Streeter, J. | bioRxiv Science

bioRxiv2021

Practices for Measuring 3D Organelle Morphology and Generating Surfaces with Amira

Analysis of 3D structures is of paramount importance in cellular biology. Although light microscopy and transmission electron microscopy (TEM) have remained staples for imaging cellular structures, they lack the ability to image in 3D. However, recent technological advances, such as serial block-face scanning electron microscopy (SBF-SEM) and focused ion beam scanning electron microscopy (FIB-SEM), have allowed researchers to observe cellular ultrastructure in 3D. Here, we propose a standardized protocol using the visualization software Amira to quantify organelle morphologies in 3D; this method allows researchers to produce accurate and reproducible measurements of cellular structure characteristics. We demonstrate this applicability by utilizing SBF-SEM and Amira to quantify mitochondria and endoplasmic reticulum (ER) structures. GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=127 SRC="FIGDIR/small/461807v1_ufig1.gif" ALT="Figure 1"> View larger version (43K): org.highwire.dtl.DTLVardef@1c40041org.highwire.dtl.DTLVardef@ecde92org.highwire.dtl.DTLVardef@10870daorg.highwire.dtl.DTLVardef@1290c3b_HPS_FORMAT_FIGEXP M_FIG C_FIG

biophysics↗

bioRxiv2021

Cardiac Specific Overexpression of Transcription Factor EB (TFEB) in Normal Hearts Induces Pathologic Cardiac Hypertrophy and Lethal Cardiomyopathy

TFEB promotes lysosomal biogenesis, autophagy, and lysosomal exocytosis. The present study characterized the consequence of inducible TFEB overexpression in cardiomyocytes in vivo. We generated cardiomyocyte-specific doxycycline inducible (Tet off) mice to achieve spatial and temporal control of TFEB overexpression, by crossing TFEB transgenic mice with mice harboring the tTA transgene (TFEB/tTA). Two weeks after doxycycline removal, an 8-fold increase in TFEB protein expression was observed in transgenic hearts. Heart weight normalized to tibia length was increased by 2.5-fold following TFEB overexpression (TFEB/tTA), characterized by induction of markers of pathological hypertrophy, such as Nppa, Nppb and Acta1, progressive contractile dysfunction and cardiac dilatation. Overexpression of TFEB resulted in premature death, associated with high degree AV block. Reversal of TFEB overexpression normalized cardiac structure and function. Mitochondrial respiration and ATP levels were preserved after 2-weeks of TFEB induction, despite reduced mitochondrial (OXPHOS) protein expression, mtDNA content, and altered mitochondrial morphology. Signaling through mTOR was induced in TFEB/tTA mice, and when inhibited by rapamycin treatment for 4 weeks, partially offset left ventricular dysfunction. Transcriptome analysis revealed early suppression of mitochondrial metabolic pathways, induction of fibrosis and altered calcium signaling. MCOLN1, a lysosomal calcium release channel, the calcineurin target RCAN1.4, and the mitochondrial calcium uniporter (MCU) were strikingly induced in TFEB/tTA mice. In summary, persistent overexpression of TFEB at high levels (8-fold protein upregulation) in cardiomyocytes promotes pathologic cardiac hypertrophy via suppression of mitochondrial bioenergetic pathways and activation of pro-fibrotic and calcium regulatory pathways.

cell biology↗