Skeletal muscle integrin expression in non-obese men with varying degrees of insulin sensitivity

Abstract

The remodeling of skeletal muscle extracellular matrix (ECM) components is related to the degree of insulin resistance (IR). Membrane receptors such as integrins provide two-way signaling (“inside-out” and “outside-in” signaling) between ECM components of skeletal muscle (e.g., collagen, laminin, fibronectin) and intracellular signaling pathways. The aim of the study was to analyze the relationship between the expression of integrins in skeletal muscle and insulin sensitivity (IS) in young, healthy, non-obese volunteers. We studied 36 healthy non-obese male participants. Subjects were divided into three subgroups on the basis of the hyperinsulinemic-euglycemic clamp: upper IS tertile, medium IS tertile, and lower IS tertile. Vastus lateralis muscle biopsies were performed before each clamp. Next, analysis of integrin mRNA expression was performed. Waist circumference, percent body fat, fasting serum insulin, total cholesterol, triglycerides and LDL-cholesterol were higher in the lower IS tertile subgroup compared to the other two subgroups (p < 0.05). The lower IS tertile showed increased expression of ITGA5, ITGA6, ITGA7, SPARC (p < 0.05) in comparison with the upper IS tertile and ITGA6 (p < 0.05) compared to the medium IS tertile. ITGA2, ITGA3, ITGA5, ITGA6, ITGA7, SPARC correlated inversely with IS (p < 0.05). Skeletal muscle integrin are associated with low IS in healthy nonobese men. Our data suggest that factors associated with ECM in muscle may be involved in modulation of insulin action even at the early stages of the development of IR.

INSULIN RESISTANCE (IR) is a pathophysiological condition of a reduced response to insulin by target tissues, as a result of which there is a disturbance in tissue glucose uptake, inhibition of the lipolysis process, as well as disturbance in glycogen synthesis and glycolysis [1-3]. Skeletal muscles are responsible for around 75% of total glucose uptake in insulin-stimulated conditions [4]. IR is present in many metabolic disorders such as obesity, but is also associated with the ageing process and with disease states such as heart and kidney failure, as well as lipodystrophy and myotonic dystrophy [5]. Moreover, it has been found that the level of sensitivity to the action of insulin is a reversible state through lifestyle changes and the use of appropriate exercise and diet [6]. The pathophysiology of IR is still not fully understood [7].

Skeletal muscle is a plastic contractile tissue in the body and it makes up approximately 40% of total body weight in normal-weight individuals. The main role of skeletal muscle includes supporting the movement and development of the skeleton and the control of glucose uptake. This tissue is made up of a large number of long, multinucleated fibres surrounded by an extracellular matrix (ECM). The ECM plays a key role in the processes of tissue regeneration, wound healing and embryogenesis, and guarantees the integrity and transmission of biochemical signals to cells from the external environment [8].

Research suggests that changes in the composition of the ECM may be associated with IR of skeletal muscle [9]. It is now known that ECM remodeling is positively correlated with IR in skeletal muscle in both rodents [10] and humans [11], as research results show that obese rodents and humans with type 2 diabetes mellitus (T2DM) have higher levels of collagen compared to lean subjects. The rearrangement of ECM compounds creates a mechanical ECM barrier and reduces vascularity, resulting in a decrease in insulin sensitivity. ECM remodeling is associated with further changes in receptor signaling, which mainly include integrins binding to intracellular focal adhesion kinase (FAK), responsible for insulin-stimulated glucose transport, and increased deposition of ECM components causes increased resistance to insulin action [12, 13]. These receptors are an interesting research subject because they are of great importance in the physiological processes of cells (adhesion, movement, differentiation and cell death) [14]. They act as the centre of signaling pathways and mediate the mechanistic connection between the skeletal muscle ECM and IR via integrin-linked kinase (ILK) and FAK, which play a key role in regulating insulin action [15, 16]. However, there are still many unresearched components of the ECM and its receptors that may affect the remodeling of this structure and may be related to IR.

