A GUT FEELING
FEAT. THE PAR2 IN YOU
The GI tract is the largest interface between you and the environment, and a primary influencer of your well-being, which is finally becoming increasingly understood as more research comes out (source). For the very first job that I landed fresh out of college, I was able to get my hands dirty (literally) in understanding the neurobiology of digestive disorders at a UCSF research lab (aka partaking in projects that required the dissection of mouse spinal cords and clearing of their intestines of poop). Oh the shit that I used to do… (cue punchline music*). Anyway, the founder of the lab had apparently done some major pioneering work on the role of this receptor, called Protease-activated Receptor 2 (PAR2 for short), in chronic pain associated with irritable bowel syndrome and inflammatory bowel disease. His team’s goal was to see if PAR2 could be exploited as a therapeutic target for chronic pain (source). Since then, I’ve developed a more holistic perspective on digestive health, but will always appreciate the impact of one problematic molecular mechanism on the whole. In homage to my time with digestive dysfunction, I’ve also created a karaoke video about the PAR2 in U in hopes of introducing an enjoyable way of learning about the science behind your well-being. -VF
An easy-to-digest overview of YOur Gut FEELINGS
SEROTONIN IS CONTROLLING
Besides being a critical processor of the nutritional requirements for this miraculous machinery we call our bodies, the human gastrointestinal system plays a major role in the “digestion” of your behavioral, emotional and physical capacities. This mechanism is monitored by a “second brain” which is officially known as the enteric nervous system (ENS): an expansive unit of over 500 million neurons (which is 0.5% the capacity of your brain and 5x that of the spinal cord), as well as a department of support cells. It relays information throughout your body from signaling pathways generated by but not limited to 30+ different cell types in the gut, molecules from digested nutrients (salts, fats, trace minerals, etc.), and the 100 trillion bacterial cells that support our digestion. Interconnected to the central nervous system (CNS) by the vagus nerve (and the lesser known prevertebral ganglia), the ENS lines the walls of the long tube of our gut, or alimentary canal, which measures about 30 feet end to end from the esophagus to the anus (source). Among one the critical communicators of the body, about 90% of the bodies’ serotonin reserves are manufactured by enterochromaffin (EC) cells in the gut with the support 2-6 pounds of bacterial flora, as discovered by a team at scientists at Caltech. Serotonin also regulates a whole entourage of biological processes including neurogenesis, cardiovascular function, intestinal motility, inflammation control, and bone mass accrual (source).
A BALANCING ACT
In Traditional Chinese Medicine, the organs, which aren’t delineated exactly the same as in Western anatomy, are responsible for regulating the whole spectrum of emotions that fluctuate throughout the day: the liver is the notorious wrangler of anger and frustration (most likely by filtering the blood of aggravating toxins); the energy center or “ming-men” of the kidneys monitors flare ups that cause fear in our hearts (which we now can partially prescribe to noradrenaline/adrenaline); our stomachs and pancreas process our worries in our immediate environments (by regulating blood sugar levels); and sadness is “digested’ by our lungs (ACE in regulating our blood pressure), skin (vitamin D for nervous system health) and large intestine (serotonin production). There’s also an additional non-physical digestive system called the triple burner residing over the head, chest, and thorax that controls all the organ relationships, and hence emotional balance — it is this heating system of the body/mind/spirit that regulates and distributes energy and water. Nowadays these functions can largely be attributed to the endocrine glands and hormonal distribution systems. It was also understood that the body maintains homeostasis (yin/yang) through processes that are analogous to the fundamental elements in our environment which, in general, are related to nutritional requirements (earth), power/organizational structure (metal), thermodynamics (fire), movement (water), and development (wood). How funny that practitioners have effectively applied this medical system for thousands of years without understanding the biochemical processes developed in Western Medicine, which have only gained traction over the last 200 years.
