Light-Induced photoreceptor degeneration in the mouse involves activation of the small GTPase Rac1.

PURPOSE: Rho GTPases play a central role in actin-based cytoskeleton reorganization, and they participate in signaling pathways that regulate gene transcription, cell cycle entry, and cell survival. This study verifies the role of Rac1 during light-induced retinal degeneration. METHODS: BALB/c mice were exposed to degenerative light stimulus, and their eyes were enucleated immediately or after the mice were kept in the dark for 6, 24, and 48 hours. Retinas were fixed and processed for immunohistochemical analysis. The distribution of Rac1 and its effectors-p21-activated kinases (PAKs) 1, 2, and 3-was studied by immunohistochemistry, whereas the expression of PAKs 3, 4, and 5 mRNA was analyzed by real-time PCR. Rac1 activity was measured using a pull-down assay. RESULTS: In control retinas, Rac1 was mostly observed in photoreceptors, plexiform layers, and Müller glial cells. In light-damaged retinas, some TUNEL-positive photoreceptors upregulated Rac1 expression. Conversely, most of the Rac1-positive cells were TUNEL-positive, mainly in early stages of retinal degeneration. The increase in Rac1 expression was preceded by enhanced Rac1 activity, detectable at the end of the light stimulus and still present 48 hours later. The distribution patterns of PAK1, PAK2, and PAK3 did not change in light-damaged retinas. However, there was a marked increase in PAK3 and PAK4 gene expression, whereas that of PAK5 mRNA remained the same. CONCLUSIONS: Rac1 may play a role in the apoptosis of light-damaged photoreceptors. The increased expression of PAK4 after light stimulus possibly functions as a protective mechanism against apoptosis.

Rat myocellular and perimysial intramuscular triacylglycerol: a histological approach.

PURPOSE: There is controversy as to the use of intramuscular triacylglycerol (IMTAG) during exercise and to whether endurance training increases its utilization, despite the various methodologies used to address these questions. We used a histological-morphometrical approach to study the relative contribution of the two compartments of IMTAG storage, intramyocellular, and perimysial adipocytes, during exercise in sedentary and endurance-trained rats. METHODS: After osmium impregnation, the soleus (SOL) and gastrocnemius (GAS) were studied under light and electron microscopy. IMTAG content (after Triton WR1339 treatment or not) and 14C-oleate incorporation into the muscles were studied. RESULTS: In GAS, training, but not exercise alone, decreased extramyocellular lipid (P < 0.001 vs sedentary), an effect not found for SOL. Both muscles presented reduced lipid inclusion number (P < 0.001) and area (P < 0.05), immediately after exercise in sedentary and trained rats. For SOL, a greater number (P < 0.001 vs sedentary) of inclusions was found 24 h after exercise in trained rats. Triton WR1339 treatment decreased IMTAG content 12 h after exercise in SOL (but not in GAS), in sedentary (33%), and trained rats (52%). CONCLUSIONS: The multi-analytical approach adopted allowed the discernment between the IMTAG compartments and provided evidence for an effect of training upon storage of lipid in perimysial adipocytes in rat gastrocnemius, as well as clearly showed that the IMTAG mobilized during submaximal exercise in sedentary and trained rats derives from intramyocellular lipid, both in SOL and GAS. Moreover, the reposition of these stores 12 h after exercise was shown to be different in GAS and SOL, as plasma triacylglycerol clearly contributed to the process only in the latter, possibly reflecting the differences in lipoprotein lipase activity in the muscles reported by others.