Integrins belong to a family of 24 heterodimeric receptors that mediate communication between most components of the ECM of skeletal muscle and cells [17, 18]. In mammals, 18 α-subunits and 8 β-subunits of integrins have been confirmed, which form stable non-covalent interactions with each other [19]. Integrins act as adhesion receptors because they have the ability to signal in two directions across the plasma membrane (so-called “inside-out” and “outside-in”), thus binding to extracellular ligands or interacting with the cytoskeleton through intracellular domains of integrins. These transmembrane glycoprotein receptors serve as a node for many signaling pathways, such as phosphoinositide 3-kinase (PI3K), and mitogen-activated protein kinase (MAPK), essential for the proper functioning of cells and for insulin signal transduction. [20, 21].

Currently, there is little research into the effects of integrins on IR in skeletal muscle. These mainly affect the α1, α2 and β1 integrin subunits in rodents. It was found that the deletion of integrin α2 prevented the occurrence of IR, whereas integrin α1 had a minor role [22]. On the other hand, in the case of the β1 subunit, its partial deletion contributes to the development of IR [18].

For the analysis of the possible relationships between skeletal muscle integrins and insulin sensitivity, it seems reasonable to study young healthy individuals without potential confounding factors, like obesity or hyperglycemia. Examining young, healthy non-obese individuals may allow the identification of factors associated with IR at the early stage of its development.

The aim of this study was to test the hypothesis that the expression of integrin genes in skeletal muscle is related to IR even in individuals without overt metabolic disturbances.

Materials and Methods

Study group

The study group comprised 36 healthy (except borderline or moderately high triglycerides (TG)) male volunteers. They were young (age between 18 and 35 years) non-obese men (body mass index (BMI) below 30 kg/m²). All attendees were recruited by local advertisements. Each participant in the study was a non-smoker with no serious illnesses and did not take any medications. We collected information about daily diets with questionnaires (no differences in self-reported total calorie intake among insulin sensitivity tertiles (lower tertile, 2,890 ± 968 kcal; medium tertile, 2,678 ± 1,138 kcal; upper tertile, 2,594 ± 1,422 kcal)). Anthropometric measurements were performed in all the subjects as previously described [23]. Next, an oral glucose tolerance test (OGTT) was performed in all participants, and each of them had a normal glucose tolerance according to World Health Organization (WHO) criteria. All tests were done after an overnight fast. The research protocol was accepted by the Ethics Committee of the Medical University of Białystok. Before starting the study, each participant gave written informed consent.

Insulin sensitivity

Insulin sensitivity (IS) was measured using the 2h hyperinsulinemic-euglycemic clamp method, as described [24]. The rate of whole-body glucose uptake (M) was calculated for the fat-free mass (FFM). The study group was then divided into three subgroups on the basis of clamp-derived IS (upper tertile, above 9.46 mg/kg ffm/min; mean insulin sensitivity = 11.32 ± 1.70 mg/kg ffm/min; medium tertile, between 9.46–5.22 mg/kg ffm/min; mean insulin sensitivity = 7.39 ± 1.40 mg/kg ffm/min; lower tertile, below 5.22 mg/kg ffm/min; mean insulin sensitivity = 3.94 ± 0.62 mg/kg ffm/min).

Muscle tissue biopsies

Local anesthesia was performed with 1% lidocaine prior to skeletal muscle biopsy. Vastus lateralis muscle biopsy was taken after a small skin incision (about 1 cm) around the patella using a 4.5 mm skeletal biopsy needle (Popper & Sons, New Hyde Park, New York, USA). The muscles were then instantaneously inserted into RNAlater solution (Thermo Scientific Inc, Waltham, Massachusetts, USA). Until the tests were carried out, tissues were stored at –80°C.

Biochemical analyses

Plasma glucose was determined by an enzymatic method with a glucose analyzer - YSI 2300 STAT PLUS (YSI Incorporated, Yellow Springs, Ohio, USA). Serum lipids were measured by the colorimetric technique using the Cobas c111 analyzer (Roche Diagnostics, Rotkreuz, Switzerland). To assess the level of insulin in the serum, a monoclonal immunoradiometric test with a sensitivity of 1 μIU/mL was used. Serum free fatty acids were tested using a commercially available enzyme assay (Wako Chemicals, Richmond, Virginia, USA). Until biochemical determinations were performed, serum samples were stored at –80°C.

