Hypophosphorylation of NF-H and NF-M subunits of neurofilaments and the associated decrease in KSPXK kinase activity in the sciatic nerves of swiss white mice inoculated in the foot pad with mycobacterium leprae.

OBJECTIVE: To study the phosphorylation state of neurofilament (NF) proteins and activity of KSPXK kinase in the sciatic nerves of Swiss white (S/W) mice inoculated in the hind foot pads with M. leprae. DESIGN: Test group includes S/W mice inoculated in the foot pads with freshly harvested human derived (viable) M. leprae. Control groups were constituted by (1) Age matched un-inoculated mice, (2) Mice similarly inoculated with M. smegmatis and (3) heat killed M. leprae. Phosphorylation state of NF was studied using Western blot analysis and phosphor-specific NF antibody (SMI 31; Sternberger Monoclonals, Inc.). The KSPXK kinase activity was assayed by using KSPXK fusion protein in a radiometric method using gamma(22)P ATP. RESULTS: Several fold increase in M. leprae numbers was seen in viable M. leprae group while M. smegmatis failed to show any fold increase in the foot pads of S/W mice. Western immunoblot analysis of cytoskeletal preparation from sciatic nerves of uninoculated mice and mice inoculated with M. smegmatis showed immunoreactivity to SMI 31 antibody and protein bands corresponding to both NF-H and NF-M at all the time points from 4-20 months post inoculation. In case of viable M. leprae; SMI 31 reactive protein bands were seen at 4 months but not at any of the later intervals, i.e., between 6-20 months. With heat killed M. leprae transient loss of immunoreactivity to SMI 31 was seen. Decrease in KSPXK kinase activity was recorded in sets inoculated with viable and heat killed M. leprae, and corroborated with loss of immunoreactivity seen in WBs reacted with SMI 31 antibody. CONCLUSIONS: Alterations in the sciatic nerve NF cytoskeleton was seen following inoculation in the hind foot pad with both viable and heat killed M. leprae. The hypophosphorylation of NF observed in this study corroborates with the earlier observations in human leprous nerves.

Alterations in neurofilament protein(s) in human leprous nerves: morphology, immunohistochemistry and Western immunoblot correlative study.

Using a specific antibody (SMI 31), the state of phosphorylation of high and medium molecular weight neurofilaments (NF-H and NF-M) was studied in 22 leprous and four nonleprous human peripheral nerves by means of immunohistochemistry, sodium dodecyl sulfate-poly acrylamide gel electrophoresis (SDS-PAGE) and Western immunoblot (WB). The results thus obtained were compared with morphological changes in the respective nerves studied through light and electron microscopy. Many of the leprous nerves showing minimal pathology revealed lack of or weak staining with SMI 31, denoting dephosphorylation. Remyelinated fibres stained intensely with SMI 31 antibody. The WB analysis of Triton X-100 insoluble cytoskeletal preparation showed absence of regular SMI 31 reactive bands corresponding to 200 and 150 kDa molecular weight (NF-H and NF-M, respectively) in 10 nerves. Three of the 10 nerves revealed presence of NF protein bands in SDS-PAGE but not in WB. Presence of additional protein band (following NF-M) was seen in four nerves. Two nerves revealed NF-H band but not NF-M band and one nerve showed trace positivity. In the remaining five nerves presence of all the three NF bands was seen. Thus, 77.3% (17/22) of human leprous nerves studied showed abnormal phosphorylation of NF protein(s). The ultrastructural study showed abnormal compaction and arraying of NF at the periphery of the axons in the fibres with altered axon to myelin thickness ratio (atrophied fibres) as well as at the Schmidt-Lantermann (S-L) cleft region. Such NF changes were more pronounced in the severely atrophied axons suggesting a direct correlation. The observed well-spaced NF in the remyelinated fibres under ultrastructural study was in keeping with both intense SMI 31 staining and presence of NF triplet bands seen in WBs in four of leprous nerves that showed a large number of regenerating fibres suggesting reversal of changes with regeneration. Findings in the present study suggest that atrophy, that is, the reduction in axonal calibre and paranodal demyelination, seen in leprous nerves may result from dephosphorylation of NF-H and NF-M proteins.