The murine long-term multi-lineage renewal marrow stem cell is a cycling cell

Prevailing wisdom holds that hematopoietic stem cells (HSCs) are predominantly quiescent. Although HSC cycle status has long been the subject of scrutiny, virtually all marrow stem cell research has been based on studies of highly purified HSCs. Here we explored the cell cycle status of marrow stem cells in un-separated whole bone marrow (WBM). We show that a large number of long-term multi-lineage engraftable stem cells within WBM are in S/G2/M phase. Using bromodeoxyuridine, we show rapid transit through the cell cycle of a previously defined relatively dormant purified stem cell, the long-term HSC (LT-HSC; Lineage(-)/c-kit(+)/Sca-1(+)/Flk-2(-)). Actively cycling marrow stem cells have continually changing phenotype with cell cycle transit, likely rendering them difficult to purify to homogeneity. Indeed, as WBM contains actively cycling stem cells, and highly purified stem cells engraft predominantly while quiescent, it follows that the population of cycling marrow stem cells within WBM are lost during purification. Our studies indicate that both the discarded lineage-positive and lineage-negative marrow cells in a stem cell separation contain cycling stem cells. We propose that future work should encompass this larger population of cycling stem cells that is poorly represented in current studies solely focused on purified stem cell populations.

Homing and long-term engraftment of long- and short-term renewal hematopoietic stem cells

Long-term hematopoietic stem cells (LT-HSC) and short-term hematopoietic stem cells (ST-HSC) have been characterized as having markedly different in vivo repopulation, but similar in vitro growth in liquid culture. These differences could be due to differences in marrow homing. We evaluated this by comparing results when purified ST-HSC and LT-HSC were administered to irradiated mice by three different routes: intravenous, intraperitoneal, and directly into the femur. Purified stem cells derived from B6.SJL mice were competed with marrow cells from C57BL/6J mice into lethally irradiated C57BL/6J mice. Serial transplants into secondary recipients were also carried out. We found no advantage for ST-HSC engraftment when the cells were administered intraperitoneally or directly into femur. However, to our surprise, we found that the purified ST-HSC were not short-term in nature but rather gave long-term multilineage engraftment out to 387 days, albeit at a lower level than the LT-HSC. The ST-HSC also gave secondary engraftment. These observations challenge current models of the stem cell hierarchy and suggest that stem cells are in a continuum of change.

Marrow cell genetic phenotype change induced by human lung cancer cells

Microvesicles have been shown to mediate varieties of intercellular communication. Work in murine species has shown that lung-derived microvesicles can deliver mRNA, transcription factors, and microRNA to marrow cells and alter their phenotype. The present studies evaluated the capacity of excised human lung cancer cells to change the genetic phenotype of human marrow cells. We present the first studies on microvesicle production by excised cancers from human lung and the capacity of these microvesicles to alter the genetic phenotype of normal human marrow cells. We studied 12 cancers involving the lung and assessed nine lung-specific mRNA species (aquaporin, surfactant families, and clara cell-specific protein) in marrow cells exposed to tissue in co-culture, cultured in conditioned media, or exposed to isolated lung cancer-derived microvesicles. We assessed two or seven days of co-culture and marrow which was unseparated, separated by ficoll density gradient centrifugation or ammonium chloride lysis. Under these varying conditions, each cancer derived from lung mediated marrow expression of between one and seven lung-specific genes. Microvesicles were identified in the pellet of ultracentrifuged conditioned media and shown to enter marrow cells and induce lung-specific mRNA expression in marrow. A lung melanoma and a sarcoma also induced lung-specific mRNA in marrow cells. These data indicate that lung cancer cells may alter the genetic phenotype of normal cells and suggest that such perturbations might play a role in tumor progression, tumor recurrence, or metastases. They also suggest that the tissue environment may alter cancer cell gene expression.

