Diabetes mellitus is a complex metabolic disorder that can be presented in two major forms, as type 1 diabetes (T1D) and the much more common type 2 diabetes (T2D). While their etiologies are different, both diabetes types are characterized by hyperglycemia resulting either from insufficient insulin levels in T1D, or an insensitivity of target cells to insulin in T2D. In T1D, the death of insulin-producing pancreatic β-cells in an autoimmune response is a comparatively rapid event, whereas in T2D loss of β-cell mass occurs over years as interactions of extrinsic stressors and intrinsic factors continually impair β-cell functioning. The decline in the total mass of functional β-cells required to provide insulin for maintaining glucose homeostasis underlies diabetes development. Insight into the molecular control mechanisms in β-cells and the pathology of diabetes has laid the foundation for the paradigm for diabetes treatment based on the application of strategies that support functional β-cells by suppressing cytotoxic cell signaling and preventing the activation of cell death pathways. Our research is focused on β-cells as the principal element in diabetes development, and on hepatocytes and cardiomyocytes as the targets of diabetic complications. Our experimental systems include the in vivo model of streptozotocin (STZ)-induced diabetes in the rat, and in vitro models employing different cell lines maintained in culture.