Relationship between promyelocytic leukemia protein nuclear bodies and TAR DNA-binding protein-43 aggregation in spinal anterior horn cells in sporadic amyotrophic lateral sclerosis.

Promyelocytic leukemia protein nuclear bodies (PML-NBs) and stress granules serve as deposition sites for stress-induced, aggregation-prone proteins. We previously reported that TAR DNA-binding protein 43 (TDP-43) colocalizes with stress granules during early aggregation in sporadic amyotrophic lateral sclerosis (ALS), and recent studies have noted PML-NB loss in familial ALS. To explore the role of PML-NBs in TDP-43 inclusion maturation, we analyzed spinal cord specimens from 12 patients with sporadic ALS and 5 controls using immunostaining for PML and TDP-43. PML-NB counts in anterior horn cells (AHCs) were significantly lower in patients with ALS than in controls (P < 0.05), especially in AHCs with TDP-43 inclusions (P < 0.01). Average numbers of PML-NB decreased progressively with inclusion type (3.1 in diffuse punctate cytoplasmic staining, 2.3 in round inclusions, and 0.8 in skein-like inclusions); all of these were significantly lower than those in inclusion-free AHCs (controls: 4.6; ALS: 5.5; P < 0.01). AHCs in ALS without inclusions showed higher PML-NB counts than in controls (P < 0.05), suggesting an early protective response. In contrast, reduced PML-NBs in mature inclusions may reflect diminished cellular defense. These findings implicate PML-NBs in the pathogenesis of sporadic ALS.