Mammalian Cell Culture and Growth Conditions Study Notes
Mammalian Cell Growth Conditions
Temperature Maintenance
Mammalian cell cultures must be maintained at a temperature of 37°C.
This is crucial for simulating physiological conditions for cell growth and replication.
Aseptic Techniques
Essential to apply aseptic techniques while working with cell cultures.
Practices include:
Wearing Personal Protective Equipment (PPE)
Sterilizing equipment to prevent contamination.
Culture Media Requirements
Cells require suitable media containing nutrients and growth factors for growth.
Composition of Cell Culture Media:
Nutrients:
Complex mixtures of:
Salts
Carbohydrates
Vitamins
Amino acids
Metabolic precursors
Growth factors
Hormones
Trace elements
Key role of media is to maintain pH and osmolality in the culture system:
pH Maintenance:
Achieved using buffering systems such as:
CO₂/sodium bicarbonate
Phosphate
HEPES
Phenol red is often added as a pH indicator to monitor changes in pH colorimetric ally.
Commonly Used Culture Media
Basic Components of Cell Culture Media:
Energy Sources:
Glucose
Pyruvate
Lipids
Salts/Ions:
Sodium (Na⁺), Potassium (K⁺), Calcium (Ca²⁺), Magnesium (Mg²⁺), Chloride (Cl⁻), Bicarbonate (HCO₃⁻), Phosphate (PO₄³⁻)
Vitamins:
B-complex (e.g., B1, B2, B6, B12), Vitamin C, sometimes Vitamin E.
Amino Acids:
Essential and non-essential amino acids.
Trace Elements & Growth Factors:
Required for enzyme function and signaling processes.
Basic Nutrients in Cell Culture Media
Glucose
Serves as the main energy source for glycolysis and ATP production.
Pyruvate:
Occasionally included as a supplementary energy substrate.
Glycolysis:
A crucial pathway occurring in the cytoplasm, invariant to oxygen availability:
Anaerobic glycolysis: Produces 2 ATP and converts glucose into lactate.
Aerobic glycolysis: Converts glucose into carbon dioxide and water, yielding 38 ATP molecules.
Carbohydrate Substitutes:
Occasionally, glucose is replaced by galactose to minimize lactic acid accumulation since galactose is metabolized slower.
Lipids in Cell Culture Media
Functions of Lipids:
Membrane synthesis (for plasma membranes and organelles)
Energy storage (in the form of triacylglycerols/fats)
Synthesis of signaling molecules (steroids, eicosanoids)
Fatty Acid Oxidation:
Beta-oxidation breaks down fatty acids into acetyl-CoA for ATP generation.
Provides key energy sources especially during fasting, exercise, or when energy demands spike.
Type of Lipids Used:
Fatty acids (saturated and unsaturated)
Examples: palmitic acid, oleic acid, linoleic acid
Cholesterol
Maintains membrane fluidity and integrity; serves as a precursor for steroid hormones.
Phospholipids for membrane assembly
Examples: phosphatidylcholine, phosphatidylethanolamine
Lipid carriers/emulsifiers such as Albumin (BSA) or cyclodextrins to improve lipid delivery.
Salts / Inorganic Ions in Cell Culture Media
Importance of Ions and Salts:
Salts maintain osmotic balance, pH stability, and membrane potential within cell cultures.
Common Ion Types:
Sodium (Na⁺): Maintains fluid balance and membrane potential.
Potassium (K⁺): Essential for membrane potential and enzyme activity.
Calcium (Ca²⁺): Integral to cellular signaling and adhesion.
Magnesium (Mg²⁺): A cofactor vital for enzyme functions and nucleic acid synthesis.
Chloride (Cl⁻): Helps maintain electrical neutrality and charge balance.
Bicarbonate (HCO₃⁻): Acts as a primary pH buffer in conjunction with CO₂ in the incubator.
Phosphate (PO₄³⁻): Involved in energy metabolism (ATP) and nucleic acid functions.
