Tight skin 2 mice exhibit a novel time line of events leading to increased extracellular matrix deposition and dermal fibrosis

• Tsk2/+ mice (a model of systemic sclerosis) develop excess dermal fibrosis with age.
• The tight skin physical phenotype occurs well prior to detectible fibrosis.
• Tsk2/+ mice have excessive elastic fibers, but fibers are not necessary for fibrosis.
• The tight skin physical trait and fibrosis are TGFβ associated.

The tight skin 2 (Tsk2) mouse model of systemic sclerosis (SSc) has many features of the human disease including tight skin, fibrosis, extracellular matrix abnormalities, and reported antinuclear antibodies (ANA). Here we report that Tsk2/+ mice develop excess dermal fibrosis with age, as skin is not significantly fibrotic until 10 weeks, a full eight weeks after the development of the physical tight skin phenotype. Concomitantly with the tight skin phenotype at two weeks of age, Tsk2/+ mice demonstrate increased levels of total transforming growth factor beta 1 (TGF-β1) and excessive accumulation of dermal elastic fibers. The increase in elastic fibers is not responsible for tight skin, however, because Tsk2/+ mice genetically engineered to lack skin elastic fibers nevertheless have tight skin and fibrosis. Finally, about two months after the first measurable increases of total collagen, a portion of Tsk2/+ mice produce ANAs, but at a similar level to wild-type littermates. The timeline of disease development in the Tsk2/+ mouse shows that fibrosis is progressive, with elastic fiber alterations and TGF-β1 over-production occurring at least two months before bona fide fibrosis, that is not dependent on ANA production.