Osteoporosis is the most common metabolic skeletal disease. It is characterized by the deterioration of the skeletal microarchitecture and bone loss, leading to ostealgia, and even bone fractures. Accumulating evidence has indicated that there is an inextricable relationship between the gut microbiota (GM) and bone homeostasis involving host–microbiota crosstalk. Any perturbation of the GM can play an initiating and reinforcing role in disrupting the bone remodeling balance during the development of osteoporosis. Although the GM is known to influence bone metabolism, the mechanisms associated with these effects remain unclear. Herein, we review the current knowledge of how the GM affects bone metabolism in health and disease, summarize the correlation between pathogen‐associated molecular patterns of GM structural components and bone metabolism, and discuss the potential mechanisms underlying how GM metabolites regulate bone turnover. Deciphering the complicated relationship between the GM and bone health will provide new insights into the prevention and treatment of osteoporosis.

The advent of single-cell RNA sequencing (scRNA-seq) has provided insight into the tumour immune microenvironment (TIME). This review focuses on the application of scRNA-seq in investigation of the TIME. Over time, scRNA-seq methods have evolved, and components of the TIME have been deciphered with high resolution. In this review, we first introduced the principle of scRNA-seq and compared different sequencing approaches. Novel cell types in the TIME, a continuous transitional state, and mutual intercommunication among TIME components present potential targets for prognosis prediction and treatment in cancer. Thus, we concluded novel cell clusters of cancer-associated fibroblasts (CAFs), T cells, tumour-associated macrophages (TAMs) and dendritic cells (DCs) discovered after the application of scRNA-seq in TIME. We also proposed the development of TAMs and exhausted T cells, as well as the possible targets to interrupt the process. In addition, the therapeutic interventions based on cellular interactions in TIME were also summarized. For decades, quantification of the TIME components has been adopted in clinical practice to predict patient survival and response to therapy and is expected to play an important role in the precise treatment of cancer. Summarizing the current findings, we believe that advances in technology and wide application of single-cell analysis can lead to the discovery of novel perspectives on cancer therapy, which can subsequently be implemented in the clinic. Finally, we propose some future directions in the field of TIME studies that can be aided by scRNA-seq technology.

Rheumatoid arthritis patients are at higher risk of developing comorbidities. The main objective of this study was to evaluate the prevalence of major comorbidities in Chinese rheumatoid arthritis patients. We also aimed to identify factors associated with these comorbidities. Baseline demographic, clinical characteristics and comorbidity data from RA patients enrolled in the Chinese Registry of rhEumatoiD arthrITis (CREDIT) from Nov 2016 to August 2017 were presented and compared with those from five other registries across the world. Possible factors related to three major comorbidities (cardiovascular disease, fragility fracture and malignancy) were identified using multivariate logistic regression analyses. A total of 13,210 RA patients were included (80.6% female, mean age 52.9 years and median RA duration 4.0 years). Baseline prevalence rates of major comorbidities were calculated: CVD, 2.2% (95% CI 2.0–2.5%); fragility fracture, 1.7% (95% CI 1.5–1.9%); malignancy, 0.6% (95% CI 0.5–0.7%); overall major comorbidities, 4.2% (95% CI 3.9–4.6%). Advanced age was associated with all comorbidities. Male gender and disease duration were positively related to CVD. Female sex and longer disease duration were potential risk factors for fragility fractures. Ever use of methotrexate (MTX) was negatively related to baseline comorbidities. Patients with rheumatoid arthritis in China have similar prevalence of comorbidities with other Asian countries. Advanced age and long disease duration are possible risk factors for comorbidities. On the contrary, MTX may protect RA patients from several major comorbidities, supporting its central role in the management of rheumatoid arthritis.

Summary: Systemic lupus erythematosus (SLE) is a systemic and poly-aetiological autoimmune disease characterized by the production of antibodies to autologous double-stranded DNA (dsDNA) which serve as diagnostic and prognostic markers. The defective clearance of apoptotic material, together with neutrophil extracellular traps (NETs), provides abundant chromatin or self-dsDNA to trigger the production of anti-dsDNA antibodies, although the mechanisms remain to be elucidated. In SLE patients, the immune complex (IC) of dsDNA and its autoantibodies trigger the robust type I interferon (IFN-I) production through intracellular DNA sensors, which drives the adaptive immune system to break down self-tolerance. In this review, we will discuss the potential resources of self-dsDNA, the mechanisms of self-dsDNA-mediated inflammation through various DNA sensors and its functions in SLE pathogenesis.

MicroRNAs (miRNAs) are a recently discovered class of post‐transcriptional regulators that induce target messenger RNA degradation or translation inhibition. miRNA‐155 (miR‐155) is an important regulator of immune cells both in humans and mice, by which these cells play critical roles in the pathogenesis of rheumatoid arthritis (RA). Recent findings showed that expression of miR‐155 was elevated in RA patients and arthritis models. Moreover, miR‐155 overexpression or knockdown performed significantly in the development of arthritis. This review summarizes the recent findings with respect to miR‐155 in immune responses and the underlying mechanisms responsible for miR‐155‐related autoimmune arthritis. Hopefully the information obtained will benefit the development of novel therapeutic strategies.