Proteolysis of milk fat globule membrane proteins in preterm milk: a transient phenomenon with a possible biological role?

Milk fat globule membrane (MFGM) proteins constitute a milk fraction currently of great interest, as they appear to significantly contribute to milk protective role. We investigated these proteins in human preterm colostrum and milk. For the former we found a peculiar 2-DE pattern, with a spot concentration at low molecular weight, which mass spectrometry analysis showed to be fragments belonging to some MFGM proteins with a well-known biological and especially immunological role: lactadherin, membrane-associated lactoferrin, butyrophilin, clusterin and heavy-chain immunoglobulin. Since we were able to rule out protease activity after specimen collection, we hypothesize the localization of the proteolytic enzymes in the alveolar cell membranes of the mammary gland. This mechanism is probably under hormonal control and the unexpected advent of preterm delivery would not allow hormonal conditions typical of lactation to occur immediately, causing a delay in enzymatic inhibition. This hypothesis is supported by some of our results, picturing a peculiar transient phenomenon of adaptation of the mammary-gland-membrane proteins after preterm delivery. Further studies will be required to verify whether the presence of protein fragments exerts a specific biological and immuno-defensive role in preterm infants, thus adding evidence to the outstanding biological role and benefits of mother's own milk in feeding preterm infants.