Grain growth in 2D polycrystals or similar cellular structures is characterized by interface motions and topological transforamtions. Focusing on the topology of such cell complexes only, regardless of their geometry, they become topological graphs of a given type. In this paper, grain growth is viewed as a sequence of discrete transformations of such topological graphs. Simple simulation models using these general features are introduced, and their first results -essentially face coordination distributions- analyzed and compared to both real and theoretical ones.