Characterization of age-associated gene expression changes in mouse sweat glands [FP_YO]
Evaporation of sweat on the skin surface is the major mechanism for dissipating heat in humans.  The secretory capacity of sweat glands (SWGs) declines during aging, leading to heat intolerance in the elderly, but the mechanisms responsible for this decline remain incompletely understood.  We investigated the molecular changes accompanying SWG aging in mice, where sweat tests confirmed a significant reduction of active SWGs in old mice relative to young mice.  We first identified SWG-enriched mRNAs by comparing the transcriptome of Eda mutant Tabby mice, which lack SWGs, with that of wild-type control mice by RNA-sequencing analysis.  This comparison revealed 171 mRNAs enriched in SWGs, including 47 mRNAs encoding core secretory proteins such as transcription factors, ion channels, ion transporters, and trans-synaptic signaling proteins.  Among these, 28 SWG-enriched mRNAs showed significantly altered abundance in the aged footpad skin, and 11 of them, including Foxa1, Best2, Chrm3, and Foxc1 mRNAs belonged to the 'core secretory' category.  Consistent with the changes in mRNA expression, immunohistology revealed that higher numbers of secretory cells from old SWGs express FOXC1 protein, the product of Foxc1 mRNA.  In sum, our study identified mRNAs enriched in SWGs, including those that encode core secretory proteins, and changes in these mRNAs and proteins with SWG aging in mice. Overall design: Footpad skin from fore paws of 3 months old and 28 months old C57BL/6JN male mice were isolated under a dissection microscope.  Four biological replicates for each age group.  One mouse = one biological replicate.  Total RNA was isolated using Qiagen RNeasy Fibrous Tissue Mini Kit (Qiagen Cat# 74704).  Sequencing library was prepared using Illumina TruSeq Stranded mRNA Library prep kit (Illumina Cat# 20020594).  Libraries were subsequently sequenced for Paired-End sequencing with Illumina NovaSeq 6000 sequencer.