Analysis of skeletal muscle gene expression

RNA was isolated using the miRNAeasy kit (Qiagen, Hilden, Germany), and its concentration and purity assessed using a spectrophotometric method (NanoDrop 2000; Thermo Scientific Inc, Waltham, Massachusetts, USA). The cDNA was then synthesized with the EvoScript Universal cDNA Master kit (Roche Diagnostics, Rotkreuz, Switzerland) according to the manufacturer’s instructions. After that, the mRNA expression was determined using the real-time PCR method. Samples were quantified using primers and Taqman probes specific for the analyzed genes using QuantStudio 7 Flex System equipment (Applied Biosystems, Waltham, Massachusetts, USA). The following assays were used: ITGA1 (ID: Hs00235006), ITGA2 (ID: Hs00158127), ITGA3 (ID: Hs01076879), ITGA4 (ID: Hs00168433), ITGA5 (ID: Hs01547673), ITGA6 (ID: Hs01041011), ITGA7 (ID: Hs01056475), ITGB1 (ID: Hs00559595), SPARC (ID: Hs00234160), ILK (ID: Hs00177914), B2M (ID: Hs00187842). Gene expression levels were normalized to beta-2-microglobulin (B2M) since its expression was the most stable among the few reference genes tested, and mRNA expression was determined by the ∆∆Ct method in QuantStudio^TM Real-Time PCR software 1.3. The analysis of the examined reactions was performed in triplicate.

Statistical analysis

The statistics were made using the STATISTICA 13.0 program (Statsoft, Krakow, Poland). The results are presented as mean ± SD. Variables that were not normally distributed were log transformed before the analysis. Absolute values were used to present data in the results. Differences between groups were determined with one-way ANOVA with the Benjamini-Hochberg correction for multiple comparisons and with the post-hoc Tukey test. Adjustment for the differences in waist circumference, TG and LDL-cholesterol among the tertiles of IS was performed with ANCOVA. The relationships between the variables were verified using Pearson product moment correlation analysis, with the Benjamini-Hochberg correction and with multiple regression analysis. The significance level was set at the value of p < 0.05.

Results

Volunteers with lower IS tertile had higher waist circumference, body fat %, fasting serum insulin, total cholesterol, TG and LDL-cholesterol compared to the upper IS tertile subgroup and medium IS tertile (Table 1). All these differences remained significant after adjustment for waist circumference, TG and LDL-cholesterol (p < 0.05). 3 subjects in the lower IS tertile had borderline TG values between 150 and 200 mg/dL and 2 subjects in the lower IS tertile had moderately high TG values between 200 and 300 mg/dL.

Table 1 Baseline clinical characteristics of study group divided on the three subgroups on the basis of the tertiles of IS. Values are presented as mean ± SD

	Upper IS tertile	Medium IS tertile	Lower IS tertile
n	12	12	12
Age [years]	24.75 ± 1.91	22.67 ± 1.92	24.58 ± 2.87
BMI [kg/m2]	25.12 ± 2.68	25.05 ± 2.26	27.01 ± 1.44
Waist circumference [cm]	87.83 ± 7.03	87.79 ± 6.37	96.33 ± 5.28ab
Body fat [%]	19.58 ± 4.80	17.38 ± 5.83	25.37 ± 4.05ab
Fasting plasma glucose [mg/dL]	85.83 ± 5.38	83.25 ± 6.71	90.36 ± 10.24
Fasting serum insulin [μIU/mL]	7.84 ± 2.79	10.47 ± 4.80	11.92 ± 4.14ab
Cholesterol [mg/dL]	156.69 ± 23.44	155.67 ± 29.19	198.67 ± 18.27ab
Triglycerides [mg/dL]	59.42 ± 12.98	77.67 ± 29.92	143.58 ± 62.81ab
HDL-cholesterol [mg/dL]	61.13 ± 12.48	62.00 ± 9.65	52.75 ± 10.04
LDL-cholesterol [mg/dL]	89.75 ± 25.22	87.09 ± 28.08	123.15 ± 12.88ab

^a p < 0.05 vs. upper IS tertile

^b p < 0.05 vs. medium IS tertile

HDL, high-density lipoprotein; LDL, low-density lipoprotein

The skeletal muscles of volunteers from the lower IS tertile subgroup showed higher mRNA expression of ITGA5 (p = 0.004), ITGA6 (p = 0.001), ITGA7 (p = 0.01) and SPARC (p = 0.002) compared to the upper IS tertile subgroup. Moreover, subjects with lower IS tertile had higher muscle expression of the ITGA6 gene (p = 0.01) in comparison with the subgroup of medium IS tertile. In both subgroups (lower IS tertile and medium IS tertile), the highest increase in gene expression was observed for ITGA5 (1.8-fold and 2.6-fold, respectively) compared to upper IS tertile (Fig. 1). The differences in muscle integrin expression among the IS tertiles remained significant after adjustment for waist circumference, TG, and LDL-cholesterol.

