Document Type

Dissertation

Degree

Ph.D.

Degree Granting Department

Medicine

Major Professor

Jun Tan

Keywords

Amyloid beta, cognition, immunomodulation, monocyte, neuroinflammation

Abstract

ABSTRACT

Alzheimer's disease (AD) is the most common progressive age related dementia and the fourth major cause of mortality in the elderly in the United States. AD is pathologically characterized by deposition of amyloid beta (Aβ) plaques in the brain parenchyma and neurofibrillary tangles (NFTs) within the neuronal soma. While pharmacological targets have been discovered, current strategies for the symptomatic or disease-modifying treatment of AD do not significantly slow or halt the underlying pathological progression of the disease. Consequently, more effective treatment is needed. One possibility for amelioration is using human umbilical cord blood cell (HUCBC) therapy. HUCBCs comprise a population of hematopoietic stem and progenitor cells. During recent years, functional recovery has been observed from the use of HUCBCs in pre-clinical animal models of brain and spinal cord injuries. Thus, modulation by cell therapy, specifically HUCBCs, may be a suitable treatment for AD and other models because of the observed cognitive and behavioral improvements. The studies presented in this dissertation centers on the suitability of using HUBCs as a potential treatment for AD. Expanding on this, the aims of the study sought to: (I) Investigate bio-distribution of HUCBC transplantation in PSAPP mice, (II) Characterize efficacy and determine therapeutic outcome of HUCBC following short and long term multi injections at early and late disease stages in PSAPP mice and (III) Determine AD-like pathological and cognitive changes associated with multiple HUCBC-derived monocyte (CD14) injections in PSAPP mice. Thus the findings of this work evolved from experiments that characterized the effects of low-dose infusions of HUCBC and HUCBC-derived monocytes into 6 month old Presenilin 1/Amyloid Precursor Protein (PSAPP) plaque-developing transgenic AD mice. Treated mice were studied using standard behavioral tests to determine the effects of infusion on the multiple cognitive domains affected by AD, followed by biochemical and histological analyses that included Aβ load and amyloid precursor protein (APP) processing. Specifically, PSAPP mice and their wild-type (WT) littermates were treated monthly with a peripheral HUCBC infusion over a period of 6 and 10 months, followed by cognitive and motor evaluation. Additionally, based on reports that tumor cells can originate from stem cells present in HUCB, we further examined whether monocytes purified from HUCBCs would have a similar significant effect on the reduction of AD-like pathology in PSAPP mice. HUCB cells homed into tissues including the brain. The principal finding was significant reduction in Aβ levels and β–amyloid plaques following low-dose infusions of both HUCBC– derived mononuclear cells as well as HUCBC-derived monocytes, with the monocytes providing a stronger effect. Results further demonstrated that HUCBC and HUCBC– derived monocyte infusion could improve memory function and locomotor ability in treated PSAPP mice. A possible reason for behavioral improvements in these animals may be the significant reduction in both Aβ levels and plaque load. This study also identified significant reduction in microglial activation and astrocytosis, both of which can contribute to AD pathology. In conclusion, our data suggest that it might be the HUCBC–derived monocytic population rather than stem cells that are responsible for the reduction in AD pathology.

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