Neurofilamentous conglomerates (NfCg), as axonal spheroids or conglomerates in motoneurons,
are the histopathologic hallmarks for early stages of amyotrophic lateral sclerosis
(ALS). We hypothesize that NfCg may be formed by post-translational modifications
of altered Nf proteins that include: (1) hyperphosphorylation, (2) glycosylation (or
glycoxidation), (3) nitration, (4) ubiquitination and/or (5) crosslinking by the Ca++-dependent
transglutaminase (TGase). These, as well as other changes, are predicted to be initiated
or accentuated by oxidative damage. The damaged Nf proteins then activate cascades
of intracellular protein degradation which include ATP-dependent ubiquitin/proteasome
proteolysis. Other proteolytic systems, either Ca++-dependent or independent, may
also be activated, such as serine and cysteine protease systems. These enzymes, either
lysosomal or non-lysosomal may also participate in the degradation of damaged Nf proteins
being balanced by their cognate inhibitors. Protein complexes formed by these protease=inhibitor
systems, along with damaged Nf proteins, may accumulate within the cell bodies as
neuronal inclusions, since a number of intracellular inclusions are found in motor
neurons in ALS. In the current study, we investigated the involvement of serine proteases
and their serpins in NfCg formation. Pairs of three serine proteases (trypsin, chymotrypsin
and thrombin) and their cognate serpins (alpha1-anti-trypsin, alpha1-anti-chymotrypsin,
and protease nexin I) were probed in motoneurons with their antibodies for both NfCg
and inclusions. Positive immunoreactivities for all serine proteases and their cognate
serpins support the contention that the imbalance of serine proteases and internalized
serpins may have a role in formation of NfCg and inclusions, and hence, the pathogenesis
of ALS.