Effects of an Interleukin-15 Antagonist on Systemic and Skeletal Alterations in Mice with DSS-Induced Colitis

Mitochondrial dysfunctions in T cells: focus on inflammatory bowel disease

Mitochondria has emerged as a critical ruler of metabolic reprogramming in immune responses and inflammation. In the context of colitogenic T cells and IBD, there has been increasing research interest in the metabolic pathways of glycolysis, pyruvate oxidation, and glutaminolysis. These pathways have been shown to play a crucial role in the metabolic reprogramming of colitogenic T cells, leading to increased inflammatory cytokine production and tissue damage. In addition to metabolic reprogramming, mitochondrial dysfunction has also been implicated in the pathogenesis of IBD. Studies have shown that colitogenic T cells exhibit impaired mitochondrial respiration, elevated levels of mROS, alterations in calcium homeostasis, impaired mitochondrial biogenesis, and aberrant mitochondria-associated membrane formation. Here, we discuss our current knowledge of the metabolic reprogramming and mitochondrial dysfunctions in colitogenic T cells, as well as the potential therapeutic applications for treating IBD with evidence from animal experiments.

Counteracting Interleukin-15 to Elucidate Its Modes of Action in Physiology and Pathology

Interleukin (IL)-15 belongs to the common gamma-dependent cytokine family, along with IL-2, IL-4, IL-7, IL-9, and IL-21. IL-15 is crucial for the homeostasis of Natural Killer (NK) and memory CD8 T cells, and to fight against cancer progression. However, dysregulations of IL-15 expression could occur and participate in the emergence of autoimmune inflammatory diseases as well as hematological malignancies. It is therefore important to understand the different modes of action of IL-15 to decrease its harmful action in pathology without affecting its beneficial effects in the immune system. In this review, we present the different approaches used by researchers to inhibit the action of IL-15, from most broad to the most selective. Indeed, it appears that it is important to selectively target the mode of action of the cytokine rather than the cytokine itself as they are involved in numerous biological processes.

Human Relevance of Preclinical Studies on the Skeletal Impact of Inflammatory Bowel Disease: A Systematic Review and Meta-Analysis

Inflammatory bowel disease (IBD) is a relapsing chronic idiopathic inflammatory condition. The increased risks of fractures in the spine and decreased BMD at all weight-bearing skeletal sites have been reported in IBD patients. The understanding of the mechanisms of IBD-induced bone loss is far from complete. Appropriate animal models are a prerequisite for studying IBD-induced bone loss, which prompted us to undertake quantitative meta-analyses by pooling data from the available IBD models that assessed various bone parameters. Sufficient data for meta-analysis are obtained from chemically- but not genetically induced models. Among the chemically induced models, only the effects of dextran sulfate sodium (DSS) and 2,4,6-trinitrobenzene sulfonic acid (TNBS) on bone parameters have been reported. Meta-analysis showed that both DSS (Hedge's g = 2.124, p = 0.001) and TNBS (Hedge's g = 6.292, p = 0.000) increased inflammatory disease severity. In pooled analysis, bone volumes in femur (Hedge's g = - 3.42, p = 0.000) and tibia (Hedge's g = - 2.49, p = 0.000) showed significant losses upon DSS administration. Similarly, bone formation rate was significantly reduced upon IBD induction (Hedge's g = - 3.495, p = 0.006). Besides, cortical thickness was reduced and trabecular microstructure deteriorated by IBD induction. Insufficient data precluded us from determining the effect of IBD on bone strength and calciotropic hormones, as well as the impact of proinflammatory cytokines on bone turnover. This meta-analysis showed that IBD induction in rodents causes significant bone loss. Impaired osteoblast function appears to be the cause of this impact.

Cytokines and Bone: Osteoimmunology

Cytokines and hematopoietic growth factors have traditionally been thought of as regulators of the development and function of immune and blood cells. However, an ever-expanding number of these factors have been discovered to have major effects on bone cells and the development of the skeleton in health and disease (Table 1). In addition, several cytokines have been directly linked to the development of osteoporosis in both animal models and in patients. In order to understand the mechanisms regulating bone cells and how this may be dysregulated in disease states, it is necessary to appreciate the diverse effects that cytokines and inflammation have on osteoblasts, osteoclasts, and bone mass. This chapter provides a broad overview of this topic with extensive references so that, if desired, readers can access specific references to delve into individual topics in greater detail.