Irisin acts through its integrin receptor in a two-step process involving extracellular Hsp90α.

Exercise benefits the human body in many ways. Irisin is secreted by muscle, increased with exercise, and conveys physiological benefits, including improved cognition and resistance to neurodegeneration. Irisin acts via αV integrins; however, a mechanistic understanding of how small polypeptides like irisin can signal through integrins is poorly understood. Using mass spectrometry and cryo-EM, we demonstrate that the extracellular heat shock protein 90α (eHsp90α) is secreted by muscle with exercise and activates integrin αVß5. This allows for high-affinity irisin binding and signaling through an Hsp90α/αV/ß5 complex. By including hydrogen/deuterium exchange data, we generate and experimentally validate a 2.98 Å RMSD irisin/αVß5 complex docking model. Irisin binds very tightly to an alternative interface on αVß5 distinct from that used by known ligands. These data elucidate a non-canonical mechanism by which a small polypeptide hormone like irisin can function through an integrin receptor.

Isolation of extracellular fluids reveals novel secreted bioactive proteins from muscle and fat tissues.

Proteins are secreted from cells to send information to neighboring cells or distant tissues. Because of the highly integrated nature of energy balance systems, there has been particular interest in myokines and adipokines. These are challenging to study through proteomics because serum or plasma contains highly abundant proteins that limit the detection of proteins with lower abundance. We show here that extracellular fluid (EF) from muscle and fat tissues of mice shows a different protein composition than either serum or tissues. Mass spectrometry analyses of EFs from mice with physiological perturbations, like exercise or cold exposure, allowed the quantification of many potentially novel myokines and adipokines. Using this approach, we identify prosaposin as a secreted product of muscle and fat. Prosaposin expression stimulates thermogenic gene expression and induces mitochondrial respiration in primary fat cells. These studies together illustrate the utility of EF isolation as a discovery tool for adipokines and myokines.

Amelioration of pathologic α-synuclein-induced Parkinson's disease by irisin.

Physical activity provides clinical benefit in Parkinson's disease (PD). Irisin is an exercise-induced polypeptide secreted by skeletal muscle that crosses the blood-brain barrier and mediates certain effects of exercise. Here, we show that irisin prevents pathologic α-synuclein (α-syn)-induced neurodegeneration in the α-syn preformed fibril (PFF) mouse model of sporadic PD. Intravenous delivery of irisin via viral vectors following the stereotaxic intrastriatal injection of α-syn PFF cause a reduction in the formation of pathologic α-syn and prevented the loss of dopamine neurons and lowering of striatal dopamine. Irisin also substantially reduced the α-syn PFF-induced motor deficits as assessed behaviorally by the pole and grip strength test. Recombinant sustained irisin treatment of primary cortical neurons attenuated α-syn PFF toxicity by reducing the formation of phosphorylated serine 129 of α-syn and neuronal cell death. Tandem mass spectrometry and biochemical analysis revealed that irisin reduced pathologic α-syn by enhancing endolysosomal degradation of pathologic α-syn. Our findings highlight the potential for therapeutic disease modification of irisin in PD.

Lysine acetylation of cytoskeletal proteins: Emergence of an actin code.

Reversible lysine acetylation of nuclear proteins such as histones is a long-established important regulatory mechanism for chromatin remodeling and transcription. In the cytoplasm, acetylation of a number of cytoskeletal proteins, including tubulin, cortactin, and the formin mDia2, regulates both cytoskeletal assembly and stability. More recently, acetylation of actin itself was revealed to regulate cytoplasmic actin polymerization through the formin INF2, with downstream effects on ER-to-mitochondrial calcium transfer, mitochondrial fission, and vesicle transport. This finding raises the possibility that actin acetylation, along with other post-translational modifications to actin, might constitute an "actin code," similar to the "histone code" or "tubulin code," controlling functional shifts to these central cellular proteins. Given the multiple roles of actin in nuclear functions, its modifications might also have important roles in gene expression.

Regulation of INF2-mediated actin polymerization through site-specific lysine acetylation of actin itself.

