Departments of Integrative Biology and Physiology, University of Minnesota, Minneapolis, MN, USA.
Departments of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, 6-155 Jackson Hall, 321 Church Street, Minneapolis, MN, USA.
Calcif Tissue Int. 2022 Nov;111(5):506-518. doi: 10.1007/s00223-022-01014-7. Epub 2022 Aug 10.
C-type natriuretic peptide (CNP) activation of guanylyl cyclase-B (GC-B) catalyzes the synthesis of cGMP in chondrocytes and osteoblasts. Elevated cGMP stimulates long bone growth, and inactivating mutations in CNP or GC-B reduce cGMP, which causes dwarfism. GC-B mice that express a GC-B mutant that cannot be inactivated by dephosphorylation exhibit increased CNP-dependent GC-B activity, which increases bone length, as well as bone mass and strength. Importantly, how GC-B increases bone mass is not known. Here, we injected 12-week-old, wild type mice once daily for 28 days with or without BMN-111 (Vosoritide), a proteolytically resistant CNP analog. We found that BMN-111 treated mice had elevated levels of osteocalcin and collagen 1 C-terminal telopeptide (CTX) as well as increased osteoblasts and osteoclasts. In BMN-111 injected mice, tibial mRNAs for Rank ligand and osteoprotegrin were increased and decreased, respectively, whereas sclerostin mRNA was elevated 400-fold, consistent with increased osteoclast activity and decreased osteoblast activity. Mineral apposition rates and trabecular bone mass were not elevated in response to BMN-111. Because 9-week-old male GC-B mice have increased bone mass but do not exhibit increased mineral apposition rates, we examined 4-week-old male GC-B mice and found that these animals had increased serum osteocalcin, but not CTX. Importantly, tibias from these mice had 37% more osteoblasts, 26% fewer osteoclasts as well as 36% and 40% higher mineral apposition and bone formation rates, respectively. We conclude that GC-B-dependent bone formation is coupled to an early juvenile process that requires both increased osteoblasts and decreased osteoclasts.
C 型利钠肽（CNP）激活鸟苷酸环化酶-B（GC-B）催化软骨细胞和成骨细胞中环鸟苷酸（cGMP）的合成。升高的 cGMP 刺激长骨生长，而 CNP 或 GC-B 的失活突变会降低 cGMP，从而导致侏儒症。表达不能被去磷酸化失活的 GC-B 突变体的 GC-B 小鼠表现出增加的 CNP 依赖性 GC-B 活性，从而增加骨长度以及骨量和骨强度。重要的是，GC-B 如何增加骨量尚不清楚。在这里，我们每天给 12 周龄的野生型小鼠注射一次或不注射 BMN-111（Vosoritide），一种蛋白水解抗性 CNP 类似物，持续 28 天。我们发现 BMN-111 处理的小鼠具有升高的骨钙素和胶原 1 C 端肽（CTX）水平以及增加的成骨细胞和破骨细胞。在 BMN-111 注射的小鼠中，胫骨 Rank 配体和骨保护素的 mRNA 分别增加和减少，而骨硬化蛋白的 mRNA 升高了 400 倍，与破骨细胞活性增加和成骨细胞活性降低一致。BMN-111 注射并没有提高骨小梁的矿化速率和骨量。由于 9 周龄的雄性 GC-B 小鼠骨量增加，但矿化速率没有增加，我们检查了 4 周龄的雄性 GC-B 小鼠，发现这些动物的血清骨钙素增加，但 CTX 没有增加。重要的是，这些小鼠的胫骨有 37%更多的成骨细胞，26%更少的破骨细胞，以及分别高 36%和 40%的矿化和骨形成速率。我们的结论是，GC-B 依赖性骨形成与一个早期的幼年过程相关，该过程需要增加成骨细胞和减少破骨细胞。
