Induction of a subgroup of acute phase protein genes in mouse liver by hyperthermia

We have demonstrated that two members of the acute phase reactant family of positively regulated genes, alpha 1-acid glycoprotein (AGP-1 and AGP-2) and C-reactive protein (CRP) are induced by hyperthermia, while two others, the serum amyloid A (SAA) and alpha 1-antitrypsin (AT) genes, are not. Albumin (ALB), a negative acute phase reactant gene, is also induced by hyperthermia. The AGP-1, AGP-2, and CRP genes require glucocorticoids, but not IL-6, IL-1 beta or TNF alpha in response to hyperthermia. As with LPS, the C/EBP beta mRNA levels increased, while the C/EBP alpha mRNA levels decreased in response to LPS. In contrast to the LPS response, C/EBP delta was unchanged. Protein pool levels and DNA-binding activities of the 35 and 20 kDa C/EBP beta isoforms increase, whereas protein pool levels of the 42 kDa C/EBP alpha decrease and the 30kDa remained high. These studies suggest that the synthesis of specific C/EBP alpha and C/EBP beta isoforms is induced by hyperthermia, and that the regulation of the AGP-1 and AGP-2 genes during heat stress may involve one of these isoforms. The difference between the responses to hyperthermia and LPS is that the former, may not involve the participation of cytokines. Furthermore, since cis-acting heat shock elements (HSE) are located in the promoter regions of the ALB, CRP, and C/EBP beta genes, these regulatory sequences may be involved in the in vivo activation of these genes by hyperthermia.     

Leukemia inhibitory factor modulates interleukin-1beta-induced activation of the hypothalamo-pituitary-adrenal axis

We have shown that leukemia inhibitory factor (LIF) is expressed in corticotroph cells and stimulates POMC gene expression and ACTH secretion in vivo and in vitro. We therefore examined the regulation of in vitro and in vivo pituitary LIF expression by cytokines known to stimulate the hypothalamo-pituitary-adrenal axis. In the corticotroph cell line AtT-20/D16v-F2, recombinant murine interleukin-1beta (IL-1beta; 0.1-10.0 ng/ml) caused a 5- to 10-fold increase in LIF messenger RNA (mRNA) levels. LIF mRNA expression was induced as early as 1 h, peaked at 2 h, and still persistently elevated above the baseline after 8 h. This effect of IL-1beta on LIF mRNA expression was abolished by preincubation with human IL-1 receptor antagonist (100 ng/ml) or antimurine IL-1beta antibody (10 microg/ml). Tumor necrosis factor-alpha (20 ng/ml) only modestly increased LIF mRNA, but was synergistic with IL-1beta (up to 2.5-fold). In contrast, IL-2 and IL-6 did not alter LIF mRNA. In C57BL/6 mice, i.p. injection of 100 ng IL-1beta increased plasma ACTH and corticosterone levels after 1 h (P < 0.02). In addition, pituitary LIF mRNA content was increased for up to 2 h in response to IL-1beta. In comparison to wild-type (+/+) B6D2F1 mice, LIF knockout mice with a deleted LIF gene (-/-) exhibited decreased plasma ACTH (631 +/- 61 vs. 376 +/- 50 pg/ml; P < 0.01) and corticosterone (783 +/- 85 vs. 433 +/- 51 ng/ml; P < 0.01) levels 1 h after i.p. IL-1beta administration. In conclusion, corticotroph LIF mRNA expression is specifically stimulated by IL-1beta and tumor necrosis factor-alpha. The attenuated hypothalamo-pituitary-adrenal response to IL-1beta in LIF knockout mice indicates that the effect of IL-1beta on ACTH secretion is modulated by LIF. Thus, LIF appears to function as an immune-neuroendocrine modulator signaling the hypothalamo-pituitary-adrenal axis.