Fig. 1

Skeletal muscle mRNA integrins expression in the tertiles of IS. a: p < 0.05 vs. upper IS tertile, b: p < 0.05 vs. medium IS tertile

Of the 10 integrins tested, 6 of them correlated with IS, namely ITGA2 (r = –0.42; p = 0.02), ITGA3 (r = –0.41; p = 0.01), ITGA5 (r = –0.49; p = 0.003), ITGA6 (r = –0.54; p = 0.001), ITGA7 (r = –0.47; p = 0.004), and SPARC (r = –0.37; p = 0.03) (Fig. 2). In multiple regression analysis, all these correlations (except ITGA2) remained significant after adjustment for waist circumference (ITGA3, β = –0.39, p = 0.01; ITGA5, β = –0.41, p = 0.01; ITGA6, β = –0.46, p = 0.003; ITGA7, β = –0.38, p = 0.01; SPARC, β = –0.34, p = 0.02). Further adjustment for TG and LDL-cholesterol did not change these results (ITGA3, β = –0.36, p = 0.014; ITGA5, β = –0,37, p = 0,016; ITGA6, β = –0.45, p = 0.02; ITGA7, β = –0.34, p = 0.035; SPARC β = –0.31, p = 0.044). All the observed differences and correlations were independent of TG and remained significant after exclusion of the subjects with borderline or moderately high TG from the analysis (except the relationship between insulin sensitivity and ITGA2).

Fig. 2

Correlations of integrins with IS in the entire study group (n = 36). a: The relationship between IS and skeletal muscle ITGA3 mRNA expression. b: The relationship between IS and skeletal muscle ITGA5 mRNA. c: The relationship between IS and skeletal muscle ITGA6 mRNA expression. d: The relationship between IS and skeletal muscle ITGA7 mRNA expression.

Lower expression of mRNA AKT (p = 0.034) and GLUT4 (p = 0.008) was detected in the skeletal muscles of volunteers from the lower IS tertile subgroup compared to the upper IS tertile subgroup. In addition, people with a lower IS tertile were characterized by lower muscle GLUT4 expression (p = 0.012) compared to the medium IS tertile (Fig. 3). GLUT4 was correlated with 4 integrins, ITGA3 (r = –0.45; p = 0.02), ITGA5 (r = –0.50; p = 0.06), ITGA6 (r = –0.50; p = 0.05), ITGA7 (r = –0.38; p = 0.04) whereas AKT with ITGA3 (r = –0.43; p = 0.02), and ITGA6 (r = –0.50; p = 0.01).

Fig. 3

Skeletal muscle mRNA expression of the genes of insulin signaling in the tertiles of IS. a: p < 0.05 vs. upper IS tertile, b: p < 0.05 vs. medium IS tertile

Discussion

In the present study, we demonstrated that skeletal muscle expression of the genes encoding integrins is associated with IS. To our knowledge, this is the first human study to show that integrins expression of skeletal muscle is associated with IS. We have shown that the increase in the expression of integrins occurs in the lower IS tertile. Notably, the study group consisted of young, healthy men who did not have confounding factors such as obesity or hyperglycemia. Thus, we have shown that skeletal muscle integrins are related to IS even at the early stage of IR development.

Insulin interacts with receptors in the cell membrane and activates signal transduction pathways, leading to a cascade of protein phosphorylation and translocation of the glucose transporter from the intracellular compartment to the surface membrane, and the stimulation of cellular glucose uptake [25]. Integrins enable bidirectional signaling across the plasma membrane. The signal from the outside of the cell is delivered to the inside of the cell by binding a skeletal muscle component, e.g., collagen, laminin, fibronectin, to the receptor (integrin) and inversely by binding the integrin to an extracellular ligand that is a component of skeletal muscle [14, 20]. Disturbances in the structure of the skeletal muscle through the accumulation of, for example, collagen, laminin and fibronectin cause a mechanical barrier and impaired communication of the signaling pathways of receptors, e.g., integrins, which can directly inhibit insulin signaling [26]. It can be hypothesized that integrins may be the cause of IR as a result of disrupted signaling pathways directly involved in normal insulin signaling. Our data suggest that an increase in integrin expression is associated with a higher degree of IR. On the other hand, it is possible that IR-related conditions such as hyperinsulinemia, hyperglycemia or dyslipidemia may intensify skeletal muscle dysfunction, leading to increased expression of integrins.

