Collaborate 2 Cure
July 24, 2017

KU Clinical Research: Fairway Auditorium
4350 Shawnee Mission Parkway  Fairway, KS 66205

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SIRT3 Deacetylates Mitochondrial Trifunctional Protein and Rescues Nonalcoholic Fatty Liver Disease in Mice

Non-alcoholic fatty liver disease (NAFLD) is a leading cause of chronic liver diseases. Mitochondrial dysfunction plays an important role in the development of NAFLD but little is known about the underlying mechanisms. We used a murine model for mitochondrial dysfunction, utilizing mice heterozygous for the mitochondrial trifunctional protein (MTP+/-), to investigate key mechanisms involved in mitochondrial dysfunction associated NAFLD. MTP is an enzymatic complex that catalyzes the last three steps in the β-oxidation of long-chain fatty acids. We have previously shown that aging MTP+/- mice exhibit impaired mitochondrial function and increased hepatic steatosis. In our recent studies, we show that high fat diet (HFD) accelerates NAFLD in young MTP+/- mice. We also show that compared to WT counterparts, MTP+/- mice display reduced hepatic sirtuin 3 (SIRT3) levels concomitant with reduced mitochondrial fatty acid oxidation (FAO). Hepatic overexpression of SIRT3 rescues the phenotype in MTP+/- mice and restores measures of mitochondrial FAO.  We demonstrate that MTP is highly acetylated in the MTP+/- mice, and that hepatic overexpression of SIRT3 deacetylates MTP.

Speaker- Jamal Ibdah, MD, PhD

Dr. Ibdah received his MD degree from the University of Jordan and a PhD degree in Biochemistry from the Medical College of Pennsylvania followed by postdoctoral research training. Dr. Ibdah completed a 3-year clinical residency in Internal Medicine at Wake Forest University School of Medicine and a 3-year combined clinical fellowship training in adult Gastroenterology at Washington University School of Medicine and research fellowship training in the Department of Pediatrics at Saint Louis Children’s Hospital.

Dr. Ibdah is currently a Professor of Internal Medicine, Medical Pharmacology and Physiology, and Raymond E. and Vaona H. Peck Endowed Research Chair, Director of the Division of Gastroenterology and Hepatology, and Director of the Missouri Digestive Health Center at the University of Missouri-Columbia as. In addition, Dr. Ibdah was appointed in 2006 as Senior Associate Dean for Research, and in 2007 as the founding Director of the MU Institute for Clinical and Translational Science, which he held till late 2015.

His current studies are focused on understanding the role of mitochondria in nonalcoholic fatty liver disease.

Sperm Mitophagy During Fertilization: The Tale of Mitochondrial Eve and Steve

Maternal inheritance of mitochondria and their genes is a developmental paradigm known by the moniker Mitochondrial Eve. Mammalian sperm-borne mitochondria are selectively degraded inside the fertilized oocyte. Due to such a post-fertilization degradation of sperm mitochondria, referred to as sperm mitophagy, the propagation of the paternal, sperm contributed mitochondrial genes, resulting in heteroplasmy, is seldom observed in mammals. Our early observations established that post-fertilization degradation of sperm mitochondria is mediated by ubiquitin-proteasome system (UPS), the major protein-turnover pathway that degrades proteins one molecule at a time. However, it was not clear how a single-molecule proteolytic pathway such as the UPC could degrade dozens of whole sperm mitochondria inside a fertilized oocyte (Sutovsky et al. 1999. Nature 25:371-2). More recently, our and others’ studies provide evidence that a whole organelle sperm mitochondrion degradation is contributed by autophagic pathway, a mechanism now referred to as sperm mitophagy and thought to be mediated by the interplay between the UPS and the autophagic pathway (Song et al., Proc. Natl. Acad. Sci USA 2016; 113(36):E5261-70.). The objectives of our research are to i) identify UPS determinants present in porcine sperm mitochondria, and ii) to characterize the UPS-controlled porcine ooplasmic autophagy receptors that may regulate sperm mitophagy after fertilization.

We determined that the ooplasmic, ubiquitin-binding autophagy receptor SQSTM1 binds to ubiquitinated mitochondrial sperm membrane proteins, targeting whole sperm mitochondria towards autophagosome. Concurrently, protein dislocase VCP extracts ubiquitinated sperm mitochondrial membrane proteins and transport them to the 26S proteasome. Ooplasmic, autophagophore-associated GABARAP protein is also involved in zygotic autophagosome formation, although it may not be essential. We also attempted to prevent sperm mitophagy and create heteroplasmic early porcine zygotes/embryos. While the sperm mitochondria were degraded completely prior to first cleavage of control zygotes, intact mitochondrial sheaths were detected in 2-4 cell embryos that were pre-injected with anti-SQSTM1 antibodies prior to fertilization and then treated with a specific VCP inhibitor during early stages of zygotic development. Based on such finding, we reconstituted the early steps of porcine sperm mitophagy in a cell-free system consisting of permeabilized boar spermatozoa co-incubated with porcine oocyte extracts. We found that SQSTM1 form oocyte extracts became detectable in the midpiece/ mitochondrial sheaths of the sperm tail after co-incubation, a translocation prevented by the infusion of anti-SQSTM1 antibody in the extract. VCP was prominent in the sperm mitochondrial sheath both before and after extract co-incubation. Such patterns are consistent with our observation of SQSTM1 and VCP associating with sperm mitochondria inside the porcine zygote. Collectively, these studies offer insight into the mechanisms guiding sperm mitochondrion recognition and disposal after fertilization, which assure normal preimplantation development and prevent a potentially detrimental effect of heteroplasmy. Better understanding of sperm mitophagy is relevant for the calibration of evolutionary clocks, safeguarding of human assisted reproductive therapies, and the optimization of reproductive performance and production traits in livestock species.

Supported by Agriculture and Food Research Initiative Competitive Grant no. 2013-67015-20961 from the USDA National Institute of Food and Agriculture and by seed funding from the MU F21C Program.

Speaker: Peter Sutovsky, PhD, Dr.h.c.

Peter Sutovsky is Professor of Animal Science in the College of Agriculture, Food and Natural Resources, University of Missouri, also appointed as Professor of Obstetrics, Gynecology and Women’s Health at the School of Medicine, University of Missouri Health System. Since the early 90’s, Peter has studied mammalian gametogenesis, fertilization, and pre-implantation embryonic development with special emphasis on the gamete and zygotic ubiquitin-proteasome system (UPS). He was the first to describe the role of UPS in the regulation of mitochondrial inheritance and introduced a novel concept of extracellular UPS, which has been validated in reproduction and outside the reproductive biology field. In particular, Peter demonstrated the importance of sperm borne proteasomes for mammalian fertilization and the role of UPS in epididymal sperm quality control, a mechanism relevant to male fertility evaluation in livestock, and the diagnosis and treatment of human male fertility. Peter’s collaborative research on the biogenesis and post-fertilization processing of sperm head perinuclear theca influenced the optimization and safeguarding of assisted reproductive technologies/therapies such as in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI). Other notable collaborations include the development of transgenic pig model for the study of 26S proteasome and work on rodent model of human endometriosis. Recently, the Sutovsky laboratory has also been focusing on biomarker-based flow cytometric semen analysis and semen nanopurification aimed at improving conception rates in livestock artificial insemination (AI).