Although liver sinusoidal endothelial cells (LSECs) have long been known to contribute to liver regeneration following injury, the exact role of these cells in liver regeneration remains poorly understood. In this work, we performed lineage tracing of LSECs in mice carrying Tie2-Cre or VE-cadherin-Cre constructs to facilitate fate-mapping of LSECs in liver regeneration. Some YFP-positive LSECs were observed to convert into hepatocytes following a two-thirds partial hepatectomy (PH). Furthermore, human umbilical vein endothelial cells (HUVECs) could be triggered to convert into cells that closely resembled hepatocytes when cultured with serum from mice that underwent an extended PH. These findings suggest that mature non-hepatocyte LSECs play an essential role in mammalian liver regeneration by converting to hepatocytes. The conversion of LSECs to hepatocyte-like (iHep) cells may provide a new approach to tissue engineering.
Some hydrolyzing enzymes have been investigated by histochemical and biochemical methods. Almost all neurons in the brain contain acid phosphatases. About half of the total activity is associated with subcellular particles. Most of the acid-phosphatase activity in the corpora cardiaca (CC) is associated with the neurosecretory materials (NSM). Elementary neurosecretory granules (ENG) have been isolated from the CC by fractionation and subfractionation procedures and subjected to in vitro enzyme activity studies. Electron micrographs of the subfraction having the highest acid-phosphatase activity are discussed in relation to three types or "stages" of ENG. About 80% of the total esterase activity in the brain and the retrocerebral system has been found to be in a "soluble" form. The remaining 20%, the "insoluble" forms, may be associated with subcellular organelles. The methods of Gomori and Burstone for acid-phosphatase localizations are compared, and differing results discussed. The possible roles or functions of acid phosphatases and esterases in the neurosecretory system are discussed.
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