Glucocorticoids, like cortisol, can affect mast cells in many ways. As I discussed in my previous post, there are many ways for mast cells to release mediators when activated. In all of these pathways, there are many molecules involved that carry the signal, like people passing the Olympic torch. In mast cells, one of the molecules that suppresses inflammatory activation signal is called SLAP (yes, really). Cortisol increases the amount of SLAP in mast cells so inflammatory activation signals are suppressed.
An important step in degranulation is changing the amount of calcium inside the cell and moving it to different parts of the cell. In some studies, glucocorticoids can affect this movement of calcium. Other studies have found that in some pathways, glucocorticoids don’t affect calcium movement, but instead interfere with things like the IgE receptor.
Cortisol is also thought to directly inhibit stem cell factor (SCF) binding to the CKIT receptor. When SCF binds to the CKIT receptor, this sends a signal to the mast cell to stay live. This means that taking glucocorticoids can let mast cells die at the appropriate time. SCF also tells mast cells to go to inflamed spaces. By blocking this signal, glucocorticoids suppress inflammation.
One of the ways that molecules carry a signal is by changing the next molecule in the pathway. A big way that cells changing molecules is by chopping off a piece of them called a phosphate group. This is done by special enzymes called phosphatases. Glucocorticoids affect the availability of phosphatases so they aren’t able to get to the right part of the cell to carry the signal. When this happens, there is less activation and less histamine release.
Arachidonic acid is the molecule modified to make eicosanoids (leukotrienes, thromboxanes and prostaglandins.) Glucocorticoids directly interfere with the production of these molecules in multiple ways. The first way is by interfering with COX-2, one of the enzymes that makes prostaglandins. Another way is by preventing arachidonic acid from being released to a place where they can be turned into leukotrienes, thromboxanes and prostaglandins. This occurs because glucocorticoids increase the amount of a powerful anti-inflammatory molecule called annexin-I. Annexin-I inhibits the molecule that releases the arachidonic acid, called phospholipase A2.
Annexin-I was the subject of an important paper earlier this year. In trying to identify exactly how mast cell stabilizers like ketotifen and cromolyn work, the researchers discovered that treatment with mast cell stabilizers decreased degranulation and increased annexin-I made by mast cells. They also found that glucocorticoids had the same effect.
Oppong E, et al. Molecular mechanisms of glucocorticoid action in mast cells. Molecular and Cellular Endocrinology 2013: 380, 119-126.
Varghese R, et al. Association among stress, hypocortisolism, systemic inflammation and disease severity in chronic urticaria. Ann Allergy Asthma Immunol 2016: 116, 344-348.
Zappia CD, et al. Effects of histamine H1 receptor signaling on glucocorticoid receptor activity. Role of canonical and non-canonical pathways. Scientific Reports 2015: 5.
Coutinho AE, Chapman KE. The anti-inflammatory and immunosuppressive effects of glucocorticoids, recent developments and mechanistic insights. Mol Cell Endocrinol 2011: 335(1), 2-13.
Sinniah A, et al. The role of the Annexin-A1/FPR2 system in the regulation of mast cell degranulation provoked by compound 48/80 and in the inhibitory action of nedocromil. International Immunopharmacology 2016: 32, 87-95.