In a study recently published in the journal Science Advances, researchers used genetically modified Drosophila and murine models to investigate the role of the newly discovered Traf2- and NCK-interacting protein kinase (TNIK) in obesity and metabolic dysfunction.
Their results reveal that TNIK plays a critical role in regulating the metabolism of glucose and fatty acids, and insulin sensitivity. This study suggests the potential of TNIK in future therapeutic interventions for obesity and its comorbidities.
TNIK, msn, and obesity
Obesity, the condition characterized by abnormal or excessive fat accumulation, is a global health concern, with about 13% of humans affected by the disease.
Current global estimates of people living with BMI ≥25 kg/m² (the clinical definition of obesity) place disease prevalence at 770 million, with this number expected to increase to 1.12 billion by 2030. Obesity presents a significant clinical health burden, with the condition depicting strong correlations with type 2 diabetes (T2D) and the increased risk of cancer, cardiovascular diseases, and mortality.
Recent genome-wide association studies (GWAS) have successfully identified genomic variants associated with obesity. However, functional in vivo studies into the phenotypic expression of these variants remains lacking.
In their previous work, the authors of the present study identified misshapen (msn), the functional ortholog (genes in different species with shared ancestry and function) of Traf2- and NCK-interacting protein kinase (TNIK) as a regulator of sugar metabolism and tolerance in Drosophila. However, the implications of TNIK and msn in obesity and T2D pathophysiology remain unknown.
TNIK is a cellular signaling protein, with previous work suggesting that its expression is controlled by the adenosine 5′-monophosphate (AMP)–activated protein kinase (AMPK). AMPK is found in mammalian skeletal muscles, and its activation is associated with the level or amount of exercise.
While AMPK has been studied as a potential therapy for improving insulin sensitivity, TNIK’s independent role as an anti-obesity therapy remains unexplored.
About the study
In the present study, researchers integrated GWAS, metabolomics, and metabolic screening approaches to elucidate the role of TNIK/msn in metabolic dysfunction. They used genetically modified Drosophila and mice to investigate the in vivo phenotypes of msn and TNIK, respectively.
Researchers began by evaluating the development of RNA interference (RNAi)–mediated whole-body knockdown (KD) msn fly larvae raised on high-sugar (HSD), high-protein (HPD), or combination diets. Combination diets were found to gravely impact fly mortality, with almost all pupa failing to metamorphosize to their adult forms.
HSD alone resulted in severely hyperglycemic larvae, with a marker delay in growth and development. Circulating glucose levels in msn RNAi larvae raised on HPD were comparable to wild-type (WT) larvae. Together, these results imply that msn loss harms whole-body sugar homeostasis, especially when the diet is sugar-rich.
Targeted metabolomic approaches were employed to test for differences in sugar metabolism in msn RNAi larvae compared with WT larvae.
In msn RNAi larvae, the metabolic response to HSD was notably different and characterized by decreased levels of several fatty acid metabolites, including oleate, palmitoleic acid, linoleate, and gamma-linolenic acid…
Phung Pham et al. (2023)
Additionally, metabolomics revealed that tyrosine metabolites were downregulated in msn RNAi larvae in response to sugar consumption. Metabolic screening revealed that de novo lipogenic genes fatty acid synthase (FAS) and acetyl–coenzyme A–carboxylase (ACC) were downregulated on sugar consumption, suggesting that msn is essential in de novo lipogenesis under high-sugar diets.
Researchers then repeated these experiments in whole-body Tnik knockout (KO) mice, a mammalian vertebrate system. KO mice displayed significantly lower fat and lean mass than their WT littermates. In WT mice, TNIK was found predominantly in the brain, heart, skeletal muscle, and spleen.
Notably, TNIK protein was not detectable in adipose tissue, including brown, gonadal, and subcutaneous adipose tissue, contrasting earlier reports that TNIK is ubiquitously expressed on a transcript level.
Phung Pham et al. (2023)
Targeted plasma metabolomics revealed that lactate and pyruvate were downregulated, while fatty acids were upregulated in KO mice compared to their WT counterparts. Researchers then raised both cohorts on a high-fat, high-sucrose (HFHS) diet and found that female KO mice had the lowest body weight (BW) gains, despite having the highest caloric intake of all study cohorts.
Magnetic resonance imaging (MRI) of these female mice revealed that these KO mice were significantly protected from fat expansion due to diet. Finally, to test whether exercise training could change the KO mice phenotype, researchers measured running capacity, bone volume fraction, and grip strength, all of which are known to increase in WT mice on increased ambulant nightly activity. Tnik KO mice did not depict did not show increases in any of these parameters.
Together, these data show that Tnik KO mice display a remarkable obesity-resistant phenotype that confers protection against BW gain and fat expansion independent of sex.
Phung Pham et al. (2023)
To test whether findings from these model systems were consistent with human physiology, researchers used data from the T2D Knowledge Portal (T2DKP) comprising 292 datasets and 326 GWAS traits. They found strong associations between TNIK variants and BMI, T2D, glycated hemoglobin (HbA1c), and blood glucose levels. These results, in combination with a case-control study from the UK Biobank, suggest the hitherto unknown role of TNIK in obesity and T2D.
Study findings
This study had four significant findings across flies, mice, and human models, all of which reveal the crucial role of TNIK in regulating glucose and lipid metabolism. Firstly, removing msn/TNIK genes in Drosophila and mice resulted in a downregulation of lipogenic programs on the consumption of HSD and HFHS, respectively. Secondly, Tnik KO mice depicted notable protection against peripheral insulin resistance, hepatic lipid accumulation, and diet-induced obesity.
Thirdly, several tissues, including the skeletal muscle, liver, and white adipose tissue (WAT), showed mechanistic changes resulting in elevated glucose and lipid handling capacity and enhanced insulin signaling. Finally, GWAS and case-control studies on humans revealed that TNIK variants, especially loss-of-function (pLOF) ones, are strongly associated with BMI, blood glucose levels, T2D, feeding behavior, and body fat accumulation.
Collectively, these findings establish a strong translational ground for TNIK as a conserved regulator of glucose and lipid metabolism in obesity, also in humans.
Phung Pham et al. (2023)
Conclusions
Researchers used a multidisciplinary approach employing GWAS, metabolomics, metabolic screening, MRI, and exercise experiments, to investigate the role of TNIK, a newly discovered protein, in glucose and lipid metabolism. They conducted these experiments on Drosophila, mice, and human cohorts and revealed for the first time the role of TNIK in obesity and T2D.
Their findings show great potential for the future therapeutic applications of TNIK in treating obesity and diabetes. Given the growing prevalence of these conditions and associated comorbidities, this is highly important.
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