Dystrophin expression in the mdx mouse restored by stem cell transplantation

Hematopoietic potential of stem cells isolated from murine skeletal muscle

We have discovered that cells derived from the skeletal muscle of adult mice contain a remarkable capacity for hematopoietic differentiation. Cells prepared from muscle by enzymatic digestion and 5-day in vitro culture were harvested, and 18 x 10(3) cells were introduced into each of six lethally irradiated recipients together with 200 x 10(3) distinguishable whole bone marrow cells. After 6 or 12 weeks, all recipients showed high-level engraftment of muscle-derived cells representing all major adult blood lineages. The mean total contribution of muscle cell progeny to peripheral blood was 56 +/- 20% (SD), indicating that the cultured muscle cells generated approximately 10- to 14-fold more hematopoietic activity than whole bone marrow. When bone marrow from one mouse was harvested and transplanted into secondary recipients, all recipients showed high-level multilineage engraftment (mean 40%), establishing the extremely primitive nature of these stem cells. We also show that muscle contains a population of cells with several characteristics of bone marrow-derived hematopoietic stem cells, including high efflux of the fluorescent dye Hoechst 33342 and expression of the stem cell antigens Sca-1 and c-Kit, although the cells lack the hematopoietic marker CD45. We propose that this population accounts for the hematopoietic activity generated by cultured skeletal muscle. These putative stem cells may be identical to muscle satellite cells, some of which lack myogenic regulators and could be expected to respond to hematopoietic signals.

Transduction of CD34(+) and CD34(-)/lin(-) hemopoietic progenitors by lentivirus vectors

BACKGROUND

While hemopoietic stem cells have been thought to reside predominantly in the CD34(+) population, recent data suggests that repopulating cells may, in fact, also reside in the lin(-)/CD34(-) population. Transduction of both these populations by murine retroviral vectors is limited by quiescence of hemopoietic stem cells.

METHODS

We therefore sought to transduce these populations using a VSV-G pseudotyped, HIV-based, human lentiviral vector, encoding eGFP. CD34(+) cells and lin(-)/CD34(-) cells were selected from the same BM samples by immunomagnetic beads (StemSep) to deplete lineage-positive cells and by CD34 selection columns (Miltenyi) to separate CD34(+) and CD34(-) populations. We transduced target cells, with or without prestimulation with cytokines, using conventional suspension culture, or fibronectin plates, or flow-through transduction. Transduction efficiency was analyzed by flow cytometry and clonogenic assay.

RESULTS

We found that transduction on fibronectin plates was more efficient than flow-through transduction, or suspension cultures, for both cell populations. Mean transduction rates on fibronectin plates, analyzed by flow cytometry, were 14% and 5% for CD34(+) cells and lin(-)/CD34(-) cells respectively, without prestimulation, and 31% and 20% with prestimulation. By contrast, a murine retroviral vector transduces CD34(+) cells with lower efficiency (mean 16.1% with prestimulation) and does not induce any significant transduction of the CD34(-)/lin(-) population (mean < 2%). When lentiviral transduction was assayed in short- and long-term clonogenic assays there was minimal transduction of CD34 cells without prestimulation, increasing to 20% with prestimulation.

DISCUSSION

Lentiviral eGFP vectors can transduce hematopoietic progenitors effectively and efficiency is improved by cytokine prestimulation and the use of fibronectin. Moreover, the human viral vectors can transduce a candidate stem-cell population that is resistant to murine retroviral transduction.

Morphometric and dynamic studies of bone changes in hyperthyroidism

Bone biopsies were performed after tetracycline double-labelling by transfixing the right iliac crest in forty hyperthyroid patients. The bone changes in cortical and trabecular bone were determined by simple measurement and point counting on decalcified and undecalcified stained sections. A slight decrease in the amount of cancellous bone was found. The mean cortical width was normal. The amount of osteoid and the length of the osteoid seams were increased, whereas the mean width of osteoid seams was decreased. The cortical osteoclastic activity and porosity were markedly increased. The trabecular osteoclasic activity was moderately increased and the mean size of periosteocytic lacunae was slightly increased. The calcification rate in cancellous bone was increased as were the active calcification surfaces (tetracycline-labelled). The osteoclastic activity in cortical bone was positively correlated to the free thyroxine index and to the urinary calcium and phosphorus excretion. The findings indicate that the bone changes in hyperthyroidism are specific and that thyroid hormone(s) stimulates both bone formation and resorption followed by increased porosity in cortical bone and by mobilization of bone mineral.