Dysregulated Nutrient Sensing

Slide 1 · Dysregulated Nutrient Sensing

Caloric restriction · IGF-1 / mTOR · Sirtuins

Mechanisms linking nutrient-responsive signaling to cellular aging

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning outcomes

Connect nutrient-responsive signaling with the biology of cellular aging.

Trace growth hormone, IGF-1, mTOR, and rapamycin model.

Explain how sirtuins link metabolic adaptation with stress responses and DNA repair.

Critically distinguish model-organism findings from evidence for human longevity.

Slide 3 · Cellular aging is a mechanistic process

Aging entails progressive loss of cellular function and viability.

Accumulating molecular damage and genetic abnormalities contribute to the decline.

Both cell-intrinsic changes and environmental insults influence the process.

Conserved genetic regulation means aging is not merely passive “wear and tear.”

Slide 4 · Nutrient sensing belongs within cellular aging

DNA damage

Accumulative genome injury

Senescence

Reduced replicative capacity

Protein homeostasis

Loss of folding / clearance

Nutrient sensing

Metabolic signaling modifies aging

Cellular aging

These mechanisms interact; Nutrient sensing is not a stand-alone cause of aging.

Slide 5 · Nutrient sensing: The central concept

Cells respond to nutrient availability by changing metabolism and growth-related programs.

The growth-promoting state is beneficial for tissue function but carries metabolic demands.

The aging literature asks whether reducing selected nutrient-responsive signals changes longevity.

Insulin/IGF-1–mTOR signaling and sirtuins.

Here “dysregulated” refers to nutrient-response pathways in the wider framework of aging.

Slide 6 · From nutrient input to cellular outcome

Nutrient availability

Metabolic context

Nutrient-responsive pathways

IGF-1 / mTOR; Sirtuins

Cellular programs

Growth, stress adaptation, repair

Aging-related outcomes

Function, damage, survival

Pathway activity is a mediator—not a direct measurement of biological age.

Slide 7 · Why study conserved pathways?

Experiments from yeast to mammals identify genetic control of longevity.

Evolutionarily conserved regulation supports a biological mechanism rather than coincidence.

Conservation does not guarantee an identical effect size or safety profile in people.

Interpretation must keep organism, intervention, and outcome distinct.

Slide 8 · Different claims require different evidence

Mechanism

A pathway changes metabolism or cellular repair.

Animal longevity

An intervention extends lifespan in tested models.

Human benefit

A clinical outcome improves safely in people.

Stronger model-organism evidence than definitive human intervention evidence.

Slide 9 · Caloric restriction: Proposed antiaging logic

Lower energy intake

Experimental caloric restriction

Changed sensing

Reduced insulin/IGF-1; Higher sirtuins

Adapted cellular functions

Less growth signaling / improved stress responses

Potential longevity

Demonstrated mainly in models

The pathways are proposed mediators; This is not a prescription for patients.

Slide 10 · What the textbook says about lifespan

Caloric restriction has increased lifespan across tested eukaryotic experimental systems.

Results in nonhuman primates are described as encouraging.

Observations in humans do not establish a general causal longevity effect.

Interventions intended to prolong human life remain largely experimental.

Slide 11 · Interpret caloric-restriction evidence

Evidence base

Defensible interpretation

Tested eukaryotic models

Consistent experimental support for lifespan effects

Nonhuman primates

Encouraging—not equivalent to proven human benefit

Humans

Do not infer lifespan extension from limited observations

Avoid treating species-to-species extrapolation as direct clinical evidence.

Slide 12 · Longevity and healthy aging are related, not identical

Lifespan

Age-related pathology

Time until death is the outcome in lifespan experiments.

Model-organism lifespan is a measurable experimental endpoint.

Disease burden and functional decline represent different outcomes.

MTOR inhibition was reported to reduce age-related pathologic changes in animal models.

Always identify which outcome a study actually measured.

Slide 13 · Nutrient-sensing components

Insulin / IGF-1

Signals nutrient availability and favors anabolic growth.

MTOR

Downstream kinase associated with growth and autophagy control.

