Do mast cells contribute to the continued survival of vertebrates?

Mast cells and wound healing: Still an open question

Mast cells, which originate from the bone marrow, possess the ability to secrete a diverse array of active molecules. These molecules include mediators (histamine, heparin), which have been identified for decades and are stored in specific granules, as well as small molecules generated instantaneously in response to stimulation (membrane lipid derivatives, nitric oxide), and a multitude of multifunctional cytokines that are secreted constitutively. Activated mast cells participate in the regulation of the local immune response and exert control over critical events of inflammation and healing with the assistance of a vast array of mediators. The involvement of these cell types in inflammatory states suggests that mast cells may function as sentinels that activate local immune processes in response to various types of stimuli and the entry of antigens. Moreover, due to their proximity to nerve fibers and reactivity to a variety of neurotransmitters, mast cells are among the cells that may facilitate local neuroimmune interactions. With this in mind, it is necessary to consider their participation in the repair of injuries in both acute and chronic conditions.

On Connective Tissue Mast Cells as Protectors of Life, Reproduction, and Progeny

The connective tissue mast cell (MC), a sentinel tissue-residing secretory immune cell, has been preserved in all vertebrate classes since approximately 500 million years. No physiological role of the MC has yet been established. Considering the power of natural selection of cells during evolution, it is likely that the MCs exert essential yet unidentified life-promoting actions. All vertebrates feature a circulatory system, and the MCs interact readily with the vasculature. It is notable that embryonic MC progenitors are generated from endothelial cells. The MC hosts many surface receptors, enabling its activation via a vast variety of potentially harmful exogenous and endogenous molecules and via reproductive hormones in the female sex organs. Activated MCs release a unique composition of preformed and newly synthesized bioactive molecules, like heparin, histamine, serotonin, proteolytic enzymes, cytokines, chemokines, and growth factors. MCs play important roles in immune responses, tissue remodeling, cell proliferation, angiogenesis, inflammation, wound healing, tissue homeostasis, health, and reproduction. As recently suggested, MCs enable perpetuation of the vertebrates because of key effects-spanning generations-in ovulation and pregnancy, as in life-preserving activities in inflammation and wound healing from birth till reproductive age, thus creating a permanent life-sustaining loop. Here, we present recent advances that further indicate that the MC is a specific life-supporting and progeny-safeguarding cell.

A survey of the currently known mast cell mediators with potential relevance for therapy of mast cell-induced symptoms

Mast cells (MCs) occupy a central role in immunological as well as non-immunological processes as reflected in the variety of the mediators by which MCs influence other cells. Published lists of MC mediators have all shown only subsets-usually quite small-of the full repertoire. The full repertoire of MC mediators released by exocytosis is comprehensively compiled here for the first time. The compilation of the data is essentially based on the largely cytokine-focused database COPE®, supplemented with data on the expression of substances in human MCs published in several articles, plus extensive research in the PubMed database. Three hundred and ninety substances could be identified as mediators of human MCs which can be secreted into the extracellular space by activation of the MC. This number might still be an underestimate of the actual number of MC mediators since, in principle, all substances produced by MCs can become mediators because of the possibility of their release by diffusion into the extracellular space, mast cell extracellular traps, and intercellular exchange via nanotubules. When human MCs release mediators in inappropriate manners, this may lead to symptoms in any or all organs/tissues. Thus, such MC activation disorders may clinically present with a myriad of potential combinations of symptoms ranging from trivial to disabling or even life-threatening. The present compilation can be consulted by physicians when trying to gain clarity about MC mediators which may be involved in patients with MC disease symptoms refractory to most therapies.

