1
|
Bisbach CM, Hutto RA, Poria D, Cleghorn WM, Abbas F, Vinberg F, Kefalov VJ, Hurley JB, Brockerhoff SE. Mitochondrial Calcium Uniporter (MCU) deficiency reveals an alternate path for Ca 2+ uptake in photoreceptor mitochondria. Sci Rep 2020; 10:16041. [PMID: 32994451 PMCID: PMC7525533 DOI: 10.1038/s41598-020-72708-x] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2020] [Accepted: 09/04/2020] [Indexed: 01/18/2023] Open
Abstract
Rods and cones use intracellular Ca2+ to regulate many functions, including phototransduction and neurotransmission. The Mitochondrial Calcium Uniporter (MCU) complex is thought to be the primary pathway for Ca2+ entry into mitochondria in eukaryotes. We investigate the hypothesis that mitochondrial Ca2+ uptake via MCU influences phototransduction and energy metabolism in photoreceptors using a mcu-/- zebrafish and a rod photoreceptor-specific Mcu-/- mouse. Using genetically encoded Ca2+ sensors to directly examine Ca2+ uptake in zebrafish cone mitochondria, we found that loss of MCU reduces but does not eliminate mitochondrial Ca2+ uptake. Loss of MCU does not lead to photoreceptor degeneration, mildly affects mitochondrial metabolism, and does not alter physiological responses to light, even in the absence of the Na+/Ca2+, K+ exchanger. Our results reveal that MCU is dispensable for vertebrate photoreceptor function, consistent with its low expression and the presence of an alternative pathway for Ca2+ uptake into photoreceptor mitochondria.
Collapse
Affiliation(s)
- Celia M Bisbach
- Biochemistry Department, University of Washington, Seattle, WA, USA
| | - Rachel A Hutto
- Biochemistry Department, University of Washington, Seattle, WA, USA
| | - Deepak Poria
- Department of Ophthalmology and Visual Sciences, Washington University School of Medicine, St. Louis, MO, USA
| | | | - Fatima Abbas
- Ophthalmology and Visual Sciences, University of Utah, Salt Lake City, UT, USA
| | - Frans Vinberg
- Ophthalmology and Visual Sciences, University of Utah, Salt Lake City, UT, USA
| | - Vladimir J Kefalov
- Department of Ophthalmology and Visual Sciences, Washington University School of Medicine, St. Louis, MO, USA
| | - James B Hurley
- Biochemistry Department, University of Washington, Seattle, WA, USA
- Ophthalmology Department, University of Washington, Seattle, WA, USA
| | - Susan E Brockerhoff
- Biochemistry Department, University of Washington, Seattle, WA, USA.
- Ophthalmology Department, University of Washington, Seattle, WA, USA.
| |
Collapse
|
2
|
Hutto RA, Bisbach CM, Abbas F, Brock DC, Cleghorn WM, Parker ED, Bauer BH, Ge W, Vinberg F, Hurley JB, Brockerhoff SE. Increasing Ca 2+ in photoreceptor mitochondria alters metabolites, accelerates photoresponse recovery, and reveals adaptations to mitochondrial stress. Cell Death Differ 2019; 27:1067-1085. [PMID: 31371786 PMCID: PMC7206026 DOI: 10.1038/s41418-019-0398-2] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2019] [Revised: 06/19/2019] [Accepted: 07/11/2019] [Indexed: 11/09/2022] Open
Abstract
Photoreceptors are specialized neurons that rely on Ca2+ to regulate phototransduction and neurotransmission. Photoreceptor dysfunction and degeneration occur when intracellular Ca2+ homeostasis is disrupted. Ca2+ homeostasis is maintained partly by mitochondrial Ca2+ uptake through the mitochondrial Ca2+ uniporter (MCU), which can influence cytosolic Ca2+ signals, stimulate energy production, and trigger apoptosis. Here we discovered that zebrafish cone photoreceptors express unusually low levels of MCU. We expected that this would be important to prevent mitochondrial Ca2+ overload and consequent cone degeneration. To test this hypothesis, we generated a cone-specific model of MCU overexpression. Surprisingly, we found that cones tolerate MCU overexpression, surviving elevated mitochondrial Ca2+ and disruptions to mitochondrial ultrastructure until late adulthood. We exploited the survival of MCU overexpressing cones to additionally demonstrate that mitochondrial Ca2+ uptake alters the distributions of citric acid cycle intermediates and accelerates recovery kinetics of the cone response to light. Cones adapt to mitochondrial Ca2+ stress by decreasing MICU3, an enhancer of MCU-mediated Ca2+ uptake, and selectively transporting damaged mitochondria away from the ellipsoid toward the synapse. Our findings demonstrate how mitochondrial Ca2+ can influence physiological and metabolic processes in cones and highlight the remarkable ability of cone photoreceptors to adapt to mitochondrial stress.
Collapse
Affiliation(s)
- Rachel A Hutto
- Biochemistry Department, University of Washington, Seattle, WA, 98109, USA
| | - Celia M Bisbach
- Biochemistry Department, University of Washington, Seattle, WA, 98109, USA
| | - Fatima Abbas
- John A. Moran Eye Center, University of Utah, Salt Lake City, UT, 84132, USA
| | - Daniel C Brock
- Biochemistry Department, University of Washington, Seattle, WA, 98109, USA
| | - Whitney M Cleghorn
- Biochemistry Department, University of Washington, Seattle, WA, 98109, USA
| | - Edward D Parker
- Opthalmology Department, University of Washington, Seattle, WA, 98109, USA
| | - Benjamin H Bauer
- Biochemistry Department, University of Washington, Seattle, WA, 98109, USA
| | - William Ge
- Biochemistry Department, University of Washington, Seattle, WA, 98109, USA
| | - Frans Vinberg
- John A. Moran Eye Center, University of Utah, Salt Lake City, UT, 84132, USA
| | - James B Hurley
- Biochemistry Department, University of Washington, Seattle, WA, 98109, USA.,Opthalmology Department, University of Washington, Seattle, WA, 98109, USA
| | - Susan E Brockerhoff
- Biochemistry Department, University of Washington, Seattle, WA, 98109, USA. .,Opthalmology Department, University of Washington, Seattle, WA, 98109, USA.
| |
Collapse
|