Gerald Shadel, Departments of Pathology and Genetics gerald.shadel@yale.edu ~1,200 proteins metabolic crossroads apoptosis signaling disease aging 1

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Mitochondrial Antiviral Signaling Mitochondria are centralized hubs for innate antiviral signaling and type I interferon production MAVS Mitochondrial Antiviral Signaling aka, IPS1 CARDIF VISA 4

anterograde signaling Nuclear-Mitochondrial Signaling anterograde signaling retrograde signaling 5

mitochondrial OXPHOS system - ROS O2 H2O2 OH DNA/RNA genetic mutation DISEASE AGING lipids oxidative damage membrane dysfunction proteins enzyme/signaling defects 6 Copyright 2001 Benjamin Cummings, an imprint of Addison Wesley Longman, Inc.

Mitochondrial Stress Signaling Pathways 7

Reactive oxygen species signaling stimulus sensor outcome Insulin signaling PPARγ mitochondria function Starvation AMPK apoptosis TORC1 HIF1 redox homeostasis Hypoxia NF-κB immunity TLR JNK1 stress resistance PGC-1α UCP2 p53 genomic stability 8

mitochondrial OXPHOS system 13 OXPHOS mRNAs 22 tRNAs mitochondrial OXPHOS system 2 rRNAs (12S and 16S) ROS mitochondrial ribosome ATP ROS ATP mtDNA 9

dual genetic origin of the OXPHOS system Schon, DiMauro and Hirano 2012 Nat Rev Genet 10

Inherited pathogenic mtDNA mutations ~300 identified so far affect every gene, but >50% in tRNA genes “common” deletion 11

Deafness www.mda.org 12

mtDNA exists usually at thousands of copies /cell and packaged into nucleoids 13

complexities of mitochondrial disease due to mtDNA heteroplasmy vs. homoplasmy mitotic segregation/genetic drift maternal bottleneck threshold effects complex genotype versus phenotype relationships 14

15 http://www.nimr.mrc.ac.uk/research/antonella-spinazzola/segregation-selection-and-epigenetic-control-of-mitochondrial-dna-variants

Mitotic segregation can lead to mtDNA genetic drift during gametogenesis, embryogenesis or in adult dividing cell populations cell division normal/asymptomatic respiration Threshold effect Some cell/tissue types may drift toward homoplasmy 16

maternal bottleneck 17 Yabuuchi et al. 2011 BBA 1820:637

maternal bottleneck Primordial Germ Cells 18 Mitochondrial research society website

19 small number of templates in PGCs are used for amplification to generate oocytes There are also proposed mechanisms of purifying selection to eliminate most deleterious mutations 19

What about natural variation “normal” levels of heteroplasmy? and “normal” levels of heteroplasmy? 20

21 some haplotypes have been linked to metabolic alterations and disease predisposition 21

22 oxidative damage, certain environmental exposures and mtDNA replication errors can cause somatic mtDNA mutations in normal individuals and as a function of age sporadic mutations (i.e. not in mother) can also occur during germline development or embryogenesis these can clonally expand in tissues and there are unique tissue-specific mechanisms at play that are not well understood (e.g. deletions in muscle) 22

homoplasmic mtDNA mutations in tumors 23

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What about carry over of small amounts of mutant mtDNA from original carrier mother? 25

Keys Points Mitochondria are multi-functional and tailored to meet the needs of specific cell types/tissues and can contribute to disease pathology by a variety of mechanisms in addition to defective energy metabolism mtDNA is maternally inherited and present usually at thousands of copies/cell which allows for natural and inherited heteroplasmic (i.e. mixed) states to exist The degree of heteroplasmy can drift dramatically during somatic cell division, germ cell development, embryogenesis, under disease states, and aging A high threshold for inherited pathogenic mtDNA mutations exists, thus small amounts of mutated mtDNA carried over during nuclear transfer may not be a major concern However, it remains unclear what effects might occur from mixed haplotypes or inherited pathogenic mutations interfacing with other heteroplasmic mutations simultaneously inherited or acquired with age 26