Astrocytes generated from patient induced pluripotent stem cells recapitulate features of Huntington's disease patient cells.

BACKGROUND: Huntington's Disease (HD) is a devastating neurodegenerative disorder that clinically manifests as motor dysfunction, cognitive impairment and psychiatric symptoms. There is currently no cure for this progressive and fatal disorder. The causative mutation of this hereditary disease is a trinucleotide repeat expansion (CAG) in the Huntingtin gene that results in an expanded polyglutamine tract. Multiple mechanisms have been proposed to explain the preferential striatal and cortical degeneration that occurs with HD, including non-cell-autonomous contribution from astrocytes. Although numerous cell culture and animal models exist, there is a great need for experimental systems that can more accurately replicate the human disease. Human induced pluripotent stem cells (iPSCs) are a remarkable new tool to study neurological disorders because this cell type can be derived from patients as a renewable, genetically tractable source for unlimited cells that are difficult to acquire, such as neurons and astrocytes. The development of experimental systems based on iPSC technology could aid in the identification of molecular lesions and therapeutic treatments. RESULTS: We derived iPSCs from a father with adult onset HD and 50 CAG repeats (F-HD-iPSC) and his daughter with juvenile HD and 109 CAG repeats (D-HD-iPSC). These disease-specific iPSC lines were characterized by standard assays to assess the quality of iPSC lines and to demonstrate their pluripotency. HD-iPSCs were capable of producing phenotypically normal, functional neurons in vitro and were able to survive and differentiate into neurons in the adult mouse brain in vivo after transplantation. Surprisingly, when HD-iPSCs were directed to differentiate into an astrocytic lineage, we observed the presence of cytoplasmic, electron clear vacuoles in astrocytes from both F-HD-iPSCs and D-HD-iPSCs, which were significantly more pronounced in D-HD-astrocytes. Remarkably, the vacuolation in diseased astrocytes was observed under basal culture conditions without additional stressors and increased over time. Importantly, similar vacuolation phenotype has also been observed in peripheral blood lymphocytes from individuals with HD. Together, these data suggest that vacuolation may be a phenotype associated with HD. CONCLUSIONS: We have generated a unique in vitro system to study HD pathogenesis using patient-specific iPSCs. The astrocytes derived from patient-specific iPSCs exhibit a vacuolation phenotype, a phenomenon previously documented in primary lymphocytes from HD patients. Our studies pave the way for future mechanistic investigations using human iPSCs to model HD and for high-throughput therapeutic screens.

Modeling neurological diseases using patient-derived induced pluripotent stem cells.

Reprogramming of somatic cells to an embryonic-like state has dramatically changed the landscape of stem cell research. Although still in its formative stages, the field of induced pluripotent stem cells (iPSCs) has the potential to advance the study of neurodegenerative and neurodevelopmental disorders at the molecular and cellular levels. The iPSC technology could be employed to establish in vitro experimental model systems for the identification of molecular lesions and to aid in the discovery of therapeutic targets and effective compounds. The derivation of patient-specific iPSCs has also opened up the possibility of generating disease-relevant cells for toxicity screening and for cellular therapy. In this article, we review the recent progress in the use of disease-specific iPSCs for in vitro and in vivo modeling of neurological diseases.

Isolation of quiescent murine hematopoietic stem cells by homing properties.

A major challenge facing investigators working in the field of hematopoietic stem cell (HSC) biology has been to develop a strategy to purify rare primitive HSCs from bone marrow. Several methods have been available including the commonly used technique of isolating HSCs based on a specific cell-surface phenotype. As surface marker expression is dynamic and may fluctuate depending on the proliferative or activation state of the cell, our laboratory has established a unique functional in vivo assay (the 2-day homing assay) to isolate murine HSCs. This protocol selects for HSCs on the basis of their ability to home to bone marrow and yields a population that can reconstitute the murine hematopoietic system with the transplantation of a single cell. In contrast to other methods that use specific cell-surface antigens to acquire HSCs, our functional assay aids in obtaining a primitive HSC that exhibits both hematopoietic and epithelial engraftment capabilities. The 2-day homing protocol involves harvesting whole bone marrow and performing a physical separation method (elutriation) to acquire a fraction of small-sized cells (fraction 25). Fraction 25 cells are then depleted of later progenitors and differentiated hematopoietic cells, labeled with a fluorescent tracking dye and transplanted into lethally irradiated recipient mice. Two days after transplantation, the bone marrow is harvested from the primary recipient, and HSCs that have homed to the bone marrow are collected by fluorescence-activated cell sorting. In addition to the traditional 2-day homing protocol, we have included in this chapter our recently developed method of using density gradient centrifugation to replace the elutriation step that also selects for a primitive HSC.