INF2 is a formin protein that accelerates actin polymerization. A common mechanism for formin regulation is autoinhibition, through interaction between the N-terminal diaphanous inhibitory domain (DID) and C-terminal diaphanous autoregulatory domain (DAD). We recently showed that INF2 uses a variant of this mechanism that we term "facilitated autoinhibition," whereby a complex consisting of cyclase-associated protein (CAP) bound to lysine-acetylated actin (KAc-actin) is required for INF2 inhibition, in a manner requiring INF2-DID. Deacetylation of actin in the CAP/KAc-actin complex activates INF2. Here we use lysine-to-glutamine mutations as acetylmimetics to map the relevant lysines on actin for INF2 regulation, focusing on K50, K61, and K328. Biochemically, K50Q- and K61Q-actin, when bound to CAP2, inhibit full-length INF2 but not INF2 lacking DID. When not bound to CAP, these mutant actins polymerize similarly to WT-actin in the presence or absence of INF2, suggesting that the effect of the mutation is directly on INF2 regulation. In U2OS cells, K50Q- and K61Q-actin inhibit INF2-mediated actin polymerization when expressed at low levels. Direct-binding studies show that the CAP WH2 domain binds INF2-DID with submicromolar affinity but has weak affinity for actin monomers, while INF2-DAD binds CAP/K50Q-actin 5-fold better than CAP/WT-actin. Actin in complex with full-length CAP2 is predominately ATP-bound. These interactions suggest an inhibition model whereby CAP/KAc-actin serves as a bridge between INF2 DID and DAD. In U2OS cells, INF2 is 90-fold and 5-fold less abundant than CAP1 and CAP2, respectively, suggesting that there is sufficient CAP for full INF2 inhibition.

Efficacy and Safety of Tranexamic Acid in Reducing Blood Loss of Lower Extremity Osteotomy in Peri-acetabulum and High Tibia: A Systematic Review and Meta-analysis.

OBJECTIVE: To assess the efficacy of tranexamic acid (TXA) in reducing total blood loss and transfusion, and the risk of thromboembolic events in patients undergoing periacetabular osteotomy (PAO) and high tibial osteotomy (HTO). METHODS: A systematic literature search was performed using PubMed, the Cochrane Central Register of Controlled Trials (CENTRAL), Embase (Ovid), Medline (Ovid), and Web of Science. ClinicalTrials.gov, American Academy of Orthopaedic Surgeons (AAOS), and Orthopaedic Trauma Association (OTA) conference proceedings were also searched to gain more eligible studies. The primary outcome measure was total blood loss and the blood transfusion rate of the TXA group versus control. The meta-analysis was conducted using the RevMan 5.3 and Stata 14.0 software. RESULTS: A total of six studies were included involving 665 patients. Three studies were PAO, and the other three were HTO. The total blood loss in PAO (WMD, -330.49; 95% CI, -390.16 to -270.83; P < 0.001) and HTO (WMD, -252.50; 95% CI, -356.81 to -148.18; P < 0.001) and hemoglobin decline (WMD, -0.74; 95% CI, -1.09 to -0.38; P < 0.001) were significantly less in the TXA group than in the control group. TXA could reduce transfusion rates in PAO (RR, 0.26; 95% CI, 0.09 to 0.75; P = 0.01) but had no effect on HTO (RR, 0.20; 95% CI, 0.01 to 4.10; P = 0.30). The wound complications (RR, 0.62; 95% CI, 0.13 to 2.94; P = 0.54) had no significant difference between TXA and control groups. CONCLUSIONS: This meta-analysis demonstrated that TXA reduces total blood loss and hemoglobin decline in patients undergoing PAO and is safe, but it has little benefit in regard to reducing transfusion rates or wound complications in HTO, so TXA might be unwarranted for routine use for HTO.

A complex containing lysine-acetylated actin inhibits the formin INF2.