Neutrophil depletion blocks early collagen degradation in repairing cholestatic rat livers

Biliary obstruction results in a well-characterized cholestatic inflammatory and fibrogenic process; however, the mechanisms and potential for liver repair remain unclear. We previously demonstrated that Kupffer cell depletion reduces polymorphonuclear cell (neutrophil) (PMN) and matrix metalloproteinase (MMP)8 levels in repairing liver. We therefore hypothesized that PMN-dependent MMP activity is essential for successful repair. Male Sprague-Dawley rats received reversible biliary obstruction for 7 days, and the rat PMN-specific antibody RP3 was administered 2 days before biliary decompression (repair) and continued daily until necropsy, when liver underwent morphometric analysis, immunohistochemistry, quantitative RT-PCR, and in situ zymography. We found that RP3 treatment did not reduce Kupffer cell or monocyte number but significantly reduced PMN number at the time of decompression and 2 days after repair. RP3 treatment also blocked resorption of type I collagen. In addition, biliary obstruction resulted in increased expression of MMP3, MMP8, and tissue inhibitor of metalloproteinase 1. Two days after biliary decompression, both MMP3 and tissue inhibitor of metalloproteinase 1 expression declined toward sham levels, whereas MMP8 expression remained elevated and was identified in bile duct epithelial cells by immunohistochemistry. PMN depletion did not alter the hepatic expression of these genes. Conversely, collagen-based in situ zymography demonstrated markedly diminished collagenase activity following PMN depletion. We conclude that PMNs are essential for collagenase activity and collagen resorption during liver repair, and speculate that PMN-derived MMP8 or PMN-mediated activation of intrinsic hepatic MMPs are responsible for successful liver repair.

Dexamethasone alters the hepatic inflammatory cellular profile without changes in matrix degradation during liver repair following biliary decompression

BACKGROUND

Biliary atresia is characterized by extrahepatic bile duct obliteration along with persistent intrahepatic portal inflammation. Steroids are standard in the treatment of cholangitis following the Kasai portoenterostomy, and were advocated for continued suppression of the ongoing immunologic attack against intrahepatic ducts. Recent reports, however, have failed to demonstrate an improved patient outcome or difference in the need for liver transplant in postoperative patients treated with a variety of steroid regimes compared with historic controls. In the wake of progressive liver disease despite biliary decompression, steroids are hypothesized to suppress inflammation and promote bile flow without any supporting data regarding their effect on the emerging cellular and molecular mechanisms of liver repair. We have previously shown in a reversible model of cholestatic injury that repair is mediated by macrophages, neutrophils, and specific matrix metalloproteinase activity (MMP8); we questioned whether steroids would alter these intrinsic mechanisms.

METHODS

Rats underwent biliary ductal suspension for 7 d, followed by decompression. Rats were treated with IV dexamethasone or saline at the time of decompression. Liver tissue obtained at the time of decompression or after 2 d of repair was processed for morphometric analysis, immunohistochemistry, and quantitative RT-PCR.

RESULTS

There was a dramatic effect of dexamethasone on the inflammatory component with the initiation of repair. Immunohistochemistry revealed a reduction of both ED1+ hepatic macrophages and ED2+Kupffer cells in repair compared with saline controls. Dexamethasone treatment also reduced infiltrating neutrophils by day 2. TNF-alpha expression, increased during injury in both saline and dexamethasone groups, was markedly reduced by dexamethasone during repair (day 2) whereas IL-6, IL-10, and CINC-1 remained unchanged compared with saline controls. Dexamethasone reduced both MMP8 and TIMP1 expression by day 2, whereas MMP9, 13, and 14 were unchanged compared with sham controls. Despite substantial cellular and molecular changes during repair, collagen resorption was the same in both groups

CONCLUSION

Dexamethasone has clear effects on both the hepatic macrophage populations and infiltrating neutrophils following biliary decompression. Altered MMP and TIMP gene expression might suggest that steroids have the potential to modify matrix metabolism during repair. Nevertheless, successful resorption of collagen fibrosis proceeded presumably through other MMP activating mechanisms. We conclude that steroids do not impede the rapid intrinsic repair mechanisms of matrix degradation required for successful repair.

