• Molecules and Cells
• /
• v.37 no.4
• /
• pp.322-329
• /
• 2014

N-acetylglucosamine kinase (GlcNAc kinase or NAGK; EC 2.7.1.59) is highly expressed and plays a critical role in the development of dendrites in brain neurons. In this study, the authors conducted structure-function analysis to verify the previously proposed 3D model structure of GlcNAc/ATP-bound NAGK. Three point NAGK mutants with different substrate binding capacities and reaction velocities were produced. Wild-type (WT) NAGK showed strong substrate preference for GlcNAc. Conversion of Cys143, which does not make direct hydrogen bonds with GlcNAc, to Ser (i.e., C143S) had the least affect on the enzymatic activity of NAGK. Conversion of Asn36, which plays a role in domain closure by making a hydrogen bond with GlcNAc, to Ala (i.e., N36A) mildly reduced NAGK enzyme activity. Conversion of Asp107, which makes hydrogen bonds with GlcNAc and would act as a proton acceptor during nucleophilic attack on the ${\gamma}$-phosphate of ATP, to Ala (i.e., D107A), caused a total loss in enzyme activity. The overexpression of EGFP-tagged WT or any of the mutant NAGKs in rat hippocampal neurons (DIV 5-9) increased dendritic architectural complexity. Finally, the overexpression of the small, but not of the large, domain of NAGK resulted in dendrite degeneration. Our data show the effect of structure on the functional aspects of NAGK, and in particular, that the small domain of NAGK, and not its NAGK kinase activity, plays a critical role in the upregulation of dendritogenesis.

• Korean Journal of Exercise Nutrition
• /
• v.23 no.4
• /
• pp.32-35
• /
• 2019

[Purpose] Fibronectin type III domain containing 5 (FNDC5)/irisin is an exercise-induced myokine, which contributes to cognitive functions. However, the relationship between the neuroprotective effects of FNDC5/irisin and hippocampal dendritic remodeling and astrocyte-secreted factors remains unclear. Therefore, we explored whether subchronic recombinant irisin treatment affected hippocampal morphology and some astrocyte-derived molecules. [Methods] Mice were intraperitoneally injected with irisin (0.5 μg/kg/day) for seven days, followed by their sacrifice two days later. Hippocampal morphometric parameters were analyzed and pgc-1a, fndc5, bdnf, and some astrocyte-derived factors mRNA levels were measured. [Results] Dendritic length, arborization, and spine density were enhanced by irisin regimen in hippocampal CA1 and CA3 areas. Hippocampal pgc-1a, fndc5, and bdnf mRNA levels were significantly increased by irisin treatment. Moreover, hevin mRNA levels were significantly enhanced, whereas tgf-b1 levels downregulated by irisin treatment. [Conclusion] FNDC5/irisin has dendritogenic activity probably through hevin induction and TGF-β1 suppression.

• Molecules and Cells
• /
• v.38 no.10
• /
• pp.876-885
• /
• 2015

N-acetyl-D-glucosamine kinase (NAGK) plays an enzyme activity-independent, non-canonical role in the dendritogenesis of hippocampal neurons in culture. In this study, we investigated its role in axonal development. We found NAGK was distributed throughout neurons until developmental stage 3 (axonal outgrowth), and that its axonal expression remarkably decreased during stage 4 (dendritic outgrowth) and became negligible in stage 5 (mature). Immunocytochemistry (ICC) showed colocalization of NAGK with tubulin in hippocampal neurons and with Golgi in somata, dendrites, and nascent axons. A proximity ligation assay (PLA) for NAGK and Golgi marker protein followed by ICC for tubulin or dynein light chain roadblock type 1 (DYNLRB1) in stage 3 neurons showed NAGK-Golgi complex colocalized with DYNLRB1 at the tips of microtubule (MT) fibers in axonal growth cones and in somatodendritic areas. PLAs for NAGK-dynein combined with tubulin or Golgi ICC showed similar signal patterns, indicating a three way interaction between NAGK, dynein, and Golgi in growing axons. In addition, overexpression of the NAGK gene and of kinase mutant NAGK genes increased axonal lengths, and knockdown of NAGK by small hairpin (sh) RNA reduced axonal lengths; suggesting a structural role for NAGK in axonal growth. Finally, transfection of 'DYNLRB1 (74-96)', a small peptide derived from DYNLRB1's C-terminal, which binds with NAGK, resulted in neurons with shorter axons in culture. The authors suggest a NAGK-dynein-Golgi tripartite interaction in growing axons is instrumental during early axonal development.