Cellular signaling and pathways are fundamental to cellular function. Think of all those cells in your body (37 trillion, remember?) and now contemplate how the heck they all work together to get the job done. This is possible because of their intricate, yet organized process of communication: cellular signaling.
Before a cell can signal to another, a roadmap needs to be in place. A cellular pathway is exactly what you’d expect; a route within a cell, like highways with toll booth checkpoints. The fees incurred at each checkpoint, in this sense, are messages being passed along the pathways, activating proteins at each. While a bit of an annoyance, having to stop and get "checked," these are incredibly important in allowing a cellular signal to continue toward its intracellular destination.
It's imperative to ensure the body receives the essential nutrients and care necessary to optimize cellular health and reduce oxidative stress.
These biological pathways are tightly regulated by enzymes and molecular chaperones, which keep the cellular environment in check. They’re highly involved in many processes: such as the metabolism of drugs and nutrients, as well as energy production. So, when a problem arises in the functionality of cellular pathways, it can translate to functional impairments of your internal system. This could manifest in a diabetic individual, for example, when they feel tired and weak after indulging in a high-carb meal.
How Cellular Signaling Works
As expected, closely related to the concept of cellular pathways is cell signaling. While cell pathways involve proteins communicating to one another within the cell, cell signaling involves cells as a whole communicating to one another, outside of the cell.
Cells are able to do this by releasing chemical messengers, typically called hormones, which bind to protein receptors on the surface of cells that recognize specific features of these hormones.
There are four primary ways cells signal one another:
1. Autocrine signaling
Simply put, autocrine signaling is the process by which a cell sends signals to itself. It’s sort of like setting an alarm, reminding you to take your vitamins. Through autocrine signaling, a cell can tell itself to increase, decrease, or maintain cellular processes based on their interactions with the environment and their own cellular state.
2. Endocrine signaling
Endocrine signaling is the way cells communicate to one another over long distances. Here, a hormone released from one cell travels through the bloodstream to bind to receptors located on another cell elsewhere in the body. In these circumstances, the cell releasing the hormone is known as a gland, such as the pituitary gland, adrenal gland, and the thyroid gland, which are involved in regulating sleep, stress, and immunity, respectively.
3. Paracrine signaling
Paracrine signaling occurs when one cell relays a message to a neighboring cell, resulting in a changed behavior. In a similar way, paracrine signaling between cells is a way for them to rapidly communicate their cellular status and local extracellular changes to one another.
4. Juxtacrine signaling
Similar to paracrine signaling, this type involves the relay of messages between two cells that are physically in contact with one another. Rather than releasing a chemical message into the extracellular space, which would normally occur in paracrine signaling, a juxtacrine message is relayed through the cellular membrane that connects the two cells together.
It is important to note that cells do not rely on one signaling method over the other, but instead, they rely on all of them collectively to efficiently relay messages near and far in the body. Miraculously, they just know what to do!
Cellular Signaling and Oxidative Stress
So, now that you’ve got the basics, what does this all have to do with the negative effects that can come with oxidative stress? After all, this type of cellular stress is what we’re focused on.
When cells begin to produce free radicals and other reactive oxygen species (ROS), cellular pathways are activated, which relay messages throughout the cell, issuing a warning about the rising levels.
If these pathways do not relay signals efficiently, ROS accumulates to dangerously high levels, and the cell begins to suffer oxidant damage. This damage can come in the form of abnormal cellular events like misfolded proteins, impaired energy production and cellular strain.
When this happens, another set of pathways are activated, prompting responses that promote survival or death of a cell, including proliferation, growth arrest, cellular senescence, and even apoptosis (i.e., cell death). Like two people in a relationship, cells suffer when they're not able to communicate with each other properly.
Mitogen-activated protein kinases (MAPK) are a family of proteins associated with cellular lifespan (i.e. the survival or death of a cell), and as such, are highly involved in signaling pathways.
Different sub-families of these proteins have been identified based on their structural differences. The three major sub-families of MAPK are extracellular signal-regulated kinases (ERK), c-Jun N-terminal kinases (JNK), and the p38 kinases. While all similarly regulated, they all have separate signaling pathways that lead to their various activations.
The ERK pathway is commonly associated with cell growth and proliferation, whereas JNK and p38 pathways deal with how a cell adapts to oxidative stress (remember, this is important, especially to us!) Because of their role in cellular stress, JNK and p38 are often called stress-activated protein kinases, or SAPK.
These SAPK’s influence a key cellular mechanism; autophagy, a protective mechanism that the cell uses when undergoing high levels of stress to clean out debris and damaged cells. In other words, it’s key to the maintenance of healthy cells, and in turn, a healthier you.
An increase in oxidative stress triggers cellular pathways that stimulate the process of autophagy. This helps the cell remove debris and damaged components of a cell that may have suffered from increased oxidative stress and cellular strain, restoring cellular homeostasis and normal processing. When pathways that lead to autophagy become impaired, oxidative stress accumulates, which can trigger cellular death responses (i.e., apoptosis).
These are just some of the ways that cellular signaling pathways overlap with oxidative stress and cellular health.
Real-World Examples of Cell Signaling Pathways
There are many ways in which cell signaling pathways influence our everyday functions. But let’s talk about a fun one: food! Let’s use a sandwich as an example, and how the carbohydrates are broken down into its carbon energy source: glucose.
As you eat your classic PB&J, revering in nostalgic childhood bliss, glucose levels rise in the blood. Glucose-sensing cells in the brain identify this increase, which triggers a series of intracellular signaling pathways to cause the release of hormones into the bloodstream. These hormones bind to receptors on the pancreas (an organ in your abdomen) via endocrine signaling to stimulate the release of insulin.
Sounds familiar, right?
Insulin circulates in the blood and binds to insulin receptors on the surface of nearly every cell in the body, triggering an intracellular pathway that activates a series of checkpoint proteins within the cell. The activation of these checkpoints leads to the opening of glucose transporter proteins along the cellular membrane. When these transporters open, glucose can freely enter the cell, triggering another series of pathways in glucose metabolism and energy production (i.e., glycolysis and mitochondrial respiration, respectively).
In an instance of poor cell signaling, problems in the body's ability to sense glucose, release insulin, metabolize glucose, or use glucose metabolites to produce energy, can significantly impact important bodily functions. It can result in say, Type 2 Diabetes Mellitus.
This is only one way that cellular pathways and cellular signaling interact to influence bodily functions and physiology. The cell relies on intracellular and extracellular signaling pathways to survive and thrive. Thus, it is imperative to ensure the body receives essential nutrients and care that is necessary to optimize cellular health and reduce oxidative stress.
Closing Thought: Take Care of your Cells
We hope we were able to teach you a little more about how your cells function, and why cell care is so important to live every day to its fullest.
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Cell pathways and signaling
Cell signaling and oxidative stress
Cell signaling and genetics
Real-World Applications & Biological Aging