Studies of protease inhibitors in the sera of patients with amyotrophic lateral sclerosis

Serine proteases purified from sera of patients with amyotrophic lateral sclerosis (ALS) induce contrasting cytopathology in murine motoneurones to IgG

Affinity purified IgG from sera of patients with amyotrophic lateral sclerosis (ALS) is claimed to enhance transmitter release, induce apoptotic death of cultured motoneurones, and elicit a distinctive cytopathology with raised Ca(2+) in mouse motoneurones. An alternative hypothesis attributes these events to serine proteases in ALS sera. To test this, motoneurones in BALB/c mice injected intraperitoneally with plasminogen affinity purified from sera of ALS patients and healthy controls were analysed using immunochemical and ultrastructural morphometric methods. The responses were validated in motoneurones of mice injected with commercially purified plasminogen, tissue plasminogen activator (tPA), or plasmin. Motoneurones in non-injected mice had normal morphology and ultrastructure without evidence of electron-dense degeneration. Purified plasminogen from both ALS patients and healthy controls, evoked electron-dense motoneurone degeneration, as did commercially purified plasminogen and tPA. The common cytopathology comprised disruption and distension of Nissl body rough endoplasmic reticulum, cytoplasmic polyribosomal proliferation, and significant Ca(2+) enhancement in mitochondria. By contrast, using affinity purified serum immunoglobulins, ALS-IgG but not IgG from healthy or disease controls, elicited necrosis, with 30% of ALS-IgGs tested evoking electron-dense degeneration in 40% of motoneurones. The primary cytopathology was extensive swelling of Golgi endoplasmic reticulum and mitochondria, with enhancement of Ca(2+) in Golgi endoplasmic reticulum and presynaptic boutons. We conclude that serine proteases purified from sera of ALS patients elicits a distinctive cytopathology and pattern of Ca(2+) enhancement in motoneurones different from that found on passive transfer of affinity purified ALS-IgG.

Proteolytic activity in amyotrophic lateral sclerosis IgG preparations

Sporadic amyotrophic lateral sclerosis is a motor neuron disease of unknown origin. Autoimmunity against voltage-gated calcium channels is one mechanism hypothesized to be the cause of the disease. In support of this hypothesis, it was previously reported that amyotrophic lateral sclerosis IgG specifically blocked the binding of 8B7 monoclonal antibody to the alpha1 subunit of voltage-gated calcium channels, suggesting overlapping epitopes of the two antibodies. It is, however, possible that the 8B7 epitope was destroyed by proteases. Data presented here show that the blocking of 8B7 binding to the alpha1 subunit by diethylaminoethyl cellulose (DEAE)-purified amyotrophic lateral sclerosis IgG was not observed with Fab fragments of amyotrophic lateral sclerosis IgG. The blocking was prevented by serine protease inhibitors. Moreover, it was reproduced by plasminogen and urokinase. These observations suggest that raised proteolytic activity in amyotrophic lateral sclerosis IgG preparations may be responsible for the blockade of 8B7 monoclonal antibody demonstrated previously. They also indicate the need to be particularly cautious when interpreting the results of incubation in amyotrophic lateral sclerosis sera or IgG preparations. Furthermore, they suggest that proteases may be partly responsible for some of the effects previously described for amyotrophic lateral sclerosis IgG. However, the proteolytic activity needs to be better defined and its possible role in amyotrophic lateral sclerosis investigated.

Alterations in serum thrombospondin in patients with amyotrophic lateral sclerosis

Thrombospondin (TSP), an endogenous extracellular matrix (ECM) glycoprotein, is secreted from platelet alpha-granules after thrombin stimulation. Alterations in blood TSP levels occur in different pathologic conditions, suggesting it is a marker for certain disorders. We previously found a marked increase in TSP deposition in the muscle ECM of patients with amyotrophic lateral sclerosis (ALS) in comparison with controls. Because the mechanism for this increase is unknown, we compared serum TSP levels in 11 patients to 15 controls using three different site-specific monoclonal antibodies (MA-I, MA-II and A6.1). We found mean serum TSP concentrations by indirect ELISA to be significantly decreased in the ALS patients. Using laser densitometry we calculated the ratio of fragmented to native TSP from Western immunoblots probed with A6.1, where a higher ratio corresponds to increased fragments. Mean values for this ratio were 6.3 +/- 4.9 and 18.3 +/- 8.2 for controls and patients, respectively. Thus significant decrease in native TSP and increase in its proteolytic fragments in ALS is consistent with increased proteolytic enzyme activity. Dysregulation of the protease: inhibitor balance in this degenerative condition may be reflected in the quantitative and qualitative changes in TSP.

Thrombospondin, a platelet alpha-granule and matrix glycoprotein, is increased in muscle basement membrane of patients with amyotrophic lateral sclerosis

In an attempt to obtain a biological marker for the enigmatic and fatal neurologic disorder, amyotrophic lateral sclerosis (ALS), several laboratories have explored alterations in various extracellular matrix components in both skeletal muscle and skin. We have studied the distribution of fibronectin, laminin, heparan sulfate proteoglycan (HSPG) and collagen types I, III and IV, along with the platelet alpha-granule glycoprotein, thrombospondin (TSP), by immunofluorescence in frozen sections of muscle from control denervating conditions and ALS patients. In ALS and control muscle, types I and III collagen were localized to the endomysium and the perimysium. Type IV collagen and laminin precisely delineated each muscle fiber (endomysium or basement membrane) but did not stain the perimysium. We found no marked quantitative or qualitative differences in the distribution of collagen types I, III and IV, laminin, fibronectin or HSPG in ALS patients compared to controls. However, when polyclonal antisera for TSP was used we found a marked increase in the deposition of this multi-domain glycoprotein in ALS patients' muscle compared to control muscle. Quantitative analysis of soluble extracts from control and ALS patients' muscle by ELISA also indicated that TSP was increased in ALS. TSP is released from platelet alpha-granules in response to thrombin stimulation. TSP elevation implies coagulation activity via the extravascular thrombolytic system in ALS and may correlate with regeneration. Other studies have indicated decreased circulating protease inhibitors and increased serine proteases in this disorder.