Isolation of bone marrow-derived stem cells using density-gradient separation.

OBJECTIVE: Our laboratory has established two unique methods to isolate murine hematopoietic stem cells on the basis of functional characteristics such as the ability of stem cells to home to bone marrow and aldehyde dehydrogenase (ALDH) activity. An essential component of both protocols is the separation of whole bone marrow into small-sized cells by counter-flow elutriation. We sought to provide the scientific community with an alternate approach to acquire our stem cells by replacing elutriation with the use of density-gradient centrifugation. METHODS: The elutriated fraction 25 population was characterized based on density using a discontinuous gradient. The long-term reconstituting potential of whole bone marrow cells collected at each density interface was determined by subjecting the fractions to the two-day homing protocol, transplanting them into lethally irradiated recipient mice, and assessing peripheral blood chimerism. We also investigated the ability of high-density bone marrow cells isolated in conjunction with the ALDH protocol to repopulate the hematopoietic system of myeloablated recipients. RESULTS: Bone marrow cells collected at the high-density interface of 1.081/1.087 g/mL (fraction 3) had the capacity for homing to marrow and the ability to provide long-term hematopoietic reconstitution. Fraction three lineage-depleted ALDH-bright cells could also engraft and provide long-term hematopoiesis at limiting dilutions. CONCLUSIONS: Density-gradient centrifugation can be used in conjunction with either of our stem cell isolation protocols to obtain cells with long-term reconstitution ability. We anticipate that this strategy will encourage and enable investigators to study the biology of HSCs isolated using functional characteristics.

Extensive cutaneous metastases in a dog with duodenal adenocarcinoma.

A 6-year-old Rottweiler was presented to the North Carolina State University College of Veterinary Medicine for evaluation of multiple cutaneous nodules. The dog had a history of anorexia, vomiting, and hind-limb paraplegia. Results of cytologic examination of the cutaneous nodules were consistent with a round cell tumor. At necropsy, primary tumors were found coalescing in the duodenum and the pancreas and extending into the associated mesentery. Numerous masses also were found throughout the skin, abdominal and thoracic viscera, and lumbar spinal cord. Histologically, the duodenal tumor had variable morphology, with some areas resembling adenocarcinoma and others resembling anaplastic round cell neoplasia; the skin and other metastatic lesions resembled round cell neoplasia. Immunohistochemistry of the cutaneous, duodenal, and pancreatic masses showed the neoplastic cells were positive for pancytokeratin, supporting an epithelial origin. In addition, low numbers of neoplastic cells were positive for periodic acid-Schiff and Alcian blue, consistent with acid mucin production by duodenal epithelium. These findings confirmed that the cutaneous nodules were metastatic lesions originating from the duodenal adenocarcinoma. Cutaneous metastasis of intestinal carcinoma is rare in domestic animals. This case demonstrates the potential difficulty in diagnosing metastatic lesions based on cytologic and histologic morphology alone, because the cutaneous metastases may not resemble the primary neoplasm morphologically.

Cytology of bone marrow.

Cytologic examination of bone marrow aspirates can provide a wealth of diagnostic information. Practitioners should not hesitate to perform bone marrow aspirates when indicated. This article is designed to assist the practitioner in the evaluation of bone marrow aspiration biopsies. The indications for marrow evaluation, methods of sample collection, sample preparation, and cytologic examination of bone marrow are discussed. Cases are provided to demonstrate accurate interpretation of bone marrow aspirates.