Sex specific effect of ATPase inhibitory factor 1 on body weight: studies in high fat diet induced obese mice and genetic association studies in humans

Plasma level of ATPase inhibitory factor 1 (IF1) is associated with type 2 diabetes risk in humans: A prospective cohort study

AIM

Mitochondrial dysfunction is associated with the development of type 2 diabetes mellitus (T2DM). It is thus of clinical relevance to identify plasma biomarkers of mitochondrial dysfunction associated with the risk of T2DM. ATPase inhibitory factor 1 (IF1) endogenously inhibits mitochondrial ATP synthase activity. Here, we analyzed association of the plasma IF1 level with markers of glucose homeostasis and with the conversion to new-onset diabetes (NOD) in individuals with prediabetes.

METHODS

In the IT-DIAB prospective study, the baseline plasma level of IF1 was measured in 307 participants with prediabetes. The primary outcome was the incidence of NOD within five years of follow-up. Cross-sectional analysis of the IF1 level was also done in two independent interventional studies. Correlations between plasma IF1 and metabolic parameters at baseline were assessed by Spearman's correlation coefficients, and the association with the risk of NOD was determined using Cox proportional-hazards models.

RESULTS

In IT-DIAB, the mean IF1 plasma level was lower in participants who developed NOD than in those who did not (537 ± 248 versus 621 ± 313 ng/mL, P   = 0.01). The plasma IF1 level negatively correlated with clinical variables associated with obesity and insulin resistance, including the body mass index (r = -0.20, P  = 0.0005) and homeostasis model assessment of insulin resistance (HOMA-IR). (r = -0.37, P < 0.0001). Conversely, IF1 was positively associated with plasma markers of cardiometabolic health, such as HDL-C (r = 0.63, P  <  0.0001) and apoA-I (r = 0.33, P  <  0.0001). These correlations were confirmed in cross-sectional analyses. In IT-DIAB, the IF1 level was significantly associated with a lower risk of T2DM after adjustment for age, sex, and fasting plasma glucose (HR [95% CI] per 1 SD = 0.76 [0.62; 0.94], P   = 0.012).

CONCLUSION

We identified for the first time the mitochondrial-related biomarker IF1 as being associated with the risk of T2DM.

The Multifaceted ATPase Inhibitory Factor 1 (IF1) in Energy Metabolism Reprogramming and Mitochondrial Dysfunction: A New Player in Age-Associated Disorders?

Significance: The mitochondrial oxidative phosphorylation (OXPHOS) system, comprising the electron transport chain and ATP synthase, generates membrane potential, drives ATP synthesis, governs energy metabolism, and maintains redox balance. OXPHOS dysfunction is associated with a plethora of diseases ranging from rare inherited disorders to common conditions, including diabetes, cancer, neurodegenerative diseases, as well as aging. There has been great interest in studying regulators of OXPHOS. Among these, ATPase inhibitory factor 1 (IF1) is an endogenous inhibitor of ATP synthase that has long been thought to avoid the consumption of cellular ATP when ATP synthase acts as an ATP hydrolysis enzyme. Recent Advances: Recent data indicate that IF1 inhibits ATP synthesis and is involved in a multitude of mitochondrial-related functions, such as mitochondrial quality control, energy metabolism, redox balance, and cell fate. IF1 also inhibits the ATPase activity of cell-surface ATP synthase, and it is used as a cardiovascular disease biomarker. Critical Issues: Although recent data have led to a paradigm shift regarding IF1 functions, these have been poorly studied in entire organisms and in different organs. The understanding of the cellular biology of IF1 is, therefore, still limited. The aim of this review was to provide an overview of the current understanding of the role of IF1 in mitochondrial functions, health, and diseases. Future Directions: Further investigations of IF1 functions at the cell, organ, and whole-organism levels and in different pathophysiological conditions will help decipher the controversies surrounding its involvement in mitochondrial function and could unveil therapeutic strategies in human pathology. Antioxid. Redox Signal. 37, 370-393.

