In vivo effects of inducible transgene expression of the age-associated glycogenes St6gal1 and Man1a on epidermal homeostasis
Glycosylation of cell-surface proteins plays several essential roles in cell-matrix interactions and receptor signaling, thereby contributing to tissue homeostasis and aging. In aged mouse skin, epidermal stem cells exhibit increased levels of a2,6-sialylated complex-type N-glycans alongside upregulation of glycogenes such as St6gal1 and Man1a; however, the functional importance of these glycosylation changes in vivo remains largely unknown. Here, we generated doxycycline-inducible transgenic mice expressing the age-related glycogenes St6gal1 and Man1a, either individually or in combination, using ubiquitous and epidermis-specific drivers. Lectin-based analyses with SNA and rHeltuba demonstrated corresponding alterations in glycosylation patterns in these mice. Transgenic Man1a induction reduced epidermal proliferation and epidermal thickness. In contrast, St6gal1 induction caused splenomegaly and elevated expression of inflammatory signature genes in the skin but did not measurably alter epidermal proliferation or morphology. Double transgenic mice exhibited a hybrid phenotype combining inflammatory and proliferative impairments, although comparison of ubiquitous and epidermis-specific induction indicated that the observed skin phenotypes depended on the epidermal expression of the transgenes. An SNA lectin-based pull-down assay followed by mass spectrometry identified candidate a2,6-sialylated proteins, including integrin family members, junctional proteins, and surface receptors, following induction of St6gal1 and Man1a. Together, these findings suggest that increased expression of the age-associated glycogenes St6gal1 and Man1a perturbs distinct aspects of epidermal homeostasis in vivo and identify candidate glycoproteins that may mediate these effects.