Interleukin 6 Knockout Inhibits Aging-Related Accumulation of p53 in the Mouse Myocardium

The effect of cytokines on osteoblasts and osteoclasts in bone remodeling in osteoporosis: a review

The complicated connections and cross talk between the skeletal system and the immune system are attracting more attention, which is developing into the field of Osteoimmunology. In this field, cytokines that are among osteoblasts and osteoclasts play a critical role in bone remodeling, which is a pathological process in the pathogenesis and development of osteoporosis. Those cytokines include the tumor necrosis factor (TNF) family, the interleukin (IL) family, interferon (IFN), chemokines, and so on, most of which influence the bone microenvironment, osteoblasts, and osteoclasts. This review summarizes the effect of cytokines on osteoblasts and osteoclasts in bone remodeling in osteoporosis, aiming to providing the latest reference to the role of immunology in osteoporosis.

IL-6 regulates the bone metabolism and inflammatory microenvironment in aging mice by inhibiting Setd7

Aging, which has become a worldwide problem, leads to the degeneration of multiple organs and tissues. Two of the main changes in aging are dysregulation of the tissue microenvironment and abnormal functioning of specific stem cells. Bone marrow stem cells (BMSCs) in the aging microenvironment are not only effector cells but also immunomodulatory cells that change the microenvironment. IL-6 is a primary inflammatory response factor associated with bone diseases. In this study, we stimulated BMSCs with IL-6 to investigate a novel mechanism of age-related osteoporosis. IL-6 activated the TLR2, TLR4 and AKT pathway as well as inhibited the expression of β-catenin and Setd7. In addition, Setd7 expression in the bone tissues of aged mice was suppressed. Setd7 not only promoted BMSC osteogenic differentiation but also mediated proinflammatory gene expression in BMSCs under IL-6 stimulation. Due to its dual functions in BMSCs, Setd7 may be a novel molecular target for age-related osteoporosis prevention and treatment.

The effect of interleukin 6 deficiency on myocardial signal transduction pathways activation induced by bacterial lipopolysaccharide in young and old mice

PURPOSE

Exaggerated release of proinflammatory mediators during sepsis contributes to inadequate vasodilatation and depressed myocardial contractility, which lead to development of shock and circulatory collapse. The aim of the study was to evaluate the effect of IL-6 and aging on activation of intracellular signaling pathways in the myocardium induced by bacterial lipopolysaccharide (LPS) administration.

MATERIAL/METHODS

LPS was injected intraperitoneally to male 3- and 24-month old mice with systemic IL-6 gene knock-out (IL-6KO) and the reference strain (WT). LPS was given intraperitoneally in single low (0.1 mg/kg) or high (10 mg/kg) dose, or in two doses (0.1 + 10 mg/kg) with 24-h delay. The expression and phosphorylation of STAT3, ERK1/2, Akt1/2/3 proteins in the left ventricular myocardium was evaluated after 24 h using Western blotting.

RESULTS

Low LPS dose induced higher STAT3 phosphorylation only in old IL-6KO mice, not affecting ERK1/2 and Akt1/2/3 phosphorylation in any group. High LPS dose upregulated STAT3 phosphorylation similarly in all groups, reduced ERK1/2 expression in young WT mice and upregulated Akt1/2/3 expression and phosphorylation in young IL-6KO mice. Pretreatment with low LPS dose attenuated phosphorylation of STAT3 in both old groups and phosphorylation of Akt1/2/3 in young IL-6KO group. Two-dose approach also significantly potentiated ERK1/2 phosphorylation in both old groups.

CONCLUSIONS

Obtained results show that IL-6 deficiency alters the activity of intracellular signaling pathways: JAK/STAT in old and Akt in young LPS-treated mice. This may indicate that lack of IL-6 attenuates Akt-related cytoprotective effect of pretreatment with low LPS dose in young but not in aged animals.

Interleukin-6 Knockout Inhibits Senescence of Bone Mesenchymal Stem Cells in High-Fat Diet-Induced Bone Loss

Obesity, a chronic low-grade inflammatory state, not only promotes bone loss, but also accelerates cell senescence. However, little is known about the mechanisms that link obesity, bone loss, and cell senescence. Interleukin-6 (IL-6), a pivotal inflammatory mediator increased during obesity, is a candidate for promoting cell senescence and an important part of senescence-associated secretory phenotype (SASP). Here, wild type (WT) and (IL-6 KO) mice were fed with high-fat diet (HFD) for 12 weeks. The results showed IL-6 KO mice gain less weight on HFD than WT mice. HFD induced trabecular bone loss, enhanced expansion of bone marrow adipose tissue (BMAT), increased adipogenesis in bone marrow (BM), and reduced the bone formation in WT mice, but it failed to do so in IL-6 KO mice. Furthermore, IL-6 KO inhibited HFD-induced clone formation of bone marrow cells (BMCs), and expression of senescence markers (p53 and p21). IL-6 antibody inhibited the activation of STAT3 and the senescence of bone mesenchymal stem cells (BMSCs) from WT mice in vitro, while rescued IL-6 induced senescence of BMSCs from IL-6 KO mice through the STAT3/p53/p21 pathway. In summary, our data demonstrated that IL-6 KO may maintain the balance between osteogenesis and adipogenesis in BM, and restrain senescence of BMSCs in HFD-induced bone loss.

IL-6 deficiency attenuates p53 protein accumulation in aged male mouse hippocampus

Our earlier studies demonstrated slower age-related memory decline in IL-6-deficient than in control mice. Therefore, in the present study we evaluated the effect of IL-6 deficiency and aging on expression of p53, connected with accumulation of age-related cellular damages, in hippocampus of 4- and 24-month-old IL-6-deficient C57BL/6J (IL-6KO) and wild type control (WT) mice. The accumulation of p53 protein in hippocampus of aged IL-6KO mice was significantly lower than in aged WT ones, while p53 mRNA level was significantly higher in IL-6-deficient mice, what indicates that the effect was independent on p53 transcription. Presence of few apoptotic cells in hippocampal dentate gyrus and lack of changes in levels of pro-apoptotic Bax, antiapoptotic Bcl-2, as well as in p21 protein in aged animals of both genotypes, points to low transcriptional activity of p53, especially in aged WT mice. Because the amount of p53 protein did not correlate with the level of Mdm2 protein, its main negative regulator, other than Mdm2-dependent mechanism was involved in p53 build-up. Significantly higher mRNA levels of autophagy-associated genes: Pten, Tsc2, and Dram1 in IL-6KO mice, in conjunction with significantly lower amount of Bcl-2 protein in 4-month-old IL-6KO mice, suggests that lack of IL-6/STAT3/Bcl-2 signaling could account for better autophagy performance in these mice, preventing excessive accumulation of proteins. Taken together, attenuated p53 protein build-up, absence of enhanced apoptosis, and transcriptional up-regulation of autophagy-associated genes imply that IL-6 deficiency may protect hippocampus from age-related accumulation of cellular damages.