Transforming growth factor-beta (TGFβ) is released from cells as part of a trimeric latent complex consisting of TGFβ, the TGFβ propeptides, and either a latent TGFβ binding protein (LTBP) or glycoprotein-A repetitions predominant (GARP) protein. LTBP1 and 3 modulate latent TGFβ function with respect to secretion, matrix localization, and activation and, therefore, are vital for the proper function of the cytokine in a number of tissues. TGFβ modulates stem cell differentiation into adipocytes (adipogenesis), but the potential role of LTBPs in this process has not been studied. We observed that 72 h post adipogenesis initiation Ltbp1, 2, and 4 expression levels decrease by 74–84%, whereas Ltbp3 expression levels remain constant during adipogenesis. We found that LTBP3 silencing in C3H/10T1/2 cells reduced adipogenesis, as measured by the percentage of cells with lipid vesicles and the expression of the transcription factor peroxisome proliferator-activated receptor gamma (PPARγ). Lentiviral mediated expression of an Ltbp3 mRNA resistant to siRNA targeting rescued the phenotype, validating siRNA specificity. Knockdown (KD) of Ltbp3 expression in 3T3-L1, M2, and primary bone marrow stromal cells (BMSC) indicated a similar requirement for Ltbp3. Epididymal and inguinal white adipose tissue fat pad weights of Ltbp3^−/- mice were reduced by 62% and 57%, respectively, compared to wild-type mice. Inhibition of adipogenic differentiation upon LTBP3 loss is mediated by TGFβ, as TGFβ neutralizing antibody and TGFβ receptor I kinase blockade rescue the LTBP3 KD phenotype. These results indicate that LTBP3 has a TGFβ-dependent function in adipogenesis both in vitro and possibly in vivo.

Significance

Understanding the control of mesenchymal stem cell fate is crucial for the potential use of these cells for regenerative medicine.

中文翻译：

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潜在转化生长因子 β 结合蛋白 3 控制脂肪生成

转化生长因子-β (TGFβ) 作为三聚体潜在复合物的一部分从细胞中释放出来，该复合物由 TGFβ、TGFβ 前肽和潜在的 TGFβ 结合蛋白 (LTBP) 或糖蛋白 A 重复优势 (GARP) 蛋白组成。LTBP1 和 3 在分泌、基质定位和激活方面调节潜在的 TGFβ 功能，因此对于许多组织中细胞因子的正常功能至关重要。TGFβ 调节干细胞分化为脂肪细胞（脂肪生成），但尚未研究 LTBPs 在这一过程中的潜在作用。我们观察到脂肪生成启动后 72 小时Ltbp1、2和4表达水平降低了 74-84%，而Ltbp3在脂肪生成过程中表达水平保持不变。我们发现 C3H/10T1/2 细胞中的 LTBP3 沉默减少了脂肪生成，这是通过具有脂质囊泡的细胞的百分比和转录因子过氧化物酶体增殖物激活受体 γ (PPARγ) 的表达来衡量的。慢病毒介导的对 siRNA 靶向具有抗性的Ltbp3 mRNA 的表达挽救了表型，验证了 siRNA 特异性。3T3-L1、M2 和原代骨髓基质细胞 (BMSC)中Ltbp3表达的敲低 (KD)表明对Ltbp3有类似的要求。Ltbp3的附睾和腹股沟白色脂肪组织脂肪垫重量^-/-与野生型小鼠相比，小鼠的数量分别减少了 62% 和 57%。LTBP3 损失后脂肪形成分化的抑制由 TGFβ 介导，因为 TGFβ 中和抗体和 TGFβ 受体 I 激酶阻断可挽救 LTBP3 KD 表型。这些结果表明 LTBP3在体外和可能体内的脂肪形成中具有 TGFβ 依赖性功能。

意义

了解间充质干细胞命运的控制对于这些细胞在再生医学中的潜在用途至关重要。