Osmotic Balance:
Cells must maintain water balance to prevent lysis (swelling) or shriveling (shrinking).
pH Buffering Overview
pH Optimal Range:
Cellular enzymes operate within a narrow pH range (~7.2–7.4).
Consequences of pH Deviations:
Denaturation of enzyme structures.
Altered lipid and protein charge, destabilizing membranes.
Disruption of ion gradients affecting nutrient transport.
Physiological pH Maintenance:
Achieved using bicarbonate and other buffers to stabilize electrical properties.
pH Buffering – CO₂-Dependent Media
Lifespan Limitation of Primary Cells:
Maintains genomic stability and prevents uncontrolled proliferation by supporting telomere shortening mechanisms.
Experimental Considerations:
Defines the number of passages cells can undergo before senescence impacts results.
Effective in stem cell research allowing bypass of Hayflick limit via telomerase activation.
Cell Growth Dynamics:
Characteristic growth curve phase variations include lag, exponential, plateau, and decline, with implications on experimental design.
Bicarbonate and pH Stabilization
Chemical Dynamics of pH Changes:
In cases of excessive H⁺:
Alkaline shift due to drop in H⁺:
Bicarbonate Level Effects:
Elevated bicarbonate leads to excessive alkalinity when CO₂ diffuses away, worsening pH stability.
Lower bicarbonate levels curb excess alkalinity and allow more controlled pH variations.
CO₂ Independent Media
Characteristics:
Designed to maintain physiological pH in reduced CO₂ conditions through alternative buffering agents instead of relying on bicarbonate.
Common Strategies:
Good’s Buffers (e.g., HEPES):
Resists pH changes due to weak acid/base properties.
Phosphate Buffers:
Maintain pH via dissociation in relation to H⁺ concentrations.
Amino Acid Buffers:
Minor buffering capabilities by utilizing free amino acids.
Potential Limitations:
HEPES phototoxicity and metabolic effects on cell types.
Membrane Potential
Significance of Resting Potential:
Crucial for nutrient transport signaling, ion regulation, and cell excitability.
Ion Distribution:
Potassium (K⁺) is predominant inside cells, while Sodium (Na⁺) is higher outside, creating a voltage difference across the membrane maintained by Na⁺/K⁺ ATPase activity.
Vitamins in Cell Culture Media
Role of Vitamins:
Essential as enzyme cofactors for metabolism, DNA synthesis, and redox stability.
Examples of Key Vitamins:
B1 (Thiamine):
Active as Thiamine pyrophosphate for sugar breakdown.
B2 (Riboflavin):
Active in FAD and FMN for electron transfer during metabolism.
B3 (Niacin):
Functions as NAD⁺/NADP⁺ in electron transport.
B6 (Pyridoxine):
Works as Pyridoxal phosphate in amino acid metabolism
B12 (Cobalamin):
Critical for DNA synthesis and metabolic processes.
Amino Acids in Cell Culture Media
Necessity of Amino Acids:
Required for protein and enzyme synthesis. Consist of essential and non-essential amino acids; essential types must be included in culture media.
Examples of Essential Amino Acids:
L-Arginine, L-Histidine, L-Isoleucine, L-Leucine, L-Lysine, L-Methionine, L-Phenylalanine, L-Threonine, L-Tryptophan, L-Valine.
Amino Acid Structure:
Comprised of:
Amino group (H₂N)
Carboxyl group (COOH)
R-group / Side Chain, which varies across amino acids, determining their specific properties.
Trace Elements and Other Components
Trace Elements in Cell Culture:
Essential as enzyme cofactors including iron, zinc, selenium, and copper.
Additional Factors in Media:
Potassium and ferric nitrates serving as nitrogen sources for nucleic acid synthesis.
Phenol Red:
A pH indicator that visually demonstrates pH changes during cell growth by changing coloration to yellow at low pH and purple at high pH.
Animal Sera in Cell Culture Media
Role of Sera:
Provides essential nutrients including amino acids, proteins, vitamins, carbohydrates, lipids, hormones, growth factors, nutrients, and attachment factors.
Buffers culture medium and protects against proteolytic enzyme activity.
Variability of Composition:
Composition varies and often consists of undefined components; however, batch-to-batch consistency has improved.
