Skewing of X chromosome inactivation (XCI) occurs when the silencing of one parental X chromosome is non-random. Here, Zito et al. report XCI patterns in lymphoblastoid cell lines, blood, subcutaneous adipose tissue samples and skin samples of monozygotic and dizygotic twins and find XCI skew to associate with tissue and age.

Eosinophilic granulomatosis with polyangiitis (EGPA) is a rare inflammatory disorder characterised by asthma, eosinophilia and vasculitis. Here, the authors describe a genome-wide association study of EGPA that reveals clinical and genetic differences between subgroups stratified by autoantibody status (ANCA).

During high-intensity exercise, muscles convert glucose to lactate, in a process that is energetically less efficient than respiration. Here the authors develop a computational model based on muscle proteomic data showing that bypassing mitochondrial complex I increases ATP production rates, and validate these model predictions in an exercise test on 5 subjects.

Systemic sclerosis (SSc) is a heterogeneous chronic autoimmune disease that affects the connective tissue. Here, López-Isac et al. identify 13 new risk loci for SSc as well as loci specific for limited cutaneous and diffuse SSc and, defining credible sets and performing functional annotation, highlight key pathways and cell types for SSc.

Osteoarthritis results from the progressive destruction of cartilage matrix. Here, Kim et al. identify tankyrase as a regulator of cartilage matrix anabolism, and find that tankyrase inhibition, by preventing SOX9 PARylation, protects from cartilage destruction in a mouse model of osteoarthritis.

Alterations to the microbiome are now associated with various diseases. Here the authors analyze microbiomes from a large population based cohort and show positive correlations between abundance of Streptococcus spp. and osteoarthritis-related knee pain.

Reactive oxygen species (ROS) stimulate GLUT4-mediated glucose transport following contraction of isolated muscle, but it is not clear if this occurs in vivo. Here, the authors show in human volunteers that exercise induces ROS increase in muscle and, using loss of-function animal models, they demonstrate that NOX2 is a major ROS source required to stimulate glucose uptake during exercise.

Interleukin-7 (IL-7) is a central cytokine in T cell homeostasis. Here the authors show that allelic variation at rs6897932, an autoimmune GWAS risk allele at IL7R, regulates surface and soluble IL-7R in stimulated monocytes, indicating a function of monocytes in IL-7-related autoimmunity.

Leflunomide is used for the treatment of rheumatoid arthritis. Here, the authors show that effectiveness is limited in patients with higher levels of serum c-reactive protein (CRP). Using animal models, they show that higher CRP induces HIF1a expression, which in turn interferes with Leflunomide signalling, and that effectiveness of the drug is restored when HIF1a is pharmacologically inhibited.

Multiple myeloma is a cancer of the bone marrow that can induce bone disease. Here, the authors profile the transcriptome of bone-lining cells and find a targetable role of bone morphogenetic protein (BMP) signalling in myeloma-induced bone-disease

HuR is an RNA-binding protein that regulates myotube differentiation in vitro. Here, the authors show that the muscle-specific ablation of HuR in mice leads to enhanced endurance capacity and an increase in oxidative fibres by destabilising PGC1α-mRNA, and show that the mice are protected against cancer cachexia

Systemic lupus erythematosus (SLE) is an autoimmune disease of substantial phenotypic heterogeneity in different ethnic groups. Here, using data from a multi-ethnic cohort, the authors describe an approach based on clinical and molecular data to subtype SLE patients into three clusters of severity.

Adolescent idiopathic scoliosis (AIS) is a common pediatric disease leading to spinal deformities. Here, the authors report GWAS followed by genome-wide meta-analysis in up to 79,211 Japanese individuals, identifying 20 genetic loci for AIS, 14 of which were previously unreported, and perform in vitro validation for rs1978060.

Autoreactivity to myeloperoxidase (MPO) causes autoimmune vasculitis and severe glomerulonephritis. Here, Ooi et al. show that a Staphylococcus aureus plasmid encodes a peptide that is homologous to an immunodominant MPO epitope and induces anti-MPO autoimmunity and glomerulonephritis in mice.

Denervation leads to muscle atrophy and neuromuscular endplate remodeling. Here, the authors show that a balanced activation of mTORC1 contributes to the dynamic regulation of autophagic flux in denervated muscle and that activation of PKB/Akt promotes the nuclear import of HDAC4, which is essential for endplate maintenance upon nerve injury

The adaptor protein SHN3 suppresses new bone formation by controlling osteoblast activity. Here, the authors show that ablation of SHN3 function, either genetically or by delivering an artificial miRNA via AAV9, rescues bone loss in osteoporotic mice, and show that engineering of the AAV9 capsid improves targeting to bone

Osteoarthritis involves whole-joint tissue degeneration. Here, the authors show that miR-204 and miR-211 in mesenchymal joint cells regulate their proliferation, catabolic and osteogenic responses, and that disease progression is ameliorated by intra-articular miR-204 delivery in mice.

