CTSL and pulmonary emphysema: Many ECM proteins also operate as CTSL substrates.37 A CTSL inhibitor (quarterhydrate, SID 26681509) was utilized further to uncover the functions of CTSL in emphysema development.38 Mice administered the CTSL inhibitor showed significantly decreased emphysema severity compared to the control group (Fig. 7a, b and Supplementary Fig. 7a).