Sirtuins

NAD-dependent enzymes that coordinate stress adaptation and repair.

MTOR is a prominent target downstream of IGF-1, not a third independent endocrine circuit.

Slide 14 · Caloric restriction engages two proposed routes

Caloric restriction

Altered nutritional state

IGF-1 signaling ↓

Attenuated anabolic program

Sirtuin activity ↑

Stress and repair adaptation

Longevity phenotype

Model-organism evidence

Parallel proposed pathways may jointly contribute to lifespan effects in models.

Slide 15 · Growth hormone links pituitary to IGF-1

Anterior pituitary

Growth hormone secretion

Responsive cell types

IGF-1 production

Target-cell signaling

Insulin-like intracellular response

Metabolic program

Anabolism, growth, replication

IGF-1 production in many cell types.

Slide 16 · IGF-1 production is not confined to one tissue

Multiple cell types can synthesize IGF-1 in response to growth hormone.

IGF-1 is part of the growth hormone–responsive cellular signaling network.

For this lecture, its relevance is the link between systemic nutrition and cell growth.

Aging effects are inferred from altered signaling intensity rather than IGF-1 abundance alone.

Slide 17 · IGF-1 resembles insulin at the signaling level

IGF-1 activates intracellular signals similar to those activated by insulin.

account, this informs cells about glucose availability.

The resulting response favors anabolic metabolism.

Anabolic signaling also supports cellular growth and replication.

Slide 18 · What an anabolic IGF-1 signal accomplishes

IGF-1 input

Nutrient / growth cue

Intracellular signaling

Insulin-like response

Anabolic state

Biosynthetic orientation

Cellular response

Growth and replication

Anabolism is an adaptive physiological program, not intrinsically pathological.

Slide 19 · Growth and metabolism: Linked responses

Strong IGF-1 signaling

Attenuated signaling

Favors anabolic activity.

Promotes cell growth and replication.

Reflects a nutrient-available state.

Associated with less cell growth.

Associated with lower metabolic activity.

May reduce subsequent cellular damage.

Slide 20 · Attenuation is not the same as elimination

The longevity association concerns reduced intensity of IGF-1 signaling.

Normal IGF-1 pathways are involved in legitimate growth and metabolic functions.

The textbook does not propose total blockade as a human therapeutic goal.

A lower-signal phenotype must be interpreted within the experimental context.

Slide 21 · Why less growth signaling may favor longevity

IGF-1 signaling ↓

Attenuation

Cell growth ↓

Less anabolic drive

Metabolic rate ↓

Lower metabolic demands

Cellular damage? ↓

Plausible explanation

Robbins explicitly qualifies reduced cellular damage as a possibility, not a settled mechanism.

Slide 22 · IGF-1 evidence: Fact versus proposal

Textbook statement

Interpretation

IGF-1 responds to growth hormone

Established source relationship

IGF-1 favors growth and replication

Established physiologic role in this account

Attenuation lowers growth / metabolism

Model-supported response

Reduced damage explains longevity

Plausible; Stated cautiously

Slide 23 · IGF-1 has several downstream effects

Anabolism

Biosynthetic program

Growth

Cell size / activity

Replication

Proliferative response

MTOR

Important downstream kinase

IGF-1 signaling

Do not simplify all IGF-1 effects into a single mTOR-only route.

Slide 24 · MTOR is a prominent nutrient-responsive kinase

MTOR stands for mechanistic target of rapamycin.

It as a major downstream kinase in IGF-1 signaling.

It connects the growth-response network with cellular maintenance pathways.

The aging literature examines how reducing mTOR activity changes outcomes.

Slide 25 · The IGF-1–mTOR axis

Growth hormone

Systemic input

IGF-1

Growth-related signal

MTOR

Downstream kinase

Anabolic / maintenance balance

Cellular consequences

Schematic summary; Other downstream signaling targets are not shown.

Slide 26 · Rapamycin: Experimentally perturbing mTOR

Rapamycin

Pharmacologic intervention

MTOR inhibition

Lower kinase activity

Cellular responses

Includes promotion of autophagy

Model outcomes

Lifespan / pathology changes

A drug effect in an animal experiment is not evidence of safe preventive use in humans.

