Estrogens and Antioxidants Prevent the Formation of Tubular Aggregates in Aging Male Mice.

Tubular aggregates (TAs), ordered arrays of sarcoplasmic reticulum (SR) tubes, are the main morphological alteration found in muscle biopsies from patients affected by TA myopathy (TAM). TAM has been linked to mutations in the genes encoding for STIM1 and ORAI1, which are two proteins that mediate Store-Operated Ca entry (SOCE). SOCE is a mechanism that allows recovery of extracellular Ca during fatigue, when the SR becomes depleted. As TAs also form in fast-twitch muscle fibers of aging male mice (not in females), we studied the effect of sex hormones on the aggregation of TAs during aging. We administered estrogen (ad libitum in drinking water) to male mice from 10 to 18 months of age and then evaluated the following: (a) the presence of TAs using histology and electron microscopy (EM); (b) oxidative stress, a mechanism that could underlie damage to proteins and membranes (and possibly their accumulation in TAs); and (c) SOCE function during ex vivo stimulation in the presence or absence of external Ca or SOCE blocker (BTP-2). The results collected indicate that treatment with estrogen (a) significantly reduced the formation of TAs; (b) reduced oxidative stress, which was elevated in aging male mice; and (c) restored SOCE, i.e., the capability of aged EDL muscles to use external Ca by promoting maintenance of Ca Entry Units (CEUs, the intracellular junctions that mediate SOCE). Finally, we also show that formation of TAs is reduced by treatment of mice with N-acetilcysteine (NAC), a potent antioxidant also administered ad libitum in drinking water.