Inverted formin 2 (INF2) is a member of the formin family of actin assembly factors. Dominant missense mutations in INF2 are linked to two diseases: focal segmental glomerulosclerosis, a kidney disease, and Charcot-Marie-Tooth disease, a neuropathy. All of the disease mutations map to the autoinhibitory diaphanous inhibitory domain. Interestingly, purified INF2 is not autoinhibited, suggesting the existence of other cellular inhibitors. Here, we purified an INF2 inhibitor from mouse brain tissue, and identified it as a complex of lysine-acetylated actin (KAc-actin) and cyclase-associated protein (CAP). Inhibition of INF2 by CAP-KAc-actin is dependent on the INF2 diaphanous inhibitory domain (DID). Treatment of CAP-KAc-actin-inhibited INF2 with histone deacetylase 6 releases INF2 inhibition, whereas inhibitors of histone deacetylase 6 block the activation of cellular INF2. Disease-associated INF2 mutants are poorly inhibited by CAP-KAc-actin, suggesting that focal segmental glomerulosclerosis and Charcot-Marie-Tooth disease result from reduced CAP-KAc-actin binding. These findings reveal a role for KAc-actin in the regulation of an actin assembly factor by a mechanism that we call facilitated autoinhibition.

Function-Oriented Studies Targeting Pectenotoxin 2: Synthesis of the GH-Ring System and a Structurally Simplified Macrolactone.

A chemical foundation for function-oriented studies of pectenotoxin 2 (PTX2) is described. A synthesis of the bicyclic GH-system, and the design and synthesis of a PTX2-analogue, is presented. While maintaining critical features for actin binding, and lacking the Achilles' heel for the natural product's anticancer activity (the AB-spiroketal), this first-generation analogue did not possess the anticancer properties of PTX2, an observation that indicates the molecular significance of features present in the natural product's CDEF-tetracycle.

Assembly and turnover of short actin filaments by the formin INF2 and profilin.

INF2 (inverted formin 2) is a formin protein with unique biochemical effects on actin. In addition to the common formin ability to accelerate actin nucleation and elongation, INF2 can also sever filaments and accelerate their depolymerization. Although we understand key attributes of INF2-mediated severing, we do not understand the mechanism by which INF2 accelerates depolymerization subsequent to severing. Here, we show that INF2 can create short filaments (<60 nm) that continuously turn over actin subunits through a combination of barbed end elongation, severing, and WH2 motif-mediated depolymerization. This pseudo-steady state condition occurs whether starting from actin filaments or monomers. The rate-limiting step of the cycle is nucleotide exchange of ADP for ATP on actin monomers after release from the INF2/actin complex. Profilin addition has two effects: 1) to accelerate filament turnover 6-fold by accelerating nucleotide exchange and 2) to shift the equilibrium toward polymerization, resulting in longer filaments. In sum, our findings show that the combination of multiple interactions of INF2 with actin can work in concert to increase the ATP turnover rate of actin. Depending on the ratio of INF2:actin, this increased flux can result in rapid filament depolymerization or maintenance of short filaments. We also show that high concentrations of cytochalasin D accelerate ATP turnover by actin but through a different mechanism from that of INF2.

Derepression of ethylene-stabilized transcription factors (EIN3/EIL1) mediates jasmonate and ethylene signaling synergy in Arabidopsis.

Jasmonate (JA) and ethylene (ET) are two major plant hormones that synergistically regulate plant development and tolerance to necrotrophic fungi. Both JA and ET induce the expression of several pathogenesis-related genes, while blocking either signaling pathway abolishes the induction of these genes by JA and ET alone or in combination. However, the molecular basis of JA/ET coaction and signaling interdependency is largely unknown. Here, we report that two Arabidopsis ET-stabilized transcription factors (EIN3 and EIL1) integrate ET and JA signaling in the regulation of gene expression, root development, and necrotrophic pathogen defense. Further studies reveal that JA enhances the transcriptional activity of EIN3/EIL1 by removal of JA-Zim domain (JAZ) proteins, which physically interact with and repress EIN3/EIL1. In addition, we find that JAZ proteins recruit an RPD3-type histone deacetylase (HDA6) as a corepressor that modulates histone acetylation, represses EIN3/EIL1-dependent transcription, and inhibits JA signaling. Our studies identify EIN3/EIL1 as a key integration node whose activation requires both JA and ET signaling, and illustrate transcriptional derepression as a common mechanism to integrate diverse signaling pathways in the regulation of plant development and defense.