Department of Biomedical Sciences, Ohio University, Athens, Ohio, USA.
Ohio Musculoskeletal and Neurological Institute (OMNI), Ohio University, Athens, Ohio, USA.
J Orthop Res. 2022 Dec;40(12):2771-2779. doi: 10.1002/jor.25322. Epub 2022 Mar 12.
Obesity promotes the development of osteoarthritis (OA). It is also well-established that obesity leads to excessive lipid deposition in nonadipose tissues, which often induces lipotoxicity. The objective of this study was to investigate changes in the levels of various lipids in mouse cartilage in the context of obesity and determine if chondrocyte de novo lipogenesis is altered. We used Oil Red O to determine the accumulation of lipid droplets in cartilage from mice fed high-fat diet (HFD) or low-fat diet (LFD). We further used mass spectrometry-based lipidomic analyses to quantify levels of different lipid species. Expression of genes involving in fatty acid (FA) uptake, synthesis, elongation, and desaturation were examined using quantitative polymerase chain reaction. To further study the potential mechanisms, we cultured primary mouse chondrocytes under high-glucose and high-insulin conditions to mimic the local microenvironment associated with obesity and subsequently examined the abundance of cellular lipid droplets. The acetyl-CoA carboxylase (ACC) inhibitor, ND-630, was added to the culture medium to examine the effect of inhibiting de novo lipogenesis on lipid accumulation in chondrocytes. When compared to the mice receiving LFD, the HFD group displayed more chondrocytes with visible intracellular lipid droplets. Significantly higher amounts of total FAs were also detected in the HFD group. Five out of six significantly upregulated FAs were ω-6 FAs, while the two significantly downregulated FAs were ω-3 FAs. Consequently, the HFD group displayed a significantly higher ω-6/ω-3 FA ratio. Ether linked phosphatidylcholine was also found to be higher in the HFD group. Fatty acid desaturase (Fad1-3), fatty acid-binding protein 4 (Fabp4), and fatty acid synthase (Fasn) transcripts were not found to be different between the treatment groups and fatty acid elongase (Elovl1-7) transcripts were undetectable in cartilage. Ceramide synthase 2 (Cers-2), the only transcript found to be changed in these studies, was significantly upregulated in the HFD group. In vitro, chondrocytes upregulated de novo lipogenesis when cultured under high-glucose, high-insulin conditions, and this observation was associated with the activation of ACC, which was attenuated by the addition of ND-630. This study provides the first evidence that lipid deposition is increased in cartilage with obesity and that this is associated with the upregulation of ACC-mediated de novo lipogenesis. This was supported by our observation that ACC inhibition ameliorated lipid accumulation in chondrocytes, thereby suggesting that ACC could potentially be targeted to treat obesity-associated OA.
肥胖会促进骨关节炎（OA）的发展。众所周知，肥胖会导致非脂肪组织中过多的脂质沉积，这通常会引起脂毒性。本研究的目的是研究肥胖小鼠软骨中各种脂质水平的变化，并确定软骨细胞是否发生了从头脂肪生成的改变。我们使用油红 O 来确定高脂肪饮食（HFD）或低脂肪饮食（LFD）喂养的小鼠软骨中脂滴的积累。我们进一步使用基于质谱的脂质组学分析来定量不同脂质种类的水平。使用定量聚合酶链反应（PCR）检测参与脂肪酸（FA）摄取、合成、延伸和去饱和的基因的表达。为了进一步研究潜在的机制，我们在高葡萄糖和高胰岛素条件下培养原代小鼠软骨细胞，以模拟与肥胖相关的局部微环境，然后检查细胞内脂滴的丰度。向培养基中加入乙酰辅酶 A 羧化酶（ACC）抑制剂 ND-630，以研究抑制从头脂肪生成对软骨细胞中脂质积累的影响。与接受 LFD 的小鼠相比，HFD 组显示出更多可见细胞内脂滴的软骨细胞。HFD 组中还检测到总 FA 的含量显著增加。上调的 6 种 FA 中有 5 种是 ω-6 FA，而下调的 2 种是 ω-3 FA。因此，HFD 组显示出明显更高的 ω-6/ω-3 FA 比值。HFD 组的醚连接磷脂酰胆碱含量也较高。在处理组之间，脂肪酸去饱和酶（Fad1-3）、脂肪酸结合蛋白 4（Fabp4）和脂肪酸合酶（Fasn）的转录本没有差异，软骨中脂肪酸延伸酶（Elovl1-7）的转录本无法检测到。在这些研究中发现的唯一变化的酰基辅酶 A 合成酶 2（Cers-2）转录本在 HFD 组中显著上调。在体外，当软骨细胞在高葡萄糖、高胰岛素条件下培养时，会诱导从头脂肪生成增加，这种观察结果与 ACC 的激活有关，而添加 ND-630 可减弱 ACC 的激活。本研究首次提供了证据，证明肥胖时软骨中的脂质沉积增加，并且这与 ACC 介导的从头脂肪生成的上调有关。我们观察到 ACC 抑制可改善软骨细胞中的脂质积累，这表明 ACC 可能成为治疗肥胖相关 OA 的潜在靶点，这一结果支持了上述观点。
