# TGF-β signaling

TGF-β (transforming growth factor β) signaling starts when TGF-β proteins (TGF-β1, β2, β3) bind a receptor complex (TβRII paired with TβRI). That complex tags messenger proteins (R-SMADs 2 and 3), which then team up with SMAD4 and move into the nucleus to adjust gene activity. That is the main ('canonical') route. Non-canonical branches also tap into MAPK, Rho-GTPase, and PI3K. TGF-β is a versatile cytokine. Depending on context, it can block cell growth, tune the immune system, drive scarring (fibrosis), or trigger cell death. In aging, elevated TGF-β1 is part of the 'old' blood environment. It has been implicated in suppressing your brain and muscle stem cells, and in driving fibrosis across many organs. So blocking the pathway is an active area of therapy research.

## Sources

- Massagué J. (2012). TGFβ signalling in context. Nature Reviews Molecular Cell Biology. https://doi.org/10.1038/nrm3434

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