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Summary Epigenetic processes, such as DNA methylation and other chromatin modifications, are believed to be largely responsible for establishing a reduced capacity for growth in the mature nervous system. Ten‐eleven translocation methylcytosine dioxygenase 3 (Tet3)‐, a member of the Tet gene family, plays a crucial role in promoting injury‐induced DNA demethylation and expression of regeneration‐associated genes in the peripheral nervous system. Here, we encapsulate Tet3 protein within a clinically tolerated poly(lactide‐co‐glycolide) microsphere system. Next, we show that Tet3‐loaded microspheres are internalized into mHippoE‐18 embryonic hippocampal cells. We compare the outgrowth potential of Tet3 microspheres with that of commonly used nerve growth factor (NGF)‐loaded microspheres in an in vitro injury model. Tet3‐containing microspheres increased levels of nuclear 5‐hydroxymethylcytosine indicating active demethylation and outperformed NGF‐containing microspheres in measures of neurite outgrowth. Our results suggest that encapsulated demethylases may represent a novel avenue to treat nerve injuries.

KEY WORDS neurotrophins; fish; juxtaglomerular cells; immunohistochemistryABSTRACT By means of immunochemistry and immunohistochemistry, we investigated in thekidney of freshwater and marine teleostean species for the presence and localization of three neuro-trophins: nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and neurotrophin(NT)-3. In both species studied, NGF-like and NT-3-like immunoreactivity were present in the kid-ney with different distribution patterns, while BDNF-like immunoreactivity was never detected. Ingoldfish, NGF-like and NT-3-like immunoreactivity were identified extensively in cells along partof the arterial branches adjacent to the afferent arterioles. In scorpion fish, NGF-like and NT-3-likeimmunoreactive cells were observed both on afferent arterioles and on adjacent secondarybranches derived from renal arteries. No immunoreactivity was detected in other renal structures.A staining pattern of immunoreactivity similar to that obtained for NGF and NT-3 was detectedutilizing S100 antibody as a juxtaglomerular (JG) cell marker. Double immunolabellings NGF/S100 and NT-3/S100 evidenced the coexistence of neurotrophin-like proteins and S100-like proteinin the same immunoreactive cells, thus identifying them as juxtaglomerular cells. Western blotanalysis revealed the presence of molecules immunoreactive to NGF and NT-3, whose molecularweights were very similar to those of the corresponding mammalian neurotrophins. These findingsextend the presence and distribution of NGF-like and NT-3-like IR in the kidney to teleost species,suggesting a probable participation of these proteins in the renal functions of freshwater andmarine teleosts. Microsc. Res. Tech. 66:17–24, 2005.