Pathologic calcification (PC) is a painful and disabling condition whereby calcium-containing crystals deposit in tissues that do not physiologically calcify: cartilage, tendons, muscle, vessels and skin. In cartilage, compression and inflammation triggered by PC leads to cartilage degradation typical of osteoarthritis (OA). The PC process is poorly understood and treatments able to target the underlying mechanisms of the disease are lacking. Here we show a crucial role of the gasotransmitter hydrogen sulfide (H₂S) and, in particular, of the H₂S-producing enzyme cystathionine γ-lyase (CSE), in regulating PC in cartilage. Cse deficiency (Cse KO mice) exacerbated calcification in both surgically-induced (menisectomy) and spontaneous (aging) murine models of cartilage PC, and augmented PC was closely associated with cartilage degradation (OA). On the contrary, Cse overexpression (Cse tg mice) protected from these features. In vitro, Cse KO chondrocytes showed increased calcification, potentially via enhanced alkaline phosphatase (Alpl) expression and activity and increased IL-6 production. The opposite results were obtained in Cse tg chondrocytes. In cartilage samples from patients with OA, CSE expression inversely correlated with the degree of tissue calcification and disease severity. Increased cartilage degradation in murine and human tissues lacking or expressing low CSE levels may be accounted for by dysregulated catabolism. We found higher levels of matrix-degrading metalloproteases Mmp-3 and -13 in Cse KO chondrocytes, whereas the opposite results were obtained in Cse tg cells. Finally, by high-throughput screening, we identified a novel small molecule CSE positive allosteric modulator (PAM), and demonstrated that it was able to increase cellular H₂S production, and decrease murine and human chondrocyte calcification and IL-6 secretion. Together, these data implicate impaired CSE-dependent H₂S production by chondrocytes in the etiology of cartilage PC and worsening of secondary outcomes (OA). In this context, enhancing CSE expression and/or activity in chondrocytes could represent a potential strategy to inhibit PC.

中文翻译：

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气体传输剂硫化氢 (H2S) 可防止软骨中的病理性钙化 (PC)

病理性钙化 (PC) 是一种痛苦和致残的病症，其中含钙晶体沉积在生理上不钙化的组织中：软骨、肌腱、肌肉、血管和皮肤。在软骨中，PC 引发的压缩和炎症导致典型的骨关节炎 (OA) 软骨退化。PC 过程知之甚少，并且缺乏能够针对疾病潜在机制的治疗方法。在这里，我们展示了气体传输剂硫化氢 (H ₂ S)的关键作用，尤其是 H ₂产生 S 的酶胱硫醚 γ-裂解酶 (CSE)，在调节软骨中的 PC 中。Cse 缺乏（Cse KO 小鼠）加剧了手术诱导（半月板切除术）和自发（老化）小鼠软骨 PC 模型的钙化，并且增强的 PC 与软骨退化 (OA) 密切相关。相反，Cse 过表达（Cse tg 小鼠）不受这些特征的影响。在体外，Cse KO 软骨细胞显示钙化增加，这可能是通过增强碱性磷酸酶 (Alpl) 表达和活性以及增加 IL-6 产生来实现的。在 Cse tg 软骨细胞中获得了相反的结果。在 OA 患者的软骨样本中，CSE 表达与组织钙化程度和疾病严重程度呈负相关。缺乏或表达低 CSE 水平的小鼠和人类组织中软骨降解增加可能是由于分解代谢失调所致。我们发现了更高水平的基质降解金属蛋白酶Mmp-3和-13在 Cse KO 软骨细胞中，而在 Cse tg 细胞中获得相反的结果。最后，通过高通量筛选，我们鉴定了一种新型小分子 CSE 正变构调节剂 (PAM)，并证明它能够增加细胞 H ₂ S 产生，并减少鼠和人软骨细胞钙化和 IL-6 分泌。总之，这些数据表明软骨细胞的CSE 依赖性 H ₂ S产生受损是软骨 PC 的病因和次要结果 (OA) 的恶化。在这种情况下，增强软骨细胞中 CSE 的表达和/或活性可能代表一种抑制 PC 的潜在策略。