Our study results show that more differences in clinical characteristics and an increase in integrin expression (ITGA5, ITGA6, ITGA7, SPARC) are observed only in the lower IS tertile subgroup, which is associated with a higher degree of IR. Moreover, in our studies we showed that ITGA3 mRNA expression exhibited a negative correlation with insulin sensitivity. ECM remodeling occurs in insulin-resistant muscles and may increase ITGA3 expression through an increase in laminin concentration. ITGA3 is a laminin receptor and directly contributes to the inhibition of insulin signaling [27]. However, the role of ITGA3 in insulin sensitivity is poorly examined. Studies done by Kang et al. on rodents fed normal chow and a high-fat diet (HFD) showed an increase in collagen in the skeletal muscles of obese mice [10]. Both the above animal studies and our data indicate an involvement of different ECM components in modulating insulin action.

SPARC is a profibrotic protein associated with inflammation, IR and triglycerides. It has been proven that increased expression of this gene occurs in the adipose tissue of obese people and the plasma of women with IR and gestational diabetes [28, 29]. Studies carried out in SPARC knockout mice have demonstrated an attenuation of T2DM and its complications in the absence of SPARC, suggesting the causal role of SPARC in the development of T2DM and its complications [30]. Tam et al. showed that a 10% overnutrition-induced weight gain in men resulted in a dramatic upregulation of the SPARC gene in skeletal muscle [31]. In our study, SPARC expression in skeletal muscle was also increased in the lower tertile IS subgroup, suggesting that SPARC is associated with IR even in healthy, non-obese individuals.

ITGA5 is a receptor for fibronectin. It is used as a receptor for SPARC on adipose stromal cells, suggesting that it may also be used as a receptor for SPARC on skeletal muscle cells [32]. SPARC increases fibronectin deposition and ITGA5 receptor expression [33]. In our study, ITGA5 expression was increased in the lower tertile IS subgroup, indicating that this gene, like SPARC, is associated with IR.

ITGA6 and ITGA7 are receptors for laminin [33]. Taylor showed that whole-body deletion of ITGA7 resulted in smaller weight gain in HFD mice, and these mice had less body fat than wild-type mice fed HFD. Mice with the ITGA7 deletion were significantly more insulin sensitive and had better glucose tolerance than control mice. Quantification of skeletal muscle proteins showed increased levels of pAkt (Ser473) and pAkt (Thr308) in ITGA7-deleted mice compared to controls when fed HFD after an intraperitoneal insulin tolerance test [34]. In our study, ITGA7 expression was increased in the lower IS tertile subgroup compared to the upper IS tertile, indicating that this gene is associated with IR. It can be hypothesized that ITGA5, ITGA6, ITGA7, SPARC are involved in the early stage of the development of abnormal insulin signaling.

Our study has several limitations. No cause-and-effect relationship can be established. However, it can be hypothesized that impaired communication of receptor signaling pathways, such as integrins, leads to the inhibition of insulin signaling and interferes with its proper functioning. On the other hand, IR may increase the expression of integrins (the higher the intensity of IR, the higher the expression of integrins). Furthermore, due to the limited amount of tissue, we could not determine protein expression. The advantage of our study is the study group of volunteers. They were young, healthy people without confounding factors such as obesity, hyperglycemia, hyperinsulinemia, dyslipidemia, or cardiovascular disorders.

In conclusion, skeletal muscle integrins are associated with low insulin sensitivity in healthy non-obese men. Our data suggest that factors associated with ECM in muscle may be involved in modulation of insulin action even at the early stages of the development of IR.

Statements and Declarations

Funding

Supported by the research fund of the Institute of Animal Reproduction and Food Research, Polish Academy of Sciences, Olsztyn, Poland, and by a Grant 2011/01/B/NZ5/05380 from the National Science Centre (Poland).

