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ALBERTO BARTOLOMÉ Y COLS. AN. R. ACAD. NAC. FARM.

and on the other, modulates an essential component of mTORC1,
Raptor (30). AMPK activation implicates a strong inhibition of
mTORC1, which can be reverted by glucose addition. We have proven
that AMPK activation can induce Raptor Ser792 phosphorylation in
pancreatic ß cells, contributing to energy deprivation-mediated im-
pairment in mTORC1/p70S6K signaling.

TSC2 interference causes an increase in p70S6K activity and insulin
resistance in IR +/+ or Rec B ß cells on Akt stimulation. Lately, some
animal and cellular models have shown the importance of the regula-
tion of mTORC1 in the physiology of ß cells. Although mTORC1/p70S6K
hyperactivity can lead to IRS-mediated insulin resistance, trials failed
to globally diminish it by blocking mTORC1 with the use of rapamycin,
because a functional mTORC1 is required for ß cell adaptation (35).
The inhibition of mTORC1 with rapamycin reverted the insulin resist-
ance on Akt stimulation in our cell lines. More importantly, IRA recon-
stituted cells overcome the insulin resistance seen above showing in-
sulin-mediated Akt stimulation even though TSC2 knockdown. Our data
suggest that the inhibition of the upstream insulin signaling mediated
by p70S6K overactivation feedback mechanism, may be differentially
modulated in IRA or IRB expressing cells. Phosphorylation of IRS-1
Ser307 is considered a marker of insulin resistance (36). The negative
loop concerning IRS-1 Ser307 phosphorylation was upregulated in Rec
B cells as compared to Rec A cells in response to insulin. This might
explain the differences observed on Akt Ser473 phosphorylation between
Rec A and Rec B cells when we interfered TSC2 expression.

In our ß cell lines, we found an increase of proliferation in all cell
lines when TSC2 was interfered. This increase was dependent on
mTORC1 activity as rapamycin addition blocked the stimulatory ef-
fect of TSC2 interference on cell proliferation. Our results point out
the higher mitogenic effect of IRA versus IRB isoform in the regula-
tion of ß cell proliferation.

Other processes related with TSC2/mTORC1 are also critical for ß
cell death or survival. We found ß cells to be more susceptive to cell
death in response to ER-stressors compared with fibroblasts. Both au-
tophagy and ER-stress is basally increased in ß cells, observed as the
increased number of puncta of LC3B and ubiquitin-protein conjuga-
tes, respectively. This may be explained as ß cells have a highly deve-

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