Neuroprotective effects of ATPase inhibitory factor 1 preventing mitochondrial dysfunction in Parkinson's disease

Mitochondrial dysfunction is a key element in the progression of Parkinson’s disease (PD). The inefficient operation of the electron transport chain (ETC) impairs energy production and enhances the generation of oxidative stress contributing to the loss of dopaminergic cells in the brain. ATPase inhibitory factor 1 (IF1) is a regulator of mitochondrial energy metabolism. IF1 binds directly to the F₁Fo ATP synthase and prevents ATP wasting during compromised energy metabolism. In this study, we found treatment with IF1 protects mitochondria against PD-like insult in vitro. SH-SY5Y cells treated with IF1 were resistant to loss of ATP and mitochondrial inner membrane potential during challenge with rotenone, an inhibitor of complex I in the ETC. We further demonstrated that treatment with IF1 reversed rotenone-induced superoxide production in mitochondria and peroxide accumulation in whole cells. Ultimately, IF1 decreased protein levels of pro-apoptotic Bax, cleaved caspase-3, and cleaved PARP, rescuing SH-SY5Y cells from rotenone-mediated apoptotic death. Administration of IF1 significantly improved the results of pole and hanging tests performed by PD mice expressing human α-synuclein. This indicates that IF1 mitigates PD-associated motor deficit. Together, these findings suggest that IF1 exhibits a neuroprotective effect preventing mitochondrial dysfunction in PD pathology.

Biglycan reduces body weight by regulating food intake in mice and improves glucose metabolism through AMPK/AKT dual pathways in skeletal muscle

While biglycan (BGN) is suggested to direct diverse signaling cascades, the effects of soluble BGN as a ligand on metabolic traits have not been studied. Herein, we tested the effects of BGN on obesity in high-fat diet (HFD)-induced obese animals and glucose metabolism, with the underlying mechanism responsible for observed effects in vitro. Our results showed that BGN administration (1 mg/kg body weight, intraperitoneally) significantly prevented HFD-induced obesity, and this was mainly attributed to reduced food intake. Also, intracerebroventricular injection of BGN reduced food intake and body weight. The underlying mechanism includes modulation of neuropeptides gene expression involved in appetite in the hypothalamus in vitro and in vivo. In addition, BGN regulates glucose metabolism as shown by improved glucose tolerance in mice as well as AMPK/AKT dual pathway-driven enhanced glucose uptake and GLUT4 translocation in L6 myoblast cells. In conclusion, our results suggest BGN as a potential therapeutic target to treat risk factors for metabolic diseases.

Circulating Inhibitory Factor 1 levels in adult patients with Prader-Willi syndrome

OBJECTIVES

Prader-Willi syndrome (PWS) is a rare genetic syndrome characterized by hyperphagia and early development of morbid obesity. Cardiovascular disease (CVD) and metabolic syndrome (MetS) are major comorbidities in these patients leading to premature death. Inhibitory factor 1 (IF1) works as a regulatory protein, inhibiting the ATP hydrolase activity of mitochondrial ATP synthase and likely playing a role in lipid metabolism. We aimed to assay IF1 in adult patients with PWS evaluating any relationship with clinical, genetic and biochemical parameters.

METHODS

We recruited 35 adult patients with genetically confirmed PWS.

RESULTS

IF1 serum concentration displayed a normal distribution with an average value of 70.7 ± 22.6 pg/mL, a median value of 66.1 pg/mL. It was above the reference range only in one patient. All parameters were compared from both sides of IF1 median without displaying any significant differences. Patients with normal or low HDL-cholesterol did not present any difference as regards IF1 levels, which were not different between patients with and without MetS. Non-esterified fatty acids (NEFA) serum levels (r=0.623; p<0.001) showed a statistically significant correlation with IF1. Cholesterol and its fractions did not present any correlation with IF1.

CONCLUSIONS

In this study we do not confirm that HDL-cholesterol and IF1 are correlated, but we show that in adult PWS patients, NEFA are correlated with serum IF1. This protein could play a role to some extent in determining the complex metabolic alterations in PWS patients.