A novel cell immunoassay to measure survival of motor neurons protein in blood cells

Abstract

Background: The motor neuron degenerative disease spinal muscular atrophy (SMA) is the leading genetic cause of infant mortality and is caused by mutations in the survival of motor neurons (SMN) gene that reduce the expression levels of the SMN protein. A major goal of current therapeutic approaches is to increase SMN levels in SMA patients. The purpose of this study was to develop a reliable assay to measure SMN protein levels from peripheral blood samples.

Methods: We developed a novel cell immunoassay to quantitatively measure SMN levels from peripheral blood mononuclear cells (PBMCs) using a single anti-SMN antibody.

Results: SMN levels determined by the cell immunoassay are comparable to levels determined by Western blot, but in contrast, the immunoassay does not involve cell lysis, requires a small amount of patient material, and can be done on a large number of samples simultaneously. SMN levels from PBMCs are not influenced by cell type heterogeneity.

Conclusion: SMN levels measured from total PBMCs provide an important snapshot of SMN protein expression, which should be a useful aid in SMA diagnosis, and a surrogate marker of efficacy of treatment in SMA clinical trials.

Figure 1

A) SMN levels in control and SMA I lymphoblastoid cell lines from four separate experiments. B) SMN and Y14 chemiluminescent intensity levels as a function of number of cells loaded per 96-well plate well. C) SMN levels from the same cell lines determined by Western blot. D) Quantification of Western blot data N = 9. Error bars are standard deviation from the mean.

Figure 2

SMN (dark grey bars), Y14 (light grey bars) and background (white bars) chemiluminescent intensity levels in (A) sorted monocytes and lymphocytes, including mixed ratios of the two cell types, and in (B) peripheral blood mononuclear cell isolated from blood obtained from five control individuals. Error bars are standard deviation from the mean, N = 3.