Pathophysiology of age-related processes, aging, longevity, senescence, death Petr Müller Pathophysiology – lectures What is ageing? • Is ageing a disease? • Which diasases are associated with ageing? Mechanisms of ageing • Regulation of aging at different levels of the human body organization • Ageing of DNA • Methylation • Telomeres • Metabolism and ageing • Cellular senescence • Organ ageing Evolutionary mechanisms of ageing • Genetics of ageing Can we treat/ slow down ageing • Experiments on model organisms • Implications for healthy ageing Pathophysiology – lectures Is ageing a disease ? Aging is the sequential or progressive change in an organism that leads to an increased risk of debility, disease, and death. Programmed lifespan Encoded in our genome Ageing associated diseases Gompertz–Makeham law of mortality The Gompertz–Makeham law states that the human death rate is the sum of an agedependent component (the Gompertz function, named after Benjamin Gompertz), which increases exponentially with age and an age-independent component (the Makeham term, named after William Makeham). Estimated probability of a person dying at each age, for the U.S. in 2003. Mortality rates increase exponentially with age after age 30. Probability of death age- independent component Cardiovascular system • Hypertension • Atherosclerosis • Stroke, MI CNS • Dementia • Neurodegenerative diseases Musculoskeletal system • Arthritis • Muscle weakness Cancer Metabolism • Decreased basal metabolism • Obesity • Diabetes mellitus type 2 DNA damage theory of aging Hayflick limit he typical normal human fetal cell will divide between 50 and 70 times before experiencing senescence. Telomere shortening and cellular senescence Telomerase hTERT and cell immortalization Progeria Hutchinson-Gilford syndrome • Autosomal dominant disease • Mutation in Lamin A • Altered histone modifications a and chromatin structure • Genomic instability Other DNA damage related premature ageing: • Werner syndrome • Cockayne syndrome Human tissues are composed of differentiated cells The daughter cells inherit the basic properties from parental cells All cells of the body retain complete genetic information that remains unchanged throughout life. DifferentiationAgeing and epigenetics Epigenetics is the study of heritable phenotype changes that do not involve alterations in the DNA sequence. Epigenetics most often involves changes that affect gene activity and expression, but the term can also be used to describe any heritable phenotypic change. Mechanisms: • Covalent modifications • RNA transcripts • MicroRNAs • mRNA • sRNAs • Prions • Structural inheritance • Nucleosome positioning • Histone variants • Genomic architecture Epigenetics definitions and mechanisms • process by which methyl groups are added to the DNA molecule. • Methylation can change the activity of a DNA segment without changing the sequence CpG islands are usually defined as regions with: 1) a length greater than 200bp, 2) a G+C content greater than 50%, 3) a ratio of observed to expected CpG greater than 0.6, In mammals however, DNA methylation is almost exclusively found in CpG dinucleotides, with the cytosines on both strands being usually methylated. DNA methylation DNA methyltransferases (in mammals) 1. maintenance methylation (Maintenance methylation activity is necessary to preserve DNA methylation after every cellular DNA replication cycle). 2. de novo methylation DNMT1 - maintanance DNMT3a and DNMT3b - the de novo methyltransferases that set up DNA methylation patterns Model of DNMT3A activity. The DNMT3A protein complex is associated at promoters of silent genes in a complex with histone methyltransferase (HMT), histone deacetylase (HDAC) and DNA methyltransferase 3L (DNMT3L). These promoters are marked by DNA methylation, histone deacetylation and histone 3 lysine 9 methylation (K9me3). DNA demethylation • TET enzymes are a family of ten-eleven translocation (TET) methylcytosine dioxygenases. • They are instrumental in DNA demethylation. Oxoguanine glycosylase (OGG1) recruits TET enzyme The implications of IDH mutations for cancer development and therapy Nature Reviews Clinical