Bone regeneration is of interest for treating a wide range of medical conditions. Here, the authors report on bioinspired matrix vesicles loaded with black phosphorus nanosheets and cell-specific aptamers for bone regeneration and demonstrate bone defect repair in vivo.

Increased inflammation during ageing promotes osteoporosis by activating osteoclast function and inhibiting osteoblasts. Here, the authors show that TGFβ1 release from bone matrix during ageing induces degradation of TRAF3 in mesenchymal progenitor cells, leading to reduced osteoblast differentiation and increased osteoclast formation, and suggesting that pharmacological stabilization of TRAF3 could ameliorate age-related osteoporosis.

A number of therapeutic agents aimed at reducing pathology in Duchenne muscular dystrophy have been developed, but may have off-target effects when delivered systemically. Here, the authors express the therapeutic LIF transgene in leukocytes, and show this results in targeting to inflamed dystrophic muscle and reduced fibrosis by suppressing type 2 immunity.

In vivo decorporation of U(VI) from bones is an unsolved challenge because of the formation of stable uranium phosphate complexes. Here, the authors develop a hydroxypyridonone-based ligand with strong uranium complexation and low cytotoxicity. They find this ligand effectively removes uranium from kidney and bones in mice, and is suitable for oral administration.

Muscle loss is associated with altered expression of proteins involved in mitochondrial homeostasis, but whether this is causative remains unclear. Here, the authors show that genetic ablation of the pro-fission protein DRP1 leads to accumulation of abnormal mitochondria that induce muscle atrophy by altering Ca²⁺ homeostasis and cellular stress responses.

Promising pilot clinical trials of mesenchymal stem cells (MSCs) therapy of lupus await validation in larger, controlled trials. Here the authors show that MSCs expand CD1c⁺ dendritic cells in cell culture by producing FLT3L, and that in lupus patients, circulating CD1c⁺ dendritic cells and FLT3L are increased following MSCs therapy.

GWAS have identified risk loci for osteoarthritis (OA), but the causal variants still have to be determined. Here, the authors apply a massively-parallel reporter assay to screen 1,605 candidate SNPs in 35 OA loci, which prioritizes six SNPs in four loci, one of which, rs4730222, is characterized in more detail.

Wwp2 is an HECT-type E3 ubiquitin ligase abundantly expressed in articular cartilage. Here, the authors show that in mice, loss of Wwp2 leads to upregulated Runx2-Adamts5 signaling in articular cartilage and development of osteoarthritis, and that disease severity is reduced by injection of Wwp2 mRNA

Function-altering variants of immune-related genes cause rare autoimmune syndromes, whereas their contribution to common autoimmune diseases remains uncharacterized. Here the authors show that rare variants of lupus-associated genes are present in the majority of lupus patients and healthy controls, but only the variants found in lupus patients alter gene function.

Systemic lupus erythematosus (SLE) shows a striking bias towards higher prevalence in females. Here, the authors perform fine-mapping of an SLE-associated locus at Xp21.2 and characterise a candidate gene, CXorf21, as IFN-responsive in immune cells that shows sexually dimorphic expression.

Arthroplasty is the main clinical option for the treatment of osteoarticular lesions, but has limited efficacy. Here, the authors use a wound dressing with autologous mesenchymal stromal cells, functionalised for local BMP2 delivery, and show feasibility and safety in standardised preclinical tests in animal models, suggesting suitability for use in clinical trials.

Size and shape of bones are important for height and body shape. Here, Styrkarsdottir et al identify 12 loci in a GWAS for bone area derived from DXA scans and show that these loci associate with other bone-related phenotypes including osteoarthritis, height, bone mineral density and risk of hip fracture.

CXCL4 is an inflammatory chemokine signaling through CXCR3 receptor. Here the authors show a CXCR3-independent function of CXCL4: it forms liquid crystals with DNA, potentiating mammalian and bacterial DNA recognition by TLR9, thereby amplifying interferon-a production in systemic sclerosis.

Loss of cartilage tissue is a hallmark of osteoarthritis. Here the authors show that BNTA, a small molecule identified in a chemical screen, promotes ECM generation in human osteoarthritic chondrocytes and cartilage explants, and suppresses pathology in a rat model of osteoarthritis.