FOOD FOR FORM
One of the most overlooked aspects of the Western healthcare system is nutrition — in fact, most medical schools in the U.S. don’t even require their students to take a single nutrition course (source). In the ancient Indian medicine system of Ayurveda, health maintenance is entirely centered around nutrition, which include food, herbs and minerals (hence the culture’s delectable diversity of spiced delights). Prescriptions are made according to two main factors: your body makeup (prakruti), which consists of the distribution of three attributes (doshas), and six primary favours that support their functions. These three doshas, known as vata, pitta, and kapha, are correlated with the qualities of various biological energies that make up the body and mind. Interestingly enough, they have parallels with the mesomorph, ectomorph, and endomorph physiology defined in Western Medicine, which are influenced by the predominance of nervous tissue, bone mass, muscle, body fat percentage, rate of metabolism, etc. So it would make sense that specific foods would be more beneficial to someone with a tendency to gain weight (e.g. light salads that counteract the kapha dosha’s tendency for a sluggish metabolism) versus someone prone to weight loss and anxiety (e.g. sour foods for the vata dosha like oranges that contain vitamin C to promote healthy nervous system function). Your gut can even “taste” the macronutrient composition of the meal to trigger adequate responses for assimilating nutrients and eliminating waste products from your meals. Since Shirazi-Beechey’s pioneering work on the gut as a direct interface with the environment, researchers have found a specific distribution of receptors that detect sugars, fats, the amino acids (proteins), and bitter compounds in the GI tract — as well as all over the body including the lungs, CNS, testes, and skin (source). In fact, in Ayurveda clear skin is indicative of a healthy digestive system and overall balance of the body or three doshas (source).
ADDRESS THE STRESS
Normally a burst of cortisol is a healthy and necessary part of responding to a stressful situation through your ever-faithful fight-flight-freeze response. In fact this little glucocorticoid hormone has some major body-credentials that include: redistributing energy reserves like making your glutes more responsive to glucose (by thwarting the effect of insulin) when you’re running away from your problems; preventing you from passing out as that blood pressure ups the ante while you finally confront your demons; restrains any infected wounds from turning you into a swollen sack of flesh (for about 30 minutes) as a potent anti-inflammatory; and helps you selectively forget that the whole mess ever happened (memory consolidation). Your digestive system, on the other end, is curbed by the sympathetic nervous system for your “spidey senses” to operate at peak capacity — except for your liver which is on overdrive pumping out proteins to breakdown into glucose molecules for efficient fuel. All is well until stress becomes a chronic issue: it makes you grow a “beer belly” (from your brain’s cues to overeat and cortisol’s hand in fat cell production); you’re at a greater risk for Type II diabetes (from insulin resistance), a heart attack (constricted blood vessels), and autoimmune diseases (insulin resistance); your muscles start to waste away (dysregulation of the parasympathetic nervous system for nutrition processing); and you’re prone to a whole slew of mental health issues (e.g. insomnia, chronic fatigue syndrome, dementia, depression, etc.) (source).
The Role OF PAR2 in You
What is PAR2 and is it important in gastrointestinal health?
Protease-activated receptor 2 (PAR2), a receptor for inflammatory proteases, is a major mediator of neurogenic inflammation and pain. Injury and inflammation trigger the activation of proteases from the circulation, immune cells, and epithelial tissues that regulate cells by cleaving protease-activated receptors (PARs). Once activated, PARs regulate multiple pathophysiological processes, including inflammation, pain, homeostasis, and healing. PAR2 activation also promotes the central (brain, spinal cord) release of neuropeptides that activate second-order spinal neurons that transmit pain. These mechanisms contribute to painful inflammation of the intestine, pancreas, and joints (source).
How does PAR2 function on the molecular level?
PAR2 is a member of a family of four G protein-coupled receptors (GPCRs) - proteases released from injury and inflammation activate PAR2 on sensory nerve endings by cleaving it at specific sites within the extracellular N-terminal domains (outside of the cell). Proteases in circulation reveal tethered ligands that bind to and activate the cleaved receptors, such as the local release of these neuropeptides, which stimulate plasma extravasation (pus), infiltration of neutrophils, and vasodilation (neurogenic inflammation) (source).
What IS the role of PAR2 on the peripheral nervous system and skin?
Here is a brief video of the Principal Investigator (PI) that I used to work for at UCSF, Dr. Martin Steinhoff, briefly discussing how PAR2 also influences neuronal signaling and outgrowth in diseased skin. I shot this during the 2011 International Itch Conference in Japan, Tokyo which was organized by another scientific researcher I was working with at the time, Dr. Akihiko Ikoma.