Oncology volume 18, pages645–661 (2021) Detection of methylation McrBC is an endonuclease which cleaves DNA containing methylcytosine* on one or both strands 1) Using methylation sensitive restriction endonucleases 2) Using bisulfite conversion Outline of the chemical reaction that underlies the bisulfite-catalyzed conversion of cytosine to uracil. Chronological age (y-axis) versus DNAm age (x-axis) across different cells and tissues In humans and other mammals, DNA methylation levels can be used to accurately estimate the age of tissues and cell types, forming an accurate epigenetic clock Methylation and aging Horvath's clock Epigenetic clock Genomic instability „Spontaneous“ mutations (aging and inflamation) CpG island Exogenous mutagens • Smoking • UV light • Alkylating agents • aflatoxin Mutation pattern Mutational signatures Ageing methylation and cancer Mutational signature associated with ageing • Ectopic expression of Oct4 (also known as Pou5f1), Sox2 and Klf4 genes (OSK) in mouse retinal ganglion cells restores youthful DNA methylation patterns and transcriptomes, promotes axon regeneration after injury, and reverses vision loss in a mouse model of glaucoma and in aged mice. • The beneficial effects of OSK-induced reprogramming in axon regeneration and vision require the DNA demethylases TET1 and TET2. Changes to DNA methylation patterns over time form the basis of ageing clocks, but whether older individuals retain the information needed to restore these patterns—and, if so, whether this could improve tissue function—is not known. Chromatine remodelation to DNA methylation Entropy Hydratation Folding is entropy driven process Autophagy Ubiquitin proteasome system Chaperones Protein homeostasis / proteostasis Sensors of proteotoxic stress HSF1 HSF2 Heat shock factors Stress UPR “Unfolded Protein Response” Increased temperature Oxidative stress Metabolic stress PERK kinase ATF6 ATF6 XBP1 NUCLEUS ER Endoplasmic Reticulum Mutations and genomic instability IRE1a Mitochondria KEAP1 NRF2 NRF2 NRF2 GolgiATF6 Oxidativestress A Homozygous Splice Mutation in the HSF4 Gene Is Associated with an Autosomal Recessive Congenital Cataract Congenital Cataract in Australian Shepard Mutation in HSF4 leads to decreased expression of crystalline genes in the lens, resulting in congenital cataracts Crystalline alpha/beta (CRYAB, CRYAA) HSF4 Alzheimer's disease. APOE4 is the strongest risk factor gene for Alzheimer's disease The evolution of prolonged life after reproduction primitive indigenous people orcas prolonged post-reproductive lifespans (PRLSs) A model of the phylogeny of H. sapiens over the last 600,000 years (vertical axis). Cooperation and cultural evolution allowed the expansion of Homo sapiens species Higher genetic diversity cohabitation of non-relatives cooperation A timeline of evolutionary events → A timeline patterns of human disease risk → Slaves to wheat: How a grain domesticated us Unlike animals, the survival of humans is currently much less determined by their genetic information. Much more important to human evolutionary fitness has become information obtained non-genetically Neolithic revolution, cooperation and cultural evolution Cultural evolution is the idea that human cultural change––that is, changes in socially transmitted beliefs, knowledge, customs, skills, attitudes, languages, and so on––can be described as a Darwinian evolutionary process Mechanisms of evolutionary adaptations in different animal species The traits related to common human diseases • Cancer • Ageing • Pathogen/infection resistance Cancer and Peto's paradox • the incidence of cancer does not appear to correlate with the number of cells in an organism • In order to build larger and longer-lived bodies, organisms required greater cancer suppression. Evolutionary „trade off“: Body size vs. risk of cancer Mice altered to express "always-on" active TP53 exhibited increased tumor suppression ability, but also showed signs of premature aging. (TP53 cannot be the only explanation) NATURE : 26 September 2012 Skin shedding and tissue regeneration in African spiny mice (Acomys) • Scar-less regeneration • Role of macrophage M1