A55 Cell death due to temperature

Topic

An insect cell dying due to temperature does not always die in the same way; there are two main pathways of temperature-induced cell death: apoptosis—an active, programmed death triggered in the cell by sustained, moderate heat—and necrosis, a passive death caused directly by extreme temperatures.

Both cell death pathways share the same physical basis: cell death kinetics follow the Arrhenius law, causing the rate of cell death to accelerate exponentially with temperature—at 45°C, this rate can be up to a thousand times higher than at 35°C.

This exponential acceleration with temperature is combined with exposure time into a single insect cell survival function, as proposed by the thermal Weibull model; the exact shape of this survival function also depends on temperature, again following the same Arrhenius law that governs the rate of cell death.

In the apoptosis pathway, sustained moderate heat first damages the insect cell's mitochondria, causing them to release cytochrome c into the rest of the cell. This released cytochrome c activates proteases known as caspases, which ultimately execute the cell's programmed death—a process that constantly competes with inhibitory proteins from the Bcl-2 family attempting to halt it.

In the necrosis pathway, by contrast, no molecular signal triggers an orderly process; when the insect cell's temperature exceeds a critical threshold, the cell membranes collapse irreversibly and almost instantaneously—a collapse that acts more like a switch than a gradual process. The temperature that ultimately proves critical for the insect cell is not a fixed value but depends on the duration of exposure: the curve describing this critical temperature shows that longer exposures allow the cell to survive at lower temperatures, whereas shorter exposures are survived only at higher temperatures. Fundamentally, this relationship between temperature and time reflects the fact that the heat-induced damage sustained by the insect cell is cumulative, regardless of whether the process ultimately resolves via the active pathway of apoptosis or the passive pathway of necrosis.

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