| dc.description.abstract | Matrix metalloproteinases (MI'v1Ps) are a family of conserved, proteolytic enzymes.
MMPs can degrade most extracellular matrix proteins. As such, they are key enzymes in
tissue remodeling processes. such as molting and metamorphosis in insects. The presence
of MMP in tracheae of 4th and 5th instar Manduca scxra (M sexta) larvae was investigated
using zymograms and Western blots, and the expression was found to decrease at the end
of the instar. Failure to completely inhibit gelatinolytic activity in a zymogram indicates
the existence of various other proteases that arc involved in the molting process. However,
delay in the appearance of the dorsal blood vessel along with a reduction in the body mass
upon inhibition of MMP supports our hypothesis that MMPs are required for molting.
MMPs are also known to be up-regulated in many disease states, where they may
cause tissue damage. Their presence may be beneficial, as their inhibition may result in
worsening of symptoms or increased mortality. We tested the hypothesis that MMPs play
a role in innate immunity in the tobacco hornworm caterpillar. Jf. sex/a. Larvae infected
with E. coli DH5a had significantly more circulating hemocytes (insect blood cells) when
compared to the larvae v,:hich received an MMP inhibitor. suggesting that MMPs may be
important for hernocyte recruitment from the hematopoietic organs such as the lymph
gland and hematopoictic cells present near the v.'ing imaginal discs. The expression of
MMP was increased by 50% in larvae that had been infected with E. coli DH5a.
However, this response was abrogated upon inhibition of MMPs. reducing expression tocontrol levels. The majority of the circulating hemocytes were granulocytes. a cell type
that phagocytoses foreign bodies. including pathogens. We used flow cytometry to assess
phagocytic ability. Hemocytes in the presence of the MMP inhibitor were less abk to
phagocytose sephadex beads. supporting the hypothesis that this MMP contributes to the
cellular innate immune response.
Our results suggest that MMP expression is high at the beginning of the in star
while it reduces as the caterpillar reaches molting. during which other proteases like
chitinases and molting fluid proteinases play a more prominent role. Our results also
suggest that M. sex/a larvae have a reduced immunity to bacterial infections when MMPs
are inhibited. Collectively, inhibition of MMPs during the molting process indicates that
the larvae. by down regulating the expression of MMPs. prevent the elicitation of immune
responses that is generally seen during the larval pupal metamorphosis. | en_US |
