Characterization of human monocyte-derived microglia-like cells

Expression of the inhibitor of apoptosis protein family in multiple sclerosis reveals a potential immunomodulatory role during autoimmune mediated demyelination

A failure of autoreactive T cells to undergo apoptosis may contribute to the pathogenesis of multiple sclerosis (MS). The role of the inhibitor of apoptosis (IAP) family of anti-apoptotic proteins such as X-linked IAP (XIAP), human inhibitor of apoptosis-1 (HIAP-1), human inhibitor of apoptosis-2 (HIAP-2), neuronal apoptosis inhibitory protein (NAIP) and Survivin in relapsing–remitting, secondary-progressive, primary-progressive or benign forms of MS is unclear. We report here that expression of the IAP family of genes in peripheral blood samples and brain tissues from MS cases support a role for differential regulation of these potent anti-apoptotic proteins in the pathology of MS. XIAP mRNA and protein levels were elevated in peripheral blood mononuclear cells from patients with active disease relative to normal subjects. In patients with active MS, HIAP-1 and HIAP-2 mRNA levels were elevated in resting T cells while NAIP mRNA was increased in whole blood. In post-mortem MS brain tissue, XIAP and HIAP-1 in myelin lesions were co-localized with microglia and T cells, respectively. Only in primary-progressive patients was Survivin expression elevated suggestive of a distinct pathological basis for this subtype of MS. Taken together, these results suggest that patterns of inhibitor of apoptosis expression in immune cells may have value in distinguishing between MS subtypes and offer insight into the mechanisms responsible for their distinct clinical courses.

From bone marrow to microglia: barriers and avenues

Microglia form a unique population of brain-resident macrophages. Although microglia have been involved in multiple disorders of the central nervous system (CNS), the issue of microglial renewal, under normal or pathological conditions, has been controversial. In mice, results from bone marrow chimera studies indicated that microglia are slowly but continuously replenished by bone marrow-derived cells. Moreover, such a microglial turnover was found to be greatly accelerated under multiple neurological conditions. However, recent works questioned the use of irradiation/reconstitution experiments to assess microglial turnover. Based on these different studies, we propose here a re-evaluation of microglia origin(s) in the inflamed CNS. We also discuss the therapeutic perspectives offered by the demonstration of an adult microglial lineage, from bone marrow to brain.

Blood into beta-cells: can adult stem cells be used as a therapy for Type 1 diabetes?

In the past 10 years there have been substantial developments in adult stem cell research, and the transplantation of these cells now holds great promise for regenerative medicine, such as in the treatment of Type 1 diabetes. A large proportion of studies have focused on stem cells sourced from hematopoietic tissues: bone marrow, umbilical cord blood and peripheral blood. Attempts to transdifferentiate these cells into insulin-producing cells, both in vivo and in vitro, have produced conflicting results. Although insulin production and normalization of blood glucose levels have been described in some studies, the true mechanism of stem cell plasticity remains in question - are the functional changes seen due to true transdifferentiation or do they result from cell fusion or other factors? There is evidence that stem cell plasticity is a true phenomenon, but whether it will ever be of therapeutic benefit for Type 1 diabetes remains uncertain.

Primary rat monocytes migrate through a BCEC-monolayer and express microglia-markers at the basolateral side

Monocytes are pluripotent cells of the immune system, circulate in the blood and cross the blood-brain barrier continuously through life. The aim of this study was to explore if primary rat monocytes can adhere and transmigrate at a monolayer of brain capillary endothelial cells (BCEC) and if the monocytes undergo differentiation toward a microglial phenotype at the basolateral side. Monocytes and as a control primary microglia were immunohistochemically stained with markers for CD68 (clone ED-1), CD11b (clone OX-42) or CD11c (clone 8A2). The primary rat monocytes (100,000 cells added) adhered at the BCEC-monolayer (approx. 1200 cells/well) within 30 min and migrated to the basolateral side within 18 h (approx. 40,000 cells/well). The transmigrated monocytes partly differentiated and expressed microglia-markers at the basolateral side. Tumor necrosis factor-alpha as well as conditioned medium derived from BCEC stimulated the differentiation of monocytes in culture. In conclusion, monocytes adhere and migrate through a BCEC-monolayer and express microglia-markers at the basolateral side.