Sources of Serum:
Fetal bovine serum offers rich growth-promoting properties;
Calf serum provides lower activity, while horse serum from controlled environments reduces contamination risks.
Handling Animal Sera
Storage Conditions:
Keep at −20°C to maintain integrity and avoid freeze-thaw cycles.
Thawing Process:
Initiate thawing at controlled temperatures to prevent precipitation.
Turbidity Considerations:
Fibrinogen presence may lead to turbidity when thawed, typically harmless and can be filtered if necessary.
Mammalian Cell Culture Support Systems – Basement Membrane
Specialized Surface Treatment Importance:
Necessary for cell differentiation and maintenance in a culture setting.
Basement Membrane Mid-Phase Treatment:
Promotes cell adhesion and remaining integral to cellular functions.
Common Substrates:
Matrigel, Vitronectin, and recombinant laminins are agents used to facilitate establishing baseline culture conditions.
Feeder Layers in Cell Cultures
Importance of Feeder Layer Cells:
Provide essential growth conditions by supplying ECM and dietary factors; create an environment that mimics in vivo conditions.
Feeder Cell Types:
Examples include mouse embryonic fibroblasts (MEFs) and human fibroblasts which enhance target cell survival and proliferation.
Prevention of Overgrowth:
Growth is inhibited via treatments with mitomycin C or irradiation.
Commonly Used Media for Cell Culture
Overview of Specific Media:
Eagle’s Minimum Essential Medium (EMEM): Standard basal medium with simple composition.
Dulbecco’s Modified Eagle’s Medium (DMEM): Enhanced medium supporting a wide range of mammalian cells, enriched with vitamins and amino acids.
Iscove's Modified Dulbecco's Medium (IMDM): Utilized for lymphocyte cultures, containing rich supplement compositions.
Key Features:
Sodium bicarbonate content and CO₂ requirements are fundamental for each medium type.
Media Requirements for Human Induced Pluripotent Stem Cells (iPSCs)
Base Medium Specifications:
Pluripotent Stem Cell SFM XF/FF is pivotal for maintaining iPSCs in a healthy undifferentiated state.
Reprogramming Process:
Derived from fibroblasts expressing specific transcription factors for enhanced self-renewal.
Components for Maintenance:
Growth factors, specific nutrients, and distinct media formulations to enhance pluripotent capacity.
This enables reproducible and less variability for iPSCs culture
ROCK Inhibition
A temporary survival enhancer used during passaging
Inhibits Rho-associated kinase (ROCK)
Prevents apoptosis (anoikis) that occurs when IPSCs are dissociated
Apoptosis occurs when anchorage-dependent cells lose contact with the ECM (anoikis)
Loss of adhesion triggers activation of the RhoA-Rock signaling pathway, which in turn leads to excessive cytoskeletal tension and mechanical stress
ROCK inhibition reduces cytoskeletal tension, stabilizes cell morphology, and prevents anoikis
Characteristics of iPSCs in Culture
Morphology:
iPSCs exhibit characteristic round colonies with tightly packed cells, indicative of high proliferation and transcriptional activity.
when grown with Pluripotent Stem Sell SFM XF/FF (feeder free medium)
Nuclear-Cytoplasmic Ratios:
High N:C ratio suggests stem cell characteristics with implications for cell function in culture.
Media Requirements for Human Embryonic Stem Cells (hESCs)
Base Medium Composition:
Mixture of DMEM and Ham's F-12 with essential supplements ensuring hESCs are maintained in an undifferentiated state.
Specific Components:
Sodium bicarbonate for pH stability, along with L-glutamine and HEPES as buffers.
Supplement Requirements:
Inclusion of basic fibroblast growth factor to promote self-renewal and inhibit differentiation.
Neuronal Stem Cells (NSCs) Media Requirements
General Characteristics:
NSCs serve as multipotent stem cells within the nervous system, requiring specific growth conditions.
Nutritional Needs:
Defined media utilizing supplements for vitamins, antioxidants, and specific growth factors essential to maintain stemness and function.