding sites at the cytoplasmic face of the membrane allosterically regulating ANO1 channel gating.\n\nSignificance statementMembrane proteins dwell in a sea of phospholipids that not only structurally stabilize the proteins by providing a hydrophobic environment for their transmembrane segments, but also dynamically regulate protein function. While many cation channels are known to be regulated by phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2), relatively little is known about anion channel regulation by phosphoinositides. Using a combination of patch clamp electrophysiology and atomistic molecular dynamics simulations, we have identified several PI(4,5)P2 binding sites in ANO1 (TMEM16A), a Cl- channel that performs myriad physiological functions from epithelial fluid secretion to regulation of electrical excitability. These binding sites form a band at the cytosolic interface of the membrane that we propose constitute a network to dynamically regulate this highly allosteric protein.

biophysics↗