U.V LIGHT SUPPRESSION + vitamin D receptor

for ANSC454 -- Includes: information on the article + figure

Figure 1 — Sc5d knockout mice (precursor deficiency)

• briefly interpret it

• main takeaway → preventing the synthesis of the vitamin D precursor in skin keratinocytes does NOT block UV light from suppressing EAE

  • A → both WT + Sc5d knockout control mice developed severe EAE

    • after daily exposure to UV → significantly suppressed EAE disease scores equally

  • B → total disease burden is reduced to the same extent in UV-treated WT + Sc5d knockout groups compared to their respective unexposed controls

  • C → the % of mice developing disease drops significantly following UV treatment regardless of whether the mice can produce 7-DHC

Figure 2 — Cyp27B1 + VDR knockout mice (enzyme + receptor deficiency)

• briefly interpret it

• main takeaway → neither the enzyme that produces active vitamin D or VDR is required for UV light to suppress EAE

  • A → Cyp27B1 knockout mice shows significant EAE disease suppression under UV-NB

    • mirrors protection seen in WT mice

  • B → VDR knockout mise display near-complete suppression of EAE symptoms when treated w/ UV lights compared to untreated VDR controls

Figure 3 — UV validation + confirmation of complete knockout

• briefly interpret it

• main takeaway → confirms that while UV exposure can synthesise vitamin D + restore calcium in normal mice, Sc5d knockout mice are genuinely blocked from producing vitamin D → proves that UV protection operates through an independent pathway

  • A → shows the spectral output of the light bulb w/ a sharp emission peak at 311-312 nm

  • B → UV light exposure restores normal serum calcium levels in vitamin D-deficient WT mice over 10 days

  • C → UV light increases serum 25(OH)D3 in WT mice whereas it remains below detection in Sc5d knockout mice

Figure 4 — Low Dose UV light responsiveness

• briefly interpret it

• main takeaway → narrow band UV light suppresses EAE in a dose-dependent manner

  • daily exposure to either 2kJ or 5 kJ of UV light significantly reduces EAE disease scores compared to unexposed controls

    • 5 kJ dose providing near-total suppression of disease onset

What is Multiple Sclerosis (MS)?

• an autoimmune disorder → no known cure

• characterised → overactive host immune response that targets + destroy the myelin sheath insulating axons in the CNS

  • specifically the brain + spinal chord

  • leads to loss of muscle control, impaired vision → leaves individuals unable to walk

• affects 2.5 million people → more common in women

What are some genetic factors linked to MS?

• strongly associated w/ specific immune recognition genes

  • particulary → HLA-DR2: encodes proteins responsible for binding + presenting antigens

What is Experimental Autoimmune Encephalomyelitis (EAE)?

• the standard mouse model used to study human MS demyelinating pathology + potential therapeutic interventions

• like MS → severe spinal cord inflammation + demyelination

  • causes quantifiable paralysis + motor dysfunctions

What are some historical Vitamin D assumptions?

• Latitude Gradient

  • studies established a strong correlation between geographical latitude + MS risk

  • Populations closer to the equator had lower incidences of MS

    • presumably because they received higher solar exposure

• Assumed Mechanism

  • Since UV radiation triggers synthesis of pre-vitamin D3 → credited the effects of sunlight on MD are credited entirely to increased vitamin D production

• Neglect of Light

  • led to widespread promotion of oral vitamin D supplementation as a potential preventative/therapeutic measure

    • overlooking the effect of the UV light itself

Physiological Metabolism of Vitamin D

• 7 DHC

  • activated by Sc5D enzyme in keratinocytes + UVB light

• Vitamin D3

  • hydroxylated in the liver

• 25-hydroxyvitamin D3

  • hydroxylated in the kidney by Cyp27B1 enzyme

• 1,25-dihydroxyvitamin D2 (Active form)

  • binds to vitamin D receptor (VDR)

• Downstream gene expression + intestinal calcium transport

What is VDR’s role?

