HISTOCHEMICAL-LOCALIZATION OF HEART-TYPE FATTY-ACID-BINDING PROTEIN IN HUMAN AND MURINE TISSUES

Cellular fatty acid-binding proteins (FABP) are a highly conserved fam ily of proteins consisting of several subtypes, among them the mammary -derived growth inhibitor (MDGI) which is quite homologous to or even identical with the heart-type FABP (H-FABP). The FABPs and MDGI have b een suggested to be involved in intracellular fatty acid metabolism an d trafficking. Recently, evidence for growth and differentiation regul ating properties of MDGI and H-FABP was provided. Using four affinity- purified polyclonal antibodies against bovine and human antigen prepar ations, the cellular localization of MDGI/H-FABP in human and mouse ti ssues and organs was studied. The antibodies were weakly cross-reactiv e with adipose tissue extracts known to lack H-FABP, but failed to rea ct by Western blot analysis with liver-type FABP (L-FABP) and intestin al-type FABP (I-FABP). MDGI/H-FABP protein was mainly detected in myoc ardium, skeletal and smooth muscle fibres, lipid and/or steroid synthe sising cells (adrenals, Leydig cells, sebaceous glands, lactating mamm ary gland) and terminally differentiated epithelia of the respiratory, intestinal and urogenital tracts. The results provide evidence that e xpression of H-FABP is associated with an irreversibly postmitotic and terminally differentiated status of cells. Since all the antisera emp loyed showed spatially identical and qualitatively equal immunostainin g, it is suggested that human, bovine and mouse MDGI/H-FABP proteins s hare highly homologous epitopes.