The goat (Capra hircus) mammary gland secretory tissue proteome as influenced by weight loss: a study using label free proteomics

Abstract Text:

The objective of this work was to study the effect of seasonal weight loss (SWL) on the mammary gland secretory tissue proteome in two goat breeds from the Canary Islands. Two lactating dairy goat breeds from the Canary Islands with different levels of tolerance to SWL were used: Majorera (tolerant) and Palmera (susceptible). Within each breed, goats with the same age and stage of lactation were divided into two groups: control (constant weight) and restricted (15% liveweight reduction). Four groups were established: Palmera control (PC, n = 6), Majorera control (MC, n = 4), Palmera Restricted (PR, n = 4) and Majorera restricted (MR, n = 5). Animals on the restricted groups were fed on standard wheat straw and animals in the control groups were fed on alfalfa hay supplemented with maize, soy and dehydrated beetroot.  At day 22 of the trial, mammary gland biopsy samples were obtained. Samples (30 mg) were ground in liquid nitrogen with mortar and pestle and added to 500 µl of ammonium bicarbonate 50 mM, urea 8M, thiourea 2M buffer and homogenized, centrifuged and supernatant recovered. Per sample, 15 µg of proteins were trypsin digested (FASP protocol) and desalted. Peptides were loaded onto reverse-phase C18 columns and analyzed on an LTQ-Orbitrap Velos mass spectrometer. Protein identification and label free quantification were performed using Mascot (Matrixscience) and Progenesis software (Nonlinear Dynamics). A total of 1010 proteins were identified, from which 96 proteins were considered statistically different among groups (fold change > 1.98 and P<0.05). After SWL, there was an increase of proteins related to apoptosis and stress processes in both breeds. Moreover, both breeds showed a decrease in the number of proteins related to protein, carbohydrate and fat biosynthesis. When both breeds were compared after SWL, Majorera breed showed higher expression of immune system related proteins compared to Palmera breed. In contrast, Palmera breed showed higher expression of proteins related to apoptosis, ketone body formation (fatty liver) and protein metabolic processes compared to Majorera breed. In conclusion, the two goat breeds have different metabolic reactions to SWL, highlighting differences particularly related to the immune system (higher expression in the tolerant breed) and apoptosis (higher expression in the susceptible breed).

Keywords: goat, label-free proteomics, mammary gland, seasonal weight loss