Intermittent Starvation Extends the Functional Lifetime of Primary Human Hepatocyte Cultures

Regulation of Metabolic Aging Through Adenosine Mono Phosphate-Activated Protein Kinase and Mammalian Target of Rapamycin: A Comparative Study of Intermittent Fasting Variations in Obese Young Women

Background/Objectives: Obesity accelerates metabolic aging through oxidative stress, inflammation, and mitochondrial dysfunction. AMP-activated protein kinase (AMPK) and mammalian target of rapamycin (mTOR) are nutrient-sensing pathways regulating metabolism. AMPK promotes energy metabolism and autophagy, while excessive mTOR activity contributes to aging. Intermittent fasting (IF), including time-restricted feeding (TRF)-limiting food intake to a 6 h window (18:6)-and alternate-day modified fasting (ADMF)-alternating 24 h fasting (≤25% daily caloric intake) with unrestricted feeding-may improve metabolic regulation. However, their effects on AMPK, mTOR, and metabolic age remain unclear. Methods: This quasi-experimental pre-test-post-test control group study compared the TRF and ADMF on metabolic age, AMPK, and mTOR in young obese women. Twenty-four participants (mean age: 21.29 ± 1.76 years; body fat: 36.92 ± 3.18%; BMI: 29.68 ± 3.70 kg/m2) were initially matched by BMI and assigned to Control, TRF, and ADMF groups. A total of 4 participants (1 Control, 3 ADMF) were excluded due to outlier values, yielding final group sizes: Control (n = 7), TRF (n = 8), and ADMF (n = 5). The intervention lasted 20 days. Results: A significant decrease in AMPK levels was observed in the ADMF group (p = 0.043), while changes in the TRF and Control groups were not significant. mTOR levels showed a decreasing trend but were not statistically significant. No significant changes were found in metabolic age. Conclusions: Twenty days of intermittent fasting intervention did not significantly affect AMPK, mTOR, or metabolic age in young obese women. TRF may more effectively enhance AMPK and reduce mTOR, while ADMF may better reduce metabolic age.

Effects of Fasting on THP1 Macrophage Metabolism and Inflammatory Profile

Fasting can affect the body's inflammatory response, and this has been linked to potential health benefits, including improvements for people with rheumatic diseases. In this work, we evaluated, in vitro, how changes in nutrient availability alter the inflammatory response of macrophages. Macrophage-differentiated THP1 cells were cultured, deprived of FCS or subjected to cycles of FCS deprivation and restoration to mimic intermittent fasting. Changes in the macrophage phenotype, the cells' response to inflammatory stimuli and the level of mitochondrial alteration were assessed. The results indicate that while periods of serum starvation are associated with a decrease in IL1β and TNFα expression, consistent with an anti-inflammatory response, intermittent serum starvation cycles promote a pro-inflammatory phenotype. Rapid changes in reducing capacity and mitochondrial response were also observed. Of note, while some changes, such as the production of oxygen free radicals, were reversed with refeeding, others, such as a decrease in reducing capacity, were maintained and even increased. This study shows that different fasting protocols can have diverging effects and highlights that time-limited nutrient changes can significantly affect macrophage functions in cell cultures. These findings help elucidate some of the mechanisms by which specific fasting dietary interventions could help control inflammatory diseases.

Engineered cocultures of iPSC-derived atrial cardiomyocytes and atrial fibroblasts for modeling atrial fibrillation

Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia treatable with antiarrhythmic drugs; however, patient responses remain highly variable. Human induced pluripotent stem cell-derived atrial cardiomyocytes (iPSC-aCMs) are useful for discovering precision therapeutics, but current platforms yield phenotypically immature cells and are not easily scalable for high-throughput screening. Here, primary adult atrial, but not ventricular, fibroblasts induced greater functional iPSC-aCM maturation, partly through connexin-40 and ephrin-B1 signaling. We developed a protein patterning process within multiwell plates to engineer patterned iPSC-aCM and atrial fibroblast coculture (PC) that significantly enhanced iPSC-aCM structural, electrical, contractile, and metabolic maturation for 6+ weeks compared to conventional mono-/coculture. PC displayed greater sensitivity for detecting drug efficacy than monoculture and enabled the modeling and pharmacological or gene editing treatment of an AF-like electrophysiological phenotype due to a mutated sodium channel. Overall, PC is useful for elucidating cell signaling in the atria, drug screening, and modeling AF.

