Abstract
In this study, we report a novel method for the in situ measurement of autophagy under nutrient starvation using a principle of semiconductor technology. A semiconductor-based field-effect transistor (FET) biosensor enables the direct detection of ionic or molecular charges under biological conditions. In particular, cellular respiration accompanied by the generation of carbon dioxide can be continuously and directly monitored as a change in pH at a cell/sensor interface. When autophagy was induced in HeLa cells on a FET biosensor under nutrient starvation, the surface potential increased more significantly for about 15 h than that for nonstarved cells. This positive shift indicates an increase in the number of hydrogen ions produced from the respiration of starved cells because the sensing surface was previously designed to be sensitive to pH variation. Therefore, we have found that cellular respiration is more activated by autophagy under nutrient starvation because the amino acids that decomposed from proteins in autophagic cells would have been rapidly spent in cellular respiration.
Highlights
For living cells, nutrient depletion may stimulate various functions
The responsivity of field effect transistor (FET) biosensors to hydrogen ions is well known to exhibit a Nernstian response; such FETs acting as pH sensors are called ion-sensitive field-effect transistors (ISFETs)[15]
This result is typical for ISFETs, which were utilized as FET biosensors with cultured cells to monitor cellular respiration activity in this study[21,22,23]
Summary
Nutrient depletion may stimulate various functions. apoptosis may be induced in cells by nutrient starvation. Autophagy is an intracellular degradation system, by which cytoplasmic contents are degraded in lysosomes, and it is dynamically induced by nutrient depletion to provide necessary amino acids within cells such as yeasts, helping them adapt to starvation, which has been reported to be essential for cellular homeostasis[1,2]. Metabolism such as cellular respiration in a cell may be activated to temporarily prevent apoptosis through autophagy. As one of the cellular events for in situ monitoring of autophagy, we focused on cellular respiration, which can be detected as a change in pH, because autophagy under nutrient starvation is closely related to cellular metabolic processes such as respiration
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