Gene expression analysis of the development of congenital hydrocephalus in the H-Tx rat

Abstract

To discover candidate genes in the pathogenesis of congenital hydrocephalus, gene arrays were utilized to analyze transcripts from the midbrain region of 5-day-old H-Tx rats; these animals develop hydrocephalus due to closure of their cerebral aqueduct between embryonic day 18 and post-natal day 5. Of the 15,924 transcripts assayed, we detected 47 differentially expressed transcripts representing 23 genes and 24 expressed sequence tags (ESTs); 17 transcripts (7 genes and 10 ESTs) were upregulated and 30 (16 genes and 14 ESTs) were downregulated in the hydrocephalic animals relative to control non-hydrocephalic animals. Seven of these genes, Cck, Nfix, Lgals3, Gsta1, Xdh, Tnf, and Tfpi-2, can be linked to hydrocephalus. In addition, 17 genes that displayed altered expression in our study are not currently known to be associated with the presence or development of hydrocephalus. These results indicate that a relatively few number of transcripts were found to be altered in the development of hydrocephalus in this model. This is the first experiment of its kind to identify changes in gene expression in a congenital model of rodent hydrocephalus that are occurring locally in the area surrounding the cerebral aqueduct. Studies are now needed to examine these candidate genes and their cognate proteins to delineate their role in hydrocephalus.

Introduction

Hydrocephalus is a condition marked by an excessive accumulation of cerebrospinal fluid (CSF) within the cerebral ventricles caused by an imbalance between the rate of CSF production and its absorption, resulting in ventricular enlargement. The reported incidence of developmental hydrocephalus is 0.48 to 0.81 per 1000 live births (Blackburn and Fineman, 1994, Fernell et al., 1994). Reports indicate that up to 78% of all patients undergoing treatment for hydrocephalus suffer persistent defects (Fernell et al., 1990, Fernell et al., 1994, Villani et al., 1995), including low IQ, mental retardation, memory loss, learning disabilities, spasticity, epilepsy, low visual acuity, cognitive function that depends on visual association, and secondary reproductive dysfunction (Ding et al., 2001, Fernell et al., 1990, Fernell et al., 1994, Hoppe-Hirsch et al., 1998, Nagasaka and Tanaka, 1991). Therefore, a clear understanding of the mechanisms involved in the genesis and progression of hydrocephalus is critical for improving diagnostic and therapeutic options.

There have been a number of studies that examined expression changes of individual genes or proteins in congenital hydrocephalus (Blackshear et al., 2003, Brewer et al., 1996, Coucke et al., 1994, Dahme et al., 1997, Graf et al., 2000, Li et al., 2005a, Morgan et al., 2005). However, very few large-scale genomic studies have addressed hydrocephalus due to closure of the cerebral aqueduct. Jones et al. (2001a,b, 2004, 2005a) mapped chromosomal loci that were associated with the development of hydrocephalus in H-Tx rats, a model of congenital obstructive hydrocephalus due to closure of the aqueduct, but did not look for the specific genes involved in the onset of the condition. Del Bigio's group (Balasubramaniam and Del Bigio, 2002) examined gene expression alterations occurring 1.5–36 weeks after inducing hydrocephalus by injecting kaolin in both juvenile and adult rats. Experimental obstructive hydrocephalus is often induced by the injection of irritating substances, such as kaolin, into the cisterna magna. This produces an intense inflammatory reaction that leads to closure of the fourth ventricle outlets resulting in hydrocephalus (Matsumoto et al., 1975). This approach, though effective, makes it difficult to separate the transcriptional events participating in the genesis of hydrocephalus from those due to an inflammatory response. Another recent study by Morgan et al. examined differences in expression using gene array technology of a small subset of stress-related genes between embryonic H-Tx and Sprague–Dawley rats (Morgan et al., 2005).

Our experiments were undertaken to more directly identify those transcripts undergoing altered expression specifically in the periaqueductal area that may be associated with hydrocephalus due to closure of the cerebral aqueduct. To clearly separate those changes in gene expression that might be due to hydrocephalus from those altered as a side effect of the induction method, we studied a congenital model of obstructive hydrocephalus utilizing the H-Tx rat where hydrocephalus results from a closure of the cerebral aqueduct between embryonic day 18 and post-natal day 5. Alterations of gene expression in these animals will be important in directing future studies to examine the specific role of these genes in the development of hydrocephalus.