Latent transforming growth factor ß binding protein 3 controls adipogenesis.

ABSTRACT

Transforming growth factor-beta (TGFß) is released from cells as part of a trimeric latent complex consisting of TGFß, the TGFß propeptides, and either a latent TGFß binding protein (LTBP) or glycoprotein-A repetitions predominant (GARP) protein. LTBP1 and 3 modulate latent TGFß 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. TGFß 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 TGFß, as TGFß neutralizing antibody and TGFß receptor I kinase blockade rescue the LTBP3 KD phenotype. These results indicate that LTBP3 has a TGFß-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.