Abstract:

Objective ACE-related carboxypeptidase(Angiotensin-converting Enzyme 2,ACE2),an enzymatic homologue of ACE,has been recently demonstrated as a functional receptor for severe acute respiratory syndrome coronavirus(SARS-CoV).Our previous study found that blood glucose levels in patients with SARS were significantly higher than control,which suggested that SARS-CoV might attack and cause damage to the pancreas.ACE2 enzyme plays a biological role in the degradation of angiotensin II,which provides a rationale for the further exploration of its role in many pathophysiological processes.In most tissues,chronic exposure to Ang II,the main effector of the RAS,increases oxidative stress, activates fibrogenesis and promotes apoptosis.An intrinsic RAS has also been demonstrated in the endocrine pancreas.ACE2 degrades Ang II and Ang I.This study intends to investigate the expression of ACE2 in human,rat and mouse exocrine and endocrine tissues of pancreas,which may give us more clue for better understanding the possible pathogenesis in pancreas lesion in SARS and diabetic patients.Methods Continuous paraffin section slides were made from human,rat and mouse pancreata for ACE2 analyses and negative controls respectively.The expressions of ACE2 protin of each of the tissues were detected by immunohistochemistry with the goat-anti ACE2 monoclonal antibody.The total RNA was extracted from rat and human pancreatic tissue(a donors tissue) by using TriZol Reagent with subsequent chloroform-isopropanol extraction according to the manufacturer's instructions,and first-strand human and rat cDNA synthesis were performed for detection of ACE2 by PCR.Results ACE2 protein was detected in whole human,rat and mouse pancreata.In the human pancreas,the distribution pattern was similar to that observed in the rat and mice: the islet showed strong positivity,and a somewhat weaker but nevertheless positive immunoreaction could be found in the acinar cells.Total RNA was extracted from rat and human pancreata tissue.The RNA samples were run down denaturing agarose gels,only samples that had intact 18S and 28S ribosomal bands were used for the study.The expression of ACE2 mRNA was detected in whole pancreata of human and rat by RT-PCR.PCR products were analyzed by agarose gel electrophoresis.The identity of PCR products was confirmed by sequence analyses.Conclusion Our data demonstrates a tissue specific pattern of ACE2 expression and suggestes that ACE2 expression in pancreas especially in islet of pancreas may cause the elevation of blood glucose levels in SARSpatients.Several large clinical trials had demonstrated that blockade of the RAS protects against the development of diabetes.The possiblemechanism is that the blockade of the RAS attenuate the deleterious actions of Ang Ⅱ on pancreatic islet structure and function and accentuate the protective actions of ACE2.So ACE2 may also play an important role in the pathogenesis of diabetes.The addition of ACE2 to the complexities of the intrinsic RAS in the endocrine pancreas may lead to the development of novel therapeutics for the treatment of diabetes.The precise role of ACE2 in pancreatic physiology and pathology will need to be studied in more detail.

Key words: ACE-related carboxypeptidase(ACE2), angiotensin-converting enzyme(ACE), SARS-CoV, RT-PCR