Decellularized Liver Nanofibers Enhance and Stabilize the Long-Term Functions of Primary Human Hepatocytes In Vitro

Owing to significant differences across species in liver functions, in vitro human liver models are used for screening the metabolism and toxicity of compounds, modeling diseases, and cell-based therapies. However, the extracellular matrix (ECM) scaffold used for such models often does not mimic either the complex composition or the nanofibrous topography of native liver ECM. Thus, here novel methods are developed to electrospin decellularized porcine liver ECM (PLECM) and collagen I into nano- and microfibers (≈200-1000 nm) without synthetic polymer blends. Primary human hepatocytes (PHHs) on nanofibers in monoculture or in coculture with nonparenchymal cells (3T3-J2 embryonic fibroblasts or primary human liver endothelial cells) display higher albumin secretion, urea synthesis, and cytochrome-P450 1A2, 2A6, 2C9, and 3A4 enzyme activities than on conventionally adsorbed ECM controls. PHH functions are highest on the collagen/PLECM blended nanofibers (up to 34-fold higher CYP3A4 activity relative to adsorbed ECM) for nearly 7 weeks in the presence of the fibroblasts. In conclusion, it is shown for the first time that ECM composition and topography synergize to enhance and stabilize PHH functions for several weeks in vitro. The nanofiber platform can prove useful for the above applications and to elucidate cell-ECM interactions in the human liver.

Starvation Protects Hepatocytes from Inflammatory Damage through Paradoxical mTORC1 Signaling

Background and aims: Sepsis-related liver failure is associated with a particularly unfavorable clinical outcome. Calorie restriction is a well-established factor that can increase tissue resilience, protect against liver failure and improve outcome in preclinical models of bacterial sepsis. However, the underlying molecular basis is difficult to investigate in animal studies and remains largely unknown.

METHODS

We have used an immortalized hepatocyte line as a model of the liver parenchyma to uncover the role of caloric restriction in the resilience of hepatocytes to inflammatory cell damage. In addition, we applied genetic and pharmacological approaches to investigate the contribution of the three major intracellular nutrient/energy sensor systems, AMPK, mTORC1 and mTORC2, in this context.

RESULTS

We demonstrate that starvation reliably protects hepatocytes from cellular damage caused by pro-inflammatory cytokines. While the major nutrient- and energy-related signaling pathways AMPK, mTORC2/Akt and mTORC1 responded to caloric restriction as expected, mTORC1 was paradoxically activated by inflammatory stress in starved, energy-deprived hepatocytes. Pharmacological inhibition of mTORC1 or genetic silencing of the mTORC1 scaffold Raptor, but not its mTORC2 counterpart Rictor, abrogated the protective effect of starvation and exacerbated inflammation-induced cell death. Remarkably, mTORC1 activation in starved hepatocytes was uncoupled from the regulation of autophagy, but crucial for sustained protein synthesis in starved resistant cells.

CONCLUSIONS

AMPK engagement and paradoxical mTORC1 activation and signaling mediate protection against pro-inflammatory stress exerted by caloric restriction in hepatocytes.

