Impact of forskolin and amino acid depletion upon System A activity and SNAT expression in BeWo cells.

Amino acid transport System A (SysA) plays an important role in mediating the transplacental transfer of neutral amino acids from mother to fetus. Given that prior work has demonstrated that SysA activity is regulated, both over gestation and in response to dietary restriction during pregnancy, we examined the response of SysA activity and sodium-dependent neutral amino acid transporter (SNAT; responsible for SysA activity) expression to cAMP analogues and amino acid deprivation in BeWo cells, an accepted model of placental syncytia. SysA activity was unaffected by forskolin, a cAMP agonist, at 48 and 72 h. Amino acid depletion was associated with an up-regulation of SysA activity, largely mediated through an enhancement of SNAT2 (Slc38a2) expression at both the protein and mRNA level. SNAT1 (Slc38a1) expression did not change in response to amino acid depletion, while SNAT4 (Slc38a4) could not be detected. In summary, SysA activity in BeWo cells responds to amino acid depletion through the differential regulation of SNAT subtypes.