Latent Transforming Growth Factor β Binding Protein 3 Controls Adipogenesis

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.