Slide 27 · Rapamycin and longevity in animal models

Extended lifespan with mTOR inhibition in diverse animal models.

It specifically notes benefit after administration to middle-aged mice.

Rapamycin affects several cellular processes; Autophagy is among them.

The observed lifespan result does not identify one exclusive mediator.

Slide 28 · Rapamycin and age-associated pathology

In animal models, mTOR inhibition can reduce age-related pathological changes.

This is a different endpoint from lifespan extension.

Interpret both benefits at the level of the organism and experimental design.

The text does not establish a standard antiaging treatment for healthy people.

Slide 29 · How mTOR inhibition connects to autophagy

MTOR activity ↓

E.g., rapamycin

Autophagy promoted

Cellular recycling

Damaged components cleared

Maintenance of protein quality

Age-related consequences

Investigated experimentally

The source states promotion of autophagy; Causal attribution of all longevity effects remains broader.

Slide 30 · Protein homeostasis depends on two systems

Keep proteins folded

Clear unsuitable proteins

Molecular chaperones maintain correct protein conformations.

Heat-shock protein chaperones provide experimental aging examples.

Autophagy–lysosome removes material for degradation.

Ubiquitin–proteasome degrades selected unwanted proteins.

Slide 31 · Chaperones protect the functional proteome

New / stressed proteins

Folding challenge

Molecular chaperones

Maintain conformation

Correctly folded proteins

Perform cell functions

Cellular proteostasis

Functional proteome sustained

Impaired folding is one recognized contributor to aging-related proteostasis failure.

Slide 32 · Two clearance routes remove unsuitable proteins

Damaged / unneeded proteins

Quality-control substrates

Autophagy–lysosome

One degradation route

Ubiquitin–proteasome

Another degradation route

Proteome maintenance

Quality control supported

Parallel disposal systems contribute to protein homeostasis.

Slide 33 · Proteostasis deteriorates with aging

Both correct protein folding and disposal of damaged proteins become less efficient.

Experimental chaperone deficiency accelerates aging in mice.

Chaperone overexpression has been associated with longer life in mice.

Similar model-based evidence implicates autophagy and proteasomal degradation.

Slide 34 · When misfolded proteins accumulate

Proteostasis impaired

Folding or clearance failure

Misfolded proteins ↑

Intracellular burden

Cell function compromised

Homeostatic stress

Apoptosis may follow

Cell loss in severe states

This is a cellular pathology consequence—not a histologic test for “nutrient-sensing disease.”

Slide 35 · MTOR inhibition has multiple effects

Autophagy

May be promoted

Protein turnover

Maintenance pathway affected

Growth response

Anabolic signaling reduced

Longevity

Model-organism outcome

MTOR activity ↓

Do not claim that autophagy alone accounts for all observed survival benefits.

Slide 36 · Sirtuins are NAD-dependent deacetylases

Sirtuins are a family of NAD-dependent protein deacetylases.

They respond to environmental and metabolic stresses.

Their roles extend beyond one substrate or one cellular compartment.

In the source model, higher sirtuin activity is proposed to contribute to caloric-restriction effects.

Slide 37 · Three defining properties of sirtuins

Enzyme family

At least seven types are described in mammals.

NAD dependent

Activity is coupled to a metabolic cofactor.

Distinct roles

Compartmental distribution and nonredundant functions.

Slide 38 · Sirtuin diversity limits simple generalizations

Mammalian sirtuins occupy different cellular compartments.

Their functions are not interchangeable.

An effect attributed to one sirtuin need not apply to all seven.

The text highlights sirtuin-6 for combined metabolic and genome-maintenance functions.

Slide 39 · Food deprivation recruits adaptive responses

Food deprivation

Environmental stress

Sirtuin responses

Metabolic adjustment

Gene-expression programs

Adaptive proteins produced

Cellular resilience

Potential benefit

This is a proposed framework for caloric-restriction adaptation.

