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Glycosphingolipids (GSLs) are key constituents of membrane bilayers playing a role in structural integrity, cell signalling in microdomains, endosomes and lysosomes, and cell death pathways. Conversion of ceramide into GSLs is controlled by GCS (glucosylceramide synthase) and inhibitors of this enzyme for the treatment of lipid storage disorders and specific cancers. With a diverse range of functions attributed to GSLs, the ability of the GSC inhibitor, eliglustat, to reduce myeloma bone disease was investigated. In pre-clinical models of multiple myeloma, osteoclast-driven bone loss was reduced by eliglustat in a mechanistically separate manner to zoledronic acid, a bisphosphonate that prevents osteoclast-mediated bone destruction. Autophagic degradation of TNF receptor-associated factor 3 (TRAF3), a key step for osteoclast differentiation, was inhibited by eliglustat as evidenced by TRAF3 lysosomal and cytoplasmic accumulation. By altering GSL composition, eliglustat prevented lysosomal degradation whilst exogenous addition of missing GSLs rescued TRAF3 degradation to restore osteoclast formation in bone marrow cells from myeloma patients. This work highlights the clinical potential of eliglustat as a therapy for myeloma bone disease. Furthermore, using eliglustat as a lysosomal inhibitor in osteoclasts may widen its therapeutic uses to other bone disorders such as bone metastasis, osteoporosis and inflammatory bone loss.

The nuclear factor I/X (NFIX) gene encodes a ubiquitously expressed transcription factor whose mutations lead to two allelic disorders characterized by developmental, skeletal, and neural abnormalities, namely, Malan syndrome (MAL) and Marshall-Smith syndrome (MSS). NFIX mutations associated with MAL mainly cluster in exon 2 and are cleared by nonsense-mediated decay (NMD) leading to NFIX haploinsufficiency, whereas NFIX mutations associated with MSS are clustered in exons 6-10 and escape NMD and result in the production of dominant-negative mutant NFIX proteins. Thus, different NFIX mutations have distinct consequences on NFIX expression. To elucidate the in vivo effects of MSS-associated NFIX exon 7 mutations, we used CRISPR-Cas9 to generate mouse models with exon 7 deletions that comprised: a frameshift deletion of two nucleotides (Nfix Del2); in-frame deletion of 24 nucleotides (Nfix Del24); and deletion of 140 nucleotides (Nfix Del140). Nfix +/Del2, Nfix +/Del24, Nfix +/Del140, Nfix Del24/Del24, and Nfix Del140/Del140 mice were viable, normal, and fertile, with no skeletal abnormalities, but Nfix Del2/Del2 mice had significantly reduced viability (p

Glycosphingolipids (GSLs) are key constituents of membrane bilayers playing a role in structural integrity, cell signalling in microdomains, endosomes and lysosomes, and cell death pathways. Conversion of ceramide into GSLs is controlled by GCS (glucosylceramide synthase) and inhibitors of this enzyme for the treatment of lipid storage disorders and specific cancers. With a diverse range of functions attributed to GSLs, the ability of the GSC inhibitor, eliglustat, to reduce myeloma bone disease was investigated. In pre-clinical models of multiple myeloma, osteoclast-driven bone loss was reduced by eliglustat in a mechanistically separate manner to zoledronic acid, a bisphosphonate that prevents osteoclast-mediated bone destruction. Autophagic degradation of TNF receptor-associated factor 3 (TRAF3), a key step for osteoclast differentiation, was inhibited by eliglustat as evidenced by TRAF3 lysosomal and cytoplasmic accumulation. By altering GSL composition, eliglustat prevented lysosomal degradation whilst exogenous addition of missing GSLs rescued TRAF3 degradation to restore osteoclast formation in bone marrow cells from myeloma patients. This work highlights the clinical potential of eliglustat as a therapy for myeloma bone disease. Furthermore, using eliglustat as a lysosomal inhibitor in osteoclasts may widen its therapeutic uses to other bone disorders such as bone metastasis, osteoporosis and inflammatory bone loss. [ABSTRACT FROM AUTHOR]

Glycosphingolipids (GSLs) are essential constituents of cell membranes and lipid rafts and can modulate signal transduction events. The contribution of GSLs in osteoclast (OC) activation and osteolytic bone diseases in malignancies such as the plasma cell dyscrasia multiple myeloma (MM) is not known. Here, we tested the hypothesis that pathological activation of OCs in MM requires de novo GSL synthesis and is further enhanced by myeloma cell-derived GSLs. Glucosylceramide synthase (GCS) inhibitors, including the clinically approved agent N-butyl-deoxynojirimycin (NB-DNJ), prevented OC development and activation by disrupting RANKL-induced localization of TRAF6 and c-SRC into lipid rafts and preventing nuclear accumulation of transcriptional activator NFATc1. GM3 was the prevailing GSL produced by patient-derived myeloma cells and MM cell lines, and exogenous addition of GM3 synergistically enhanced the ability of the pro-osteoclastogenic factors RANKL and insulin-like growth factor 1 (IGF-1) to induce osteoclastogenesis in precursors. In WT mice, administration of GM3 increased OC numbers and activity, an effect that was reversed by treatment with NB-DNJ. In a murine MM model, treatment with NBDNJ markedly improved osteolytic bone disease symptoms. Together, these data demonstrate that both tumor-derived and de novo synthesized GSLs influence osteoclastogenesis and suggest that NB-DNJ may reduce pathological OC activation and bone destruction associated with MM., Introduction Sphingolipids and their glycosylated derivatives, glycosphingolipids (GSLs), are essential structural components of mammalian cell membranes and are characterized by heterogenic composition among tissues and even in the same cell [...]

Alarmins are endogenous molecules that are constitutively available and released upon tissue damage and activate the immune system. Current evidence indicates that uncontrolled and excessive release of alarmins contributes to [...]

A major discovery of recent decades has been the existence of stem cells and their potential to repair many, if not most, tissues. With the aging population, many attempts have been made to use exogenous stem cells to promote tissue repair, so far with limited success. An alternative approach, which may be more effective and far less costly, is to promote tissue regeneration by targeting endogenous stem cells. However, ways of enhancing endogenous stem cell function remain poorly defined. Injury leads to the release of danger signals which are known to modulate the immune response, but their role in stem cell-mediated repair in vivo remains to be clarified. Here we show that high mobility group box 1 (HMGB1) is released following fracture in both humans and mice, forms a heterocomplex with CXCL12, and acts via CXCR4 to accelerate skeletal, hematopoietic, and muscle regeneration in vivo. Pretreatment with HMGB1 2 wk before injury also accelerated tissue regeneration, indicating an acquired proregenerative signature. HMGB1 led to sustained increase in cell cycling in vivo, and using Hmgb1-/- mice we identified the underlying mechanism as the transition of multiple quiescent stem cells from G0 to GAlert. HMGB1 also transitions human stem and progenitor cells to GAlert. Therefore, exogenous HMGB1 may benefit patients in many clinical scenarios, including trauma, chemotherapy, and elective surgery. [ABSTRACT FROM AUTHOR]