The Immunosuppressive Potential of Cholesterol Sulfate Through T Cell Microvilli Disruption

Atopic Dermatitis: The Relationship Between Immune Mediators and Skin Lipid Barrier

Atopic dermatitis (AD) is a chronic inflammatory skin disease that is prevalent worldwide with complex etiology. Skin barrier defects and abnormal immune activation are crucial in the occurrence and development of AD. In the classic model of the skin barrier, lipids are essential for the formation and maintenance of this barrier as a "mortar" component. However, abnormally activated immune responses promote the lipid barrier deficiency through the secretion of various types of immune mediators directly or indirectly. In this review, we first introduce the skin lipid barrier (SLB) under both normal and abnormal conditions, highlighting the contributions of lipids derived from keratinocytes and sebaceous glands (SGs). Subsequently, the relationships between the immune mediators of Th1, Th2, Th17, Th22, and other types (adipokines, prostaglandins, leukotrienes) and SLB are elaborated in turn. Finally, the therapies for restoring SLB to treat AD are summarized, with a focus on the restoration effect of dupilumab on SLB. We hope that this review will offer a comprehensive perspective for understanding the pathogenesis of lipid metabolism disorders and SLB deficiency caused by immune mediators in AD. It also aims to provide guidance for further research on targeting inflammatory mediators to restore SLB.

Cholesterol Sulfate: Pathophysiological Implications and Potential Therapeutics

Cholesterol sulfate (CS) is a naturally occurring cholesterol derivative that is widely distributed across various tissues and body fluids. In humans, its biosynthesis is primarily mediated by the sulfotransferase (SULT) 2B1b (SULT2B1b). Over the years, CS has been found to play critical roles in various physiological processes, including epidermal cell adhesion, sperm capacitation, platelet adhesion, coagulation, glucolipid metabolism, bone metabolism, gut microbiota metabolism, neurosteroid biosynthesis, T-cell receptor signaling, and immune cell migration. In this review, we first introduce the endogenous regulation of CS biosynthesis and metabolism. We then highlight current advances in the understanding of the physiological roles of CS. Finally, we delve into the implications of CS in various diseases, with a particular focus on its mechanism of action and potential therapeutic applications. A comprehensive understanding of CS's physiological function, biosynthesis regulation, and role as a disease modifier offers novel insights that could pave the way for innovative therapeutic strategies targeting a wide range of conditions.

Mechanoimmunology of T-Cell Activation

T-cell activation, a pivotal process in the adaptive immune response, is initiated when the T cell receptor (TCR) recognises and binds to antigenic peptide-major histocompatibility complex (pMHC) molecules on the cell membrane. Emerging evidence indicates that mechanical cues regulate T-cell activation by modulating TCR signalling and mechanotransduction pathways, although the precise underlying mechanisms remain elusive. This review highlights recent findings suggesting that the TCR functions as a mechanosensor, capable of sensing and transmitting mechanical forces through conformational changes. Key steps in T-cell mechanotransduction are discussed, including the roles of the cytoskeleton, mechanosensitive channels such as Piezo 1 and microvilli in facilitating activation. Additionally, we analyse the mechanical responses of chimeric antigen receptor T cells. Understanding the mechanobiological mechanisms underlying T-cell activation offers novel insights and potential strategies for advancing immunotherapies and treating immune-related disorders.

Sulfonation metabolism in the gut microbiota is the main metabolic pathway of cholesterol in hypercholesterolemic mice

The interactions between dietary cholesterol and intestinal microbiota strongly affect host health. Sulfonation is a major conjugating pathway responsible for regulating the chemical and functional homeostasis of endogenous and exogenous molecules. However, the role of cholesterol sulfonation metabolism in the host remains unclear. This work was designed to profile cholesterol-specific host-microbe interaction and conversion focusing on cholesterol sulfonation metabolism. Results indicated that the serum and fecal cholesterol sulfate (CHS) levels were significantly higher than those of total bile acid (TBA) levels in hypercholesterolemic mice. Deletion of the gut microbiota by antibiotics could dramatically increase total cholesterol (TC) levels but it decreased CHS levels in a pseudo-germ-free (PGF) mouse host. 16S rRNA gene sequencing assay and correlation analysis between the abundance of various intestinal bacteria (phylum and class) and the CHS/TC ratio showed that the intestinal genera Bacteroides contributed essentially to cholesterol sulfonation metabolism. These results were further confirmed in an in situ and ex vivo mouse intestinal model, which indicated that the sulfonation metabolism rate of cholesterol could reach 42% under high cholesterol conditions. These findings provided new evidence that the sulfonation metabolic pathway dominated cholesterol metabolism in hypercholesterolemic mice and microbial conversion of cholesterol-to-CHS was of vital importance for cholesterol-lowering by Bacteroides. This suggested that the gut microbiota could regulate cholesterol metabolism and that it was feasible to reduce cholesterol levels by dietary interventions involving the gut microbiota.

