Mitochondria in Sex Hormone-Induced Disorder of Energy Metabolism in Males and Females

Androgens have a complex role in the regulation of insulin sensitivity in the pathogenesis of type 2 diabetes. In male subjects, a reduction in androgens increases the risk for insulin resistance, which is improved by androgen injections. However, in female subjects with polycystic ovary syndrome (PCOS), androgen excess becomes a risk factor for insulin resistance. The exact mechanism underlying the complex activities of androgens remains unknown. In this review, a hormone synergy-based view is proposed for understanding this complexity. Mitochondrial overactivation by substrate influx is a mechanism of insulin resistance in obesity. This concept may apply to the androgen-induced insulin resistance in PCOS. Androgens and estrogens both exhibit activities in the induction of mitochondrial oxidative phosphorylation. The two hormones may synergize in mitochondria to induce overproduction of ATP. ATP surplus in the pancreatic β-cells and α-cells causes excess secretion of insulin and glucagon, respectively, leading to peripheral insulin resistance in the early phase of type 2 diabetes. In the skeletal muscle and liver, the ATP surplus contributes to insulin resistance through suppression of AMPK and activation of mTOR. Consistent ATP surplus leads to mitochondrial dysfunction as a consequence of mitophagy inhibition, which provides a potential mechanism for mitochondrial dysfunction in β-cells and brown adipocytes in PCOS. The hormone synergy-based view provides a basis for the overactivation and dysfunction of mitochondria in PCOS-associated type 2 diabetes. The molecular mechanism for the synergy is discussed in this review with a focus on transcriptional regulation. This view suggests a unifying mechanism for the distinct metabolic roles of androgens in the control of insulin action in men with hypogonadism and women with PCOS.

Some mechanisms of inflammation development in type 2 diabetes mellitus

Inflammation plays a key role in the development and progression of type 2 diabetes (T2DM), a disease characterized by peripheral insulin resistance and systemic glucolipotoxicity. The main source of inflammation in the early stages of the disease is visceral adipose tissue (VT). Macrophages are innate immune cells that are present in all peripheral tissues, including VT. Violation of the response of VT (MT) macrophages to changes in the microenvironment underlies aberrant inflammation and the development of local and systemic insulin resistance. The inflammatory activation of macrophages is regulated at several levels: stimulation of cell surface receptors, intracellular signaling, transcription, and metabolic levels. Which are activated by the transformation of macrophages along the pro-inflammatory or anti-inflammatory pathways. Such polarization of macrophages in modern immunology is divided into classical anti-inflammatory M1 polarization and alternative anti-inflammatory M2 polarization of macrophages. The M1 / M2 ratio of macrophages in the process of inflammation ensures the resolution of inflammation at different stages of its development. The review considers the main mechanisms involved in VT inflammation and the development of insulin resistance in T2DM, supported with the participation of immunocompetent cells, M1 / M2, as well as growth factors and humoral immunity factors secreted during this process.

Developmental Programming: Prenatal Testosterone Excess on Liver and Muscle Coding and Non-Coding RNA in Female Sheep

Prenatal testosterone (T)-treated female sheep manifest peripheral insulin resistance, ectopic lipid accumulation and insulin signaling disruption in liver and muscle. This study investigated transcriptional changes and transcriptome signature of prenatal T excess-induced hepatic and muscle-specific metabolic disruptions. Genome-wide coding and non-coding (nc) RNA expression in liver and muscle from 21-month-old prenatal T-treated (T propionate 100mg intramuscular twice weekly from days 30 to 90 of gestation; Term: 147 days) and control females were compared. Prenatal T (1) induced differential expression of mRNAs in liver (15 down, 17 up) and muscle (66 down, 176 up) (FDR<0.05, absolute log2 fold change>0.5); (2) downregulated mitochondrial pathway genes in liver and muscle; (3) downregulated hepatic lipid catabolism and PPAR signaling gene pathways; (4) modulated ncRNA metabolic processes gene pathway in muscle and (5) downregulated 5 uncharacterized long ncRNA (lncRNA) in the muscle but no ncRNA changes in the liver. Correlation analysis showed downregulation of lncRNAs LOC114112974 and LOC105607806 was associated with decreased TPK1, and LOC114113790 with increased ZNF470 expression. Orthogonal Projections to Latent Structures Discriminant Analysis identified mRNAs HADHA and SLC25A45, and miRNAs MIR154A, MIR25 and MIR487B in liver and ARIH1 and ITCH and miRNAs MIR369, MIR10A and MIR10B in muscle as potential biomarkers of prenatal T-excess. These findings suggest downregulation of mitochondria, lipid catabolism, and PPAR signaling genes in liver and dysregulation of mitochondrial and ncRNA gene pathways in muscle are contributors of lipotoxic and insulin resistant hepatic and muscle phenotype. Gestational T excess programming of metabolic dysfunctions involve tissue-specific ncRNA modulated transcriptional changes.

