SYK kinase mediates brown fat differentiation and activation

A Novel TLR4-SYK Interaction Axis Plays an Essential Role in the Innate Immunity Response in Bovine Mammary Epithelial Cells

Mammary gland epithelium, as the first line of defense for bovine mammary gland immunity, is crucial in the process of mammary glands’ innate immunity, especially that of bovine mammary epithelial cells (bMECs). Our previous studies successfully marked SYK as an important candidate gene for mastitis traits via GWAS and preliminarily confirmed that SYK expression is down-regulated in bMECs with LPS (E. coli) stimulation, but its work mechanism is still unclear. In this study, for the first time, in vivo, TLR4 and SYK were colocalized and had a high correlation in mastitis mammary epithelium; protein−protein interaction results also confirmed that there was a direct interaction between them in mastitis tissue, suggesting that SYK participates in the immune regulation of the TLR4 cascade for bovine mastitis. In vitro, TLR4 also interacts with SYK in LPS (E. coli)-stimulated or GBS (S. agalactiae)-infected bMECs, respectively. Moreover, TLR4 mRNA expression and protein levels were little affected in bMECsSYK- with LPS stimulation or GBS infection, indicating that SYK is an important downstream element of the TLR4 cascade in bMECs. Interestingly, IL-1β, IL-8, NF-κB and NLRP3 expression in LPS-stimulated or GBS-infected bMECsSYK- were significantly higher than in the control group, while AKT1 expression was down-regulated, implying that SYK could inhibit the IL-1β, IL-8, NF-κB and NLRP3 expression and alleviate inflammation in bMECs with LPS and GBS. Taken together, our solid evidence supports that TLR4/SYK/NF-κB signal axis in bMECs regulates the innate immunity response to LPS or GBS.

A dominant function of LynB kinase in preventing autoimmunity

Here, we report that the LynB splice variant of the Src-family kinase Lyn exerts a dominant immunosuppressive function in vivo, whereas the LynA isoform is uniquely required to restrain autoimmunity in female mice. We used CRISPR-Cas9 gene editing to constrain lyn splicing and expression, generating single-isoform LynA knockout (LynAKO) or LynBKO mice. Autoimmune disease in total LynKO mice is characterized by production of antinuclear antibodies, glomerulonephritis, impaired B cell development, and overabundance of activated B cells and proinflammatory myeloid cells. Expression of LynA or LynB alone uncoupled the developmental phenotype from the autoimmune disease: B cell transitional populations were restored, but myeloid cells and differentiated B cells were dysregulated. These changes were isoform-specific, sexually dimorphic, and distinct from the complete LynKO. Despite the apparent differences in disease etiology and penetrance, loss of either LynA or LynB had the potential to induce severe autoimmune disease with parallels to human systemic lupus erythematosus (SLE).

Src family kinases involved in the differentiation of human preadipocytes

BACKGROUND

Obesity is characterized by the excess accumulation of white adipose tissue (WAT). Src family kinases (SFKs) are non-receptor tyrosine kinases consisting of eight members (SRC, FYN, YES1, HCK, LCK, LYN, FGR and BLK) that have been studied extensively in mammalian cells. Although individual members in murine cells provide some clues that are associated with the regulation of adipogenesis, the specific role of this family in adipocyte differentiation has rarely been assessed, especially in human adipocytes.

METHODS

Herein, we first explored the expression profiles of SFKs during human preadipocyte differentiation. Then, we used the pyrazolo-pyrimidinyl-amine compound PP1, a potent SFK inhibitor, to evaluate the function of SFKs during adipocyte differentiation. Furthermore, we adopted a loss-of-function strategy with siRNAs to determine the role of FGR in adipocyte differentiation.

