Spastin, an AAA ATPase mutated in the neurodegenerative disease hereditary spastic paraplegia, severs microtubules. Many other AAA proteins form ring-shaped hexamers and contain pore loops, which project into the ring's central cavity and act as ratchets that pull on target proteins, leading, in some cases, to conformational changes. We show that Spastin assembles into a hexamer and that loops within the central pore recognize C-terminal amino acids of tubulin. Key pore loop amino acids are required for severing, including one altered by a disease-associated mutation. We also show that Spastin contains a second microtubule binding domain that makes a distinct interaction with microtubules and is required for severing. Given that Spastin engages the MT in two places and that both interactions are required for severing, we propose that severing occurs by forces exerted on the C-terminal tail of tubulin, which results in a conformational change in tubulin, which releases it from the polymer.

Ertugliflozin added to metformin in patients with inadequately controlled T2DM improved glycaemic control, reduced body weight and BP, but increased the incidence of genital mycotic infections.

Mutations in the AAA adenosine triphosphatase (ATPase) Spastin (SPG4) cause an autosomal dominant form of hereditary spastic paraplegia, which is a retrograde axonopathy primarily characterized pathologically by the degeneration of long spinal neurons in the corticospinal tracts and the dorsal columns. Using recombinant Spastin, we find that six mutant forms of Spastin, including three disease-associated forms, are severely impaired in ATPase activity. In contrast to a mutation designed to prevent adenosine triphosphate (ATP) binding, an ATP hydrolysis–deficient Spastin mutant predicted to remain kinetically trapped on target proteins decorates microtubules in transfected cells. Analysis of disease-associated missense mutations shows that some more closely resemble the canonical hydrolysis mutant, whereas others resemble the ATP-binding mutant. Using real-time imaging, we show that Spastin severs microtubules when added to permeabilized, cytosol-depleted cells stably expressing GFP-tubulin. Using purified components, we also show that Spastin interacts directly with microtubules and is sufficient for severing. These studies suggest that defects in microtubule severing are a cause of axonal degeneration in human disease.

AimsTo assess ertugliflozin in patients with type 2 diabetes who are inadequately controlled by metformin and sitagliptin.Materials and MethodsIn this double‐blind randomized study (Clinicaltrials.gov NCT02036515), patients (glycated haemoglobin [HbA1c] 7.0% to 10.5% [53‐91 mmol/mol] receiving metformin ≥1500 mg/d and sitagliptin 100 mg/d; estimated glomerular filtration rate [eGFR] ≥60 mL/min/1.73 m2) were randomized to ertugliflozin 5 mg once‐daily, 15 mg once‐daily or placebo. The primary efficacy endpoint was change from baseline in HbA1c at Week 26; treatment was continued until Week 52.ResultsA total of 464 patients were randomized (mean baseline HbA1c, 8.0% [64.3 mmol/mol]; eGFR, 87.9 mL/min/1.73 m2). After 26 weeks, placebo‐adjusted least squares (LS) mean changes in HbA1c from baseline were −0.7% (−7.5 mmol/mol) and −0.8% (−8.3 mmol/mol) for ertugliflozin 5 and 15 mg, respectively (both P < .001); 17.0%, 32.1% and 39.9% of patients receiving placebo, ertugliflozin 5 mg or ertugliflozin 15 mg, respectively, had HbA1c <7.0% (53 mmol/mol). Significant reductions in fasting plasma glucose, body weight (BW) and systolic blood pressure (SBP) were observed with ertugliflozin relative to placebo. The positive effects of ertugliflozin on glycaemic control, BW and SBP were maintained through Week 52. A higher incidence of genital mycotic infections was observed in male and female patients receiving ertugliflozin (3.7%‐14.1%) vs placebo (0%‐1.9%) through Week 52. The incidence of urinary tract infections, symptomatic hypoglycaemia and hypovolaemia adverse events were not meaningfully different across groups.ConclusionsErtugliflozin added to metformin and sitagliptin was well‐tolerated, and provided clinically meaningful, durable glycaemic control, BW and SBP reductions vs placebo over 52 weeks.

Ertugliflozin 5 and 15 mg treatment for 26 weeks provides effective glycaemic control, reduces body weight and is generally well tolerated, when used as monotherapy.