Smoothelin-Like Protein 1 Regulates Development and Metabolic Transformation of Skeletal Muscle in Hyperthyroidism

Hyperthyroidism triggers a glycolytic shift in skeletal muscle (SKM) by altering the expression of metabolic proteins, which is often accompanied by peripheral insulin resistance. Our previous results show that smoothelin-like protein 1 (SMTNL1), a transcriptional co-regulator, promotes insulin sensitivity in SKM. Our aim was to elucidate the role of SMTNL1 in SKM under physiological and pathological 3,3′,5-Triiodo-L-thyronine (T3) concentrations. Human hyper- and euthyroid SKM biopsies were used for microarray analysis and proteome profiler arrays. Expression of genes related to energy production, nucleic acid- and lipid metabolism was changed significantly in hyperthyroid samples. The phosphorylation levels and activity of AMPKα2 and JNK were increased by 15% and 23%, respectively, in the hyperthyroid samples compared to control. Moreover, SMTNL1 expression showed a 6-fold decrease in the hyperthyroid samples and in T3-treated C2C12 cells. Physiological and supraphysiological concentrations of T3 were applied on differentiated C2C12 cells upon SMTNL1 overexpression to assess the activity and expression level of the elements of thyroid hormone signaling, insulin signaling and glucose metabolism. Our results demonstrate that SMTNL1 selectively regulated TRα expression. Overexpression of SMTNL1 induced insulin sensitivity through the inhibition of JNK activity by 40% and hampered the non-genomic effects of T3 by decreasing the activity of ERK1/2 through PKCδ. SMTNL1 overexpression reduced IRS1 Ser307 and Ser612 phosphorylation by 52% and 53%, respectively, in hyperthyroid model to restore the normal responsiveness of glucose transport to insulin. SMTNL1 regulated glucose phosphorylation and balances glycolysis and glycogen synthesis via the downregulation of hexokinase II by 1.3-fold. Additionally, mitochondrial respiration and glycolysis were measured by SeaHorse analysis to determine cellular metabolic function/phenotype of our model system in real-time. T3 overload strongly increased the rate of acidification and a shift to glycolysis, while SMTNL1 overexpression antagonizes the T3 effects. These lines of evidence suggest that SMTNL1 potentially prevents hyperthyroidism-induced changes in SKM, and it holds great promise as a novel therapeutic target in insulin resistance.

Structural Lessons From the Mutant Proinsulin Syndrome

Insight into folding mechanisms of proinsulin has been provided by analysis of dominant diabetes-associated mutations in the human insulin gene (INS). Such mutations cause pancreatic β-cell dysfunction due to toxic misfolding of a mutant proinsulin and impairment in trans of wild-type insulin secretion. Anticipated by the “Akita” mouse (a classical model of monogenic diabetes mellitus; DM), this syndrome illustrates the paradigm endoreticulum (ER) stress leading to intracellular proteotoxicity. Diverse clinical mutations directly or indirectly perturb native disulfide pairing leading to protein misfolding and aberrant aggregation. Although most introduce or remove a cysteine (Cys; leading in either case to an unpaired thiol group), non-Cys-related mutations identify key determinants of folding efficiency. Studies of such mutations suggest that the hormone’s evolution has been constrained not only by structure-function relationships, but also by the susceptibility of its single-chain precursor to impaired foldability. An intriguing hypothesis posits that INS overexpression in response to peripheral insulin resistance likewise leads to chronic ER stress and β-cell dysfunction in the natural history of non-syndromic Type 2 DM. Cryptic contributions of conserved residues to folding efficiency, as uncovered by rare genetic variants, define molecular links between biophysical principles and the emerging paradigm of Darwinian medicine: Biosynthesis of proinsulin at the edge of non-foldability provides a key determinant of “diabesity” as a pandemic disease of civilization.

Non-thyroidal illness syndrome and SARS-CoV-2-associated multisystem inflammatory syndrome in children

Purpose COVID-19 disease may result in a severe multisystem inflammatory syndrome in children (MIS-C), which in turn may alter thyroid function (TF). We assessed TF in MIS-C, evaluating its impact on disease severity. Methods We retrospectively considered children admitted with MIS-C to a single pediatric hospital in Milan (November 2019–January 2021). Non-thyroidal illness syndrome (NTIS) was defined as any abnormality in TF tests (FT3, FT4, TSH) in the presence of critical illness and absence of a pre-existing hormonal abnormality. We devised a disease severity score by combining severity scores for each organ involved. Glucose and lipid profiles were also considered. A principal component analysis (PCA) was performed, to characterize the mutual association patterns between TF and disease severity. Results Of 26 (19 M/7F) patients, median age 10.7 (IQR 5.8–13.3) years, 23 (88.4%) presented with NTIS. A low FT3 level was noted in 15/23 (65.3%), while the other subjects had varying combinations of hormone abnormalities (8/23, 34.7%). Mutually correlated variables related to organ damage and inflammation were represented in the first dimension (PC1) of the PCA. FT3, FT4 and total cholesterol were positively correlated and characterized the second axis (PC2). The third axis (PC3) was characterized by the association of triglycerides, TyG index and HDL cholesterol. TF appeared to be related to lipemic and peripheral insulin resistance profiles. A possible association between catabolic components and severity score was also noted. Conclusions A low FT3 level is common among MIS-C. TF may be useful to define the impact of MIS-C on children’s health and help delineate long term follow-up management and prognosis.

