CTSD and heart failure: Increased circulating CTSD levels were found in patients with coronary heart disease (Naseem et al., 2005; Goncalves et al., 2016) and diabetes mellitus (Feron et al., 2009; Mellor et al., 2011b; Mellor et al., 2011; Goncalves et al., 2016; Liu et al., 2017; Hoes et al., 2020), which correlated with the severity of heart failure (Hoes et al., 2020).