Examination of Cellular Stress and its Effects on Mitochondrial DNA

This document focuses on the role of mitochondria in living organisms, emphasizing their function as energy producers, the implications of mitochondrial DNA (mtDNA), and how stress affects these processes.

Definition: Mitochondria are often referred to as the "powerhouse of the cell." They are essential for energy production in cells.
- Location: Mitochondria are located in the cytosol (the liquid medium within cells) of eukaryotic cells, which are cells that possess a clear nucleus and a surrounding nuclear membrane.
- Energy Production: Mitochondria are responsible for approximately 90% of ATP production, which is stored in adenosine triphosphate (ATP) molecules.
- Signaling Role: Beyond energy production, mitochondria play a vital role in influencing cellular functions through signaling molecules.

Enzyme: A biological macromolecule, often a protein, that acts as a catalyst, accelerating chemical reactions without being consumed.
ATP Synthase: An enzyme that catalyzes the formation of ATP from adenosine diphosphate (ADP) and inorganic phosphate (Pi).

Definition: The ETC is a series of protein complexes that transport electrons from electron donors to electron acceptors while coupling this transfer with the movement of protons (H+ ions) across a membrane.
- Many enzymes involved in the ETC are embedded within the mitochondrial membrane.

Electron Microscope View: Electron microscopy reveals the intricate structure of mitochondria.

Inner Membrane: The membrane that contains the electron transport chain and ATP synthase enzymes.
Intermembrane Space: The space between the inner and outer membranes.
Matrix: The innermost compartment of the mitochondria, containing enzymes and mitochondrial DNA (mtDNA).
Outer Membrane: The outer layer enclosing the mitochondria.

Phosphorylation: The addition of a phosphoryl group (PO3-) to an organic molecule.
Oxidative Phosphorylation: A process linking ATP synthesis with electron movement in the mitochondrial electron transport chain, coupled with oxygen consumption and energy generation.
Stress responses lead to increased reactive oxygen species (ROS) that can harm mtDNA.

Stress can lead to oxidative stress, causing the intracellular buildup of ROS, which adversely affects mtDNA due to its less protected nature.

Each mitochondrion contains its genome, mtDNA, which is:
- Double-stranded like nuclear DNA.
- Inherited maternally.
- Replicates independently from nuclear DNA.
- Smaller and carries fewer genetic instructions (37 genes total).
Unlike nuclear DNA, mtDNA is particularly susceptible to damage from oxidative stress.

Understanding mtDNA can improve insights into psychological stress and disorders.

Psychologists may be interested in mitochondria and mtDNA because,
- Traditional psychometric measures of stress exist (e.g., Beck Depression Inventory, Perceived Stress Scale), but there are no reliable biological measures.
- Biological measures could quantitatively reflect an individual’s stress and functional resources.

In adaptive crises, mitochondria can exit cells and become ccf-mtDNA, indicating cellular stress.
Elevated levels of ccf-mtDNA are linked with increased mortality in critically ill patients, indicating poor health.
Associations found with diseases such as cancer, diabetes, and myocardial infarction.

ccf-mtDNA release correlates with psychological stress:
- Higher levels found in individuals with major depressive disorder (MDD).
- Levels stay elevated in MDD patients unresponsive to SSRIs, whereas responders show lower levels.

Recent findings suggest chronic psychological stress disrupts mitochondrial functions, reducing the enzymatic activity of ETC complexes, causing:
- Altered oxygen consumption rates.
- Changes in intracellular content and genomic sequences due to genomic instability.

Studies using the Trier Social Stress Test (TSST) show acute psychological stress leads to significant ccf-mtDNA release:
- Hummeel et al.: 1.6-fold increase in plasma ccf-mtDNA after stress.
- Trumpff et al.: Observed 2-3 fold increase in serum ccf-mtDNA shortly after stress exposure.

Under oxidative stress, mtDNA faces much greater risks (10- to 200-times) of mutation compared to nuclear DNA, especially in high-energy-demanding cells like muscle and brain cells.

Excessive oxidative damage may lead to mtDNA release into the bloodstream, which can be quantified and reflect individual stress levels.
Released mtDNA can induce inflammatory responses in the body.

The liberated mitochondrial DNA triggers pro-inflammatory responses via various pathways, including:
- Activation of neutrophils and pattern recognition receptors (PRRs) response.

Understanding mitochondrial health is crucial for addressing psychological disorders and chronic diseases.
The study design involves a single-arm trial, replicating previous findings with different induced stress via distress-inducing images from the IAPS.

Exclusion Criteria: Pregnant/lactating women, smokers, individuals with mental health issues within the past three months, and certain health conditions.
Inclusion Criteria: Healthy participants aged 20-30, residing in Canada.

Stress Protocol: Participants will endure a 10-minute stress exposure, followed by a resting phase, with blood tests assessing ccf-mtDNA levels before and after stress.
Assessment Tools: Profile of Mood States (POMS) will evaluate the impact of stress on mood changes.

Detailed steps for blood sample processing include centrifugation and serum isolation procedures to ensure accurate measurement of ccf-mtDNA.

Hypothesis: Participants will show significant increases in ccf-mtDNA within 30-45 minutes post-stressor.
Analytic Plan: Descriptive statistics on demographics and variables, assessing in-group differences between baseline and post-stressor conditions.

Findings indicated significant differences in nDNA but not in ccf-mtDNA. Suggests potential for further investigation into stress-related nDNA changes as a marker for chronic stress and potential pathways for assessing emotional health.