The serine proteases CAP1/Prss8 (prostasin) and CAP3/St14 (matriptase) are identified as ENaC channel-activating proteases in vitro highly suggesting that they are required for proteolytic activation of ENaC in vivo. The present study tested whether CAP3 is relevant for renal proteolytic ENaC activation and affects ENaC-mediated Na+ absorption following Na+-deprivation conditions. CAP3 knockout mice exhibit significant decrease in CAP1 protein expression with altered ENaC subunit and decreased pNCC protein abundances, but overall maintain sodium balance. RNAscope-based analyses reveal co-expression of CAP3 and CAP1 with alpha ENaC in distal tubules of the cortex from wildtype mice. Double CAP1/CAP3-deficiency maintained Na+ and K+ balance on Na+-deprived diet, restored ENaC subunit protein abundances but showed reduced NCC activity under Na+-deprivation. Overall, our data clearly show that CAP3 is not required for direct proteolytic activation of ENaC, but for its protein abundances. Our study reveal a complex regulation of ENaC by these serine proteases on the expression level rather than on its proteolytic activation.

Pigs are susceptible to cold stress due to the absence of brown fat caused by the partial deletion of uncoupling protein 1 during their evolution. Some local pig breeds in China, exhibit potential cold adaptability, but research has primarily focused on fat and intestinal tissues. Skeletal muscle plays a key role in adaptive thermogenesis in mammals, yet the molecular mechanism of cold adaptation in porcine skeletal muscle remains poorly understood. This study investigated the cold adaptability of two pig breeds, Mashen pigs (MS) and Large White pigs (LW), in a 4-day cold (4°C) or room temperature (25°C) environment. We recorded phenotypic changes and collected blood, and longissimus dorsi muscle for transcriptome sequencing. Finally, a candidate gene was randomly selected for functional exploration in porcine skeletal muscle satellite cells. A decrease in body temperature and body weight in both LW and MS pigs under cold stress, accompanied by increased shivering frequency and respiratory frequency. However, MS pigs demonstrated stable physiological homeostasis, indicating a certain level of cold adaptability. LW pigs primarily responded to cold stress by regulating heat production and Glycolipid energy metabolism. MS pigs exhibited a distinct response to cold stress, involving regulation of heat production, energy metabolism pathways, robust fatty acid oxidation ability, and stronger immune response. Furthermore, the functional exploration of PRSS8 in porcine skeletal muscle satellite cells revealed it affected cellular energy metabolism and thermogenesis by regulating ERK phosphorylation. These findings shed light on the diverse transcriptional responses of skeletal muscle in LW and MS pigs under cold stress, offering valuable insights into the molecular mechanisms underlying cold adaptation in pigs.