AimTo evaluate the efficacy and safety of ertugliflozin and sitagliptin co‐administration vs the individual agents in patients with type 2 diabetes who are inadequately controlled with metformin.MethodsIn this study (http://Clinicaltrials.gov NCT02099110), patients with glycated haemoglobin (HbA1c) ≥7.5% and ≤11.0% (≥58 and ≤97 mmol/mol) with metformin ≥1500 mg/d (n = 1233) were randomized to ertugliflozin 5 (E5) or 15 (E15) mg/d, sitagliptin 100 mg/d (S100) or to co‐administration of E5/S100 or E15/S100. The primary endpoint was change from baseline in HbA1c at Week 26.ResultsAt Week 26, least squares mean HbA1c reductions from baseline were greater with E5/S100 (−1.5%) and E15/S100 (−1.5%) than with individual agents (−1.0%, −1.1% and −1.1% for E5, E15 and S100, respectively; P < .001 for all comparisons). HbA1c <7.0% (<53 mmol/mol) was achieved by 26.4%, 31.9%, 32.8%, 52.3% and 49.2% of patients in the E5, E15, S100, E5/S100 and E15/S100 groups, respectively. Fasting plasma glucose reductions were significantly greater with E5/S100 and E15/S100 compared with individual agents. Body weight and systolic blood pressure (SBP) significantly decreased with E5/S100 and E15/S100 vs S100 alone. Glycaemic control, body weight and SBP effects of ertugliflozin were maintained to Week 52. Genital mycotic infections were more common among ertugliflozin‐treated patients compared with those treated with S100. Incidences of symptomatic hypoglycaemia and adverse events related to hypovolaemia or urinary tract infection were similar among groups.ConclusionsIn patients with uncontrolled type 2 diabetes while using metformin, co‐administration of ertugliflozin and sitagliptin provided more effective glycaemic control through 52 weeks compared with the individual agents.

AAA1 adenosine triphosphatases (ATPases) are molecular machines that perform a wide variety of cellular functions. For instance, they can act in vesicle transport, organelle assembly, membrane dynamics and protein unfolding. In most cases, the ATPase domains of these proteins assemble into active ring-shaped hexamers. As AAA1 proteins have a common structure, a central issue is determining how they use conserved mechanistic principles to accomplish specific biological actions. Here, we review the features and motifs that partially define AAA1 domains, describe the cellular activities mediated by selected AAA1 proteins and discuss the recent work, suggesting that various AAA1 machines with very different activities employ a common core mechanism. The importance of this mechanism to human health is demonstrated by the number of genetic diseases caused by mutant AAA1 proteins.

IntroductionThis study assessed the safety and efficacy of ertugliflozin (an oral sodium-glucose cotransporter 2 inhibitor) vs. glimepiride in patients with type 2 diabetes mellitus (T2DM) inadequately controlled on metformin.MethodsThis phase III, double-blind, non-inferiority study (NCT01999218) randomized patients with HbA1c ≥ 7.0% and ≤ 9.0% on stable metformin ≥ 1500 mg/day 1:1:1 to ertugliflozin 15 or 5 mg once-daily (QD), or glimepiride (titrated from 1 mg QD). The primary hypothesis was that ertugliflozin 15 mg was non-inferior to glimepiride on HbA1c (non-inferiority criterion: upper bound of the 95% confidence interval [CI] about the treatment difference < 0.3%).ResultsMean baseline HbA1c of randomized patients (N = 1326) was 7.8%. Mean and median doses of glimepiride were 3.0 mg/day throughout the study. At week 52, the least squares mean change (95% CI) from baseline in HbA1c was − 0.6% (− 0.7, − 0.5), − 0.6% (− 0.6, − 0.5), and − 0.7% (− 0.8, − 0.7) in the ertugliflozin 15 mg, ertugliflozin 5 mg, and glimepiride groups, respectively. The between-group difference for ertugliflozin 15 mg and glimepiride of 0.1% (− 0.0, 0.2) met the pre-specified non-inferiority criterion. Relative to glimepiride, greater body weight and systolic blood pressure (SBP) reductions were observed with ertugliflozin. The overall incidence of adverse events (AEs) was similar across groups. The incidence of symptomatic hypoglycemia and genital mycotic infection (GMI) were, respectively, lower and higher with ertugliflozin relative to glimepiride. The incidences of urinary tract infection and hypovolemia AEs were not meaningfully different among the groups.ConclusionsErtugliflozin 15 mg was non-inferior to glimepiride in reducing HbA1c when added to metformin in patients with T2DM. Ertugliflozin had an acceptable safety profile and resulted in less hypoglycemia and more GMIs than glimepiride.Clinical Trial RegistrationClinicaltrials.gov NCT01999218.Electronic supplementary materialThe online version of this article (10.1007/s13300-017-0354-4) contains supplementary material, which is available to authorized users.