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Int J Clin Exp Pathol 2010;3(7):691-705

Original Article
Persistent hyperinsulinemic hypoglycemia of infancy: constitutive activation of the
mTOR pathway with associated exocrine-islet transdifferentiation and therapeutic

Sanda Alexandrescu, Nina Tatevian, Oluyinka Olutoye, Robert E Brown

Department of Pathology and Laboratory Medicine, University of Texas Health Science Center-Medical School at Houston, Houston, TX, USA  
Baylor College of Medicine, Houston, TX, USA

Received July 26, 2010; accepted July, 2010; available online July, 2010

Abstract: Background: Amino-acids stimulate the mammalian target of rapamycin complex(mTORC)1; mTORC1 integrates amino-acid and
energy-sensing pathways in beta-cells. Rapamycin inhibits mTORC1. We examined the mTOR pathway and cell cycle data in the exocrine
pancreas in diffuse persistent hyperinsulinemic hypoglycemia of infancy (PHHI). Design: Tissues from two diffuse PHHI cases, one pediatric
control and from adult pancreatic tissue microarray were analyzed. The case studies are newborns of non-diabetic mothers, one with SUR1
mutation, and the other with a family history of PHHI. Immunostaining for (p)-mTOR(Ser2448), phospholipase(PLD)1, cell cycle analytes (
Ki-67, Skp2, p27Kip1), and insulin were performed. Cell cycle analytes were assessed by automated cellular imaging. Multispectral imaging of
double immunostaining for insulin/p-mTOR and transmission electron microscopy (TEM) was performed. Results: Hematoxylin-eosin showed
beta-cell hyperplasia in the exocrine pancreas, without mass effect. Overexpression of (p)-mTOR on the plasmalemmal, but not nuclear
compartment, consistent with mTORC1, was noted in acinar elements. Residual expression was noted in islets. Double immunostaining
revealed occasional acinar cells co-expressing mTOR and insulin. No such co-expressions were seen in the control. TEM showed acinar cells
containing zymogen and hormone-secreting granules. No nuclear Skp2 was noted. Obversely, p27Kip1 was expressed. Mitotic index was 1/40
HPF.Conclusion: Morphoproteomic, histopathologic and morphometric findings in this study of diffuse PHHI coincide with existing genomic
and signal transduction data in: 1) supporting a role for a constitutively activated and overexpressed mTORC1 pathway in the acinar pancreas
in its pathogenesis; 2) reaffirming transdifferentiation of acinar-to-islet cells; 3) raising the possibility of rapamycin as a therapeutic option in

Keywords: mTOR, PHHI, transdifferentiation, rapamycin

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Address all correspondence to:
Robert E. Brown, M.D.
Professor and Harvey S. Rosenberg Chair
Department of Pathology and Laboratory Medicine
University of Texas Health Science Center Medical School at Houston
6431 Fannin Street, MSB 2.286
Houston, TX 77030
Telephone number: 713-500-5332
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