Genetic Deletion of LRP5 and LRP6 in Macrophages Exacerbates Colitis-Associated Systemic Inflammation and Kidney Injury in Response to Intestinal Commensal Microbiota

Regulation of bone homeostasis: signaling pathways and therapeutic targets

As a highly dynamic tissue, bone is continuously rebuilt throughout life. Both bone formation by osteoblasts and bone resorption by osteoclasts constitute bone reconstruction homeostasis. The equilibrium of bone homeostasis is governed by many complicated signaling pathways that weave together to form an intricate network. These pathways coordinate the meticulous processes of bone formation and resorption, ensuring the structural integrity and dynamic vitality of the skeletal system. Dysregulation of the bone homeostatic regulatory signaling network contributes to the development and progression of many skeletal diseases. Significantly, imbalanced bone homeostasis further disrupts the signaling network and triggers a cascade reaction that exacerbates disease progression and engenders a deleterious cycle. Here, we summarize the influence of signaling pathways on bone homeostasis, elucidating the interplay and crosstalk among them. Additionally, we review the mechanisms underpinning bone homeostatic imbalances across diverse disease landscapes, highlighting current and prospective therapeutic targets and clinical drugs. We hope that this review will contribute to a holistic understanding of the signaling pathways and molecular mechanisms sustaining bone homeostasis, which are promising to contribute to further research on bone homeostasis and shed light on the development of targeted drugs.

Research progress in the role of gut microbiota in acute kidney injury

Acute kidney injury (AKI) remains a global public health problem with high incidence, high mortality rates, expensive medical costs, and limited treatment options. AKI can further progress to chronic kidney disease (CKD) and eventually end-stage renal disease (ESRD). Previous studies have shown that trauma, adverse drug reactions, surgery, and other factors are closely associated with AKI. With further in-depth exploration, the role of gut microbiota in AKI is gradually revealed. After AKI occurs, there are changes in the composition of gut microbiota, leading to disruption of the intestinal barrier, intestinal immune response, and bacterial translocation. Meanwhile, metabolites of gut microbiota can exacerbate the progression of AKI. Therefore, elucidating the specific mechanisms by which gut microbiota is involved in the occurrence and development of AKI can provide new insights from the perspective of intestinal microbiota for the prevention and treatment of AKI.

Low-density lipoprotein receptor-related protein 6 ablation in macrophages differentially inhibits lung injury-mediated inflammation and metastasis

Low-density lipoprotein receptor-related protein 6 (LRP6) is a receptor protein for Wnt ligands. Yet, their role in immune cell regulation remains elusive. Here we demonstrated that genetic deletion of LRP6 in macrophages using LysM-cre Lrp6fl/fl (Lrp6MKO) mice showed differential inhibition of inflammation in the bleomycin (BLM)-induced lung injury model and B16F10 melanoma lung metastasis model. Lrp6MKO mice showed normal immune cell populations in the lung and circulating blood in homeostatic conditions. In the BLM-induced lung injury model, Lrp6MKO mice showed a decreased number of monocyte-derived alveolar macrophages, reduced collagen deposition and alpha-smooth muscle actin (αSMA) protein levels in the lung. In B16F10 lung metastasis model, Lrp6MKO mice reduced lung tumor foci. Monocytic and granulocytic-derived myeloid-derived suppressor cells (M-MDSCs and G-MDSCs) were increased in the lung. In G-MDSCs, hypoxia-inducible factor 1α (HIF1α)+ PDL1+ population was markedly decreased but not in M-MDSCs. Taken together, our results show that the role of LRP6 in macrophages is differential depending on the inflammation microenvironment in the lung.

The Transcription Factor RXRα in CD11c+ APCs Regulates Intestinal Immune Homeostasis and Inflammation

APCs such as dendritic cells and macrophages play a pivotal role in mediating immune tolerance and restoring intestinal immune homeostasis by limiting inflammatory responses against commensal bacteria. However, cell-intrinsic molecular regulators critical for programming intestinal APCs to a regulatory state rather than an inflammatory state are unknown. In this study, we report that the transcription factor retinoid X receptor α (RXRα) signaling in CD11c+ APCs is essential for suppressing intestinal inflammation by imparting an anti-inflammatory phenotype. Using a mouse model of ulcerative colitis, we demonstrated that targeted deletion of RXRα in CD11c+ APCs in mice resulted in the loss of T cell homeostasis with enhanced intestinal inflammation and increased histopathological severity of colonic tissue. This was due to the increased production of proinflammatory cytokines that drive Th1/Th17 responses and decreased expression of immune-regulatory factors that promote regulatory T cell differentiation in the colon. Consistent with these findings, pharmacological activation of the RXRα pathway alleviated colitis severity in mice by suppressing the expression of inflammatory cytokines and limiting Th1/Th17 cell differentiation. These findings identify an essential role for RXRα in APCs in regulating intestinal immune homeostasis and inflammation. Thus, manipulating the RXRα pathway could provide novel opportunities for enhancing regulatory responses and dampening colonic inflammation.