Release of CXCL12 From Apoptotic Skeletal Cells Contributes to Bone Growth Defects Following Dexamethasone Therapy in Rats

Exogenous growth hormone functionally alleviates glucocorticoid-induced longitudinal bone growth retardation in male rats by activating the Ihh/PTHrP signaling pathway

Glucocorticoid (GC)-induced longitudinal bone growth retardation is a common and severe adverse effect in pediatric patients receiving GC immunosuppressive therapy. Molecular mechanisms underlying GC-induced growth inhibition are unclear. GC withdrawal following short-term high-dose use is common, including in the immediate post-transplant period. However, whether skeleton growth recovery is sufficient or whether growth-promoting therapy is required following GC withdrawal is unknown. The aim of this study was to investigate the effect of exogenous growth hormone (GH) on growth plate impairment in GC-induced longitudinal bone growth retardation. Here, apoptotic chondrocytes in the hypertrophic layer of growth plates increased whereas Indian Hedgehog (Ihh) and Parathyroid Hormone Related Peptide (PTHrP) protein levels in the growth plate decreased following GC exposure. The hypertrophic zone of the growth plate expanded following GC withdrawal. Subcutaneously injected GH penetrated the growth plate and modified its organization in rats following GC withdrawal. Ihh and PTHrP expression in GC-induced apoptotic chondrocytes decreased in vitro. GH promoted chondrocyte proliferation by activating Ihh/PTHrP signaling. Downregulating Ihh using specific siRNAs increased chondrocyte apoptosis and inhibited PTHrP, Sox9, and type II collagen (Col2a1) protein expression. GH inhibited apoptosis of Ihh-deficient growth plate chondrocytes by upregulating PTHrP, Sox9, and Col2a1 expression. Thus, reversal of the effect of GC on growth plate impairment following its withdrawal is insufficient, and exogenous GH provides growth plate chondral protection and improved longitudinal growth following GC withdrawal by acting on the Ihh/PTHrP pathway.

Microenvironment in subchondral bone: predominant regulator for the treatment of osteoarthritis

Osteoarthritis (OA) is a degenerative joint disease in the elderly. Although OA has been considered as primarily a disease of the articular cartilage, the participation of subchondral bone in the pathogenesis of OA has attracted increasing attention. This review summarises the microstructural and histopathological changes in subchondral bone during OA progression that are due, at the cellular level, to changes in the interactions among osteocytes, osteoblasts, osteoclasts (OCs), endothelial cells and sensory neurons. Therefore, we focus on how pathological cellular interactions in the subchondral bone microenvironment promote subchondral bone destruction at different stages of OA progression. In addition, the limited amount of research on the communication between OCs in subchondral bone and chondrocytes (CCs) in articular cartilage during OA progression is reviewed. We propose the concept of 'OC-CC crosstalk' and describe the various pathways by which the two cell types might interact. Based on the 'OC-CC crosstalk', we elaborate potential therapeutic strategies for the treatment of OA, including restoring abnormal subchondral bone remodelling and blocking the bridge-subchondral type H vessels. Finally, the review summarises the current understanding of how the subchondral bone microenvironment is related to OA pain and describes potential interventions to reduce OA pain by targeting the subchondral bone microenvironment.

β-Catenin signaling is important for osteogenesis and hematopoiesis recovery following methotrexate chemotherapy in rats

Cancer chemotherapy can significantly impair the bone formation and cause myelosuppression; however, their recovery potentials and mechanisms remain unclear. This study investigated the roles of the β-catenin signaling pathway in bone and bone marrow recovery potentials in rats treated with antimetabolite methotrexate (MTX) (five once-daily injections, 0.75 mg/kg) with/without β-catenin inhibitor indocyanine green (ICG)-001 (oral, 200 mg/kg/day). ICG alone reduced trabecular bone volume and bone marrow cellularity. In MTX-treated rats, ICG suppressed bone volume recovery on Day 11 after the first MTX injection. ICG exacerbated MTX-induced decreases on Day 9 osteoblast numbers on bone surfaces, their formation in vitro from bone marrow stromal cells (osteogenic differentiation/mineralization), as well as expression of osteogenesis-related markers Runx2, Osx, and OCN in bone, and it suppressed their subsequent recoveries on Day 11. On the other hand, ICG did not affect MTX-induced increased osteoclast density and the level of the osteoclastogenic signal (RANKL/OPG expression ratio) in bone, suggesting that ICG inhibition of β-catenin does nothing to abate the increased bone resorption induced by MTX. ICG also attenuated bone marrow cellularity recovery on Day 11, which was associated with the suppressed recovery of CD34⁺ or c-Kit⁺  hematopoietic progenitor cell contents. Thus, β-catenin signaling is important for osteogenesis and hematopoiesis recoveries following MTX chemotherapy.

Cxcl12 Deletion in Mesenchymal Cells Increases Bone Turnover and Attenuates the Loss of Cortical Bone Caused by Estrogen Deficiency in Mice

CXCL12 is abundantly expressed in reticular cells associated with the perivascular niches of the bone marrow (BM) and is indispensable for B lymphopoiesis. Cxcl12 promotes osteoclastogenesis and has been implicated in pathologic bone resorption. We had shown earlier that estrogen receptor α deletion in osteoprogenitors and estrogen deficiency in mice increase Cxcl12 mRNA and protein levels in the BM plasma, respectively. We have now generated female and male mice with conditional deletion of a Cxcl12 allele in Prrx1 targeted cells (Cxcl12^∆Prrx1 ) and show herein that they have a 90% decrease in B lymphocytes but increased erythrocytes and adipocytes in the marrow. Ovariectomy increased the expression of Cxcl12 and B-cell number in the Cxcl12^f/f control mice, but these effects were abrogated in the Cxcl12^∆Prrx1 mice. Cortical bone mass was not affected in Cxcl12^∆Prrx1 mice. Albeit, the cortical bone loss caused by ovariectomy was greatly attenuated. Most unexpectedly, the rate of bone turnover in sex steroid-sufficient female or male Cxcl12^∆Prrx1 mice was dramatically increased, as evidenced by a more than twofold increase in several osteoblast- and osteoclast-specific mRNAs, as well as increased mineral apposition and bone formation rate and increased osteoclast number in the endosteal surface. The magnitude of the Cxcl12^∆Prrx1 -induced changes were much greater than those caused by ovariectomy or orchidectomy in the Cxcl12^f/f mice. These results strengthen the evidence that CXCL12 contributes to the loss of cortical bone mass caused by estrogen deficiency. Moreover, they reveal for the first time that in addition to its effects on hematopoiesis, CXCL12 restrains bone turnover-without changing the balance between resorption and formation-by suppressing osteoblastogenesis and the osteoclastogenesis support provided by cells of the osteoblast lineage. © 2020 American Society for Bone and Mineral Research.

Determining Oxidative Damage by Lipid Peroxidation Assay in Rat Serum

It has been well-established that malondialdehyde (MDA), which is generated during the process of lipid peroxidation, is a commonly known biomarker for oxidative stress. Therefore, the serum levels of MDA are detected by using the lipid peroxidation assay with commercially available kit to determine the induction of oxidative stress in rat models.