A longitudinal study followed human fibroblast cultures across repeated passages. Cells were grouped by initial telomere length (long vs short). Cultures with shorter starting telomeres reached irreversible growth arrest earlier and showed increased expression of a DNA damage response marker, while cultures with longer starting telomeres maintained proliferative capacity for more passages. No differences in nutrient conditions were reported.
Which outcome is expected concerning aging?
- Cells with shorter initial telomeres are expected to show only a brief, reversible pause in growth that resolves within hours of passaging.
- Cells with shorter initial telomeres are expected to avoid senescence longer because telomere loss signals continued proliferation.
- Cells with shorter initial telomeres are expected to die primarily by necrosis, since telomere shortening causes immediate membrane rupture.
- Cells with shorter initial telomeres are expected to enter senescence sooner, consistent with telomere shortening contributing to replicative aging. (correct answer)
Explanation: This question tests understanding of telomere shortening as a mechanism of replicative aging. Telomeres are protective DNA-protein structures at chromosome ends that shorten with each cell division, eventually triggering senescence when critically short. The vignette shows cells with shorter initial telomeres reaching growth arrest earlier and showing DNA damage responses, while longer telomeres allow more passages before senescence. Answer D correctly identifies that shorter initial telomeres lead to earlier senescence, consistent with telomere shortening driving replicative aging. Answer B incorrectly suggests telomere loss signals continued proliferation, when critically short telomeres actually trigger growth arrest through DNA damage checkpoints. When analyzing cellular aging, remember the telomere clock: starting length determines replicative lifespan, with senescence occurring when telomeres reach a critical minimum length.