Here, we present novel network-based approaches applied towards a deeper understanding of biological function and disease. We aim to further study and understand currently poorly described mechanisms by which ''biologically central'' genes interact with each other and with other genes in the cell. We define as biologically central (BC) the genes that belong to one of the following four gene categories: aging (A) genes, cancer (C) genes, HIV-interacting (HIV) genes, and pathogen-interacting (PI) genes. Our hypothesis is that BC genes, i.e., their protein products (henceforth, we use terms ''gene'' and ''protein'' interchangeably), will have a topologically central role in the human PPI network. We use two different concepts to define ''topological centrality'': graphlet degree centrality and domination (defined below).