DEV30322 L19 PDF: Stem Cell Ageing and Strategies for Rejuvenation

🥽 Lecture 19: Stem Cell Ageing and Strategies for Rejuvenation Describe key changes that arise in tissues with age Our population is ageing Age is associated with a decline in maintenance and regeneration of many...

🥽 Lecture 19: Stem Cell Ageing and Strategies for Rejuvenation Describe key changes that arise in tissues with age Our population is ageing Age is associated with a decline in maintenance and regeneration of many tissues. Some key changes are: Vital Organ Decline: Lecture 19: Stem Cell Ageing and Strategies for Rejuvenation 1  Nearly all vital organs lose function with age. Example: Cardiac failure is a major age-related cause of death. Susceptibility to Diseases: Increased risk of cancer with age. Higher incidence of chronic diseases such as diabetes. Changes in Tissue Properties: Stiffness: Some connective tissues become loose (e.g., skin). Other tissues develop stiffness and fibrosis. Reduced Repair Capacity: Slower wound healing. Delayed repair of GI tract infections and other tissues. Loss of Tissue Mass: Example: Muscle mass decreases with age. Physical Changes: Wrinkles, spots, gray hair. Weight gain. Increased inflammation. As we age stem cells in many tissues decline and accumulate mutations. Changes in stem cells with age: Lecture 19: Stem Cell Ageing and Strategies for Rejuvenation 2  Stem Cell Numbers: Decline in Some Tissues: Reduction in the number of stem cells. Increase in Other Tissues: Increase in stem cell numbers, but with reduced functionality. Functional Decline: Decreased functionality of individual stem cells. Reduced number of functional stem cells overall. Accumulation of Mutations: Stem cells accumulate mutations with age, impacting their function. Stem cell activity varies across life stages, with a natural decline as we move past reproductive years. Lecture 19: Stem Cell Ageing and Strategies for Rejuvenation 3  Development and Growth Phase: High stem cell activity. Purpose: Growth and development of organs and tissues into adulthood. Reproductive Years: Intermediate stem cell activity. Purpose: Maintenance of tissues without significant expansion. Protected Aging Phase: Decline in stem cell activity. Evolutionary Perspective: Post-reproductive age. Less evolutionary pressure to maintain active stem cells. Contributes to tissue degeneration with age. Explain how stem cell dynamics and diversity change with age. Lecture 19: Stem Cell Ageing and Strategies for Rejuvenation 4  Aging leads to reduced stem cell diversity and changes in their functionality, impacting tissue maintenance and repair. Examples of stem cell changes: Blood (Hematopoietic Stem Cells): Youth: Around 1,000 active hematopoietic stem cells. High diversity, represented by different colors. Aging: Diversity collapses. Dominance of certain clones, shown by predominance of red-colored cells. Skin: Youth: Many active stem cells. Each has its domain contributing to skin production. Aging: Expansion of certain clones occupying large areas. Lecture 19: Stem Cell Ageing and Strategies for Rejuvenation 5  Collapse of others, leading to reduced diversity. List key extrinsic and intrinsic factors that change in stem cells with age Mechanisms underlying functional deterioration of stem cells with age: Stem Cell Intrinsic Mechanisms DNA Damage and Telomere Shortening: Accumulation of DNA damage. Telomere shortening leads to cellular senescence. Mitochondrial Dysfunction: Reduced mitochondrial efficiency with age. Epigenetic Alterations: Age-associated changes in epigenetic markers. Changes in Metabolism: Alterations in cellular metabolic processes as stem cells age. Stem Cell Extrinsic Mechanisms Systemic or Circulatory Factors: Influences from the circulatory system impact stem cell behavior. Local Niche Microenvironment Growth Signals: Growth factors or signals from adjacent cells regulate stem cell activity. Stiffness of Tissue Extracellular Matrix: Increased tissue stiffness and fibrosis with age alter stem cell behavior. Lecture 19: Stem Cell Ageing and Strategies for Rejuvenation 6  Describe experimental protocols that can test whether niche microenvironment or systemic factors can promote age-related changes Testing Niche Microenvironment Influence - using TRANSPLANTATION experiment Young Stem Cells in Different Environments: Procedure: Transplant stem cells (mammary, intestinal, hematopoietic) from a young mouse into both a young and an old mouse. Observation: If stem cell function declines in the old mouse, it indicates the aging phenotype is driven by signals from the microenvironment. Old Stem Cells in Different Environments: Procedure: Transplant dysfunctional stem cells from an old mouse into both a young and an old mouse. Observation: If the phenotype is rescued in the young mouse, it confirms the microenvironment's role in influencing the aging phenotype. Testing Systemic Effects - using PARABOSIS experiment Lecture 19: Stem Cell Ageing and Strategies for Rejuvenation 7  Procedure: Link the blood supply of two animals to share systemic factors. Young-Young or Old-Old Pairing: Control scenarios. Young-Old Pairing: Experimental scenario to examine systemic influence. Observation: If young systemic factors improve the aging phenotype in the old mouse, it indicates systemic factors' importance. If old systemic factors negatively impact the young mouse, it shows systemic aging influence. Conclusion