AKT Isoforms in Macrophage Activation, Polarization, and Survival.

Macrophages display an array of activation phenotypes depending on the activation signal and the cellular microenvironment. The type and magnitude of the response depend on signaling molecules as well as on the epigenetic and metabolic status of the cells at the time of activation. The AKT family of kinases consists of three isoforms encoded by independent genes possessing similar functions and structures. Generation of research tools such as isoform-specific gene deletion mutant mice and cells and isoform-specific antibodies has allowed us to understand the role of each kinase isoform in macrophage activation and homeostasis. This chapter discusses the current evidence on the role of AKT kinases in macrophage activation, polarization, and homeostasis, highlighting the gaps in knowledge and future challenges in the field.

Correlation of systemic metabolic inflammation with knee osteoarthritis.

PURPOSE: The aim of this study was to analyze local and systematic inflammatory status in knee osteoarthritis (KOA), focusing on intra-articular and remote adipose tissue depots, and to explore its potential association with metabolic syndrome (MetS). METHODS: Patients (n = 27) with end-stage KOA were enrolled in the study and samples from infrapatellar fat pad (IFP), synovium, subcutaneous adipose tissue (SAT), synovial fluid (SF), and serum were collected. In homogenates from the tissues, mRNA expression of developmental endothelial locus-1 (DEL-1) was determined. Interleukin 6 (IL-6) and interleukin 8 (IL-8) were measured in tissues and SF and serum samples by enzyme-linked immunosorbent assay. RESULTS: Fifteen patients fulfilled MetS criteria (w-MetS group) and 12 did not (non-MetS). In the entire population, IL-6 levels were significantly higher in IFP compared to synovium (median (interquartile range), 26.05 (26.16) vs. 15.75 (14.8) pg/mg of total protein, p = 0.043), but not to SAT (17.89 (17.9) pg/mg); IL-8 levels were significantly higher in IFP (17.3 (19.3) pg/mg) and SAT (24.2 (26) pg/mg) when compared to synovium (8.45 (6.17) pg/mg) (p = 0.029 and < 0.001, respectively). Significantly higher IL-6 concentrations in SF were detected in w-MetS patients compared to non-MetS (194.8 (299) vs. 64.1 (86.9) pg/ml, p = 0.027). Finally, DEL-1 mRNA expression was higher in IFP compared to synovium (eightfold, p = 0.019). CONCLUSIONS: Our findings support the critical role of IFP in knee joint homeostasis and progression of KOA. Furthermore, in KOA patients w-MetS, SAT is thought to play an important role in intra-knee inflammation via secretion of soluble inflammatory mediators, such as IL-6.