Mast Cell Dynamics in the Ovary Are Governed by GnRH and Prolactin

Gonadotrophin releasing hormone (GnRH) facilitates the migration of mast cells (MCs) into the involuting mammary gland. As GnRH is also expressed in the ovary, we examined changes in ovarian MCs. MCs in the ovary were mainly in interstitial tissue and their number increased during the estrous cycle to produce 2 peaks, one at diestrus 2 (20:00 hours) and another at proestrus (17:00 hours). Laser microdissection demonstrated that GnRH mRNA is expressed throughout ovarian tissues (corpora lutea, follicles, and interstitial tissues). GnRH immunoreactivity was also ubiquitous, but MCs were the most strongly immunostained. Analysis of GnRH mRNA in the ovary showed it to fluctuate similarly to the variation in MC number during the estrous cycle, and MCs also expressed GnRH. Local administration of a GnRH agonist (GnRHa) into the hemilateral ovarian bursa increased MCs in the administered ovary. MC number and GnRH mRNA were significantly lowered in the pregnant ovary. Prolactin administration suppressed the normal peaks in MC number in the ovary at both diestrus and proestrus. By contrast, a dopamine agonist, administered when prolactin was elevated during pseudopregnancy, increased ovarian MC number. Furthermore, prolactin inhibited GnRHa-induced peritoneal MC migration in a Transwell assay. These data clearly demonstrate that ovarian MC number is regulated positively by local GnRH expression and negatively by prolactin. The suppressive effect of prolactin on GnRH and MCs would be part of its luteotrophic action.

Mast cell ontogeny: From fetal development to life-long health and disease

Mast cells (MCs) are evolutionarily ancient innate immune cells with important roles in protective immunity against bacteria, parasites, and venomous animals. They can be found in most organs of the body, where they also contribute to normal tissue functioning, for example by engaging in crosstalk with nerves. Despite this, they are most widely known for their detrimental roles in allergy, anaphylaxis, and atopic disease. Just like macrophages, mast cells were conventionally thought to originate from the bone marrow. However, they are already present in fetal tissues before the onset of bone marrow hematopoiesis, questioning this dogma. In recent years, our view of myeloid cell ontogeny has been revised. We now know that the first mast cells originate from progenitors made in the extra-embryonic yolk sac, and later get supplemented with mast cells produced from subsequent waves of hematopoiesis. In most connective tissues, sizeable populations of fetal-derived mast cells persist into adulthood, where they self-maintain largely independently from the bone marrow. These developmental origins are highly reminiscent of macrophages, which are known to have critical functions in development. Mast cells too may thus support healthy development. Their fetal origins and longevity also make mast cells susceptible to genetic and environmental perturbations, which may render them pathological. Here, we review our current understanding of mast cell biology from a developmental perspective. We first summarize how mast cell populations are established from distinct hematopoietic progenitor waves, and how they are subsequently maintained throughout life. We then discuss what functions mast cells may normally have at early life stages, and how they may be co-opted to cause, worsen, or increase susceptibility to disease.

Mast Cells in Regeneration of the Skin in Burn Wound with Special Emphasis on Molecular Hydrogen Effect

The mechanisms of regeneration for the fibrous component of the connective tissue of the dermis are still insufficiently studied. The aim of this study was to evaluate the effectiveness of the use of molecular hydrogen on the local therapy of a II degree burn wound with the intensification of collagen fibrillogenesis in the skin. We analyzed the involvement of mast cells (MCs) in the regeneration of the collagen fibers of the connective tissue using water with a high content of molecular hydrogen and in a therapeutic ointment for the cell wounds. Thermal burns led to an increase in the skin MC population, accompanied by a systemic rearrangement of the extracellular matrix. The use of molecular hydrogen for the treatment of burn wounds stimulated the regeneration processes by activating the formation of the fibrous component of the dermis, accelerating wound healing. Thus, the intensification of collagen fibrillogenesis was comparable to the effects of a therapeutic ointment. The remodeling of the extracellular matrix correlated with a decrease in the area of damaged skin. Skin regeneration induced by the activation of the secretory activity of MCs may be one of the possible points of implementation of the biological effects of molecular hydrogen in the treatment of burn wounds. Thus, the positive effects of molecular hydrogen on skin repair can be used in clinical practice to increase the effectiveness of therapy after thermal exposure.