Identification and quantification of apoptosis in the kidney using morphology, biochemical and molecular markers

Renal cell apoptosis is important in both physiological conditions such as normal renal development and pathological processes affecting the glomerular, vascular or tubulointerstitial compartments. Apoptosis may result in the detrimental loss of cells following many renal diseases or damaging changes, with significant loss of function. In contrast, apoptosis may control and limit inflammatory processes in both the acute and chronic phases of renal disease. Investigators interested in the presence of apoptotic cells in different forms of renal disease and development need methods to accurately determine the level of apoptosis within the kidney. Apoptosis is a gene-driven mode of cell death that may be identified by distinct morphological features, endonuclease-initiated DNA degradation, and by the involvement of specific apoptosis-regulating proteins. Many research papers that analyse the presence of apoptosis use the in situ terminal deoxyribonucleotidyl transferase-mediated deoxyuridine triphosphate nick end labelling (TUNEL) assay that detects DNA strand breaks in situ in tissue sections. Localization of activated caspase-3 is now seen as an alternative to TUNEL. This review will discuss some methods of identifying apoptosis in the kidney, using both morphological and biochemical or molecular characteristics, and also discuss some of the pitfalls of entire reliance on biochemical means of apoptotic cell identification without some morphological checks and balances. Although there are some caveats to the methods for identifying apoptotic cells in renal disease, those investigators who take the time to undertake such analysis often gain insightful data that provide explanations for the disease or condition being studied.