SPP1 and chronic obstructive pulmonary disease: Conversely, post-PR, osteopontin, a protein known for its dystrophic effects, and tenacin C, a necroptosis compensatory factor facilitating muscle regeneration, were upregulated at protein levels (by 280 pg·mL−1and 40 pg·mL−1, respectively) in atrophic patients with COPD, whereas fibronectin protein levels were decreased.