Expression of Pork Plectin during Postmortem Aging

The current study investigated the distribution and degradation of pork plectin during postmortem aging. Longissimus thoracis (LT) muscles from 12 pig carcasses were vacuum-packaged and aged at 4 °C for 0 h, 6 h, 12 h, 1 day, 3 days, 7 days, and 13 days. Immunofluorescence analysis showed that pork plectin was distributed in a honeycomb-like pattern in the cross section and a regularly striated pattern in the longitudinal section. However, plectin was found preferentially expressed in fibers that were stained with high anti-fast-MyHC. Double immunostaining revealed the colocalization of plectin and desmin in the cytoplasm and beneath the sarcolemma. Western blot analysis showed that the amount of intact plectin was rapidly reduced during the early postmortem aging (P < 0.05) and almost disappeared at day 3. The degraded 240 kDa plectin accumulated fast and was further cleaved after 3 days of aging (P < 0.05). The plectin degradation could be significantly blocked by calpain inhibitor MDL-28170 rather than Caspase-3 inhibitor Ac-DEVD-CHO (P < 0.05). Double immunostaining of μ-calpain and plectin showed a large amount of overlap at 0 h and 3 days of postmortem. Accordingly, these findings showed that plectin was preferentially expressed in fast muscle fiber and regularly distributed along with desmin at the strategic cellular sites. Plectin suffered a prominent and prompt degradation during postmortem aging, which might be attributed to μ-calpain.