Modulation of human iPSC-derived hepatocyte phenotype via extracellular matrix microarrays

In vitro human liver models are essential for drug screening, disease modeling, and cell-based therapies. Induced pluripotent stem cell (iPSC)-derived hepatocyte-like cells (iHeps) mitigate sourcing limitations of primary human hepatocytes (PHHs) and enable precision medicine; however, current protocols yield iHeps with very low differentiated functions. The composition and stiffness of liver's extracellular matrix (ECM) cooperatively regulate hepatic phenotype in vivo, but such effects on iHeps remain unelucidated. Here, we utilized ECM microarrays and high content imaging to assess human iHep attachment and functions on ten major liver ECM proteins in single and two-way combinations robotically spotted onto polyacrylamide gels of liver-like stiffnesses; microarray findings were validated using hydrogel-conjugated multiwell plates. Collagen-IV supported higher iHep attachment than collagen-I over 2 weeks on 1 kPa, while laminin and its combinations with collagen-III, fibronectin, tenascin C, or hyaluronic acid led to both high iHep attachment and differentiated functions; laminin and its combination with tenascin or fibronectin led to similar albumin expression in iHeps and PHHs. Additionally, several collagen-IV-, laminin-, fibronectin-, and collagen-V-containing combinations on 1 kPa led to similar or higher CYP3A4 staining in iHeps than PHHs. Lastly, collagen-I or -III mixed with laminin, collagen-IV mixed with lumican, and collagen-V mixed with fibronectin led to high and stable functional output (albumin/urea secretions; CYP1A2/2C9/3A4 activities) in iHep cultures versus declining PHH numbers/functions for 3 weeks within multiwell plates containing 1 kPa hydrogels. Ultimately, these platforms can help elucidate ECM's role in liver diseases and serve as building blocks of engineered tissues for applications. STATEMENT OF SIGNIFICANCE: We utilized high-throughput extracellular matrix (ECM) microarrays and high content imaging to assess the attachment and differentiated functions of iPSC-derived human hepatocyte-like cells (iHep) on major liver ECM protein combinations spotted onto polyacrylamide gels of liver-like stiffnesses. We observed that iHep responses are regulated in unexpected ways via the cooperation between ECM stiffness and protein composition. Using this approach, we induced mature functions in iHeps on substrates of physiological stiffness and select ECM coatings at higher levels over 3+ weeks than analogous primary human hepatocyte cultures, which is useful for building platforms for drug screening, disease modeling, and regenerative medicine.

Elucidating Extracellular Matrix and Stiffness Control of Primary Human Hepatocyte Phenotype Via Cell Microarrays

How the liver's extracellular matrix (ECM) protein composition and stiffness cooperatively regulate primary human hepatocyte (PHH) phenotype is unelucidated. Here, we utilize protein microarrays and high content imaging with single-cell resolution to assess PHH attachment/functions on 10 major liver ECM proteins in single and two-way combinations robotically spotted onto polyacrylamide gels of 1 kPa or 25 kPa stiffness. Albumin, cytochrome-P450 3A4 (CYP3A4), and hepatocyte nuclear factor alpha (HNF4α) positively correlate with each other and cell density on both stiffnesses. The 25 kPa stiffness supports higher average albumin and HNF4α expression after 14 days, while ECM protein composition significantly modulates PHH functions across both stiffnesses. Unlike previous rodent data, PHH functions are highest only when collagen-IV or fibronectin are mixed with specific proteins, whereas non-collagenous proteins without mixed collagens downregulate functions. Combination of collagen-IV and hyaluronic acid retains high CYP3A4 on 1 kPa, whereas collagens-IV and -V better retain HNF4α on 25 kPa over 14 days. Adapting ECM conditions to 96-well plates containing conjugated hydrogels reveals novel regulation of other functions (urea, CYP1A2/2A6/2C9) and drug-mediated CYP induction by the ECM protein composition/stiffness. This high-throughput pipeline can be adapted to elucidate ECM's role in liver diseases and facilitate optimization of engineered tissues.