Based on Experimental Results - No Environmental Effect? If there is no phenotype modification, the aging phenotype is likely due to intrinsic, non-reversible changes in the stem cells. Describe the effects of age on spermatogonial stem cells, muscle and liver Spermatogonial stem cell function with age is largely influenced by changes in the niche. As age increases, the number of functional spermatogonial stem cells in the testes declines significantly. Experiment: Spermatogonial stem cells from different ages were transplanted into a young testis environment. Key Finding: Even old spermatogonial stem cells had a degree of function rescued when transplanted into a young niche. Lecture 19: Stem Cell Ageing and Strategies for Rejuvenation 8  Conclusion: The decline in stem cell function with age is primarily controlled by changes in the niche or microenvironment within the testes, not by intrinsic changes in the stem cells themselves. Can systemic factors alter the ageing phenotype? → Parabiosis experiments show that systemic factors from young animals can rejuvenate stem cell function and tissue regeneration in old mice, suggesting that circulating factors play a significant role in aging. Overview of the Experiment: Parabiosis surgery was used to join the circulatory systems of a young and old mouse. The goal was to investigate whether systemic factors from one animal could influence stem cell function in the other. Key Findings in Various Tissues: 1. Muscle Regeneration: Young Mouse: Effective muscle regeneration after injury. Old Mouse: Poor muscle regeneration after injury. Young-Old Parabiosis: The old mouse's muscle regeneration capacity was restored, indicating systemic rejuvenation factors from the young animal. 2. Delta-Notch Pathway: Involved in muscle regeneration and potentially modulated by systemic factors circulating between the young and old mice. 3. Hepatocyte Proliferation: Lecture 19: Stem Cell Ageing and Strategies for Rejuvenation 9  Old Mice: Hepatocyte proliferation is downregulated. Young Mice: Hepatocytes can proliferate in response to injury. Young-Old Parabiosis: The complex CEBP-Brahma (a transcriptional repressor) is downregulated in both the young and old animals, affecting hepatocyte proliferation. Liver regeneration was due to a decrease in the inhibitory cEBP α Brm complex 4. Neurogenesis and Angiogenesis: Old Mice: Reduced rates of neurogenesis and angiogenesis. Young-Old Parabiosis: The experiment led to observable changes in both neurogenesis and angiogenesis rates in the old mouse. Lecture 19: Stem Cell Ageing and Strategies for Rejuvenation 10  Name a systemic growth factor that can promote a “youthful” phenotype Factors Promoting Aging Reversal GDF-11 (Growth Differentiation Factor 11): Present in the circulation of young animals. When supplied to old mice, GDF-11 promotes: Increased muscle function Enhanced tissue regeneration Conclusion: GDF-11 is one example of a factor that may have rejuvenating effects on aging tissues. Factors Promoting Aging CCL-11: Upregulated in the circulation of old mice. When applied to young mice, it leads to: Decreased muscle function Reduced tissue regeneration Conclusion: CCL-11 is an example of a factor that promotes aging by inhibiting muscle function and tissue repair. Lecture 19: Stem Cell Ageing and Strategies for Rejuvenation 11  Stem cell intrinsic defects that accumulate with age Key Intrinsic Changes in Aging Cells 1. Proteasome System Breakdown: The ubiquitin-proteasome system, responsible for degrading proteins, becomes less active with age. Result: Accumulation of toxic protein aggregates within cells. 2. Unfolded Protein Response (UPR) Downregulation: The ability to manage misfolded proteins is reduced, which can contribute to cellular stress. 3. Mitochondrial Damage: Mitochondria show reduced function with age, often accompanied by mutations in mitochondrial DNA. Mitochondria are less effective in generating energy, leading to reduced cellular function. Consequences of These Intrinsic Changes 1. Altered Metabolism: Mitochondrial damage shifts the cell's metabolism from oxidative phosphorylation to glycolysis. This metabolic shift affects the production of epigenetic molecules, resulting in epigenetic alterations in the genome. 2. Increased Reactive Oxygen Species (ROS): Protein aggregates and mitochondrial damage lead to increased ROS production. ROS contribute to: DNA damage Increased mutation rates Lecture 19: Stem Cell Ageing and Strategies for Rejuvenation 12  Cell death Disruption of cell function Hematopoietic Stem Cells (HSCs) Diversity Decline: As we age, the diversity of hematopoietic stem cells decreases. Some dominant clones emerge, leading to less diversity in the stem cell population. Decline in Function: The number of active functional stem cells decreases. Skewed Differentiation: There's an increased production of myeloid cells compared to lymphoid cells. Altered Niche Signals: Changes in Wnt signaling, chemotactic signals, and other signals in the hematopoietic stem cell niche contribute to age-related changes. Muscle Stem Cells (Satellite Cells) Decline in Number: Unlike HSCs, muscle stem cells (satellite cells) decrease in number with age. Decreased Function: There is a general decline in function of muscle stem cells with age. Skewed Differentiation: Muscle stem cells shift more toward a fibroblast-like lineage rather than muscle regeneration. Fibrosis: Lecture 19: Stem Cell Ageing and Strategies for Rejuvenation 13  This skewed differentiation contributes to the development of fibrosis in aging muscle tissue. Outline the changes that occur in intestinal stem cells with age and experiments that demonstrate this + Describe changes in metabolism with ageing Experimental Approach Young vs. Old Mice: Young mice: 2 months of age Old mice: 22 months of age Techniques Used: 1. Histology: Examined tissue morphology (e.g., crypt length, villi length). 