Glucocorticoid-induced, caspase-dependent organ apoptosis early after burn injury

Abstract

Immune suppression and increased apoptotic loss of circulating lymphocytes have been reported after burn injury. However, little is known about the underlying mechanisms responsible for the increased apoptosis of lymphoid and parenchymal cells in solid organs and the role played by inflammatory mediators, such as tumor necrosis factor-alpha (TNF-alpha) and Fas ligand (FasL), as well as by glucocorticoids. To evaluate the role of endogenously produced glucocorticoids and FasL, mice subjected to a 20% steam burn were pretreated with a glucocorticoid receptor antagonist (mifepristone) or a neutralizing murine Fas fusion protein. Three and twenty-four hours after burn injury, histological analysis, caspase-3 activity, and in situ terminal deoxynucleotidyl transferase dUTP nick-end labeling staining and phenotyping of lymphocyte populations for apoptosis were evaluated. Burn injury increased the number of apoptotic cells and caspase-3 activity in thymus and spleen, but not in other solid organs. Increased apoptosis was seen in several T and B cell populations from both thymus and spleen. Mifepristone pretreatment significantly reduced the apoptosis and caspase-3 activity after burn injury, whereas blocking FasL activity had only minimal effects. We conclude that corticosteroids, and not FasL, are primarily responsible for the increased caspase-3 activity and apoptosis in thymus and spleen cell populations early after burn injury.

Gene expression analysis in burn wounds of rats

“…Their activation, in many instances, appears to be over by 10 days (Table 3). Inflammation-related genes and stress response genes remained the mainstay of upregulated gene expression for the first 24 h in agreement with earlier reports (10). Genes involved in cell migration, such as membrane type matrix metalloproteinase #X83537 and versican V3 #AF072892, appear to be activated later.…”

Role of TNF-α in gut mucosal changes after severe burn

“…Another study by Guy-Grand et al (5) showed increased villous cell apoptosis in TNF-␣ treated normal animals, which appears to be dependent on the presence of intraepithelial lymphocytes. This differs from increased apoptosis in lymphatic tissues such as spleen and thymus found in reaction to burn injury, which was linked to increased FasL mRNA expression and increased caspase-3 activity (2,3). Apparently the apoptotic response is triggered differently in distinct tissues.…”

Adrenalectomy in mice does not prevent loss of intestinal lymphocytes after exercise

“…In vitro exposure to GCs induces thymocyte apoptosis (18,26), and blocking GC receptors, inhibiting GC biosynthesis, and ADX reduce lymphocyte cell death (6,15,43). Furthermore, surgical removal of the adrenal glands is associated with less DNA fragmentation and lower nitric oxide production of splenic macrophages (5).…”

“…Lymphocyte loss and/or apoptosis have been observed in other situations characterized by extreme physiological stress, including burn injury (15), electrical shock (48), and chronic restraint stress (42), and may reflect release of stress hormones, in particular glucocorticoids (GCs). GCs trigger apoptosis in lymphocytes by acting on an intracellular pathway via the mitochondria (2), which results in the accumulation of mitochondrial derived cytochrome c within the cytosol, loss of mitochondrial membrane integrity, externalization of phosphatidylserine at cell membranes, and DNA fragmentation (27,45).…”