Neutrophils invade lumbar dorsal root ganglia after chronic constriction injury of the sciatic nerve

To test whether neutrophils (PMN) target lumbar dorsal root ganglia (DRG) following axonal injury leading to neuropathic pain, we visualized PMN infiltration in DRG tissue sections and estimated PMN count by flow cytometry following sciatic chronic constriction injury (CCI). Seven days after CCI, results show PMN within DRG where their count increased by three fold ipsilateral to injury compared to contralateral or sham, concomitant with peak neuropathic pain behavior. Superoxide burst in PMN isolated from rats d7 after CCI was elevated by 170% +/-18 compared to naïve and MCP-1 mRNA expression in DRG increased by 8.9+/-2.9 fold, but that of MIP-2, CINC-1, and RANTES did not change. We conclude that CCI causes PMN invasion of the DRG whereby the functional implication of their close proximity to neuronal axon and soma remains unknown.

Kupffer cells abrogate cholestatic liver injury in mice

BACKGROUND & AIMS

Biliary obstruction and cholestasis can cause hepatocellular apoptosis and necrosis. Ligation of the common bile duct in mice provides an excellent model in which to study the underlying mechanisms. Kupffer cells play a key role in modulating the inflammatory response observed in most animal models of liver injury. This study was performed to determine the role of Kupffer cells in the injury attending cholestasis.

METHODS

Mice were not treated or were rendered Kupffer cell-depleted by intravenous inoculation of multilamellar liposome-encapsulated dichloromethylene diphosphonate, the common bile duct was ligated and divided; sham-operated animals served as controls. Similarly, interleukin-6 (IL-6)-deficient and tumor necrosis factor-receptor-deficient mice underwent bile duct ligation (BDL) or sham operations.

RESULTS

Serum alanine transaminase levels were increased in all BDL mice at 3 days after surgery, but were significantly higher in IL-6-deficient mice or mice rendered Kupffer cell-depleted before ligation. Histologic examination of BDL livers showed portal inflammation, neutrophil infiltration, bile duct proliferation, and hepatocellular necrosis. Photoimage analyses confirmed more necrosis in the livers of Kupffer cell-depleted and IL-6-deficient animals. Purified Kupffer cells derived from BDL animals produced more IL-6 in culture. Similarly, Kupffer cells obtained by laser capture microdissection from the livers of BDL mice expressed increased levels of IL-6 messenger RNA. Recombinant mouse IL-6 administered 1 hour before BDL completely reversed the increased liver damage assessed otherwise in Kupffer cell-depleted mice.

CONCLUSIONS

These findings indicate that Kupffer cells abrogate cholestatic liver injury by cytokine-dependent mechanisms that include the production of IL-6.

Repair after cholestatic liver injury correlates with neutrophil infiltration and matrix metalloproteinase 8 activity

BACKGROUND

Although timely surgical treatment of liver disease can interrupt inflammation and reduce fibrosis, the mechanisms of repair are unknown. We questioned whether these mechanisms of repair include changes in the inflammatory infiltrate and associated biological activity of matrix metalloproteinases (MMPs) 8 and 2.

METHODS

Rats (n >or= 3) underwent biliary ductal suspension for 7 days followed by decompression. Livers were collected after 7 days of obstruction (d0) and after 2, 5, and 7 days of repair (d2, d5, d7, respectively), and assessed morphometrically for collagen, polymorphonuclear cells (PMNs), Kupffer cells (KCs), and inflammatory mononuclear phagocytes (MNPs). In situ zymography was performed by using fluorogenic substrates for MMP-8 and MMP-2 to spatially localize enzymatic activity.

