Structural Analysis of Inner Ear Hair Cell Mitochondria Near the Striated Organelle

Abstract

Mitochondria are important organelles found in every cell of the body. The current depiction of a mitochondrion, containing an inner membrane (IM), outer membrane and cristae that increase the surface area of the IM, has been the universally accepted model for decades. Although the basic function and structure of mitochondria have been studied, careful analysis of electron microscopy data has led to the identification of structurally different subpopulations of mitochondria in the inner ear (Lysakowski and Goldberg, JCN, 1997). There are several known mitochondrial‐related deafness and vestibular disorders, such as dizziness, vertigo and nystagmus (Iwasaki et al., Laryng, 2011). In order to further characterize inner ear mitochondrial subpopulations and relate them to these diseases, we used IMOD software to create 3D models of mitochondria located near different energy‐demanding cellular components. From these models, we collect quantitative data, such as crista surface area and volume and whole mitochondrion values. With these data, we can approximate a mitochondrion's energy output. The main structure of interest in this study was the striated organelle (SO), a cytoskeletal structure found in the apicolateral region of hair cells (Vranceanu et al., PNAS, 2012). We expected that mitochondria near the SO would have a fairly large energy output. It was hypothesized that there would be more points on the IM that joined with cristae membranes, the so‐called “crista junctions” (Rabl et al., JCB, 2009; Zick et al., BBA, 2009) on the side facing the striated organelle (Perkins et al., JNS, 2010). In the future, models of the different subpopulations can be compared structurally, which can lead to an explanation of differences in physiology or sensitivity to noxious agents. Exploring these differences should lead to determining the population of mitochondria affected in mitochondrial‐related deafness or vestibular disorders.Support or Funding InformationSupported by NIH R21‐DC013181 (AL) and P41‐RR004050 (GP, ME).