Human sulfotransferase SULT2B1 physiological role and the impact of genetic polymorphism on enzyme activity and pathological conditions

Human SULT2B1gene is responsible for expressing SULT2B1a and SULT2B1b enzymes, which are phase II metabolizing enzymes known as pregnenolone and cholesterol sulfotransferase (SULT), respectively. They are expressed in several tissues and contribute to steroids and hydroxysteroids homeostasis. Genetic variation of the SULT2B1 is reported to be associated with various pathological conditions, including autosomal recessive ichthyosis, cardiovascular disease, and different types of cancers. Understanding the pathological impact of SULT2B1 genetic polymorphisms in the human body is crucial to incorporating these findings in evaluating clinical conditions or improving therapeutic efficacy. Therefore, this paper summarized the most relevant reported studies concerning SULT2B1 expression, tissue distribution, substrates, and reported genetic polymorphisms and their mechanisms in enzyme activity and pathological conditions.

Transient hydroxycholesterol treatment restrains TCR signaling to promote long-term immunity

T cell receptor (TCR) plays a fundamental role in adaptive immunity, and TCR-T cell therapy holds great promise for treating solid tumors and other diseases. However, there is a noticeable absence of chemical tools tuning TCR activity. In our study, we screened natural sterols for their regulatory effects on T cell function and identified 7-alpha-hydroxycholesterol (7a-HC) as a potent inhibitor of TCR signaling. Mechanistically, 7a-HC promoted membrane binding of CD3ε cytoplasmic domain, a crucial signaling component of the TCR-CD3 complex, through alterations in membrane physicochemical properties. Enhanced CD3ε membrane binding impeded the condensation between CD3ε and the key kinase Lck, thereby inhibiting Lck-mediated TCR phosphorylation. Transient treatments of TCR-T cells with 7a-HC resulted in reduced signaling strength, increased memory cell populations, and superior long-term antitumor functions. This study unveils a chemical regulation of TCR signaling, which can be exploited to enhance the long-term efficacy of TCR-T cell therapy.

Revisiting the effect of cholesteryl sulfate on clotting and fibrinolysis: Inhibition of human thrombin and other human blood proteases

Cholesteryl sulfate (CS) was quantitatively synthesized by microwave-assisted sulfonation of cholesterol followed by sodium exchange chromatography. In vitro effects of CS on human thrombin and other serine proteases of the coagulation and fibrinolysis processes were investigated using a series of biochemical and biophysical techniques. CS was found to inhibit thrombin with an IC50 value of 140.8 ± 21.8 μM at pH 7.4 and 25 ○C. Michaelis-Menten kinetics indicated that thrombin inhibition by CS is non-competitive (allosteric) in nature. Fluorescence-based binding studies indicated that CS binds to thrombin with a KD value of 180.9 ± 18.9 μM. Given the lack of competition with heparins and a hirudin peptide in competitive inhibition assays, it appears that CS does not bind to thrombin's exosites 1 or 2 and it rather recognizes a different allosteric exosite. CS was found to partially inhibit thrombin-mediated fibrinogen activation with an IC50 value of 175.5 ± 17.5 μM and efficacy of ∼26.0 ± 6.6%. Likewise, CS selectively doubled the activated partial thromboplastin time with EC2x of 521 μM. Interestingly, CS was found to also inhibit factors Xa and XIa as well as plasmin with IC50 values of ∼85-250 μM and efficacy of 94-100%. Nevertheless, CS most potently inhibited factor XIIa with an IC50 Value of ∼17 μM and efficacy of 60%. Surprisingly, CS did not inhibit factor IXa. These results encourage further in vitro and in vivo investigation of CS to better understand its (patho-) physiological roles in coagulation and hemostasis.