In their study of deformed W-algebras associated with complex simple Lie algebras, E. Frenkel-Reshetikhin (1998) introduced certain two parameter deformations of the Cartan matrices. They play an important role in the representation theory of quantum affine algebras. In this talk, we explain a representation-theoretic interpretation of these deformed Cartan matrices and their inverses in terms of the generalized preprojective algebras recently introduced by Geiss-Leclerc-Schröer (2017). We also discuss its application to the representation theory of quantum affine algebras in connection with the theory of cluster algebras. This talk is based on a joint work with Kota Murakami (arXiv:2109.07985).