Cell Aging and Organelle Functions

Study Notes

Aging is a biological process causing a decline in physical function due to accumulated cellular damage.
Cell cultures show changes in cell appearance as they age.
Cellular function and fate are influenced by neighboring cells and signaling molecules.

Endoplasmic Reticulum (ER): Responsible for protein synthesis and folding, as well as membrane production.
During aging, the ER loses its oxidative power, leading to faulty protein maturation (unfolded/misfolded proteins).
ER homeostasis (balance of synthesis and breakdown of proteins) is disrupted during aging. ER stress results from an excess of unfolded/misfolded proteins.
Factors contributing to ER stress can include genetic or environmental factors.

Lysosomes are important for cellular recycling by digesting waste materials.
Autophagy is a recycling process where the ER isolates "garbage" into a bubble (autophagosome), which then fuses with a lysosome for degradation.
Impaired lysosome function leads to the accumulation of faulty proteins, resulting in age-related neurodegenerative disorders like Alzheimer's and Parkinson's disease.
Caloric restriction and Rapamycin treatment can maintain lysosome function.

Mitochondria are responsible for energy production via the conversion of oxygen and nutrients to ATP.
Mitochondrial DNA (mtDNA) inherited maternally, is less protected from damage compared to nuclear DNA.
Aging is associated with damage to mitochondria, causing mtDNA mutations, defective proteins, and increased free radical production which can worsen aging.

Senescence is a process where cells stop dividing due to stress in order to avoid damage and abnormal cell growth.
Tumor suppressor proteins (p16, p53, p21) initiate the process to give time for DNA repair.
Senescent cells produce the SASP which has both beneficial and detrimental actions. Healthy signaling allows cells to stop dividing once the cellular damage exceeds the threshold.
Chronic senescent cell accumulation can lead to diseases and a decreased lifespan.

The immune system has two major components: innate and adaptive.
Innate immunity involves physical barriers and non-specialized cells, while adaptive immunity includes specialized cells (B and T cells).
Aging affects both. Innate immune system shows decreased cell function.
Adaptive immune system shows a decline in naïve T-cell and B-cell numbers, increased memory cells, reduced diversity of T-cell receptors and shrinkage of the thymus.
Reduced immune function with age raises vulnerability to infections, and hinders vaccine efficacy.
CMV (cytomegalovirus) has a chronic effect on the immune system with aging, which leads to reduced immune function.

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