RESULTS

Here, we found that SRC, FYN, YES1, LYN and FGR were expressed in human preadipocytes and induced after the initiation of differentiation. Furthermore, the SFK inhibitor PP1 suppressed adipocyte differentiation. We also found that PP1 significantly suppressed the SFK activity in preadipocytes and decreased the expression of adipogenic genes in early and late differentiation. Given that FGR exhibited the most expression enhancement in mature adipocytes, we focused on FGR and found that its knockdown reduced lipid accumulation and adipogenic gene expression.

CONCLUSIONS

Collectively, these findings suggest that SFKs, especially FGR, are involved in the differentiation of human preadipocytes. Our results lay a foundation for further understanding the role of SFKs in adipocyte differentiation and provide new clues for anti-obesity therapies.

Inhibition of Syk promotes chemical reprogramming of fibroblasts via metabolic rewiring and H2 S production

Chemical compounds have recently been introduced as alternative and non-integrating inducers of pluripotent stem cell fate. However, chemical reprogramming is hampered by low efficiency and the molecular mechanisms remain poorly characterized. Here, we show that inhibition of spleen tyrosine kinase (Syk) by R406 significantly promotes mouse chemical reprogramming. Mechanistically, R406 alleviates Syk / calcineurin (Cn) / nuclear factor of activated T cells (NFAT) signaling-mediated suppression of glycine, serine, and threonine metabolic genes and dependent metabolites. Syk inhibition upregulates glycine level and downstream transsulfuration cysteine biosynthesis, promoting cysteine metabolism and cellular hydrogen sulfide (H₂ S) production. This metabolic rewiring decreased oxidative phosphorylation and ROS levels, enhancing chemical reprogramming. In sum, our study identifies Syk-Cn-NFAT signaling axis as a new barrier of chemical reprogramming and suggests metabolic rewiring and redox homeostasis as important opportunities for controlling cell fates.

Characterizing the structure-activity relationships of natural products, tanshinones, reveals their mode of action in inhibiting spleen tyrosine kinase

The cytosolic non-receptor protein kinase, spleen tyrosine kinase (SYK), is an attractive drug target in autoimmune, inflammatory disorder, and cancers indications. Here, we employed pharmacophore-based drug screening combined with biochemical assay and molecular dynamics (MD) simulations to identify and characterize inhibitors targeting SYK. The built pharmacophore model, phar-TanI, successfully identified tanshinone (TanI (IC50 = 1.72 μM)) and its analogs (TanIIA (IC50 = 3.2 μM), ST32da (IC50 = 46 μM), and ST32db (IC50 = 51 μM)) which apparently attenuated the activities of SYK in vitro. Additionally, the MD simulations followed by Ligplot analyses revealed that TanI and TanIIA interfered SYK activity through binding deeply into the active site. Besides, TanI and TanIIA mainly interact with residues L377, A400, V433, M448, M450, A451, E452, L453, G454, P455, and L501, which are functional hotspots for structure-based inhibitor optimization against SYK. The structure-activity relationships (SAR) study of the identified SYK inhibitors demonstrated that the pharmacophore model, phar-TanI is reliable and precise in screening inhibitors against SYK. This study disclosed the structure-function relationships of tanshinones from Traditional Chinese Medicine (Danshen), revealing their binding site and mode of action in inhibiting SYK and provides applicability in developing new therapeutic agents.

Phosphocholine accumulation and PHOSPHO1 depletion promote adipose tissue thermogenesis

Phosphocholine phosphatase-1 (PHOSPHO1) is a phosphocholine phosphatase that catalyzes the hydrolysis of phosphocholine (PC) to choline. Here we demonstrate that the PHOSPHO1 transcript is highly enriched in mature brown adipose tissue (BAT) and is further induced by cold and isoproterenol treatments of BAT and primary brown adipocytes. In defining the functional relevance of PHOPSPHO1 in BAT thermogenesis and energy metabolism, we show that PHOSPHO1 knockout mice are cold-tolerant, with higher expression of thermogenic genes in BAT, and are protected from high-fat diet-induced obesity and development of insulin resistance. Treatment of mice with the PHOSPHO1 substrate phosphocholine is sufficient to induce cold tolerance, thermogenic gene expression, and allied metabolic benefits. Our results reveal a role of PHOSPHO1 as a negative regulator of BAT thermogenesis, and inhibition of PHOSPHO1 or enhancement of phosphocholine represent innovative approaches to manage the metabolic syndrome.

