Plummer, Timothy B.

Abstract The management of systemic amyloidosis relies on the treatment of the underlying etiology and differs radically for different amyloid types. Therefore, given that at least 25 different proteins have been associated with amyloidosis, accurate identification of proteins deposited as amyloid fibrils is an important clinical problem. In this study, we describe a novel method that can characterize amyloid subtypes using laser microdissection (LMD) and mass spectrometry (MS) on routinely processed paraffin-embedded tissues. The study used 60 cases consisting of 16 transthyretin, 9 serum amyloid-associated protein, 20 immunoglobulin light chain lambda, 5 immunoglobulin light chain kappa, and 10 amyloid negative control samples. The biopsy specimens studied included heart, kidney, gastrointestinal tract, lung and decalcified bone marrow specimens. The amyloid type in all cases was previously characterized based on clinical findings, immunohistochemistry and, where indicated, by molecular testing for transthyretin mutations. Amyloid plaques were captured from an 10 micron paraffin section exhibiting positive Congo Red staining using LMD. Proteins were extracted, digested with trypsin and identified following MS/MS using the Mascot search algorithm analysis. MS correctly identified each of the 4 types of amyloidosis analyzed. Serum Amyloid P component and Apolipoprotein E were also identified as constituents of the amyloid deposition. The analysis was successful on all tissue types including decalcified bone marrow specimens and small biopsy specimens such as endomycardial biopsies and renal biopsies. The use of LMD from paraffin embedded biopsies and subsequent analysis by MS allows identification of the type of amyloid protein deposited with high specificity and sensitivity. This method promises to be a clinical test for accurate identification of amyloid proteins in routinely processed biopsy specimens and overcomes many of the specificity and sensitivity issues associated with current methods such as immunohistochemistry.

Abstract When activated on or in the vicinity of cells, complement usually causes loss of function and sometimes cell death. Yet the liver, which produces large amounts of complement proteins, clears activators of complement and activated complexes from portal blood without obvious injury or impaired function. We asked whether and to what extent hepatocytes resist injury and loss of function mediated by exposure to complement. Using cells isolated from porcine livers as a model system, we found that, in contrast to endothelial cells, hepatocytes profoundly resist complement-mediated lysis and exhibit normal synthetic and conjugative functions when complement is activated on their surface. The resistance of hepatocytes to complement-mediated injury was not a function of cell surface control of the complement cascade but rather an intrinsic resistance of the cells dependent on the PI3K/Akt pathway. The resistance of hepatocytes to complement might be exploited in developing approaches to the treatment of hepatic failure or more broadly to the treatment of complement-mediated disease.

The Drosophila immune deficiency (IMD) pathway, homologous to the mammalian tumor necrosis factor (TNF‐α) signaling pathway, initiates antimicrobial peptide (AMP) production in response to infection by gram‐negative bacteria. A membrane‐spanning peptidoglycan recognition protein, PGRP‐LC, functions as the receptor for the IMD pathway. This receptor is activated via pattern recognition and binding of monomeric peptidoglycan (DAP‐type PGN) through the PGRP ectodomain. In this article, we show that the receptor PGRP‐LC is down‐regulated in response to Salmonella/Escherichia coli infection but is not affected by Staphylococcus infection in vivo, and an ectodomain‐deleted PGRP‐LC lacking the PGRP domain is an active receptor. We show that the receptor PGRP‐LC regulates and integrates two host defense systems: the AMP production and melanization. A working model is proposed in which pathogen invasion and tissue damage may be monitored through the receptor integrity of PGRP‐LC after host and pathogen are engaged via pattern recognition. The irreversible cleavage or down‐regulation of PGRP‐LC may provide an additional cue for the host to distinguish pathogenic microbes from nonpathogenic ones and to subsequently activate multiple host defense systems in Dro‐sophila, thereby effectively combating bacterial infection and initiating tissue repair.—Schmidt, R. L., Trejo, T. R., Plummer, T. B., Platt, J. L., Tang, A. H. Infection‐induced proteolysis of PGRP‐LC controls the IMD activation and melanization cascades in Drosophila. FASEB J . 22, 918–929 (2008)

Human cells can fuse with damaged or diseased somatic cells in vivo. Whether human cells fuse in vivo in the absence of disease and with cells of disparate species is unknown. Such a question is of current interest because blood exchanges between species through direct physical contact, via insect vectors or parasitism, are thought to underlie the transmission of zoonotic agents. In a model of human‐pig chimerism, we show that some human hematopoietic stem cells engrafted in pigs contain both human and porcine chromosomal DNA. These hybrid cells divide, express human and porcine proteins, and contribute to porcine nonhematopoietic tissues. In addition, the hybrid cells contain porcine endogenous retroviral DNA sequences and are able to transmit this virus to uninfected human cells in vitro. Thus, spontaneous fusion can occur in vivo between the cells of disparate species and in the absence of disease. The ability of these cell hybrids to acquire and transmit retroviral elements together with their ability to integrate into tissues could explain genetic recombination and generation of novel pathogens.

Acute vascular or humoral rejection, a vexing outcome of organ transplantation, has been attributed by some to activation and by others to apoptosis of endothelial cells in the graft. We asked which of these processes causes acute vascular rejection by tracing the processes during the development of acute vascular rejection in porcine cardiac xenografts performed in baboons. Apoptosis, assayed by terminal deoxynucleotidyl transferase–mediated dUTP nick end-labeling (TUNEL), expression of activated caspase-3, and proapoptotic genes Bax and Bcl-x L , was not detected until acute vascular rejection was well advanced, and even then, apoptosis was largely confined to myocytes. Activation of the endothelium, as evidenced by expansion of rough endoplasmic reticulum and increased ribosomal antigen and phospho-p70 S6 kinase, occurred early in the course of acute vascular rejection and progressed through the disease process. These findings suggest that acute vascular rejection is caused by an active metabolic process and not by apoptosis in the endothelium.