Astrocyte ALDH1L1 and GFAP Expression in the Brainstems of Young and Aged Mice
Bethany Mensink, OMS II1; Corbin Ballam, OMS II1; Mildred Mattox, BS2; Joyce Morris-Wiman, PhD2
1West Virginia School of Osteopathic Medicine, Lewisburg; 2Department of Biomedical Sciences, West Virginia School of Osteopathic Medicine, Lewisburg
Introduction: Astrocytes, once thought to be mere supportive cells, play a dominant role in aging and associated neurodegeneration, as well as in injury and neuroinflammation. Previous studies have shown astrocyte numbers to be reduced in the hippocampus of aged rodents, a region responsible for memory. Dysmorphic astrocytes have been viewed in several regions of the cerebral cortex of aged mice, and there are indications that theses astrocytes may no longer be neuroprotective but may be neurotoxic. The brainstem region, specifically the pons and midbrain region, was chosen for investigation due to its involvement with critical functions such as swallowing, vision, hearing, motor control, and the sleep/wake cycle—functions that deteriorate with normal aging. Two proteins were examined: GFAP, the traditional marker for astrocytes, and ALDH1L1, recently identified in cortical astrocytes. Evidence suggests that GFAP may only label a subpopulation of astrocytes and is expressed in other CNS cell types. ALDH1L1 has been proposed as a more specific astrocyte marker. However, its distribution in the brainstem has not yet been examined.
Hypothesis: We propose that a difference in astrocyte number as detected by ALDH1L1 and GFAP would be observed in the brainstems between young and aged mice.
Methods: Total protein was extracted from the midbrain-pons region of 3-month-old mice using standard protocols. Proteins were separated by SDS PAGE and transferred to nitrocellulose membranes for western blot analysis. Membranes were probed with the following antibodies: anti-GFAP (Encor Biotechnology Inc), anti-ALDH1L1 (Neuromab) and monoclonal G3PDH (Millipore). Band intensities were analyzed using Kodak Molecular Imaging software; GFAP and ALDH1L1 values were normalized to G3PDH to control between group variability.
Results: There was a trend (P=.0596) toward a significantly increased expression of GFAP compared to ALDH1L1 in the midbrain-pons from old animals, but no significant difference was observed in young animals. No significant differences were observed in ALDH1L1 or GFAP expression between old and young midbrain-pons.
Conclusion: The lack of any significant change between young and aged in the expression of either ALDH1L1 or GFAP suggests that astrocytes may not have a role in aging in the mouse brainstem. ALDH1H1 was expressed in the midbrain-pons region of both young and aged mice, but the results of this study do not support its use as a more sensitive marker than GFAP.