RESULTS

Cholestatic injury resulted in significantly elevated (P <or= .001) collagen deposition (3-fold), and elevated numbers of MNPs (10-fold), KCs (5-fold), and PMNs (4-fold), compared with shams. PMNs remained elevated through d7, while collagen deposition, KCs, and MNPs returned to sham levels by d2. In situ zymography showed no significant changes in MMP-2 activity after cholestatic injury and repair. MMP-8 activity was significantly (P <or= .05) elevated only during repair. Activity was localized to fibrotic portal triads containing PMNs.

CONCLUSIONS

Cholestatic injury results in increased fibrosis, MNPs, KCs, and PMNs but no MMP-2 or MMP-8 activity. Biliary decompression results in increased MMP-8 activity co-localized to areas of portal fibrosis and PMN accumulation. We conclude that secretion of MMP-8 by neutrophils may play a critical role in resolving the fibrotic scar generated during cholestasis.

Macrophage phenotype during cholestatic injury and repair: the persistent inflammatory response

BACKGROUND/PURPOSE

Biliary decompression for congenital or acquired obstruction (eg, biliary atresia) does not uniformly lead to liver repair, restore function, or prevent cholangitis. The authors hypothesize that failed repair is caused by altered macrophage (Mo) phenotypes central to an ongoing inflammatory and fibrogenic response.

METHODS

In adult rats, biliary obstruction was performed by suspension of the common bile duct for 5 or 7 days. Decompression followed release of the loop until death during the course of liver repair. To determine Mo phenotype in the presence or absence of resident macrophages, animals were either administered gadolinium chloride or saline before injury and repair. At death, hepatic Mo were isolated, stained with MAC-1 (CD11b/CD 18) and OX-3 (MHC class II), and quantified with flow cytometry. Liver sections were immunostained for ED-1 and ED2; positive Mo were counted per square millimeter of tissue.

RESULTS

Obstruction led to bile duct proliferation, fibrosis, and inflammation. Decompression relieved jaundice and ductal hyperplasia. After injury, hepatic Mo showed an 80% phenotypic conversion to MAC-1 and OX-3-positive cells. Cells isolated from livers at 9 days of repair persisted with 60% MAC-1 and 77% OX-3 expression. Gadolinium reduced Kupffer cells at all stages of repair. Recruited Mo in treated animals increased 4-fold greater than controls.

CONCLUSIONS

Kupffer cells appear to limit the recruitment and persistence of a systemic macrophage phenotype in liver injury and repair. Cell surface markers for systemic macrophages appear after injury and persist during repair, despite adequate biliary decompression. After biliary decompression, this macrophage phenotype accounts for inflammatory complications such as cholangitis and ongoing fibrosis.

Kupffer cell inactivation delays repair in a rat model of reversible biliary obstruction

BACKGROUND

During cholestatic liver injury, Kupffer cells (KC) and activated macrophages modulate cell proliferation and subsequent matrix deposition. The role of KC in the restoration of cell architecture and matrix metabolism during repair following chronic cholestatic liver injury is unknown.

MATERIALS AND METHODS

To determine the effect of KC inactivation, adult male Sprague-Dawley rats underwent bile duct suspension (BDS) for 5 days followed by reversal of the obstruction. Saline (control) and gadolinium chloride (10 mg/kg) were administered 1 day prior to BDS and 1 day prior to reversal, to inactivate KC during both injury and repair. Serum bilirubin and quantitative cell morphometry were compared to verify the reversibility of the model. Collagen content of the liver was measured in trichrome-stained paraffin sections using NIH imaging software.