Application of Metabolomics in the Study of Starvation-Induced Autophagy in Saccharomyces cerevisiae: A Scoping Review

This scoping review is aimed at the application of the metabolomics platform to dissect key metabolites and their intermediates to observe the regulatory mechanisms of starvation-induced autophagy in Saccharomyces cerevisiae. Four research papers were shortlisted in this review following the inclusion and exclusion criteria. We observed a commonly shared pathway undertaken by S. cerevisiae under nutritional stress. Targeted and untargeted metabolomics was applied in either of these studies using varying platforms resulting in the annotation of several different observable metabolites. We saw a commonly shared pathway undertaken by S. cerevisiae under nutritional stress. Following nitrogen starvation, the concentration of cellular nucleosides was altered as a result of autophagic RNA degradation. Additionally, it is also found that autophagy replenishes amino acid pools to sustain macromolecule synthesis. Furthermore, in glucose starvation, nucleosides were broken down into carbonaceous metabolites that are being funneled into the non-oxidative pentose phosphate pathway. The ribose salvage allows for the survival of starved yeast. Moreover, acute glucose starvation showed autophagy to be involved in maintaining ATP/energy levels. We highlighted the practicality of metabolomics as a tool to better understand the underlying mechanisms involved to maintain homeostasis by recycling degradative products to ensure the survival of S. cerevisiae under starvation. The application of metabolomics has extended the scope of autophagy and provided newer intervention targets against cancer as well as neurodegenerative diseases in which autophagy is implicated.

Challenges for the Applications of Human Pluripotent Stem Cell-Derived Liver Organoids

The current organoid culture systems allow pluripotent and adult stem cells to self-organize to form three-dimensional (3D) structures that provide a faithful recapitulation of the architecture and function of in vivo organs. In particular, human pluripotent stem cell-derived liver organoids (PSC-LOs) can be used in regenerative medicine and preclinical applications, such as disease modeling and drug discovery. New bioengineering tools, such as microfluidics, biomaterial scaffolds, and 3D bioprinting, are combined with organoid technologies to increase the efficiency of hepatic differentiation and enhance the functional maturity of human PSC-LOs by precise control of cellular microenvironment. Long-term stabilization of hepatocellular functions of in vitro liver organoids requires the combination of hepatic endodermal, endothelial, and mesenchymal cells. To improve the biological function and scalability of human PSC-LOs, bioengineering methods have been used to identify diverse and zonal hepatocyte populations in liver organoids for capturing heterogeneous pathologies. Therefore, constructing engineered liver organoids generated from human PSCs will be an extremely versatile tool in in vitro disease models and regenerative medicine in future. In this review, we aim to discuss the recent advances in bioengineering technologies in liver organoid culture systems that provide a timely and necessary study to model disease pathology and support drug discovery in vitro and to generate cell therapy products for transplantation.

Messenger RNA Expression of Albumin, Transferrin, Transthyretin, Asialoglycoprotein Receptor, Cytochrome P450 Isoform, Uptake Transporter, and Efflux Transporter Genes as a Function of Culture Duration in Prolonged Cultured Cryopreserved Human Hepatocytes as Collagen-Matrigel Sandwich Cultures: Evidence for Redifferentiation upon Prolonged Culturing