Competing interests

The authors have no relevant financial or non-financial interests to disclose.

Author contributions

All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by Róża Aleksandrowicz, Magdalena Stefanowicz and Marek Strączkowski. The first draft of the manuscript was written by Róża Aleksandrowicz, and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.

Ethics approval

This study was performed in line with the principles of the Declaration of Helsinki. Approval was granted by the Ethics Committee of Medical University of Białystok (Date: 30 June 2011/No: R-I-002/300/2011).

Consent to participate

Informed consent was obtained from all individual participants included in the study.

References

• 1   da Silva Rosa  SC,  Nayak  N,  Caymo  AM,  Gordon  JW (2020) Mechanisms of muscle insulin resistance and the cross-talk with liver and adipose tissue. Physiol Rep 8: e14607.
• 2   Mastrototaro  L,  Roden  M (2021) Insulin resistance and insulin sensitizing agents. Metabolism 125: 154892.
• 3   Petersen  MC,  Shulman  GI (2018) Mechanisms of insulin action and insulin resistance. Physiol Rev 98: 2133–2223.
• 4   Gilbert  M (2021) Role of skeletal muscle lipids in the pathogenesis of insulin resistance of obesity and type 2 diabetes. J Diabetes Investig 12: 1934–1941.
• 5   Abdul-Ghani  MA,  DeFronzo  RA (2010) Pathogenesis of insulin resistance in skeletal muscle. J Biomed Biotechnol 2010: 476279.
• 6   Merz  KE,  Thurmond  DC (2020) Role of skeletal muscle in insulin resistance and glucose uptake. Compr Physiol 10: 785–809.
• 7   Yaribeygi  H,  Farrokhi  FR,  Butler  AE,  Sahebkar  A (2019) Insulin resistance: review of the underlying molecular mechanisms. J Cell Physiol 234: 8152–8161.
• 8   Ahmad  K,  Shaikh  S,  Ahmad  SS,  Lee  EJ,  Choi  I (2020) Cross-talk between extracellular matrix and skeletal muscle: implications for myopathies. Front Pharmacol 11: 142.
• 9   Csapo  R,  Gumpenberger  M,  Wessner  B (2020) Skeletal muscle extracellular matrix—what do we know about its composition, regulation, and physiological roles? a narrative review. Front Physiol 11: 253.
• 10   Kang  L,  Ayala  JE,  Lee-Young  RS,  Zhang  Z,  James  FD, et al. (2011) Diet-induced muscle insulin resistance is associated with extracellular matrix remodeling and interaction with integrin alpha2beta1 in mice. Diabetes 60: 416–426.
• 11   Berria  R,  Wang  L,  Richardson  DK,  Finlayson  J,  Belfort  R, et al. (2006) Increased collagen content in insulin-resistant skeletal muscle. Am J Physiol Endocrinol Metab 290: E560–E565.
• 12   Sylow  L,  Tokarz  VL,  Richter  EA,  Klip  A (2021) The many actions of insulin in skeletal muscle, the paramount tissue determining glycemia. Cell Metab 33: 758–780.
• 13   Huang  D,  Khoe  M,  Ilic  D,  Bryer-Ash  M (2006) Reduced expression of focal adhesion kinase disrupts insulin action in skeletal muscle cells. Endocrinology 147: 3333–3343.
• 14   Huang  J,  Li  X,  Shi  X,  Zhu  M,  Wang  J, et al. (2019) Platelet integrin αIIbβ3: signal transduction, regulation, and its therapeutic targeting. J Hematol Oncol 12: 1–22.
• 15   Hynes  RO (2002) Integrins: bidirectional, allosteric signaling machines. Cell 110: 673–687.
• 16   Williams  AS,  Kang  L,  Wasserman  DH (2015) The extracellular matrix and insulin resistance. Trends Endocrinol Metab 26: 357–366.
• 17   Cooper  J,  Giancotti  FG (2019) Integrin signaling in cancer: mechanotransduction, stemness, epithelial plasticity, and therapeutic resistance. Cancer Cell 35: 347–367.