RESULTS

Reversibility of the obstruction was verified by normalization of direct serum bilirubin, which peaked at 8.42 +/- 0.76 mg/dL following 5 days of BDS and returned to sham-operated levels 2 days after reversal, 0.36 +/- 0.15 mg/dL. Hematoxylin and eosin (H&E)-stained paraffin-embedded liver sections from gadolinium-treated animals at 4 and 7 days after reversal exhibited persistent bile duct proliferation, matrix deposition, and inflammation. Gadolinium-treated animals had altered collagen metabolism compared to saline controls. Whereas the collagen content in the saline group slowly returned to sham-operated levels over time, the treatment group demonstrated progressive accumulation of collagen during repair which was statistically significant at 7 days following reversal (8.79%/mm(2) +/- 2.17 in gadolinium group vs 2. 33%/mm(2) +/- 0.34 in saline group, P = 0.0003).

CONCLUSIONS

These results demonstrate that inactivation of resident hepatic macrophages during liver repair impairs collagen metabolism, inhibits the resolution of fibrosis, and allows the persistence of inflammatory cell infiltrates in the portal areas. This is the first evidence of profibrogenic responses in the absence of an intact KC compartment during repair after cholestatic injury.

A prospective study of Shiga-like toxin-associated diarrhea in a pediatric population

Although population-based studies have shown that children have the highest age-specific incidence of infection with the Shiga-like toxin-producing E. coli (SLTEC), these sporadic case series were not focused specifically on the pediatric age group. We undertook a prospective study to determine the frequency of detection of SLT in an exclusively pediatric population. The study design minimized ascertainment and referral bias by systematically defining the population by the presence of diarrheal symptoms rather than by specific diagnosis, previous submission of stool for culture, or referral to a diarrhea study. All children < 10 years of age hospitalized at a tertiary care pediatric hospital, irrespective of admission diagnosis, were surveyed prospectively at admission and for 2 days thereafter for the presence of defined diarrheal symptoms. From May 1, 1991, to April 30, 1992, 227 patients and 92 age- and season-matched controls were enrolled. Fecal SLT was detected in six (2.6%) patients, three of whom had E. coli O157:H7 organisms were isolated; SLT was not found in any of the controls. SLT was more commonly detected in children 2-10 years of age and in bloody stools. Salmonella was isolated in six (2.6%) cases, Shigella in five (2.2%), and Yersinia in three (1.3%); rotavirus was detected in 46 (20.3%). Two patients with SLT-associated diarrhea had hemolytic uremic syndrome (HUS), and four had hemorrhagic colitis. SLT-associated diarrhea occurred in the summer and fall months in contradistinction to that with rotavirus, which occurred in the winter and spring.(ABSTRACT TRUNCATED AT 250 WORDS)

Induction of beta-lactamase and methicillin resistance in unusual strains of methicillin-resistant Staphylococcus aureus

Two unusual, heterogeneously-resistant, strains of Staphylococcus aureus appeared resistant to oxacillin, but susceptible to methicillin by disc diffusion methods. In agar dilution tests, both strains were oxacillin-resistant. One was susceptible to methicillin, and the other gave a paradoxical reaction, with growth only on plates containing low (0.5, 1 and 2 mg/l) and high (32 and 64 mg/l) concentrations of antibiotic. Induction of methicillin resistance was tested by inoculating each strain on to agar plates containing an inhibitory concentration of methicillin (8 mg/l), and then placing discs containing inducers (oxacillin, nafcillin, methicillin and CBAP [2-(2'-carboxyphenyl) benzoyl-6-aminopenicillanic acid]) on the agar surface. Colonies grew only around discs containing effective inducers. Oxacillin and CBAP were much more potent inducers of methicillin resistance and beta-lactamase than was nafcillin or methicillin. These data suggest that the mechanism that regulates induction of the low-affinity penicillin binding protein (PBP-2') may be altered in these strains. Similar mechanisms appear to induce both beta-lactamase and methicillin resistance.

Spurious oxacillin resistance in Staphylococcus aureus because of defective oxacillin disks

Clinical isolates of Staphylococcus aureus wee inappropriately categorized as intermediate or resistant to oxacillin on the basis of tests with two lots of oxacillin disks. The potency of one lot was tested and found to be below accepted limits. Routine quality control tests failed to detect the defective disks.