Antiphospholipid syndrome is characterised by increased neutrophil extracellular trap formation (NETosis) and, consequently, increased thrombotic events. Here Ali et al. show that treatment with adenosine receptor agonists suppresses NETosis and venous thrombosis in mouse models of antiphospholipid syndrome.

TMCO1 is a recently described endoplasmic reticular Ca²⁺ channel. Here, the authors show it is important for osteoblast function and bone formation in mice, and identify a novel pathway linking local increases in Ca²⁺ at the ER surface with the posttranslational modification of RUNX2.

Excessive mechanical stress promotes the development of osteoarthritis. Here Chang et al. identify gremlin-1 as a factor expressed in chondrocytes in response to mechanical stress, and contributing to osteoarthritis via activation of the NF-κB pathway.

Parathyroid hormone (PTH) is used to treat osteoporosis, but its therapeutic mechanism remains unclear. Here, the authors show that Tgif1 is a PTH target gene, and that its deletion impairs the function of osteoblasts and PTH-induced bone formation in mice.

GWAS have identified numerous genetic loci for bone mineral density (BMD) and fracture risk. Here, the authors map these variants to putative target genes using ATAC-seq and Capture C of human osteoblasts and confirm ING3 and EPDR1 as BMD genes in in vitro osteoblast differentiation experiments.

Modulation of the cholinergic pathway and spleen function can reduce inflammation with invasive implants. Here, the authors show that non-invasive ultrasound stimulation of the spleen reduces disease severity in a mouse model of inflammatory arthritis, partly via altering B and T cell function.

Dermal myofibroblasts are responsible for fibrosis development in scleroderma. Here the authors show that a bioengineered recombinant human TRAIL ligand reverses established fibrosis in mouse models of scleroderma by targeting the death receptor 5 and inducing apoptosis of myofibroblasts.

Mammalian joints have poor regenerative capacity following amputation. Here, the authors show that in mice, stimulation of the amputation wound with BMP2 and BMP9 stimulates regeneration of a synovial joint that includes bone, cartilage and a synovial cavity.

Metabolic pathways are increasingly recognized as crucial determinants of T cell function. Here the authors show that the balance between IFNγ and IL-10 production in human CD4 T cells is modulated by the cholesterol biosynthetic pathway.

Insulin resistance is associated with development of type 2 diabetes. Here the authors show that TAZ interacts with c-Jun and Tead4, inducing expression of the insulin receptor substrate 1 (IRS1) leading to increased glucose uptake in muscle, and that its activity is counteracted by statin administration.

Osteoarthritis (OA) is associated with cartilage degeneration, and no effective therapy exists. Here, the authors show that the HPIP protein modulates OA progression by regulating Wnt signaling, and that its knockdown in joints via AAV-mediated gene silencing attentuates pathology.

Bone is innervated, and its turnover is affected by sympathetic nerve activity. Here, the authors show that prostaglandin E2, secreted by osteoblasts, activates the EP4 receptor on sensory nerves, inhibiting sympathetic nerve activity and modulating bone formation in mice.

Estrogen promotes negative energy balance and preserves skeletal physiology. Here the authors show that loss of estrogen signalling after ablating estrogen receptor alpha (ERa) in specific hypothalamic neuronal populations leads to a marked sex-dependent increase in bone mass in female mice.

Osteoarthritis is characterised by degeneration of joint cartilage. Here the authors show that the RNA-binding protein ZFP36L1 is upregulated in chondrocytes of humans and mice with osteoarthritis, and that its knockdown in mouse joints protects chondrocytes against apoptosis by modulating the function of heat shock proteins.

The role of innate T cell subsets in the pathogenesis of spondyloarthritis (SpA) is not well understood. Here, the authors examine the role of invariant natural killer T (iNKT) and γδ-T cells in SpA and show that disease-derived iNKT and γδ-T cells have unique and Th17-skewed phenotype and gene expression profiles within inflamed joints.

Optogenetics is a promising alternative approach for restoration of neuromuscular function. Here the authors establish a closed-loop functional optogenetic stimulation for the control of limb joint angle in murine models, which demonstrates improved control and less fatigue than electrical stimulation systems.

B cells contribute to rheumatoid arthritis pathogenesis and bone erosion, but the underlying mechanisms are still unclear. Here the authors show, using mouse models and patient tissues, that B cells directly inhibit osteoblast differentiation by producing CCL3 and TNF, thereby providing a potentially new direction for arthritis therapy.

Myoblast fusion in skeletal muscle is a complex process but how this is regulated is unclear. Here, the authors identify Ash1L, a histone methyltransferase, as modulating myoblast fusion via activation of the myogenesis gene Cdon, and observe decreased Ash1L expression in Duchenne muscular dystrophy.