Novel intracytoplasmic inclusions immunoreactive for phosphorylated-TDP43 and cystatin C in anterior horn cells in a case of sporadic amyotrophic lateral sclerosis

Autophagy Is a Common Degradation Pathway for Bunina Bodies and TDP-43 Inclusions in Amyotrophic Lateral Sclerosis

Bunina bodies (BBs) coexisting with TDP-43-immunoreactive (TDP-43-IR) skein-like inclusions (SIs) and round inclusions (RIs) in lower motor neurons are a frequent feature of sporadic amyotrophic lateral sclerosis (sALS). Since previous studies have shown that BBs and TDP-43-IR inclusions are often detected in association with autophagy-related structures (autophagosomes and autolysosomes), we examined the anterior horn cells (AHCs) of the spinal cord from 15 patients with sALS and 6 control subjects, using antibodies against autophagy-related proteins (LC3, cathepsin B, and cathepsin D). Among AHCs with SIs, 43.9% contained BBs, whereas 51.7% of AHCs with RIs did so. The cytoplasm of AHCs showed diffuse immunoreactivity for LC3, cathepsin B and cathepsin D in both sALS and controls. Ultrastructurally, SIs and mature BBs contained autophagosomes and autolysosomes. Mature BBs were localized in the vicinity of SIs. RIs also contained autophagosomes, autolysosomes, and early-stage BBs. These findings suggest that autophagy is a common degradation pathway for BBs and TDP-43-IR inclusions, which may explain their frequent coexistence.

Colocalization of Bunina bodies and TDP-43 inclusions in a case of sporadic amyotrophic lateral sclerosis with Lewy body-like hyaline inclusions

Sporadic amyotrophic lateral sclerosis (sALS) is characterized pathologically by loss of upper and lower motor neurons with occurrence of transactivation response DNA-binding protein 43 kDa (TDP-43)-immunoreactive skein-like and round hyaline inclusions. Lewy body-like hyaline inclusions (LBHIs) are also found in a small proportion of sALS cases as well as in individuals with familial ALS with mutations in the Cu/Zu superoxide dismutase (SOD1) gene. LBHIs in sALS are immunopositive for TDP-43, but not for SOD1. The occurrence of Bunina bodies (BBs) is another key pathological feature of sALS. BBs are immunonegative for TDP-43 but immunopositive for cystatin C, transferrin, peripherin and sortilin-related receptor CNS expressed 2 (SorCS2). Despite differences between BBs and TDP-43 inclusions in terms of protein constituents and ultrastructure, the two inclusions are known to be linked. We recently encountered a case of sALS of 10 months duration in which many round hyaline inclusions, LBHIs and BBs were found in the anterior horn cells of the spinal cord. Our immunohistochemical and ultrastructural examinations revealed the presence of BBs within the skein-like and round hyaline inclusions, and in the LBHIs. Colocalization of BB-related proteins (cystatin C, transferrin and SorCS2) and TDP-43 was also confirmed in the halo of LBHIs as well as in the marginal portion of the skein-like and round hyaline inclusions. These findings suggest that there is some relationship between BBs and TDP-43-immunoreactive inclusions in terms of their formation processes.