UVM Theses and Dissertations
Format:
Print
Author:
Finucane, Kiera
Dept./Program:
Animal Sciences
Year:
2007
Degree:
MS
Abstract:
The volume of milk produced by the mammary gland correlates with the amount of lactose it synthesizes, as lactose is the main osmotic factor in milk. Lactose synthesis is dependent on the provision of glucose. A facilitative glucose transport process mediates glucose uptake in the mammary gland. The lactating bovine mammary gland expresses facilitative glucose transporters GLUT1, GLUT8 and GLUT12 and their mRNA expression increases fiom five to several hundred-fold from late pregnancy to early lactation. We hypothesized that glucose transporter protein expression and localization in the mammary gland change during the onset of lactation.
In specific aim 1, we studied expression and localization changes of GLUT1, 8 and 12 in the mammary gland of non-lactating and lactating cows. Western blot analysis of membrane preparations from mammary tissues obtained from dry and lactating cows showed GLUT1 protein was enriched in the plasma membrane and Golgi membrane preparations and its abundance was higher in the lactating cows compared to nonlactating cows. Imrnunofluorescence staining showed GLUT1 localized mainly in blood vessel wall and mammary ducts in non-lactating tissue and in the basolateral membrane of mammary epithelial cells in lactating cows. In addition, GLUT8 and GLUT12 also showed increased expression in the apical and basolateral membranes of mammary epithelial cells in lactating cows compared to non-lactating cows.
In specific aim 2, we studied expression and localization changes of GLUT1, 8 and 12 in the bovine mammary gland in the periparturient period. GLUT1 mRNA expression in early lactation increased significantly when compared to late pregnancy (P<0.05) and GLUT8 mRNA tended to increase during this same timeframe (P=0.129). Western blot analysis showed that GLUTl proteins in the mammary gland also tended to increase during the onset of lactation (P=0.134). This is consistent with the results of immunofluorescence staining of mammary tissue sections, showing stronger GLUT1 staining in the basolateral membrane and intracellular location in lactating tissue compared to the non-lactating tissue. The GLUT8 and GLUT12 staining was also stronger in the lactating tissue in which GLUT8 is primarily localized in the basolateral membrane while GLUT12 is localized in the apical membrane of alveolar cells.
In conclusion, our data indicate that GLUTl, 8 and 12 expression increase during the onset of lactation, as well as undergo changes in localization to support milk synthesis. This study is the first to report expression and localizations of GLUT8 and GLUT12 proteins in the bovine mammary gland and characterize their changes with the onset of lactation.
In specific aim 1, we studied expression and localization changes of GLUT1, 8 and 12 in the mammary gland of non-lactating and lactating cows. Western blot analysis of membrane preparations from mammary tissues obtained from dry and lactating cows showed GLUT1 protein was enriched in the plasma membrane and Golgi membrane preparations and its abundance was higher in the lactating cows compared to nonlactating cows. Imrnunofluorescence staining showed GLUT1 localized mainly in blood vessel wall and mammary ducts in non-lactating tissue and in the basolateral membrane of mammary epithelial cells in lactating cows. In addition, GLUT8 and GLUT12 also showed increased expression in the apical and basolateral membranes of mammary epithelial cells in lactating cows compared to non-lactating cows.
In specific aim 2, we studied expression and localization changes of GLUT1, 8 and 12 in the bovine mammary gland in the periparturient period. GLUT1 mRNA expression in early lactation increased significantly when compared to late pregnancy (P<0.05) and GLUT8 mRNA tended to increase during this same timeframe (P=0.129). Western blot analysis showed that GLUTl proteins in the mammary gland also tended to increase during the onset of lactation (P=0.134). This is consistent with the results of immunofluorescence staining of mammary tissue sections, showing stronger GLUT1 staining in the basolateral membrane and intracellular location in lactating tissue compared to the non-lactating tissue. The GLUT8 and GLUT12 staining was also stronger in the lactating tissue in which GLUT8 is primarily localized in the basolateral membrane while GLUT12 is localized in the apical membrane of alveolar cells.
In conclusion, our data indicate that GLUTl, 8 and 12 expression increase during the onset of lactation, as well as undergo changes in localization to support milk synthesis. This study is the first to report expression and localizations of GLUT8 and GLUT12 proteins in the bovine mammary gland and characterize their changes with the onset of lactation.