The members of the class II phosphoinositide 3-kinase (PI3K) family can be activated by several stimuli, indicating that these enzymes can regulate many intracellular processes. Nevertheless, to date, there has been no definitive identification of their in vivo product, their mechanism(s) of activation, or their precise intracellular roles. By metabolic labeling, we here identify phosphatidylinositol 3-phosphate as the sole in vivo product of the insulin-dependent activation of PI3K-C2α, confirming the emerging role of such a phosphoinositide in signaling. We demonstrate that activation of PI3K-C2α involves its recruitment to the plasma membrane and that activation is mediated by the GTPase TC10. This is the first report showing a membrane targeting-mediated mechanism of activation for PI3K-C2α and that a small GTP-binding protein can activate a class II PI3K isoform. We also demonstrate that PI3K-C2α contributes to maximal insulin-induced translocation of the glucose transporter GLUT4 to the plasma membrane and subsequent glucose uptake, definitely assessing the role of this enzyme in insulin signaling.
ABSTRACT Background The symptoms, comorbidities and treatment burden associated with chronic kidney disease (CKD) can be debilitating and limit life participation in patients with CKD not requiring kidney replacement therapy (KRT). The aim of this study was to identify the characteristics, content and psychometric properties of patient-reported outcome measures (PROMs) used to assess life participation in patients with CKD. Methods We searched MEDLINE, Embase, PsycINFO and CINAHL from database inception to February 2023 for all studies that reported life participation in patients with CKD (stages 1–5 not requiring kidney replacement therapy). We analysed the characteristics, dimensions of life participation and psychometric properties of the measures. Results From the 114 studies included, 20 (18%) were randomized trials, 3 (3%) were non-randomized trials and 91 (80%) were observational studies. Forty-one different measures were used to assess life participation, of which six (15%) were author-developed measures. Twelve (29%) measures assessed life participation specifically, while 29 (71%) measures assessed broader constructs such as quality of life, which included questions relevant to life participation. The 36-Item Short Form Health Survey (SF-36) and Kidney Disease Quality of Life Short Form (KDQOL-SF) were the most frequently used, in 39 (34%) and 24 (21%) studies, respectively. Many content domains for life participation were assessed, including physical activities (walking, running and sports), social activities, leisure activities, work or study and self-care. None of the measures for life participation were developed specifically for CKD. Four measures (EuroQol 5-dimension 3-level (EQ-5D-3L), Functional Assessment of Cancer Therapy - Anemia, Short Form 6-dimension and Short-From 36-dimension (SF-36)) had validation data collected in patients with CKD. Conclusion The measures for life participation used in patients with CKD vary in content, with few validated in the CKD population. There is a need for a validated measure to assess life participation in a meaningful and consistent way in all patients with CKD worldwide.
We have shown previously that palmitate treatment of C2C12 skeletal muscle myotubes causes inhibition of the protein kinase B (PKB) pathway and hence reduces insulin-stimulated glycogen synthesis through the elevation of intracellular ceramide levels. Ceramide is known to activate both atypical protein kinase C (aPKC) zeta and protein phosphatase (PP) 2A, and each of these effectors has been reported to inhibit PKB. In the present study, palmitate pretreatment was found to elevate PP2A-like activity in myotubes and to prevent its inhibition by insulin. Incubation with the phosphatase inhibitor okadaic acid before insulin stimulation protected against the effect of the fatty acid on PKB phosphorylation. Palmitate was unable to inhibit PKB activity and glycogen synthesis in cells overexpressing the activated PKB mutant (T308D,S473D)-PKBalpha, which is unaffected by phosphatase. In contrast, PKB activity and glycogen synthesis were still inhibited by palmitate in cells overexpressing a membrane-targeted and, hence, activated PKB mutant that retains sensitivity to phosphatase. Although aPKC activity was also increased in palmitate-treated cells, overexpression of wild-type or kinase-dead aPKCzeta did not alter the inhibitory effects of the lipid on either stimulation of PKB or glycogen synthesis by insulin. We conclude that palmitate disrupts insulin signaling in C2C12 myotubes by promoting PP2A-like activity and, therefore, the dephosphorylation of PKB, which in turn reduces the stimulation of glycogen synthesis.
Patient and caregiver involvement can enhance the uptake and impact of research, however, the involvement of patients and caregivers who are underserved and marginalized is often limited. A better understanding of how to make involvement in research more broadly accessible, supportive, and inclusive for patients with CKD and caregivers is needed. We conducted a national workshop involving patients, caregivers, clinicians and researchers across Australia to identify strategies to increase the diversity of patients and caregivers involved in CKD research. Six themes were identified. Building trust and a sense of safety was considered pivotal to establishing meaningful relationships to support knowledge exchange. Establishing community and connectedness was expected to generate a sense of belonging to motivate involvement. Balancing stakeholder goals, expectations and responsibilities involved demonstrating commitment and transparency by researchers. Providing adequate resources and support included strategies to minimize the burden of involvement for patients and caregivers. Making research accessible and relatable was about nurturing patient and caregiver interest by appealing to intrinsic motivators. Adapting to patient and caregiver needs and preferences required tailoring the approach for individuals and the target community. Strategies and actions to support these themes may support more diverse and equitable involvement of patients and caregivers in research in CKD.
We have previously shown that glycogen synthesis is reduced in lipid-treated C(2)C(12) skeletal muscle myotubes and that this is independent of changes in glucose uptake. Here, we tested whether mitochondrial metabolism of these lipids is necessary for this inhibition and whether the activation of specific protein kinase C (PKC) isoforms is involved. C(2)C(12) myotubes were pretreated with fatty acids and subsequently stimulated with insulin for the determination of glycogen synthesis. The carnitine palmitoyltransferase-1 inhibitor etomoxir, an inhibitor of beta-oxidation of acyl-CoA, did not protect against the inhibition of glycogen synthesis caused by the unsaturated fatty acid oleate. In addition, although oleate caused translocation, indicating activation, of individual PKC isoforms, inhibition of PKC by pharmacological agents or adenovirus-mediated overexpression of dominant negative PKC-alpha, -epsilon, or -theta mutants was unable to prevent the inhibitory effects of oleate on glycogen synthesis. We conclude that neither mitochondrial lipid metabolism nor activation of PKC-alpha, -epsilon, or -theta plays a role in the direct inhibition of glycogen synthesis by unsaturated fatty acids.
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