CUL4A‐mediated ZEB1/microRNA‐340‐5p/HMGB1 axis promotes the development of osteoporosis

Abstract

Understanding the molecular mechanisms underlying osteoclast differentiation provides insights into bone loss and even osteoporosis. The specific mechanistic actions of cullin 4A (CUL4A) in osteoclast differentiation and resultant osteoporosis is poorly explored. We developed a mouse model of osteoporosis using bilateral ovariectomy (OVX) and examined CUL4A expression. It was noted that CUL4A expression was increased in the bone marrow of OVX mice. Overexpression of CUL4A promoted osteoclast differentiation, and knockdown of CUL4A alleviated osteoporosis symptoms of OVX mice. Bioinformatic analyses were applied to identify the downstream target genes of microRNA‐340‐5p (miR‐340‐5p), followed by interaction analysis. The bone marrow macrophages (BMMs) were isolated from femur of OVX mice, which were transfected with different plasmids to alter the expression of CUL4A, Zinc finer E‐box binding homeobox 1 (ZEB1), miR‐340‐5p, and Toll‐like receptor 4 (TLR4). ChIP assay was performed to detect enrichment of ZEB1 promoter by H3K4me3 antibody in BMMs. ZEB1 was overexpressed in the bone marrow of OVX mice. Overexpression of CUL4A mediated H3K4me3 methylation to increase ZEB1 expression, thus promoting osteoclast differentiation. Meanwhile, ZEB1 could inhibit miR‐340‐5p expression and upregulate HMGB1 to induce osteoclast differentiation. Overexpressed ZEB1 activated the TLR4 pathway by regulating the miR‐340‐5p/HMGB1 axis to induce osteoclast differentiation, thus promoting the development of osteoporosis. Overall, E3 ubiquitin ligase CUL4A can upregulate ZEB1 to repress miR‐340‐5p expression, leading to HMGB1 upregulation and the TLR4 pathway activation, which promotes osteoclast differentiation and the development of osteoporosis.

The critical role of toll-like receptor 4 in bone remodeling of osteoporosis: from inflammation recognition to immunity

“…Also, TLR4 can be activated by LPS and ovariectomized surgery. Mechanistically, overexpressed Zinc finer E-box binding homeobox 1 (ZEB1), down-regulated KDM4A, overexpressed miR-137, overexpression of circ_0134944, and inhibition of miR-630 ( 12 , 38 , 39 ). Rajpar et al.…”

“…Chen et al. ( 38 ) reported that E3 ubiquitin ligase CUL4A promoted osteoclast differentiation by upregulating ZEB1 to repress miR-340-5p expression, causing HMGB1 upregulation and the TLR4 activation, thus inducing the development of osteoporosis. Wang et al.…”

“…Also, TLR4 can be activated by LPS and ovariectomized surgery. Mechanistically, overexpressed Zinc finer E-box binding homeobox 1 (ZEB1), down-regulated KDM4A, overexpressed miR-137, overexpression of circ_0134944, and inhibition of miR-630 (12,38,39). Rajpar et al (40) reported that mechanical loading of osteoblasts enhanced the activation of TLR4 receptors by endogenous DAMPS and/or TLR4 agonists.…”

“…As shown in Figure 1 with the flow diagram, thirty studies were finally included. Among them, six included studies (39,(41)(42)(43)(44)(45) provided the clinical data from osteoporosis patients (Table 1), 17 studies (12,37,38,40,(46)(47)(48)(49)(50)(51)(52)(53)(54)(55)(56)(57)(58) reported the molecular mechanisms underlying the role of TLR4 in osteoporosis (Table 2), and seven studies (59)(60)(61)(62)(63)(64)(65) provided the data of specific treatments-targeted TLR4 for osteoporosis (Table 3). The key information of the 30 eligible studies included the study object, disease modeling method, the status of TLR4, effect on osteoblast or osteoclast, associated genes or pathways, and the main findings of the independent study.…”

CUL4A‐mediated ZEB1/microRNA‐340‐5p/HMGB1 axis in osteoporosis and their modulation by essential fatty acids (EFAs)

“…Osteoporosis is due to an imbalance in the ratio between proliferation, maturation, and function of osteoblasts and osteoclasts with the balance tilted more towards osteoclasts. In a recent study, Chen et al [1] showed that cullin 4A (CUL4A) expression was increased in the bone marrow of bilateral ovariectomy (OVX) mice that led to promotion of osteoclast differentiation. It was found that the bone marrow macrophages (BMMs) isolated from femur of OVX mice showed an increase in Zinc finer E-box binding homeobox 1 (ZEB1), and toll-like receptor 4 (TLR4) expression and consequent changes in miR-340-5p expression and upregulation of HMGB1 led to the induction of osteoclast differentiation-all these events ultimately promoted the development of osteoporosis.…”