Slide 40 · DNA damage is also a sirtuin-related stimulus

DNA damage

Genotoxic stress

Sirtuin-associated adaptation

Stress response

DNA repair machinery

Some enzymes activated

Genomic integrity

Maintenance outcome

Robbins particularly emphasizes sirtuin-6 in activating DNA repair enzymes.

Slide 41 · Sirtuins influence several adaptive outputs

Metabolism

Restrict selected metabolic activity

Survival

Reduce apoptosis in stated contexts

Protein quality

Promote folding programs

Oxidative injury

Counteract ROS effects

Sirtuins

These are source-described effects of regulated gene expression—not unconditional effects in every tissue.

Slide 42 · Sirtuins and metabolic restraint

Sirtuin-dependent gene programs may inhibit metabolic activity.

A lower metabolic program may aid adaptation to food limitation.

This complements the decline in growth-related IGF-1 signaling.

Such interactions are presented as candidate explanations of longevity.

Slide 43 · Sirtuins and apoptosis

Decreased apoptosis among sirtuin-associated adaptive effects.

A stress-survival response can preserve viable cells during adverse conditions.

This does not mean blocking apoptosis is universally beneficial.

Cellular context remains essential when interpreting any antiapoptotic signal.

Slide 44 · Sirtuins and protein folding

Sirtuin response

Stress-adaptation signaling

Gene-expression effects

Protein-quality programs

Protein folding ↑

Fewer misfolded species

Homeostasis supported

Functional proteins maintained

Connect this route to the parallel aging mechanism of defective protein homeostasis.

Slide 45 · Counteracting oxygen-radical injury

Oxidative stress

Harmful free radicals

Sirtuin-regulated proteins

Protective response

Harmful ROS effects ↓

Reduced injury pressure

Cell preservation

Proposed benefit

The textbook does not provide a numerical ROS reduction or a human effect size.

Slide 46 · Sirtuins and glucose handling

The source states that sirtuins can increase insulin sensitivity.

It also describes effects that increase glucose metabolism.

These actions create therapeutic interest in diabetes.

A plausible disease target is not the same as validated clinical efficacy.

Slide 47 · Sirtuin-6 has two important roles

Nutritional adaptation

Genome preservation

Helps mediate metabolic changes during caloric restriction.

Places nutrient availability in a cellular stress-response context.

Promotes genomic integrity.

Activates DNA repair enzymes through deacylation.

This dual function is explicitly emphasized.

Slide 48 · Sirtuin-6 connects enzyme activity to repair

Sirtuin-6

Deacylation activity

DNA repair enzymes

Activation

Damage repair

Genome maintenance

Genomic integrity

Aging-relevant consequence

The text specifies deacylation here; Do not replace it with an invented detailed molecular cascade.

Slide 49 · Sirtuins bridge distinct aging mechanisms

Metabolic response

Adaptation during reduced nutrient intake.

Protein homeostasis

Support protein-folding responses.

DNA integrity

Activate repair machinery, particularly via sirtuin-6.

Slide 50 · IGF-1/mTOR and sirtuins are complementary

Dimension

IGF-1 / mTOR axis

Sirtuins

Primary function

Signals nutrients and growth

Adapts to deprivation / stress

Restriction model

Signal intensity decreases

Activity increases

Main source outputs

Less growth, altered autophagy

Metabolic adjustment, folding, repair

Human clinical status

Experimental longevity strategies

Experimental longevity strategies

This is a model-specific comparison—not a binary “bad vs good” classification.

Slide 51 · Integrated proposed response to caloric restriction

Caloric restriction

Nutritional perturbation

IGF-1 / mTOR signaling ↓

Less anabolic drive

Sirtuin adaptations ↑

Stress response / repair

Cell maintenance

Potential aging benefit

The branches are conceptual responses, not a demonstrated linear cascade.

Slide 52 · Mechanisms of aging converge on cell function

DNA damage

Mutations / impaired repair

Senescence

Limited proliferation

Proteostasis loss

Misfolded proteins

Nutrient sensing

Changes in growth / stress programs

Reduced cell function

Different proximal mechanisms can converge on cell dysfunction and cell loss.