• upregulates calcium-binding proteins + transport channels

  • drives calcium pumps that move Ca2+ from the intestinal lumen into the bloodstream

What happens if there is an absence of active vitamin D or functional VDR?

• impairs calcium uptake → leads to hypocalcemia + reduced bone mineral density

What drove them to make this study?

• prior observations → UVB light can suppress EAE symptoms independently of circulating vitamin D levels

• wants to figure out → is vitamin D synthesis, enzyme conversion (Cyp27B1), or VDR required for UV phototherapy to suppress autoimmune demyelination in vivo

Cre-LoxP system

• idea → global knockouts of essential developmental genes often cause embryonic lethality

  • can’t do functional analysis in adult tissue

• floxed genes → LoxP targets DNA sequences that flank the gene of interest

• tissue specificity → cre-recombinase expression is placed under the control of a tissue-specific promoter

  • cre-recombinase → recombines/digests/inverts the floxed sequence specifically within cells expressing that promoter

    • leaves the target gene intact in non-targeed tissue types

What is the Keratinocyte-specific Sc5d knockout model for?

• gene → encodes an essential enzyme required to produce 7-DHC

  • Important precursor to pre-vitamin D3 synthesis in skin

• study purpose → generates mice completely incapable of synthesising pre-vitamin D3 in epidermal keratinocytes upon UV exposure

What is the global Cyp27B1 knockout models for?

• gene → encodes 1-(alpha)- hydroxylase: enzyme responsible for converting 25-hydroxyvitamin D3 into active 1,25-(OH)2D3 in the kidney

• study purpose → eliminates the organism’s ability to produce the biologically active vitamin D3 hormone even if precursors are present

What is the global VDR knockout models for?

• gene → encodes the nuclear VDR which is required for all classic vitamin D genomic signaling + calcium transport regulation

• study purpose → eliminates all downstream vitamin D signaling pathway throughout the entire body (no chance for vitamin D functionality)

• note → maintained on specialised high-calcium diet to prevent hypocalcemia + metabolic bone pathology

What is MOG and what was it used for?

• the antigen (sequence) that host immune system from the pathogen source

  • injected this peptide to induce MS conditions

    • along w/ bacteria into the source to start the immune response

What are the foundings of the experiment?

• UVB lights do help suppression of EAE disease suppression

• vitamin D had no effect on disease suppression

New Questions + Next Investigations arising from the Article

• What is the primary skin-derived mediator transmitting the UV signal to the CNS?

  • systematically test candidate skin photoproducts/signaling cascades activated by 300-315 nm light → like NO synthesis, photoisomerised UCA, or neuroendocrine factors like endorpins, serotonin, and melanin

• How does local skin irradiation modulate systemic neuroinflammation?

  • Trace skin-resident immune cells (i.e., regulatory T cells) following UV-light exposure to determine whether they migrate to systemic lymph nodes or the CNS to suppress auto-reactive T-cell attack on myelin

• Are current clinical recommendations for MS incomplete?

  • Re-evaluate clinical trials comparing oral vitamin D supplementation against controlled UV phototherapy.

  • since vitamin D supplements do NOT replicate the non-vitamin D pathways induced by UVB light → researchers must investigate whether phototherapy or novel non-vitamin D therapeutics provide superior disease protection

Sample Exam Question — Can we propose that EAE progression/suppression is independent of calcium levels?

• YES!

  • active vitamin D → typically binds to the VDR to upregulate calcium transporters + maintain serum calcium levels.

    • Sc5d knockout mice exposed to UV-NB, serum 259OH)D3 remains below detection limites because precursor synthesis is also blocked.

  • even w/ vitamin D synthesis, activation + signalling blocked, or when special calcium diets are supplied to maintain baseline survival → UV-light exposure still achieves an equivalent ~80% suppression of EAE symptoms

• UV-light protects against auto-reactive neuroinflammation through a non-calcium, non-vitamin D mechanism.