Regulation of Insulin Sensitivity by Skeletal Muscle Specific Modulation Of p21‐Activated Kinase 1 (PAK1)
Authors: Salunkhe Vishal Ashok , Tunduguru Ragadeepthi , Ahn Miwon , Olson Erika M. , Veluthakal Rajakrishnan , Zhang Jing , Aslamy Arianne , Thurmond Debbie C. 
Published: June 2021

Impaired skeletal muscle (skm) insulin signaling results in insulin resistance and the development of type 2 diabetes (T2D). Insulin binding to its receptors on skm cells leads to an intracellular signaling cascade resulting in glucose transporter type 4 (GLUT4) translocation to the plasma membrane (PM) and glucose uptake. The p21–activated kinase 1 (PAK1) is a required element for skm insulin sensitivity. It has been shown that whole body PAK1−/− knock‐out (KO) mice exhibit glucose intolerance and insulin resistance. In clonal skm cells (L6‐GLUT4myc) PAK1 inhibition was shown to impair insulin‐induced filamentous actin (F‐actin) remodeling and GLUT4 translocation; coupled with a loss of normal insulin‐stimulated cofilin dephosphorylation (i.e. activation). Recently, we have shown that PAK1 is essential in the process of actin polymerization via p41‐ARC (Actin‐related protein 2/3 complex subunit 1B). However, the effect of skm specific PAK1 modulations on in vivo glucose homeostasis, and downstream effectors of PAK1 are yet to be fully determined.We hypothesize that PAK1 is essential for insulin signaling in skm, and that upon diabetogenic stress, i) reduced PAK1 levels in skm will adversely affect whole body insulin sensitivity, whereas ii) PAK1 enrichment can preserve or restore insulin sensitivity. To study the effects of PAK1 modulation on insulin sensitivity in vivo, state‐of‐the‐art inducible skm‐specific PAK1 KO and overexpressing mouse models are used. L6‐GLUT4myc clonal cells are used to identify key downstream effectors of PAK1 using cutting‐edge imaging, mass spectrometry, and metabolomic analyzes.Importantly, both PAK1 and p41‐ARC protein levels were found to be significantly reduced in the skm of human T2D donors compared to healthy human donors (n=3–4). We have generated a doxycycline‐inducible skm‐specific, i) PAK1 depletion mouse model (skm‐PAK1‐KO) and ii) PAK1 overexpressing transgenic mouse model (skm‐PAK1‐Tg). PAK1 deletion in skm resulted into impaired in vivo insulin sensitivity in skm‐PAK1‐KO mice compared to control mice (n=10, per group), studied by intraperitoneal insulin tolerance test (IPITT). Moreover, this was coupled with reduced insulin‐induced GLUT4 translocation in skm of skm‐PAK1‐KO mice compared to the control mice (n=2). Conversely, overexpression of PAK1 in L6‐GLUT4myc cells significantly improved GLUT4 translocation under insulin resistance condition (5 nM of insulin for 12 h) compared to control cells (n=4). Altogether, these findings emphasize the i) importance of PAK1 in skm and thereby whole body glucose homeostasis and ii) potential protective effect of PAK1 enrichment on skm insulin sensitivity under diabetogenic conditions. Moreover, this study in future is aimed at determining key downstream effectors of PAK1, which might serve as insulin sensitizers.Support or Funding InformationThis study was supported by grants from the National Institutes of Health (DK067912 and DK102233 to D.C.T.), the American Heart Association (15PRE21970002 to RT, 17POST33661194 to JZ), as well a gift from the Ruth and Robert Lanman Endowment (to D.C.T.).This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.