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Anti-inflammatory role of MerTK in the RPE independent of diurnal outer segment phagocytosis

Award Number: R21EY033188
ORGANIZATION: NATIONAL EYE INSTITUTE
OPDIV: NIH
AWARD CLASS: DISCRETIONARY
AWARD ACTIVITY TYPE: SCIENTIFIC/HEALTH RESEARCH (INCLUDES SURVEYS)
PERIOD OF PERFORMANCE START DATE: 09/01/2021
PERIOD OF PERFORMANCE END DATE: 07/31/2024

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Anti-inflammatory role of MerTK in the RPE independent of diurnal outer segment phagocytosis - Diurnal RPE phagocytosis is an essential aspect of lifelong continuous renewal of photoreceptor outer segments. Phagocytosis of distal photoreceptor outer segment tips requires activity of RPE surface receptors of the TAM (Tyro3/Axl/MerTK) receptor tyrosine kinase family. In human patients, mutations in the mertk gene cause an unusually severe form of retinitis pigmentosa with blindness in teenage years. The retina in mice and rats lacking MerTK develops normally but rapidly degenerates postnatally, with onset of photoreceptor death before 4 weeks of age. Neuroinflammation and specifically activation and redistribution of retinal microglia has been reported in adult MerTK-deficient animals and has been assumed to be a consequence of photoreceptor distress and debris accumulation caused by lack of daily clearance phagocytosis of spent outer segment tips by the RPE. However, we find that, surprisingly, robust increase in pro-inflammatory cytokines and microglia activation in MerTK-deficient rat and mouse retina precede postnatal onset of photoreceptor outer segment renewal and daily RPE phagocytosis. Moreover, our results show that anti-inflammatory treatment is effective in preventing microglia activation and extending photoreceptor survival and function only if applied at early postnatal age several days prior to the onset of diurnal outer segment renewal and RPE phagocytosis. In wild- type retina, MerTK is expressed early postnatally and mainly by the RPE (and not detected in microglia). This implies that loss of MerTK affects the RPE specifically, directly and before outer segment renewal begins. Thus, all available evidence supports microglia stimulation by MerTK-deficient RPE independently of RPE phagocytic activity and outer segment renewal. Here, we propose highly focused, key proof-of-principle pilot studies to rigorously scrutinize our completely novel concept that lack of MerTK in itself and unrelated to RPE phagocytosis causes RPE cells to release a pro-inflammatory cytokine, which elicits early onset, harmful neuroinflammation that in turn accelerates photoreceptor dysfunction and demise. We will test our hypothesis in 3 independent specific aims. Aim 1 will explore double mutant mice we just generated to test if cytokine is required for neuroinflammation in mertk-/- retina. Aim 2 will explore if inducing cytokine loss in the RPE alone is sufficient to eliminate early postnatal harmful neuroinflammation and whether cytokine mediator must be expressed early postnatally to induce neuroinflammation in mertk-/- retina. Aim 3 will explore polarized, differentiated RPE cell models (primary, unpassaged wild-type and MerTK-deficient RPE and passage 1 human RPE cells) to determine whether MerTK expression and its kinase signaling activity are directly linked mechanistically to cytokine transcription, translation, and/or release by RPE cells. Upon completion, this pilot study will have yielded unambiguous confirmation or disproof of our novel hypothesis and generated in vivo and culture models for large scope mechanistic and pre-translational follow-up.


Issue Date FY	Funding FY	Legal Entity Name	Legal Entity Address	Legal Entity City	Legal Entity State	Legal Entity Zip Code	Legal Entity COUNTY	Legal Entity COUNTRY	Assistance Listing	Award Code	Budget Year	Action Date	Action Type	Action Amount

Issue Date FY: 2025 ( Subtotal = -$9,274 )
2025	2022	FORDHAM UNIVERSITY	441 E FORDHAM RD	BRONX	NY	10458	BRONX	USA	Vision Research	000	2	3/18/2025	NON-COMPETING CONTINUATION	-$9,274
														Subtotal = -$9,274

Issue Date FY: 2022 ( Subtotal = $196,904 )
2022	2022	FORDHAM UNIVERSITY	441 E FORDHAM RD	BRONX	NY	10458	BRONX	USA	Vision Research	000	2	8/4/2022	NON-COMPETING CONTINUATION	$196,904
														Subtotal = $196,904

Issue Date FY: 2021 ( Subtotal = $239,086 )
2021	2021	FORDHAM UNIVERSITY	441 E FORDHAM RD	BRONX	NY	10458	BRONX	USA	Vision Research	000	1	8/10/2021	NEW	$239,086
														Subtotal = $239,086

Grand Total All Awards = $426,716

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Anti-inflammatory role of MerTK in the RPE independent of diurnal outer segment phagocytosis

Award Number: R21EY033188

ORGANIZATION: NATIONAL EYE INSTITUTE

OPDIV: NIH

AWARD CLASS: DISCRETIONARY

AWARD ACTIVITY TYPE: SCIENTIFIC/HEALTH RESEARCH (INCLUDES SURVEYS)

PERIOD OF PERFORMANCE START DATE: 09/01/2021

PERIOD OF PERFORMANCE END DATE: 07/31/2024

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