A CLOSER LOOK at YOUR GUT LINING
The gut is far from a simple hollow tube — it’s full of cells that sense and respond to the contents, with ramifications for appetite, defense, and disease that researchers are just starting to uncover. This is an immunofluorescence stained cross-section of the lining of the small intestine that highlights the diversity of cells that constitute its structure: See the infographic “Protease-Activated Receptor (PAR2) Activation” that’s just below for a key to some the major cells found in the gut (and also pretty much throughout your body).
This is an immunofluorescence stained cross-section of the lining of the small intestine (image source).
THE CELLS IN YOUR GUT THAT carry PAR RECEPTORS
This is a summary of the pathophysiological effects of PAR agonists PAR1 and PAR2 are expressed by endothelial cells, epithelial cells, neurons, myocytes/smooth muscles, fibroblasts, and inflammatory cells. PARs trigger pathways related to inflammation, hyperalgesia, tissue repair and protection in these cell types.
Summary of the pathophysiological effects of PAR agonists PAR1 and PAR2.
I gut A feeling Feat. the par2 in u
As promised, here is the karaoke number on this multi-talented molecule that I've created in homage to my brief stint in GI research, but my lifelong respect for gut health. I used this research publication as a reference for the concepts and experiments conducted in PAR2 gut research, which was produced by a group of researchers that I used to work with. I’ve also included key below with definitions for the terms in the video that probably aren’t known by the typical lay-person. I hope you enjoy it!
P.S. This is not intended to downplay the importance of digestive diseases nor hurt anyone’s feelings — hopefully it will do the opposite, and maybe cause a slight cramp in your gut from a good guffaw.
KEY FOR "I Gut a Feelin’” Karaoke video
Basic Anatomy of the digestive system
Key for the basic identification of digestive organs for the "I Gut a Feelin’” karaoke video.
Cathepsin
“Catheptic activity” (derived from the Greek word kathépsein, meaning to digest or to boil down) was first described in the gastric juice during the 1920s. Cathepsins are now classified based on their structure and catalytic type - the one used in mice experiments referenced in the research publication that I mentioned, Cathepsin S (for Serine), was found to excite the neurons in the colon.
C-FOS/C-Fos Immunohistochemistry Staining
C-Fos is a proto-oncogene that is expressed as a protein c-fos in some neurons upon depolarization (activation). It can be detected by immunohistochemical staining on tissue, such as activated nociceptive neurons in the spinal cord. We commonly used this tool to see if there was a central nervous system response (i.e. spinal cord) from mouse experiments on the gut.
Chronic Colitis
Colitis refers to the inflammation of the inner lining of the colon, which can be caused by several conditions including infection, Crohn’s disease, allergic reactions, and can have painful ulcers.
Colonic Air Balloon
A colonic balloon is just as it sounds, and used as part of an experimental technique for creating visceral gut pain in mice.
Confocal scope/Confocal Microscopy
Confocal microscopy is a type of microscopic imaging that uses lasers programmed to focus on a specific plane of tissue that’s been labeled with immunofluorescent markers. It’s used to create pretty, magnified images like the one included above.
Crohn’s/Crohn’s disease
Crohn’s disease is an inflammatory bowel disease that can cause severe abdominal pain, severe diarrhea, fatigue, weight loss, and malnutrition. I don’t have Crohn’s (as conveniently compatible with the lyrics), but I have known one person who’s successfully managed his symptoms with a combination of medications, vitamins, diet, exercise, and medicinal marijuana.
Gallstones
Gallstones are hardened deposits of the digestive bile, that can form within the gallbladder. They can cause pain, nausea, and vomiting if they block the ducts of the gallbladder on their way out. This is a more common condition in patients with Crohn’s disease.
MPO/Myeloperoxidase Assay
Myeloperoxidase (MPO) is a peroxidase enzyme found the most in neutrophil granulocytes (a type of white blood cell ) — basically in the presence of pus released during inflammation. Think about the times you used hydrogen peroxide to disinfect a scrape. The peroxidase in blood, cells, bacteria that break down the H2O2 into water and oxygen (which is responsible for the disinfectant properties against some bacterial strains).