• 18   Ahmad  K,  Choi  I,  Lee  YH (2020) Implications of skeletal muscle extracellular matrix remodeling in metabolic disorders: diabetes perspective. Int J Mol Sci 21: 3845.
• 19   Moreno-Layseca  P,  Icha  J,  Hamidi  H,  Ivaska  J (2019) Integrin trafficking in cells and tissues. Nat Cell Biol 21: 122–132.
• 20   Pulous  FE,  Petrich  BG (2019) Integrin-dependent regulation of the endothelial barrier. Tissue Barriers 7: 1685844.
• 21   Aleksandrowicz  R,  Straczkowski  M (2023) Link between insulin resistance and skeletal muscle extracellular matrix remodeling. Endocr Connect 12: e230023.
• 22   Bayer  ML,  Svensson  RB,  Schjerling  P,  Williams  AS,  Wasserman  DH, et al. (2020) Influence of the integrin alpha-1 subunit and its relationship with high-fat diet upon extracellular matrix synthesis in skeletal muscle and tendon. Cell Tissue Res 381: 177–187.
• 23   Strączkowski  M,  Nikołajuk  A,  Majewski  R,  Filarski  R,  Stefanowicz  M, et al. (2018) The effect of moderate weight loss, with or without (1, 3)(1, 6)-β-glucan addition, on subcutaneous adipose tissue inflammatory gene expression in young subjects with uncomplicated obesity. Endocrine 61: 275–284.
• 24   Karczewska-Kupczewska  M,  Kowalska  I,  Nikołajuk  A,  Adamska  A,  Zielińska  M, et al. (2012) Circulating brain-derived neurotrophic factor concentration is downregulated by intralipid/heparin infusion or high-fat meal in young healthy male subjects. Diabetes Care 35: 358–362.
• 25   Turcotte  LP,  Fisher  JS (2008) Skeletal muscle insulin resistance: roles of fatty acid metabolism and exercise. Phys Ther 88: 1279–1296.
• 26   Coletta  DK,  Mandarino  LJ (2011) Mitochondrial dysfunction and insulin resistance from the outside in: extracellular matrix, the cytoskeleton, and mitochondria. Am J Physiol Endocrinol Metab 301: E749–E755.
• 27   Roumans  NJ,  Vink  RG,  Fazelzadeh  P,  van Baak  MA,  Mariman  EC (2017) A role for leukocyte integrins and extracellular matrix remodeling of adipose tissue in the risk of weight regain after weight loss. Am J Clin Nutr 105: 1054–1062.
• 28   Galimov  A,  Hartung  A,  Trepp  R,  Mader  A,  Flück  M, et al. (2015) Growth hormone replacement therapy regulates microRNA-29a and targets involved in insulin resistance. J Mol Med (Berl) 93: 1369–1379.
• 29   Xu  L,  Ping  F,  Yin  J,  Xiao  X,  Xiang  H, et al. (2013) Elevated plasma SPARC levels are associated with insulin resistance, dyslipidemia, and inflammation in gestational diabetes mellitus. PLoS One 8: e81615.
• 30   Taneda  S,  Pippin  JW,  Sage  EH,  Hudkins  KL,  Takeuchi  Y, et al. (2003) Amelioration of diabetic nephropathy in SPARC-null mice. J Am Soc Nephrol 14: 968–980.
• 31   Tam  CS,  Covington  JD,  Bajpeyi  S,  Tchoukalova  Y,  Burk  D, et al. (2014) Weight gain reveals dramatic increases in skeletal muscle extracellular matrix remodeling. J Clin Endocrinol Metab 99: 1749–1757.
• 32   Nakamura  K,  Nakano  S,  Miyoshi  T,  Yamanouchi  K,  Matsuwaki  T, et al. (2012) Age-related resistance of skeletal muscle-derived progenitor cells to SPARC may explain a shift from myogenesis to adipogenesis. Aging (Albany NY) 4: 40–48.
• 33   Atorrasagasti  C,  Onorato  AM,  Mazzolini  G (2022) The role of SPARC (secreted protein acidic and rich in cysteine) in the pathogenesis of obesity, type 2 diabetes, and non-alcoholic fatty liver disease. J Physiol Biochem. doi: 10.1007/s13105-022-00913-5. Online ahead of print.
• 34   Taylor  J (2018) The role of integrin alpha 7 in diet-induced obesity and signalling. Doctoral thesis, University of East Anglia. https://ueaeprints.uea.ac.uk/id/eprint/71162 accessed on February 17, 2023.