A second limitation is that most conclusions on the phenotypes caused by MeCP2 alterations are derived from overexpression, and it is not entirely clear how much MeCP2 protein is overexpressed. Furthermore, there are few data on the MeCP2 cKO. One is left to assume that the phenotype of the MeCP2 cKO is the converse of the iTG, and it would have been good to test this more completely.
Third, in this regard, the reduction in cardiac function with MeCP2 iTG and improvement with MeCP2 cKO are relatively subtle, and the proximate mechanisms are not clarified fully. For example, the current study finds an ≈10% area fibrosis in the MeCP2 iTG after TAC; this might not account for the 25% drop in FS with TAC; systolic function is preserved in the human heart with 10% area fibrosis.16 The MeCP2 iTG after TAC increases apoptosis, but the fraction of TUNEL-positive cells is fairly small (0.04%) and increased only 2-fold from WT. Given the findings on metabolic genes and mitochondria, assays of myocardial high-energy phosphates in the iTG and cKO after TAC could have been informative. There are scant data of any kind in the cKO after TAC.
Overall, the last part of the model shown in the Figure needs to be taken as preliminary. Possibly miR-212/132 induction could be cardioprotective partly by repressing targets other than MeCP2 (Table).