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Polyphosphoinositide metabolism in aging human erythrocytes
Canadian Journal of Biochemistry and Cell Biology = Revue Canadienne De Biochimie Et Biologie Cellulaire
|September 1, 1985
Summary
Erythrocyte polyphosphoinositide metabolism remains largely intact with age. While membrane phosphoinositide phosphatase activity slightly declines, key synthesis and breakdown pathways are preserved in aging red blood cells.
Area of Science:
- Biochemistry
- Cell Biology
- Gerontology
Background:
- Human erythrocytes (red blood cells) undergo aging processes that can affect cellular functions.
- Polyphosphoinositides are crucial membrane lipids involved in various cellular signaling pathways.
- Understanding age-related changes in erythrocyte lipid metabolism is important for comprehending red blood cell senescence.
Purpose of the Study:
- To investigate age-dependent changes in the metabolism of polyphosphoinositides in human erythrocytes.
- To compare the synthesis and degradation capacities of polyphosphoinositides in young versus old erythrocytes.
Main Methods:
- Human erythrocytes were fractionated by density gradient centrifugation to isolate young and old cells.
- Polyphosphoinositide synthesis was measured by [gamma-32P]ATP incorporation into specific phosphoinositides (PtdIns4P, PtdIns(4,5)P2).
- Enzyme activities of phosphoinositide kinases and phosphatases, as well as a Ca2+-dependent phosphodiesterase, were assayed in isolated membranes and cytosol.
Main Results:
- No significant age-dependent changes were observed in the synthesis of PtdIns4P and PtdIns(4,5)P2.
- Activities of PtdIns and PtdIns4P kinases, and cytosolic PtdIns(4,5)P2 phosphatase, remained unaffected by erythrocyte age.
- A slight decline (12%) in membrane cation-independent PtdIns4P phosphatase activity was noted in old cells.
- Ca2+-dependent polyphosphoinositide phosphodiesterase activity significantly decreased (57%) in old erythrocytes, correlating with cell age markers.
Conclusions:
- The capacity for interconversion of phosphoinositides within the erythrocyte membrane is maintained throughout the cell's lifespan.
- Despite a reduction in Ca2+-dependent phosphodiesterase activity in senescent cells, irreversible polyphosphoinositide loss from the membrane is unlikely, even when Ca2+ homeostasis fails.