Peripheral insulin resistance is associated with copeptin in patients with chronic kidney disease

Background - Insulin resistance is associated to cardiovascular disease risk and worsened kidney function. Patients with CKD have higher levels of insulin resistance. Elevated levels of copeptin (a surrogate for vasopressin levels), has been associated to increased incidence and progression of CKD as well as incident diabetes mellitus. The purpose of our study was to study the relationship between insulin resistance, copeptin, and CKD. Methods - We performed a cross-sectional study to investigate if insulin resistance was associated with higher copeptin levels in non-diabetic patients with stage 3-4 CKD vs controls. We measured plasma copeptin levels and utilized data from 52 patients with stage 3-4 CKD and 85 controls (eGFR ≥ 60mL/min/1.73m2) enrolled in The Insulin Resistance in Chronic Kidney Disease (IRCKD) study. We then used a multivariable linear regression model to assess the independent relationship between peripheral or hepatic insulin resistance and copeptin across levels of eGFR. Results - We found that in patients with CKD (eGFR 30-60 mL/min/1.73m2), but not in controls, peripheral insulin resistance was significantly correlated with higher levels of log copeptin (r = -0.21, p = 0.04). In patients with CKD when adjusted for age, sex, BMI, serum osmolality, log IL6, and log leptin-adiponectin ratio, each 1 SD decrease in insulin sensitivity was associated to a 38.9% increase in serum copeptin levels. The relationship between hepatic insulin resistance, copeptin, and eGFR is similar between controls and patients with reduced eGFR. Conclusion -Peripheral insulin resistance is associated with elevated copeptin levels in non-diabetic patients with stage 3-4 CKD. Further research into how the interaction between peripheral insulin resistance and elevated vasopressin impacts CKD progression could be of interest.

Biochemical Aspects of Diabetes Mellitus

Diabetes is a heterogeneous syndrome, characterized by a complex disorder in the regulation of the body's energy metabolism, which affects the use of carbohydrates, lipids and proteins, as well as other metabolisms. These alterations result from an insulin-secreting defect associated with variable peripheral insulin resistance. The biochemical changes that these two disorders cause lead to functional cellular changes followed by irreversible anatomical lesions in many tissues and organs. Diabetes is the most common disease of the endocrine system and is triggered when the amount of insulin secreted in the body is not optimal or when peripheral cells do not respond to its action (insulin is a hormone that participates in lowering blood glucose). This condition causes disorders of the entire metabolism and, over time, can affect the functioning of various organs in the body

Serum Corticosterone and Insulin Resistance as Early Biomarkers in the hAPP23 Overexpressing Mouse Model of Alzheimer’s Disease

Increasing epidemiological evidence highlights the association between systemic insulin resistance and Alzheimer’s disease (AD). As insulin resistance can be caused by high-stress hormone levels and since hypercortisolism appears to be an important risk factor of AD, we aimed to investigate the systemic insulin functionality and circulating stress hormone levels in a mutant humanized amyloid precursor protein (APP) overexpressing (hAPP23+/−) AD mouse model. Memory and spatial learning of male hAPP23+/− and C57BL/6 (wild type, WT) mice were assessed by a Morris Water Maze (MWM) test at the age of 4 and 12 months. The systemic metabolism was examined by intraperitoneal glucose and insulin tolerance tests (GTT, ITT). Insulin and corticosterone levels were determined in serum. In the hippocampus, parietal and occipital cortex of hAPP23+/− brains, amyloid-beta (Aβ) deposits were present at 12 months of age. MWM demonstrated a cognitive decline in hAPP23+/− mice at 12 but not at 4 months, evidenced by increasing total path lengths and deteriorating probe trials compared to WT mice. hAPP23+/− animals presented increased serum corticosterone levels compared to WT mice at both 4 and 12 months. hAPP23+/− mice exhibited peripheral insulin resistance compared to WT mice at 4 months, which stabilized at 12 months of age. Serum insulin levels were similar between genotypes at 4 months of age but were significantly higher in hAPP23+/− mice at 12 months of age. Peripheral glucose homeostasis remained unchanged. These results indicate that peripheral insulin resistance combined with elevated circulating stress hormone levels could be potential biomarkers of the pre-symptomatic phase of AD.