Defensins are cationic peptides with broad-spectrum antimicrobial activity. They are members of a supergene family consisting of a and b subtypes and each subtype is comprised of a number of different isoforms. For example, human a-defensin (HAD) has six isoforms, which are expressed by polymorphonuclear leukocytes and Paneth cells. In contrast, human b-defensin (HBD) has two isoforms that are expressed by epithelial cells of the skin, gut, respiratory and urogenital tracts. Recently, HBD-1 was detected in human brain biopsy tissue. However, little is known about the expression of HBD-1 or HBD-2 in the CNS and whether neural cells can secrete these peptides. For the present study, human astrocyte, microglial, meningeal ®broblast and neuronal cultures were probed for the expression of HBD-1 and HBD-2 mRNA and protein. Each cell type was either maintained in tissue culture medium alone or in medium containing lipopolysaccharide (LPS) at concentrations ranging from 0.1 to 1 mg/mL, interleukin-1 beta (IL-1b) at 1±50 ng/mL, or tumor necrosis factor alpha (TNF-a) at the same concentrations. The expression of HBD-1 and HBD-2 mRNAs was monitored by RT-PCR. The cDNA products were sequenced to characterize the gene product. HBD-2 protein was detected by immunoblot, immunoprecipitation and immunocytochemistry. Results of these studies showed that HBD-1 mRNA was detected in all cell cultures except in those enriched for neurons. In contrast, HBD-2 mRNA was detected only in astrocyte cultures that were treated with LPS, IL-1b or TNF-a. The detection of the respective proteins correlated positively with the mRNA results. As such, these data represent the ®rst demonstration of HBD-2 expression by astrocytes and suggest that this peptide may play a role in host defense against bacterial CNS pathogenesis.

Signaling of RANK (receptor activator of nuclear factor kappa B) through its ligand RANKL appears critical in osteolysis associated with aseptic loosening (AL). The purpose of this study was to investigate the role of RANK in a murine osteolysis model developed in RANK knockout (RANK À/À ) mice. Ultra high molecular weight polyethylene (UHMWPE) debris was introduced into established air pouches on RANK À/À mice, followed by implantation of calvaria bone from syngeneic littermates. Wild type C57BL/6 (RANK þ/þ ) mice injected with either UHMWPE or saline alone were included in this study. Pouch tissues were collected 14 days after UHMWPE inoculation for molecular and histology analysis. Results showed that UHMWPE stimulation induced strong pouch tissue inflammation in RANK À/À mice, as manifested by inflammatory cellular infiltration, pouch tissue proliferation, and increased gene expression of IL-1b, TNFa, and RANKL. However, the UHMWPE-induced inflammation in RANK À/À mice was not associated with the osteoclastic bone resorption observed in RANK þ/þ mice. In RANK þ/þ mice subjected to UHMWPE stimulation, a large number of TRAP þ cells were found on the implanted bone surface, where active osteoclastic bone resorption was observed. No TRAP þ cells were found in UHMWPE-containing pouch tissues of RANK À/À mice. Consistent with the lack of osteoclastic activity shown by TRAP staining, no significant UHMWPE particle-induced bone resorption was found in RANK À/À mice. A well preserved bone collagen content (Van Gieson staining) and normal plateau surface contour [microcomputed tomography (mCT)] of implanted bone was observed in RANK À/À mice subjected to UHMWPE stimulation. In conclusion, this study provides the evidence that UHMWPE particles induce strong inflammatory responses, but not associated with osteoclastic bone resorption in RANK À/À mice. This indicates that RANK signaling is essential for UHMWPE particle-induced osteoclastic bone resorption, but does not participate in UHMWPE particle-induced inflammatory response. ß

In some rodent models, there is evidence that hematopoietic stem cells (HSC) can differentiate into neural cells. However, it is not known whether humans share this potential, and, if so, what conditions are sufficient for this transdifferentiation to occur. We addressed this question by assessing the ability of fetal human liver CD34(+)/CD133(+)/CD3(-) hematopoietic stem cells to generate neural cells and astrocytes in culture. We cultured fetal liver-derived hematopoietic stem cells in human astrocyte culture-conditioned medium or using a method wherein growing human astrocytes were separated from cultured, nonadherent hematopoietic stem cells by a semipermeable membrane in a double-chamber co-culture system. Hematopoietic stem cell cultures were probed for neural progenitor cell marker expression (nestin and bone morphogenic protein-2 [BMP-2]) during growth in both culture conditions. RT-PCR, western blotting, and immunocytochemistry assays showed that cells cultured in either condition expressed nestin mRNA and protein and BMP-2 mRNA. HSC similarly cultured in nonconditioned medium or in the absence of astrocytes did not express either marker. Cells expressing these neural markers were transferred and cultured on poly-D-lysine-coated dishes with nonconditioned growth medium for further study. Immunocytochemistry demonstrated that these cells differentiated into astrocytes after 8 days in culture as indicated by their morphology and expression of the astrocytic markers glial fibrillary acidic protein (GFAP) and S100, as well as by their rate of proliferation, which was identical to that of freshly isolated fetal brain astrocytes. These findings demonstrate that neural precursor gene expression can be induced when human hematopoietic stem cells are exposed to a suitable microenvironment. Furthermore, the neural stem cells generated in this environment can then differentiate into astrocytes. Therefore, human hematopoietic stem cells may be an alternative resource for generation of neural stem cells for therapy of central nervous system defects resulting from disease or trauma.

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This study demonstrates the susceptibility of human NSCs, compared with astrocytes, to EtOH and indicates that alterations in PKC signal transduction in NSC may play a role in EtOH-induced neuropathological processes.