Binding requirements for latent transforming growth factor Beta2 activation.

Although the mechanism for activation of latent TGFß1 and TGFß3 is understood to involve the binding of the TGFß propeptide (LAP) to both an integrin and an insoluble substrate, the activation of latent TGFß2 has been unclear because the TGFß2 LAP does not have the classical integrin binding sequence found in the other two TGFß isoform LAPs. To assess the potential requirement for covalent linkage with a matrix or cell surface protein for the activation of latent TGFß2, we generated mice in which the TGFß2 Cys residue predicted to be involved in binding was mutated to Ser (Tgfb2C24S). We reasoned that, if covalent interaction with a second molecule is required for latent TGFß2 activation, mutant mice should display a Tgfb2 null (Tgfb2-/-)-like phenotype. Tgfb2C24S mice closely phenocopy Tgfb2-/- mice with death in utero between E18 and P1 and with congenital heart and kidney defects similar to those described for Tgfb2-/- mice. The mutant latent TGFß2 is secreted at levels similar to WT, yet TGFß signaling monitored as nuclear pSmad2 is suppressed. We conclude that, like latent TGFß1, latent TGFß2 activation requires binding to an immobilized matrix or plasma membrane molecule.

Evidence That Anemia Accelerates AS Progression Via Shear-Induced TGF-ß1 Activation: Heyde's Syndrome Comes Full Circle.

The severity of aortic stenosis (AS) is associated with acquired von Willebrand syndrome (AVWS) and gastrointestinal bleeding, leading to anemia (Heyde's syndrome). We investigated how anemia is linked with AS and AVWS using the LA100 mouse model and patients with AS. Induction of anemia in LA100 mice increased transforming growth factor (TGF)-ß1 activation, AVWS, and AS progression. Patients age >75 years with severe AS had higher plasma TGF-ß1 levels and more severe anemia than AS patients age <75 years, and there was a correlation between TGF-ß1 and anemia. These data are compatible with the hypothesis that the blood loss anemia of Heyde's syndrome contributes to AS progression via WSS-induced activation of platelet TGF-ß1 and additional gastrointestinal bleeding via WSS-induced AVWS.

Collagen type VI regulates TGFß bioavailability in skeletal muscle.

Collagen VI-related disorders (COL6-RDs) are a group of rare muscular dystrophies caused by pathogenic variants in collagen VI genes (COL6A1, COL6A2, and COL6A3). Collagen type VI is a heterotrimeric, microfibrillar component of the muscle extracellular matrix (ECM), predominantly secreted by resident fibroadipogenic precursor cells in skeletal muscle. The absence or mislocalizatoion of collagen VI in the ECM underlies the non-cell autonomous dysfunction and dystrophic changes in skeletal muscle with an as of yet elusive direct mechanistic link between the ECM and myofiber dysfunction. Here, we conduct a comprehensive natural history and outcome study in a novel mouse model of COL6-RDs (Col6a2-/- mice) using standardized (Treat-NMD) functional, histological, and physiologic parameter. Notably, we identify a conspicuous dysregulation of the TGFß pathway early in the disease process and propose that the collagen VI deficient matrix is not capable of regulating the dynamic TGFß bioavailability at baseline and also in response to muscle injury. Thus, we propose a new mechanism for pathogenesis of the disease that links the ECM regulation of TGFß with downstream skeletal muscle abnormalities, paving the way for developing and validating therapeutics that target this pathway.