2. Recovery After Induced Injury: Used chemotherapy drug (5-FU) to assess tissue recovery by measuring the number of proliferating cells over a time course. 3. Molecular Profiling: Analyzed molecular changes in the tissue. 4. Metabolic Profiling: Examined metabolic alterations with aging. 5. Functional Organoid-Based Assays: Assessed stem cell function by measuring how efficiently stem cells from young versus old mice could form organoids in vitro. Findings Morphological Changes: Crypt Length: Slight increase in crypt length in older mice. Villi Length: Reduction in the number of cells per villus. Lecture 19: Stem Cell Ageing and Strategies for Rejuvenation 14  Injury Recovery: Proliferation After Injury: Older mice showed slower recovery compared to young mice. Time course recovery was slower, although older mice eventually caught up. Stem Cell Function: Organoid Formation: Stem cells from old mice were significantly less efficient at forming organoids compared to those from young mice. Direct measurement showed decline in stem cell function with age. Lecture 19: Stem Cell Ageing and Strategies for Rejuvenation 15  The decline in intestinal stem cell function with age is partly driven by reduced Wnt signaling and metabolic changes. Experimental Approach: Stem Cell Isolation: Tissue Digestion: Isolated cells from the intestinal crypts. Crypt Structure: Green Cells: Represent stem cells located at the base of the crypt. Paneth Cells: Niche cells surrounding stem cells in the crypt. Key Findings: 1. Reduced Wnt Signaling: Old stem cells showed reduced Wnt signaling, a key pathway involved in stem cell maintenance and function. 2. Changes in Metabolism: Metabolic changes were also observed in the old stem cells. Testing Causality: Wnt Experiment: Compared stem cells from young and old mice by adding increasing amounts of Wnt. Lecture 19: Stem Cell Ageing and Strategies for Rejuvenation 16  Results: Adding Wnt partially rescued stem cell function in old cells, though full restoration was not achieved. This indicates that Wnt signaling is a key pathway disrupted in aging, but additional factors beyond Wnt are necessary to fully restore function. Explain the effects of caloric restriction Caloric Restriction can reduce the effects of ageing Calorie Restriction and Lifespan Calorie restriction has been shown to increase lifespan in various model organisms, including rats. Rats on a restricted diet show decreased weight and increased lifespan compared to those on a normal diet. Effects on Senescence Calorie-restricted rats exhibit reduced markers of senescence, suggesting the diet may reduce aging-related damage. Study Design and Methods The study used single-cell sorting and single-cell transcriptional analysis to analyze tissue composition in rats. Computational algorithms were used to interpret transcriptional data and predict underlying mechanisms. Lecture 19: Stem Cell Ageing and Strategies for Rejuvenation 17  Findings: Impact of Calorie Restriction Inflammation and Immune Cells: Inflammation and the presence of immune cells increase with age in many tissues. Calorie restriction reversed this phenotype. Cell Communication: Age-related decline in cell-to-cell communication was observed, and calorie restriction helped to restore this function. Conclusions Calorie restriction can alleviate aging by reducing inflammation and restoring cellular communication. The study suggests that calorie restriction reverses transcriptional changes related to gene expression and communication between cells. Further research is needed to fully understand how calorie restriction affects stem cells and aging processes. Implications for Aging Research To combat aging, a multi-pronged approach may be necessary, targeting both intrinsic and extrinsic factors of aging. Calorie restriction presents a promising area of future research in understanding and potentially mitigating aging. Outline potential therapeutic strategies to reverse ageing. Lecture 19: Stem Cell Ageing and Strategies for Rejuvenation 18  Strategies to Reverse or Reduce Aging: Modulating Metabolism and stem cell function with NAD precursors can rejuvenate ageing phenotypes Mitochondrial Dysfunction with Age Mitochondria become less functional, resulting in decreased ATP production. Increased NADH substrates are observed in aged tissues. NAD Supplementation Nicotinamide adenine dinucleotide (NAD) is a key substrate for mitochondrial enzymes. NAD supplementation has been shown to boost mitochondrial function and enhance tissue repair. Impact on Aging Tissues Studies show that NAD supplementation can reverse tissue degeneration and improve tissue repair, particularly in skeletal muscle. Potential for Rejuvenation Targeting metabolic pathways, especially those related to mitochondrial function, is a promising approach for rejuvenating aged tissues and reducing aging effects. Lecture 19: Stem Cell Ageing and Strategies for Rejuvenation 19