Huntingtin-associated Protein-1 Deficiency in Orexin-producing Neurons Impairs Neuronal Process Extension and Leads to Abnormal Behavior in Mice

Yung-Feng Lin,Xingshun Xu,Austin Cape,Shihua Li,Xiao-Jiang Li

doi:10.1074/jbc.m110.107318

Abstract

Huntingtin-associated protein-1 (Hap1) is a neuronal protein that associates with huntingtin, the Huntington disease protein. Although Hap1 and huntingtin are known to be involved in intracellular trafficking, whether and how the impairment of Hap1-associated trafficking leads to neurological pathology and symptoms remain to be seen. As Hap1 is enriched in neuronal cells in the brain, addressing this issue is important in defining the role of defective intracellular trafficking in the selective neuropathology associated with Hap1 dysfunction. Here, we find that Hap1 is abundantly expressed in orexin (hypocretin)-producing neurons (orexin neurons), which are distinctly distributed in the hypothalamus and play an important role in the regulation of feeding and behavior. We created conditional Hap1 knock-out mice to selectively deplete Hap1 in orexin neurons via the Cre-loxP system. These mice show process fragmentation of orexin neurons and reductions in food intake, body weight, and locomotor activity. Sucrose density gradient fractionation reveals that loss of Hap1 in the mouse brain also reduces the distribution of trafficking protein complexes and cargo proteins in the fractions that are enriched in synaptosomes. These results suggest that Hap1 is critical for the transport of multiple proteins to the nerve terminals to maintain the integrity of neuronal processes and that selective disruption of the processes of orexin neurons can cause abnormal feeding and locomotor activity.

Highlights

Conditional Knock-out of Huntingtin-associated protein-1 (Hap1) in Orexin-positive Neurons— Orexin neurons are a small group of neurons located in the lateral hypothalamic region (Fig. 1A)
We analyzed the expression of Hap1 via Western blotting and found that Hap1 in the hypothalamus of Orexin-Hap1Ϫ/Ϫ mice is apparently reduced compared with wild-type and Orexin-Hap1ϩ/Ϫ mice (Fig. 2C)
By selectively eliminating Hap1 expression in orexin neurons in the mouse brain, in a subset of hypothalamic neurons, we identified a disruption of neuronal processes of orexin neurons, as well as decreased feeding and locomotor behavior in mice

Summary

Introduction

We discovered that a lack of Hap1 can affect neuronal process extension and reduce the distribution of trafficking protein complexes in sucrose density gradient fractions enriched in synaptosomes. The mechanism ence seen between control and mutant males at the end of underlying this sex-dependent phenomenon remains to be recording or at ages over 100 days, suggesting that Hap1 in investigated, our data suggest a role for Hap1 in orexin neuroorexin neurons may be more important for early animal devel- nal activities and associated animal behaviors.

Results

Conclusion