Role of Lysine‐Specific Demethylase 1 in Metabolically Integrating Osteoclast Differentiation and Inflammatory Bone Resorption Through Hypoxia‐Inducible Factor 1α and E2F1

Abstract

Objective. Hypoxia occurs in tumors, infections, and sites of inflammation, such as in the affected joints of patients with rheumatoid arthritis (RA). It alleviates inflammatory responses and increases bone resorption in inflammatory arthritis by enhancing osteoclastogenesis. The mechanism by which the hypoxia response is linked to osteoclastogenesis and inflammatory bone resorption is unclear. This study was undertaken to evaluate whether the protein lysinespecific demethylase 1 (LSD1) metabolically integrates inflammatory osteoclastogenesis and bone resorption in a state of inflammatory arthritis.Methods. LSD1-specific inhibitors and gene silencing with small interfering RNAs were used to inhibit the expression of LSD1 in human osteoclast precursor cells derived from CD14-positive monocytes, with subsequent assessment by RNA-sequencing analysis. In experimental mouse models of arthritis, inflammatory osteolysis, or osteoporosis, features of accelerated bone loss and inflammatory osteolysis were analyzed. Furthermore, in blood samples from patients with RA, cis-acting expression quantitative trait loci (cis-eQTL) were analyzed for association with the expression of hypoxiainducible factor 1α (HIF-1α), and associations between HIF-1α allelic variants and extent of bone erosion were evaluated.Results. In human osteoclast precursor cells, RANKL induced the expression of LSD1 in a mechanistic target of rapamycin-dependent manner. Expression of LSD1 was higher in synovium from RA patients than in synovium from osteoarthritis patients. Inhibition of LSD1 in human osteoclast precursors suppressed osteoclast differentiation. Results of transcriptome analysis identified several LSD1-mediated hypoxia and cell-cycle pathways as key genetic pathways involved in human osteoclastogenesis. Furthermore, HIF-1α protein, which is rapidly degraded by the proteasome in a normoxic environment, was found to be expressed in RANKL-stimulated osteoclast precursor cells. Induction of LSD1 by RANKL stabilized the expression of HIF-1α protein, thereby promoting glycolysis, in conjunction with up-regulation of the transcription factor E2F1. Analyses of cis-eQTL revealed that higher HIF-1α expression was associated with increased bone erosion in patients with RA. Inhibition of LSD1 decreased pathologic bone resorption in mice, both in models of accelerated osteoporosis and models of arthritis and inflammatory osteolysis.Conclusion. LSD1 metabolically regulates osteoclastogenesis in an energy-demanding inflammatory environment. These findings provide potential new therapeutic strategies targeting osteoclasts in the management of inflammatory arthritis, including in patients with RA.

Female LSD1 Conditional Knockout Mice Have an Increased Bone Mass

“…Much of our data agrees with a study determining the role of LSD1 in human osteoclasts [22]. This group showed that knockdown of LSD1 using shRNA in human osteoclasts suppresses differentiation and decreased pathological bone resorption in an arthritis mouse model [22].…”

“…This group showed that knockdown of LSD1 using shRNA in human osteoclasts suppresses differentiation and decreased pathological bone resorption in an arthritis mouse model [22]. They also demonstrated that RANKL stimulation induces LSD1 expression via the mTOR pathway [22]. While these results agreed with ours, the use of shRNAs in their study may cause off target effects and further studies would need to be performed to confirm their findings.…”

Changes in the composition of gut and vaginal microbiota in patients with postmenopausal osteoporosis

“…Results of the functional analysis indicated that carbohydrate metabolism by GM was significantly decreased, and that complex carbohydrates were absorbed and converted into simple sugars, which were further fermented to produce short-chain fatty acids such as butyric acid (49). And, after further analysis of the correlation between key predicted pathways and clinical parameters, the proteasome pathway significantly reduced in the osteoporosis group was significantly positively correlated with BMD, and could degrade HIF-1 a protein which is associated with bone erosion and expressed in RANKLstimulated osteoclast precursor cells (50). Furthermore, sphingolipid metabolism by VM, which was enriched in the osteoporosis group than the control group, is known to play a key role in the regulation of inflammation signaling pathways.…”

HIF-1α Regulates Bone Homeostasis and Angiogenesis, Participating in the Occurrence of Bone Metabolic Diseases

“…However, Hulley et al [ 25 ] believe that HIF-1α mainly acts as a regulator of osteoclast-mediated bone resorption and has almost no effect on osteoclast differentiation. In the inflammatory environment of high-energy metabolism, lysine-specific demethylase 1 (LSD1) induced by RANKL in a rapamycin-dependent manner stabilizes the expression of HIF-1α, thus promoting glycolysis and leads to pathological bone resorption [ 26 ]. Such an interaction between HIF-1α and RANKL plays a vital role in osteoclast differentiation and physiological/pathological bone resorption mediated by osteoclast.…”