Age-dependent upregulation of C1q and Ctsd in PS knockout mice. The same nitrocellulose membrane was re-probed for Ctsd, C1q, and Tubulin. Note a progressive, age-dependent upregulation of C1q and Ctsd in the KO mice but not the matched wild-type controls. Tubulin was used as a loading control. Molecular weights of Ctsd species correlate best to active intermediate (48 kD) and mature heavy chain (34 kD).