Histological and Tissue-Level Outcomes of Stem Cell Therapies in Neurodegenerative Disorders: A Systematic Review

Neurodegenerative diseases, which afflict millions worldwide and threaten public health, have no cure. Neurodegenerative diseases lack effective therapies, burdening society and the economy. Over the past 20 years, regenerative cell therapy (stem cell therapy) has advanced, opening novel neurodegenerative disease treatments. Thus, the current review aimed to systematically highlight experimental and clinical studies of potentially effective therapeutic strategies for stem cells and report histological, cellular, or ultrastructural outcomes following stem cell interventions in neurodegenerative diseases. PRISMA-compliant computerized literature searches of PubMed, Scopus, and Web of Science identified studies on embryonic, induced pluripotent, mesenchymal, or neural stem cells (NSCs) in neurodegenerative disease models and histological and tissue-level outcomes. Search terms included nervous system diseases, histology, neuron regeneration, stem cells, stem cell treatment, and transplantation. Peer-reviewed articles published between 2000 and 2025 were selected. Experimental animal and clinical studies that reported histological or tissue-level results after stem cell treatments were included. Eighty-six studies met the eligibility criteria, covering models of Parkinson's disease, Alzheimer's disease, amyotrophic lateral sclerosis (ALS), and Huntington's disease. Across these studies, stem cell therapies were linked to improved neuron survival, better synaptic structure, diminished gliosis, and some restoration of tissue structure. These effects depended on the type of stem cell used, the disease model, and how the treatment was given. Overall, the evidence suggests that stem cell therapies can lead to significant histological and tissue-level improvements in neurodegenerative diseases, supporting their potential for regeneration. Further standardized and translational studies are needed to clarify the underlying mechanisms and improve treatment strategies.