Cytoskeletal protein immunoexpression in fetal neural grafts: Distribution of phosphorylated and nonphosphorylated neurofilament protein and microtubule-associated protein 2 (MAP-2)

Abstract

The present study examined the immunocytochemical expression of important cytoskeletal proteins within the neurons of an extended series of neocortical grafts and smaller group of ventral mesencephalic (nigral) grafts. Using antibodies that were directed at all three neurofilament (NF) epitopes, NF-L, NF-M, and NF-H, we attempted to determine whether these neurons would have an altered cytoskeletal profile following the stress of transplantation, because previous studies have shown such changes following ischemia or direct brain injury. We studied phosphorylated NF protein, which is found predominantly in axons, nonphosphorylated NF protein, which is found predominantly in the somata-dendritic compartment, and MAP-2, a specific microtubule marker that is localized exclusively in the somato-dendritic compartment. The results show that in all neocortical grafts examined, both phosphorylated and nonphosphorylated NF immunoexpression was significantly downregulated and appeared only in relatively few axons and somatic profiles, respectively, even though there were numerous Nissl-stained neuronal profiles in the grafts. There was no particular pattern to the immunopositive profiles. At later times occasional neuronal profiles were positive for phosphorylated NF protein, suggesting a reaction to cellular injury. In contrast to neocortical grafts, the cytoskeletal profiles of MAP-2 and phosphorylated NF protein in nigral grafts appeared very similar to age-matched control although the nonphosphorylated NF protein expression did appear somewhat lessened at 1-2 mo postoperative. Because cytoskeletal proteins play important roles in neuronal size, shape, and structural stability, they may subserve key cellular issues in neural grafting. These results show a significant loss of cytoskeletal protein expression in neocortical grafts that does not occur in nigral grafts. These results suggest that fetal neurons from different brain regions (i.e., graft source) may respond differently to the grafting procedure insofar as their cytoskeletal makeup is concerned. In addition, a potential lack of appropriate growth substrates or synaptic contacts may also produce cytoskeletal alterations. As such, the cytoskeletal protein profiles in central nervous system (CNS) grafts may be useful markers for functional performance, perhaps reflecting a degree of cellular injury.