cellular response to starvation

Definition

Target type: biologicalprocess

Any process that results in a change in state or activity of a cell (in terms of movement, secretion, enzyme production, gene expression, etc.) as a result of deprivation of nourishment. [GOC:jl]

Cellular response to starvation is a complex and multifaceted process that involves a coordinated interplay of signaling pathways, metabolic adjustments, and gene expression changes to ensure survival in the face of nutrient deprivation. When a cell experiences starvation, it initiates a cascade of events aimed at preserving energy and promoting adaptation.

1. **Nutrient Sensing and Signaling:**
- The cell senses the decline in essential nutrients like glucose, amino acids, and lipids through various sensors, including AMPK (AMP-activated protein kinase), mTOR (mammalian target of rapamycin), and GCN2 (general control nonderepressible 2).
- These sensors activate signaling pathways that trigger a global cellular response.

2. **Metabolic Reprogramming:**
- **Glucose Metabolism:** Cells shift from glucose dependence to alternative energy sources.
- **Glycogenolysis:** Breakdown of stored glycogen to release glucose.
- **Gluconeogenesis:** Synthesis of glucose from non-carbohydrate sources like amino acids and glycerol.
- **Lipid Metabolism:** Increased breakdown of stored lipids (lipolysis) to generate energy.
- **Fatty Acid Oxidation:** Fatty acids are broken down to produce ATP.
- **Ketone Body Production:** Liver produces ketone bodies (acetone, acetoacetate, and beta-hydroxybutyrate) from fatty acids, which can be used as an alternative energy source by the brain.
- **Amino Acid Metabolism:** Increased protein breakdown to provide amino acids for gluconeogenesis and other metabolic processes.

3. **Gene Expression Changes:**
- **Transcriptional Regulation:** Signaling pathways activate or repress transcription factors, influencing gene expression.
- **Increased Expression:** Genes involved in autophagy, amino acid transport, lipid metabolism, and stress response.
- **Decreased Expression:** Genes involved in cell growth, proliferation, and protein synthesis.
- **Translation Regulation:** Reduced protein synthesis to conserve energy.
- **MicroRNA Regulation:** MicroRNAs play a role in fine-tuning gene expression, contributing to the adaptive response.

4. **Autophagy:**
- Autophagy is a cellular process that degrades and recycles damaged organelles and proteins, providing essential nutrients and energy.
- Enhanced autophagy during starvation allows cells to survive by breaking down unnecessary components.

5. **Stress Response:**
- Starvation triggers various stress responses, including the unfolded protein response (UPR), which aims to restore protein homeostasis.
- Other stress responses involve antioxidant defenses and DNA repair mechanisms.

6. **Cell Fate Decisions:**
- If starvation persists, cells may undergo programmed cell death (apoptosis) to eliminate damaged or dysfunctional cells.
- However, if the stress is transient, cells can successfully adapt to the nutrient deprivation and survive.

In summary, cellular response to starvation is a highly orchestrated process involving metabolic adjustments, gene expression changes, and cellular adaptation mechanisms to promote survival in the face of nutrient scarcity. This complex response allows cells to conserve energy, utilize alternative energy sources, and maintain essential functions until nutrient availability returns.'
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