Hepatic gene expression as a function of culture duration was evaluated in prolonged cultured human hepatocytes. Human hepatocytes from seven donors were maintained as near-confluent collagen-Matrigelsandwich cultures, with messenger RNA expression for genes responsible for key hepatic functions quantified by real-time polymerase chain reaction at culture durations of 0 (day of plating), 2, 7, 9, 16, 23, 26, 29, 36, and 43 days. Key hepatocyte genes were evaluated, including the differentiation markers albumin, transferrin, and transthyretin; the hepatocyte-specific asialoglycoprotein receptor 1 cytochrome P450 isoforms CYP1A2, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP3A4, and CYP3A7; uptake transporter isoforms SLC10A1, SLC22A1, SLC22A7, SLCO1B1, SLCO1B3, and SLCO2B1; efflux transporter isoforms ATP binding cassette (ABC)B1, ABCB11, ABCC2, ABCC3, ABCC4, and ABCG2; and the nonspecific housekeeping gene hypoxanthine ribosyl transferase 1 (HPRT1). The well established dedifferentiation phenomenon was observed on day 2, with substantial (>80%) decreases in gene expression in day 2 cultures observed for all genes evaluated except HPRT1 and efflux transporters ABCB1, ABCC2, ABCC3 (<50% decrease in expression), ABCC4 (>400% increase in expression), and ABCG2 (no decrease in expression). All genes with a >80% decrease in expression were found to have increased levels of expression on day 7, with peak expression observed on either day 7 or day 9, followed by a gradual decrease in expression up to the longest duration evaluated of 43 days. Our results provide evidence that cultured human hepatocytes undergo redifferentiation upon prolonged culturing. SIGNIFICANCE STATEMENT: This study reports that although human hepatocytes underwent dedifferentiation upon 2 days of culture, prolonged culturing resulted in redifferentiation based on gene expression of differentiation markers, uptake and efflux transporters, and cytochrome P450 isoforms. The observed redifferentiation suggests that prolonged (>7 days) culturing of human hepatocyte cultures may represent an experimental approach to overcome the initial dedifferentiation process, resulting in "stabilized" hepatocytes that can be applied toward the evaluation of drug properties requiring an extended period of treatment and evaluation.

Bioengineered Liver Models for Investigating Disease Pathogenesis and Regenerative Medicine

Owing to species-specific differences in liver pathways, in vitro human liver models are utilized for elucidating mechanisms underlying disease pathogenesis, drug development, and regenerative medicine. To mitigate limitations with de-differentiated cultures, bioengineers have developed advanced techniques/platforms, including micropatterned cocultures, spheroids/organoids, bioprinting, and microfluidic devices, for perfusing cell cultures and liver slices. Such techniques improve mature functions and culture lifetime of primary and stem-cell human liver cells. Furthermore, bioengineered liver models display several features of liver diseases including infections with pathogens (e.g., malaria, hepatitis C/B viruses, Zika, dengue, yellow fever), alcoholic/nonalcoholic fatty liver disease, and cancer. Here, we discuss features of bioengineered human liver models, their uses for modeling aforementioned diseases, and how such models are being augmented/adapted for fabricating implantable human liver tissues for clinical therapy. Ultimately, continued advances in bioengineered human liver models have the potential to aid the development of novel, safe, and efficacious therapies for liver disease.

Latest impact of engineered human liver platforms on drug development

Drug-induced liver injury (DILI) is a leading cause of drug attrition, which is partly due to differences between preclinical animals and humans in metabolic pathways. Therefore, in vitro human liver models are utilized in biopharmaceutical practice to mitigate DILI risk and assess related mechanisms of drug transport and metabolism. However, liver cells lose phenotypic functions within 1–3 days in two-dimensional monocultures on collagen-coated polystyrene/glass, which precludes their use to model the chronic effects of drugs and disease stimuli. To mitigate such a limitation, bioengineers have adapted tools from the semiconductor industry and additive manufacturing to precisely control the microenvironment of liver cells. Such tools have led to the fabrication of advanced two-dimensional and three-dimensional human liver platforms for different throughput needs and assay endpoints (e.g., micropatterned cocultures, spheroids, organoids, bioprinted tissues, and microfluidic devices); such platforms have significantly enhanced liver functions closer to physiologic levels and improved functional lifetime to >4 weeks, which has translated to higher sensitivity for predicting drug outcomes and enabling modeling of diseased phenotypes for novel drug discovery. Here, we focus on commercialized engineered liver platforms and case studies from the biopharmaceutical industry showcasing their impact on drug development. We also discuss emerging multi-organ microfluidic devices containing a liver compartment that allow modeling of inter-tissue crosstalk following drug exposure. Finally, we end with key requirements for engineered liver platforms to become routine fixtures in the biopharmaceutical industry toward reducing animal usage and providing patients with safe and efficacious drugs with unprecedented speed and reduced cost.

