Fig. 11

Metabolic processes of Cer and S1P in adipose tissue and mechanisms contributing to adipose tissue remodelling. SMase facilitates the conversion of SM into Cer. CDase is responsible for catalysing the conversion of Cer into Sph. S1P can be attributed to the enzymatic activity of SPHK. S1P can in turn be reversibly dephosphorylated by SPP/LPP to regenerate Sph, which is then converted back to Cer. Ceramide kinase (CerK) catalyzes Cer to produce CerP (C1P), which can in turn be reversibly dephosphorylated by CPP/LPP to regenerate Cer, which is then converted back to SM. Elevated levels of Cer and S1P in adipose tissue lead to the convergence of monocytes from blood to adipose tissue and their differentiation into macrophages. Activation of the Tgf-β/Smad signalling pathway by macrophages causes increased secretion of collagen and α-SMA by fibroblasts, resulting in excessive deposition of extracellular matrix. At the same time, macrophages aggregated to and infiltrated the adipose tissue, causing an inflammatory response in the adipose tissue. Adipose tissue inflammation-fibrosis interactions result in adipose tissue remodelling and dysfunction