A Pdia4 inhibitor for use in preventing, alleviating and/or treating diabetes and/or diabetes-related complications in a subject in need thereof is disclosed, wherein the Pdia4 inhibitor does not comprise cytopiloyene. A Pdia4 inhibitor and one other anti-diabetic agent for use in combination therapy in preventing, alleviating, treating diabetes and diabetes-related complications, and/or reversing diabetes in a subject in need thereof is also disclosed, wherein the Pdia4 inhibitors for use in combination therapy may comprise cytopiloyene. Also disclosed are methods for diagnosing, treating and monitoring diabetes, and methods of screening for a Pdia4 inhibitor and/or an anti-diabetic agent.