HepaRG Maturation in Silk Fibroin Scaffolds: Toward Developing a 3D In Vitro Liver Model

In vitro liver models are necessary tools for the development of new therapeutics. HepaRG cells are a commonly used cell line to produce hepatic progenitor cells and hepatocytes. This study demonstrates for the first time the suitability of 3% silk scaffolds to support HepaRG growth and differentiation. The modulus and pore size of 3% silk scaffolds were shown to be within the desired range for liver cell growth. The optimal seeding density for HepaRG cells on silk scaffolds was determined. The growth and maturation of scaffolded HepaRG cells was evaluated for 28 days, where the first 14 days of culture were a proliferation period and the last 14 days of culture were a differentiation period using dimethyl sulfoxide (DMSO) treatment. After the first 14 days of culture, the scaffolded HepaRG cells exhibited increased metabolic activity and albumin secretion compared to monolayer cultured controls and preserved these attributes through the duration of culture. Additionally, after the first 14 days of culture, the scaffolded HepaRG cells displayed a significantly reduced expression of genes associated with hepatocyte maturation. This difference in expression was no longer apparent after 28 days of culture, suggesting that the cells underwent rapid differentiation within the scaffold. The functionalization of silk scaffolds with extracellular matrix (ECM) components (type I collagen and/or an arginylglycylaspartic acid (RGD)-containing peptide) was investigated to determine the impact on HepaRG cell attachment and maturation. The inclusion of ECM components had no noticeable impact on cell attachment but did significantly influence CYP3A4 expression and albumin secretion. Finally, the matrix support provided by the 3% silk scaffolds could prime the HepaRG cells for steatosis liver model applications, as evidenced by lipid droplet accumulation and expression of steatosis-related genes after 24 h of exposure to oleic acid. Overall, our work demonstrates the utility of silk scaffolds in providing a modifiable platform for liver cell growth.

Physiologically inspired culture medium prolongs the lifetime and insulin sensitivity of human hepatocytes in micropatterned co-cultures

Given significant species-specific differences in liver functions, cultures of primary human hepatocytes (PHHs) are useful for assessing drug metabolism and to mitigate the risk of drug-induced hepatotoxicity in humans. While significant advances have been made to keep PHHs highly functional for 2-4 weeks in vitro, especially upon co-culture with both liver- and non-liver-derived non-parenchymal cells (NPCs), the functional lifespan of PHHs is 200-400 days in vivo. Therefore, it is desirable to determine culture conditions that can further prolong PHHs functions in vitro for modeling chronic drug exposure, disease pathogenesis, and to provide flexibility to the end-user for staggering drug incubations across multiple culture batches. Most PHH culture platforms utilize supraphysiologic levels of glucose and insulin and bovine-derived serum when including NPCs, which can alter PHH functions. Therefore, here we developed a culture medium containing physiologic levels of glucose (5 mM), insulin (500 pM), and human serum (10 % v/v) and tested its effects on micropatterned co-cultures (MPCCs) in which PHHs are organized onto collagen domains of empirically optimized dimensions and surrounded by 3T3-J2 murine fibroblasts that express liver-like molecules and induce higher PHH functions than liver-derived NPCs. Our physiologically-inspired culture medium allowed better retention of PHH morphology, polarity, and functions (albumin and urea, cytochrome-P450 activities, and sensitivity to insulin-mediated inhibition of gluconeogenesis) for up to 10 weeks relative to the traditional medium. Finally, PHHs in the physiologic medium displayed clinically-relevant responses to prototypical drugs for hepatoxicity and cytochrome-P450 induction. Ultimately, our physiologic culture medium could find broader utility for the continued development of PHH-NPC co-cultures for drug development, investigating the effects of patient-derived sera on PHH functions and disease phenotypes, and for use in cell-based therapies.