Identification of key candidate genes and pathways in multiple myeloma by integrated bioinformatics analysis

Multiple myeloma (MM) is a common hematologic malignancy for which the underlying molecular mechanisms remain largely unclear. This study aimed to elucidate key candidate genes and pathways in MM by integrated bioinformatics analysis. Expression profiles GSE6477 and GSE47552 were obtained from the Gene Expression Omnibus database, and differentially expressed genes (DEGs) with p < .05 and [logFC] > 1 were identified. Functional enrichment, protein–protein interaction network construction and survival analyses were then performed. First, 51 upregulated and 78 downregulated DEGs shared between the two GSE datasets were identified. Second, functional enrichment analysis showed that these DEGs are mainly involved in the B cell receptor signaling pathway, hematopoietic cell lineage, and NF‐kappa B pathway. Moreover, interrelation analysis of immune system processes showed enrichment of the downregulated DEGs mainly in B cell differentiation, positive regulation of monocyte chemotaxis and positive regulation of T cell proliferation. Finally, the correlation between DEG expression and survival in MM was evaluated using the PrognoScan database. In conclusion, we identified key candidate genes that affect the outcomes of patients with MM, and these genes might serve as potential therapeutic targets.

Scans for signatures of selection in Russian cattle breed genomes reveal new candidate genes for environmental adaptation and acclimation

Domestication and selective breeding has resulted in over 1000 extant cattle breeds. Many of these breeds do not excel in important traits but are adapted to local environments. These adaptations are a valuable source of genetic material for efforts to improve commercial breeds. As a step toward this goal we identified candidate regions to be under selection in genomes of nine Russian native cattle breeds adapted to survive in harsh climates. After comparing our data to other breeds of European and Asian origins we found known and novel candidate genes that could potentially be related to domestication, economically important traits and environmental adaptations in cattle. The Russian cattle breed genomes contained regions under putative selection with genes that may be related to adaptations to harsh environments (e.g., AQP5, RAD50, and RETREG1). We found genomic signatures of selective sweeps near key genes related to economically important traits, such as the milk production (e.g., DGAT1, ABCG2), growth (e.g., XKR4), and reproduction (e.g., CSF2). Our data point to candidate genes which should be included in future studies attempting to identify genes to improve the extant breeds and facilitate generation of commercial breeds that fit better into the environments of Russia and other countries with similar climates.

GSK3 is a negative regulator of the thermogenic program in brown adipocytes

Brown adipose tissue is a promising therapeutic target in metabolic disorders due to its ability to dissipate energy and improve systemic insulin sensitivity and glucose homeostasis. β-Adrenergic stimulation of brown adipocytes leads to an increase in oxygen consumption and induction of a thermogenic gene program that includes uncoupling protein 1 (Ucp1) and fibroblast growth factor 21 (Fgf21). In kinase inhibitor screens, we have identified glycogen synthase kinase 3 (GSK3) as a negative regulator of basal and β-adrenergically stimulated Fgf21 expression in cultured brown adipocytes. In addition, inhibition of GSK3 also caused increased Ucp1 expression and oxygen consumption. β-Adrenergic stimulation triggered an inhibitory phosphorylation of GSK3 in a protein kinase A (PKA)-dependent manner. Mechanistically, inhibition of GSK3 activated the mitogen activated protein kinase (MAPK) kinase 3/6-p38 MAPK-activating transcription factor 2 signaling module. In summary, our data describe GSK3 as a novel negative regulator of β-adrenergic signaling in brown adipocytes.