Slide 53 · Aging links cellular changes to organ disease

Molecular damage + dysregulation

Multiple pathways

Cell dysfunction / loss

Tissue-level effects

Declining tissue function

Reduced reserve

Age-associated disease

Greater susceptibility

Atherosclerosis and type 2 diabetes as illustrative chronic-disease consequences.

Slide 54 · Nutrient sensing has no unique diagnostic morphology

IGF-1/mTOR and sirtuin activity are biochemical signaling states, not standalone histologic entities.

Morphologic manifestations are indirect and depend on the tissue and broader disease process.

Microscopy cannot, by itself, establish a causal nutrient-sensing defect.

Interpret claims using pathway biology, model system, and relevant clinical endpoints.

No synthetic H&E or immunostain is presented as evidence for this abstract mechanism.

Slide 55 · Match the claim to the evidence

Claim

Evidence

Caloric restriction prolongs life

Strong model-organism evidence; Primate findings encouraging

Reduced mTOR improves aging phenotypes

Animal lifespan and pathology outcomes

Sirtuins affect stress responses

Experimental molecular and model-system findings

Antiaging medication extends human life

Not established in the supplied section

Slide 56 · The clinical translation remains unresolved

The textbook cautions that longevity interventions remain largely experimental.

Long-term human safety and efficacy are not fully understood.

Rapamycin animal findings do not justify routine preventive administration.

Sirtuin-based approaches are mechanistically interesting but not proven longevity therapies.

Slide 57 · A popular claim is not a therapeutic conclusion

The source mentions publicity about a red-wine constituent and sirtuin activation.

A biochemical possibility does not establish a lifespan effect in humans.

Food or supplement narratives cannot replace controlled clinical outcome studies.

Keep proposed targets separate from validated interventions.

Slide 58 · Application: Reduced IGF-1 signaling

An experimental model shows lower IGF-1 signaling and reduced rates of cell growth and metabolism. Which proposed aging mechanism is most consistent with this phenotype?

A. Intensified anabolic drive

B. Attenuation of nutrient-responsive growth signaling

C. Loss of all growth hormone production

D. A specific histologic pattern of nutrient-sensing failure

Slide 59 · Application answer: Attenuation of growth signaling

Correct: B. Lower IGF-1 activity attenuates nutrient-responsive growth signals.

The text links this to lower growth and metabolic activity.

Reduced cellular damage remains a proposed explanation, not a demonstrated necessity.

The scenario alone says nothing about a diagnostic morphology or human treatment.

Slide 60 · Application: Rapamycin and experimental aging

A mouse study reports longer lifespan after rapamycin exposure. What inference is best supported by the Robbins discussion?

A. All human aging pathways are now explained

B. MTOR inhibition can influence lifespan in animal models

C. Autophagy is proven to be the only causal mediator

D. Long-term preventive therapy is established in humans

Slide 61 · Application answer: Identify the evidence level

Correct: B. Animal models support a longevity effect of mTOR inhibition.

Rapamycin has multiple biological effects, including increased autophagy.

A single observed outcome does not establish a unique mechanism.

Human safety, benefit, and suitable clinical application remain separate questions.

Slide 62 · Synthesize the chapter model

Nutrient sensing

IGF-1 / mTOR; Sirtuins

Metabolic choice

Growth vs adaptation

Cell quality control

Protein folding, autophagy, DNA repair

Aging phenotype

Function, pathology, survival

The strongest argument is mechanistic coherence plus animal experiments; Clinical translation requires direct testing.

Slide 63 · Five conclusions to retain

Caloric restriction is linked to longer lifespan in experimental eukaryotic systems.

Reduced insulin/IGF-1–mTOR signaling is a major proposed mediator.

MTOR inhibition can extend lifespan and modify age-related pathology in animal models.

Sirtuins coordinate adaptive metabolism, proteostasis, and genome maintenance.

None of these results by itself proves a safe human antiaging treatment.

Slide 64 · Selected source

Robbins, Cotran & Kumar

Pathologic Basis of Disease

Cell Injury, Cell Death, and Adaptations

Cellular Aging — Dysregulated Nutrient Sensing

Diagrams are original, editable teaching schematics.