Metformin Protects ARPE-19 Cells from Glyoxal-Induced Oxidative Stress

The protective effects and mechanisms of metformin against oxidative stress were evaluated both in vivo and in vitro. ARPE-19 cells comprised the normal group, the glyoxal-treated group (0.5 mM glyoxal), and the glyoxal+metformin group (0.5 mM glyoxal and 0.1 mM metformin). In the in vitro model, differences in cell viability, ROS production, NO products, cellular apoptosis, and the expressions of phospho-AMPKα, total-AMPKα, Sirt1, Nrf2, TXNIP, ZO-1, and Occludin were assessed. In the glyoxal-treated group, cell viability and NO production were decreased, while ROS production and cell apoptosis were increased (p < 0.05), compared with the control group. These changes were prevented by metformin treatment. Protein expressions of phospho-AMPKα, Sirt1, TXNIP, ZO-1, and Occludin, but not Nrf2, were decreased significantly in the glyoxal-treated group compared to normal controls. Metformin treatment significantly increased the above protein expressions and slightly increased TXNIP expression. Immunofluorescence showed that metformin prevented the glyoxal-induced, disorganized tight junctions in ARPE-19 cells. To confirm metformin's protection, Sprague-Dawley rats were injected intravenously with sodium iodate (SI) to induce oxidative stress in the retinal pigment epithelium (RPE). Metformin was then delivered intraperitoneally or intravitreally. One day and three days after SI and metformin treatments, the RPE-Bruch's membrane-choriocapillaris complex was isolated and immune-stained with ZO-1 antibodies. The morphology of the RPE showed enlarged cellular bodies and disorganized ZO-1 staining in SI-treated rats. Metformin treatment prevented these changes. The results indicated that metformin maintained the barrier functions of RPE cells both in vivo and in vitro. Metformin exerted its protection against oxidative stress possibly via activating AMPK/Sirt1 and increasing TXNIP. Metformin has been proposed as a candidate drug for age-related macular degeneration (AMD) by both preclinical and clinical studies. The cellular and animal models used in this study might be useful for the interpretation of the molecular mechanisms involved in the drug activity.

Assessing the compatibility of primary human hepatocyte culture within porous silk sponges

Donor organ shortages have prompted the development of alternative implantable human liver tissues for patients suffering from end-stage liver failure. Purified silk proteins provide desirable features for generating implantable tissues, including sustainable sourcing from insects/arachnids, biocompatibility, tunable mechanical properties and degradation rates, and low immunogenicity upon implantation. While different cell types were previously cultured for weeks within silk-based scaffolds, it remains unclear whether such scaffolds can be used to culture primary human hepatocytes (PHH) isolated from livers. Therefore, here we assessed the compatibility of PHH culture within porous silk scaffolds that enable diffusion of oxygen/nutrients through the pores. We found that incorporation of type I collagen during the fabrication and/or autoclaving of porous silk scaffolds, as opposed to simple adsorption of collagen onto pre-fabricated silk scaffolds, was necessary to enable robust PHH attachment/function. Scaffolds with small pores (73 ± 25 μm) promoted larger PHH spheroids and consequently higher PHH functions than large pores (235 ± 84 μm) for at least 1 month in culture. Further incorporation of supportive fibroblasts into scaffolds enhanced PHH functions up to 5-fold relative to scaffolds with PHHs alone and 2D co-cultures on plastic. Lastly, encapsulating PHHs within protein hydrogels while housed in the silk scaffold led to higher functions than protein hydrogel-only or silk-only controls. In conclusion, porous silk scaffolds containing extracellular matrix proteins can be used for the culture of PHHs ± supportive non-parenchymal cells, which can be further built on in the future to create optimized silk-based liver tissue surrogates for cell-based therapy.

Porous silk scaffolds hybridized with extracellular matrix proteins are useful for culture of primary human hepatocytes ± supportive non-parenchymal cells.