Post-Stroke Administration of L-4F Promotes Neurovascular and White Matter Remodeling in Type-2 Diabetic Stroke Mice

WHOM is  going to do the followup human research on this? With NO stroke leadership and NO strategy, nothing will occur.

Post-Stroke Administration of L-4F Promotes Neurovascular and White Matter Remodeling in Type-2 Diabetic Stroke Mice

Min Zhou^1†, Rongwen Li¹, Poornima Venkat¹, Yu Qian^1†, Michael Chopp^1,2, Alex Zacharek¹, Julie Landschoot-Ward¹, Brianna Powell¹, Quan Jiang^1,2* and Xu Cui^1*

• ¹Department of Neurology, Henry Ford Hospital, Detroit, MI, United States
• ²Department of Physics, Oakland University, Rochester, MI, United States

Patients with type 2 diabetes mellitus (T2DM) exhibit a distinct and high risk of ischemic stroke with worse post-stroke neurovascular and white matter (WM) prognosis than the non-diabetic population. In the central nervous system, the ATP-binding cassette transporter member A 1 (ABCA1), a reverse cholesterol transporter that efflux cellular cholesterol, plays an important role in high-density lipoprotein (HDL) biogenesis and in maintaining neurovascular stability and WM integrity. Our previous study shows that L-4F, an economical apolipoprotein A member I (ApoA-I) mimetic peptide, has neuroprotective effects via alleviating neurovascular and WM impairments in the brain of db/db-T2DM stroke mice. To further investigate whether L-4F has neurorestorative benefits in the ischemic brain after stroke in T2DM and elucidate the underlying molecular mechanisms, we subjected middle-aged, brain-ABCA1 deficient (ABCA1^−B/−B), and ABCA1-floxed (ABCA1^fl/fl) T2DM control mice to distal middle cerebral artery occlusion. L-4F (16 mg/kg, subcutaneous) treatment was initiated 24 h after stroke and administered once daily for 21 days. Treatment of T2DM-stroke with L-4F improved neurological functional outcome, and decreased hemorrhage, mortality, and BBB leakage identified by decreased albumin infiltration and increased tight-junction and astrocyte end-feet densities, increased cerebral arteriole diameter and smooth muscle cell number, and increased WM density and oligodendrogenesis in the ischemic brain in both ABCA1^−B/−B and ABCA1^fl/fl T2DM-stroke mice compared with vehicle-control mice, respectively (p < 0.05, n = 9 or 21/group). The L-4F treatment reduced macrophage infiltration and neuroinflammation identified by decreases in ED-1, monocyte chemoattractant protein-1 (MCP-1), and toll-like receptor 4 (TLR4) expression, and increases in anti-inflammatory factor Insulin-like growth factor 1 (IGF-1) and its receptor IGF-1 receptor β (IGF-1Rβ) in the ischemic brain (p < 0.05, n = 6/group). These results suggest that post-stroke administration of L-4F may provide a restorative strategy for T2DM-stroke by promoting neurovascular and WM remodeling. Reducing neuroinflammation in the injured brain may contribute at least partially to the restorative effects of L-4F independent of the ABCA1 signaling pathway.

Introduction

Type-2 diabetes (T2DM) constitutes ~90% of all diabetic patients and is a major risk factor for ischemic and hemorrhagic stroke. Epidemiological investigation in both younger (15–49 years) (1) and elderly (>65 years) (2) diabetic patients show a 10 years cumulative recurrent ischemic stroke rate of 29.7% for T2DM, and 12.0% for non-diabetic patients in the 15–49 age group (1), and 4.26% of stroke events and 1.79% of death rates during 6 years of follow-up for >65 age group. Moreover, diabetic-stroke patients exhibit a high level of neuroinflammation, worse neurovascular and white matter (WM) injury with severe and long-lasting neurological deficits compared with non-diabetic stroke patients (1–6). Neuroinflammation is involved in the onset and progression of stroke which is triggered by the infiltration of blood macrophages (M1 macrophage) and the activation of glial cells (microglia and astrocytes) which then released proinflammatory cytokines/factors. These inflammatory mediators not only lead to neurotoxicity and neuronal dysfunction and also induce blood–brain barrier (BBB) disruption and leakage. BBB damage allows the trafficking of immune cells and/or plasma proteins into the brain parenchyma which amplifies neuroinflammation and exacerbates neurovascular and WM injury (7). Therefore, there is a compelling need to develop therapeutic strategies for T2DM-stroke patients and elucidate the underlying molecular biological mechanisms.

After adjusting for all possible covariables, blood levels of low-density lipoprotein (LDL) cholesterol show a significant association with increased risk of stroke and mortality (2, 8). However, high-density lipoprotein (HDL) and HDL-increasing agents, such as Niacin, GW3965, T090317, etc., have demonstrated anti-neuroinflammation capabilities (9–14) and protection of brain vasculature and WM after stroke in preclinical studies (15–20). In T2DM patients, levels of both HDL and apolipoproteins and their functions such as the antioxidative capacity are impaired, which contribute to neurovascular and WM damage after stroke (8–12, 21–25).

In humans, the circulating blood contains only about 40% of the total amount of HDL, and most of the HDL in the central nervous system (CNS) is synthesized in situ mainly by the ATP-binding cassette transporter member A 1 (ABCA1), a reverse cholesterol transporter that efflux cellular cholesterol (26, 27). ABCA1 not only plays a key role in HDL biogenesis and in maintaining brain cholesterol metabolism, but it also exerts highly anti-atherogenic effects and has remarkable anti-inflammatory properties (28–33). We have previously demonstrated that deficiency of ABCA1 in the brain induces worse neurological functional deficits after stroke, increases BBB leakage and aggravates OL loss and WM injury (17, 34–36). The Apolipoprotein A-I (ApoA-I) mimetic peptide, 4F (D-4F, synthesized from D-amino acids, and L-4F, synthesized from L-amino acids) increases cholesterol efflux (37–43) and has anti-inflammatory effects (44–46). In our previous study, we have shown that treatment of stroke in type 1 diabetes mellitus (T1DM) rats with D-4F or db/db-T2DM stroke mice treated with L-4F significantly decreases neurovascular and WM damage and improves neurological function in the early stage (4–7 days) after stroke (45, 46). However, whether L-4F is capable of crossing the BBB and whether long-term post-stroke treatment with L-4F promotes neurovascular and WM remodeling and improves recovery of neurological function in T2DM, and whether ABCA1 mediates L-4F-induced neurorestoration have not been studied. Therefore, in this study, we employ middle-aged, brain-ABCA1 deficient (ABCA1^−B/−B) and ABCA1-floxed (ABCA1^fl/fl) control mice that were induced with T2DM and subjected to stroke, to test whether L-4F treatment initiated at 24 h after onset of ischemic stroke enhances neurological recovery. We also test if L-4F treatment improves vascular and WM rewiring in T2DM stroke and whether L-4F decreases inflammation via ABCA1 dependent signaling pathway. We demonstrate that L-4F can pass through the BBB and has neurorestorative capabilities in promoting neurovascular and WM remodeling, and oligodendrogenesis in the ischemic brain of T2DM-stroke mice. Our data also indicate that reducing neuroinflammation in the injured brain may contribute at least partially to the neurorestorative effects of L-4F independent of the ABCA1 signaling pathway.

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