The mechanisms underlying the age-dependent reversal of female cardioprotection are poorly understood and complicated by findings that estrogen replacement is ineffective at reducing cardiovascular mortality in postmenopausal women. Although several protective signals have been identified in young animals, including PKC and Akt, how these signals are affected by age, estrogen deficiency, and ischemia-reperfusion (I/R) remains unknown. To determine the independent and combined effects of age and estrogen deficiency on I/R injury and downstream PKC-Akt signaling, adult and aged female F344 rats (n = 12/age) with ovaries intact or ovariectomy (Ovx) were subjected to I/R using Langendorff perfusion (31-min global-ischemia). Changes in cytosolic (s), nuclear (n), mitochondrial (m) PKC (delta, epsilon) levels, and changes in total Akt and mGSK-3beta phosphorylation after I/R were assessed by Western blot analysis. Senescence increased infarct size 50% in ovary-intact females (P < 0.05), whereas no differences in LV functional recovery or estradiol levels were observed. Ovx reduced functional recovery to a greater extent in aged compared with adult rats (P < 0.05). In aged (vs. adult), levels of m- and nPKC(-delta, -epsilon) were markedly decreased, whereas mGSK3beta levels were increased (P < 0.05). Ovx led to greater levels of sPKC(-delta, -epsilon) independent of age (P < 0.05). I/R reduced p-Akt(Ser473) levels by 57% and increased mGSK-3beta accumulation 1.77-fold (P < 0.05) in aged, ovary-intact females. These data suggest, for the first time, that estrogen alone cannot protect the aged female myocardium from I/R damage and that age- and estrogen-dependent alterations in PKC, Akt, and GSK-3beta signaling may contribute to loss of ischemic tolerance.

These results provide novel evidence for cardioprotection through acute PKCdelta inhibition in aged rat heart following I/R. Our results also suggest, for the first time, a key role for mitochondrial GSK-3beta as a cellular basis for the protection associated with PKCdelta inhibition with ageing.

Korzick DH, Kostyak JC, Hunter JC, Saupe KW. Local delivery of PKCε-activating peptide mimics ischemic preconditioning in aged hearts through GSK-3␤ but not F 1-ATPase inactivation.

Key Points Bone marrow-specific deletion of Pak2 is associated with macrothrombocytopenia and abnormal megakaryocyte morphology and function. Pak2 deletion is associated with defects in megakaryocyte endomitosis and the activation of Aurora-A and LIM kinase.

Megakaryocytes are large, polyploid cells that produce platelets. We have previously reported that calcium-and integrin-binding protein 1 (CIB1) regulates endomitosis in Dami cells. To further characterize the role of CIB1 in megakaryopoiesis, we used a Cib1 ؊/؊ mouse model. Cib1 ؊/؊ mice have more platelets and BM megakaryocytes than wild-type (WT) controls (P < .05). Furthermore, subsequent analysis of megakaryocyte-CFU production revealed an increase with Cib1 deletion compared with WT (P < .05). In addition, BM from Cib1 ؊/؊ mice, cultured with thrombopoietin (TPO) for 24 hours, produced more highly polyploid megakaryocytes than WT BM (P < .05). Subsequent analysis of TPO signaling revealed enhanced Akt and ERK1/2 phosphorylation, whereas FAK Y925 phosphorylation was reduced in Cib1 ؊/؊ megakaryocytes treated with TPO. Conversely, platelet recovery in Cib1 ؊/؊ mice after platelet depletion was attenuated compared with WT (P < .05). This could be the result of impaired adhesion and migration, as adhesion to fibrinogen and fibronectin and migration toward an SDF-1␣ gradient were reduced in Cib1 ؊/؊ megakaryocytes compared with WT (P < .05). In addition, Cib1 ؊/؊ megakaryocytes formed fewer proplatelets compared with WT (P < .05), when plated on fibrinogen. These data suggest that CIB1 plays a dual role in megakaryopoiesis, initially by negatively regulating TPO signaling and later by augmenting proplatelet production. IntroductionMature megakaryocytes produce platelets by extending proplatelet projections into sinusoidal vessels in BM. 1 Before this process, the megakaryocyte must differentiate from progenitor cells by undergoing multiple rounds of endomitosis. Megakaryocyte endomitosis occurs primarily through cell signaling initiated by the cytokine thrombopoietin (TPO), which is produced constitutively in the liver. 2 TPO binding to its receptor, c-Mpl, results in the activation of Janus kinase 2 (Jak2). Jak2 phosphorylates tyrosine residues on c-Mpl, which enables the subsequent activation of other signaling pathways, such as PI3K/Akt and MAPK. [3][4][5][6][7][8] In addition, focal adhesion kinase (FAK) is activated and acts as a negative regulator of TPO-induced signaling by activating Lyn, an Src-family kinase. 9 Specifically, Western blot analysis revealed that impaired TPO-induced FAK phosphorylation is concomitant with heightened Akt and ERK1/2 phosphorylation. 9 Once mature, megakaryocytes must migrate from an "osteoblastic niche" to a "vascular niche" where they interact with BM endothelial cells. 10 Integrins play a key role in cell migration, and the most abundantly expressed integrin on the megakaryocyte is ␣ IIb ␤ 3 , which is the major receptor for the highly expressed BM extracellular matrix (ECM) protein fibronectin (Fn). 11,12 The exact mechanism underlying megakaryocyte migration toward the vasculature is unknown, but stromal cell-derived factor-1␣ (SDF-1␣) appears to provide the homing signal. 13 Calcium-and integrin-binding protein 1 (CIB1) was first identified as a binding partner of th...